High rate of unnecessary thymectomy and its cause. Can computed tomography distinguish thymoma, lymphoma, thymic hyperplasia, and thymic cysts?

Screening differentially expressed proteins to distinguish thymoma (B1 and B3) from thymic cysts based on tandem mass tag (TMT) technology

The therapeutic approach to thymic cysts remains a subject of controversy. Predicted biomarkers for identifying thymic cysts and thymoma (THYM) are crucial. In this research, patients diagnosed with thymic cysts (MTC, n = 6) and thymoma (B1, n = 6; B3, n = 6) were enrolled. Proteins of superior quality were subjected to TMT labeling and UPLC-MS, and differentially expressed proteins (DEPs) were identified. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interactive network analyses were applied to the DEPs. Some key differentially expressed genes(DEGs) were corroborated through GEPIA 32. The pan-cancer expression levels of key DEGs remarkably linked with prognosis were determined utilizing The University of ALabama at Birmingham CANcer data analysis Portal (UALCAN). Eventually, 49 DEPs were identified in the B1 vs. MTC comparison (17 upregulated and 32 downregulated), 27 in the B3 vs. MTC comparison (8 upregulated and 19 downregulated), and 38 in the B3 vs. B1 comparison (9 upregulated and 29 downregulated). IL13RA1 (down), galectin-3 binding protein (LGALS3BP)(up), PRCSH (down), C3 (down), MXRA5 (down), TNN (down), CFHR1 (down), SUN3 (down) were jointly altered in both B1 vs. NZ and B3 vs. NZ. GEPIA validated that LGALS3BP was significantly upregulated in thymoma patients. In conclusion, LGALS3BP might be an essential biomarker to identify thymoma from the thymic cyst.

Upfront Thoracic Magnetic Resonance Imaging for the Evaluation of Thymic Lesions to Reduce Non-Therapeutic Diagnostic Thymectomy: A Narrative Review

Background: Thymic pathologies represent the most common lesions of the anterior mediastinum. They may be classified as malignant or benign. Current diagnostic pathways recommend an initial assessment with computed tomography (CT) imaging to delineate potentially malignant thymic lesions. Despite this, high rates of non-therapeutic thymectomy continue to be observed. This carries with it significant anaesthetic, operative, and post-operative risks, in addition to healthcare costs. Consequently, there is a growing interest in magnetic resonance imaging (MRI) as a primary diagnostic modality for lesions of the anterior mediastinum. This narrative review outlines the current approaches to the evaluation of thymic lesions, with a discussion of the strengths and limitations of CT and MRI imaging modalities. It also evaluates the current discourse on the use of upfront MRI for thymic and anterior mediastinal lesion assessment. Methods: A narrative review was performed following a search on the Medline database. Articles that were evaluated had explored the role of MRI on the evaluation of thymic and anterior mediastinal lesions. Results: Current work-up for thymic and anterior mediastinal lesions are highly variable and centre around the use of CT. Upfront MRI demonstrates a similar accuracy to CT for various thymic and anterior mediastinal pathologies; however, the efforts to integrate this approach into routine practice remain in their infancy, with no standardised guidelines that exist. Conclusions: This narrative review demonstrates that there is a paucity of evidence relating to the sensitivity and specificity of MRI compared to CT for thymic lesion analysis and their subsequent relationship with non-therapeutic thymectomy. Future prospective trials to assess the role of MRI in thymic lesion determination are required to understand whether MRI can more accurately characterise these lesions to reduce non-therapeutic thymectomy. Additionally, further research efforts are required to characterise best-practice methods for integrating MRI into diagnostic pathways for these lesions in a cost-effective and resource-conscious manner.

Behaviour of simple thymic cysts over time; is surveillance required?

AIM

Anterior mediastinal lesions can be a source of uncertainty on imaging, and thymic cysts present a unique diagnostic challenge. Differentiation of non-simple fluid-containing benign simple thymic cysts from small thymic neoplasms is challenging with computed tomography (CT) alone. Additionally, the malignant potential of simple thymic cysts is unclear and guidelines for imaging surveillance are not established.

MATERIALS AND METHODS

All imaging studies containing the phrase "thymic cyst" were identified at our institution between October 2012 and October 2022. Studies were excluded if the main radiological diagnosis was anything other than a thymic cyst. This yielded 107 individual patient records, of which 11 did not meet inclusion criteria, leaving 96 unique patients.

RESULTS

While most cysts evaluated remained stable throughout the period of surveillance (53%; n=51), some increased in size (13%), some decreased in size (6%), and some fluctuated (5%). Some cysts changed in internal attenuation/signal characteristics in keeping with interval haemorrhage (6%). 34% of cysts (n=31) demonstrate internal average attenuation values of more than 20HU. Of the entire cohort of patients studied over 10 years, none developed malignancy within the period of surveillance.

CONCLUSION

Unilocular thymic cysts are most often discovered incidentally but their imaging characteristics can be difficult to interpret on CT, as they are commonly hyperdense and may change in size and internal content. Once simple thymic cysts are adequately characterised with magnetic resonance imaging (MRI) then extended radiological surveillance may not be required.

Development and Validation of a CT-Radiomics Nomogram for the Diagnosis of Small Prevascular Mediastinal Nodules: Reducing Nontherapeutic Surgeries

RATIONALE AND OBJECTIVES

The preoperative diagnosis of small prevascular mediastinal nodules (SPMNs) presents a challenge, often leading to unnecessary surgical interventions. Our objective was to develop a nomogram based on preoperative CT-radiomics features, serving as a non-invasive diagnostic tool for SPMNs.

MATERIALS AND METHODS

Patients with surgically resected SPMNs from two medical centers between January 2018 and December 2022 were retrospectively reviewed. Radiomics features were extracted and screened from preoperative CT images. Logistic regression was employed to establish clinical, radiomics, and hybrid models for differentiating thymic epithelial tumors (TETs) from cysts. The performance of these models was validated in both internal and external test sets by area under the receiver operating characteristic curve (AUC), while also comparing their diagnostic capability with human experts.

RESULTS

The study enrolled a total of 363 patients (median age, 53 years [IQR:45-59 years]; 175 [48.2%] males) for model development and validation, including 136 TETs and 227 cysts. Lesions' enhancement status, shape, calcification, and rad-score were identified as independent factors for distinction. The hybrid model demonstrated superior diagnostic performance compared to other models and human experts, with an AUC of 0.95 (95% CI:0.92-0.98), 0.94 (95% CI:0.89-0.99), and 0.93 (95% CI:0.83-1.00) in the training set, internal test set, and external test set respectively. The calibration curve of the model demonstrated excellent fit, while decision curve analysis underscored its clinical value.

CONCLUSION

The radiomics-based nomogram effectively discriminates between the most prevalent types of SPMNs, namely TETs and cysts, thus presenting a promising tool for treatment guidance.

Practical methods to differentiate thymic malignancies by positron-emission tomography and tumor markers

PURPOSE

An accurate diagnosis of thymic malignancies is important, but challenging due to the broad range of differential diagnoses. This study aims to evaluate the efficacy of PET/CT and tumor markers for diagnosing thymic malignancies.

METHODS

Patients admitted to our department between January 2012 and December 2021 with primary anterior mediastinal tumors were retrospectively evaluated. We evaluated the relationship between the maximum standardized uptake value (SUVmax), tumor markers, and pathological diagnosis in four groups: thymic carcinoma, thymoma, lymphoma, and others.

RESULTS

In total, 139 patients were included in this study. The SUVmax was significantly higher in lymphoma, thymic carcinoma, and thymoma, in that order. The cytokeratin 19 fragment (CYFRA 21-1) was significantly higher in thymic carcinoma than in the other groups. An ROC curve analysis indicated that the optimal cut-off values of SUVmax for thymic carcinoma plus lymphoma and CYFRA 21-1 for thymic carcinoma were 7.97 (AUC = 0.934) and 2.95 (AUC = 0.768), respectively. Using a combination of cut-off values (SUVmax = 8, CYFRA 21-1 = 3), the accuracy rate for diagnosing thymic carcinoma was 91.4%.

CONCLUSIONS

The SUVmax and CYFRA 21-1 levels are significant indicators for the diagnosis of thymic carcinoma. Combining these indicators resulted in a more accurate diagnosis of thymic malignancies, which could facilitate the decision-making process for determining the optimal treatment strategies.

Does Surgical Removal of the Thymus Have Deleterious Consequences?

The role of immunosenescence, particularly the natural process of thymic involution during aging, is increasingly acknowledged as a factor contributing to the development of autoimmune diseases and cancer. Recently, a concern has been raised about deleterious consequences of the surgical removal of thymic tissue, including for patients who undergo thymectomy for myasthenia gravis (MG) or resection of a thymoma. This review adopts a multidisciplinary approach to scrutinize the evidence concerning the long-term risks of cancer and autoimmunity postthymectomy. We conclude that for patients with acetylcholine receptor antibody-positive MG and those diagnosed with thymoma, the removal of the thymus offers prominent benefits that well outweigh the potential risks. However, incidental removal of thymic tissue during other thoracic surgeries should be minimized whenever feasible.

Robotic surgery for thymic cysts: clinical features, management, and results of a multicentric study

Thymic cysts are rare, radiological diagnosis is often incidental, and cysts seldom assume clinical relevance for symptoms of compression. Thymoma were occasionally found inside both complex and simple thymic cysts. Given the challenges in accurately clinical diagnosing and since the occasionally discovering of thymoma inside both complex and simple thymic cysts, the management of thymic cysts remains controversial. Advancements in surgical tools such as robotics, applied to thymic conditions, could potentially transform the approach to thymic cysts. We report one the largest multicentric series of thymic cysts surgically treated with robotic approach, focusing on preoperative findings and surgical results. Cases were gathered from three Italian thoracic surgery centers with homogeneous clinical practice, significant experience in thymic neoplasms, and thoracic robotic skilled. Surgical intervention was indicated for patients with radiological diagnosis of thymic cysts under the following circumstances: the presence of symptoms, concurrent myasthenia gravis, cysts growing in follow-up, and the complexity of the cyst with suspicion of neoplasm. Data were collected and matched according to postoperative and pathological features to identify potential prognostic factors. Population include 57 patients, 29/28 male/female ratio with mean age of 59.46 ± 11.67 years. The average size of the thymic cysts was 29.14 ± 24.53 ranged between 3 and 150 mm. All patients undergone CT scan and mean of values of density was 25.82 ± 11-82 Hounsfield. Surgical procedures were robotic approach in all case including total/extended thymectomy 35 (61.4%) and cyst resection/partial thymectomy 22 (38.6%). There were no mortality or recurrence. Major complications rate was 5.3%. No correlations were observed between preoperative features and complication. Pathological examination revealed microfoci of thymic tumor in four cases. Robot-assisted surgery for thymic cysts showed excellent early clinical outcomes with low rate of postoperative complications also in case of large lesion. Thymic cysts should not be underestimated due to the risk of coexistent thymic neoplasm.

Distinguishing thymic cysts from low-risk thymomas via [18F]FDG PET/CT

BACKGROUND

Thymic cysts are a rare benign disease that needs to be distinguished from low-risk thymoma. [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is a non-invasive imaging technique used in the differential diagnosis of thymic epithelial tumours, but its usefulness for thymic cysts remains unclear. Our study evaluated the utility of visual findings and quantitative parameters of [18F]FDG PET/CT for differentiating between thymic cysts and low-risk thymomas.

METHODS

Patients who underwent preoperative [18F]FDG PET/CT followed by thymectomy for a thymic mass were retrospectively analyzed. The visual [18F]FDG PET/CT findings evaluated were PET visual grade, PET central metabolic defect, and CT shape. The quantitative [18F]FDG PET/CT parameters evaluated were PET maximum standardized uptake value (SUVmax), CT diameter (cm), and CT attenuation in Hounsfield units (HU). Findings and parameters for differentiating thymic cysts from low-risk thymomas were assessed using Pearson's chi-square test, the Mann-Whitney U-test, and receiver operating characteristics (ROC) curve analysis.

RESULTS

Seventy patients (18 thymic cysts and 52 low-risk thymomas) were finally included. Visual findings of PET visual grade (P < 0.001) and PET central metabolic defect (P < 0.001) showed significant differences between thymic cysts and low-risk thymomas, but CT shape did not. Among the quantitative parameters, PET SUVmax (P < 0.001), CT diameter (P < 0.001), and CT HU (P = 0.004) showed significant differences. In ROC analysis, PET SUVmax demonstrated the highest area under the curve (AUC) of 0.996 (P < 0.001), with a cut-off of equal to or less than 2.1 having a sensitivity of 100.0% and specificity of 94.2%. The AUC of PET SUVmax was significantly larger than that of CT diameter (P = 0.009) and CT HU (P = 0.004).

CONCLUSIONS

Among the [18F]FDG PET/CT parameters examined, low FDG uptake (SUVmax ≤ 2.1, equal to or less than the mediastinum) is a strong diagnostic marker for a thymic cyst. PET visual grade and central metabolic defect are easily accessible findings.

Thymic Imaging Pitfalls and Strategies for Optimized Diagnosis

Thymic imaging is challenging because the imaging appearance of a variety of benign and malignant thymic conditions are similar. CT is the most commonly used modality for mediastinal imaging, while MRI and fluorine 18 fluorodeoxyglucose (FDG) PET/CT are helpful when they are tailored to the correct indication. Each of these imaging modalities has limitations and technical pitfalls that may lead to an incorrect diagnosis and mismanagement. CT may not be sufficient for the characterization of cystic thymic processes and differentiation between thymic hyperplasia and thymic tumors. MRI can be used to overcome these limitations but is subject to other potential pitfalls such as an equivocal decrease in signal intensity at chemical shift imaging, size limitations, unusual signal intensity for cysts, subtraction artifacts, pseudonodularity on T2-weighted MR images, early imaging misinterpretation, flow and spatial resolution issues hampering assessment of local invasion, and the overlap of apparent diffusion coefficients between malignant and benign thymic entities. FDG PET/CT is not routinely indicated due to some overlap in FDG uptake between thymomas and benign thymic processes. However, it is useful for staging and follow-up of aggressive tumors (eg, thymic carcinoma), particularly for detection of occult metastatic disease. Pitfalls in imaging after treatment of thymic malignancies relate to technical challenges such as postthymectomy sternotomy streak metal artifacts, differentiation of postsurgical thymic bed changes from tumor recurrence, or human error with typical "blind spots" for identification of metastatic disease. Understanding these pitfalls enables appropriate selection of imaging modalities, improves diagnostic accuracy, and guides patient treatment. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

A basaloid carcinoma with multilocular thymic cyst mimicking a mediastinal teratoma

This case report details a rare thymic basaloid carcinoma initially misinterpreted as a mediastinal teratoma, underscoring the diagnostic challenges posed by such tumors. A 71-year-old female presented with an asymptomatic anterior mediastinal tumor discovered incidentally during a routine health examination. Surgical intervention, followed by pathological and immunohistochemical analysis including CK-pan, p63, p40, and CD117 molecules, led to a definitive diagnosis of basaloid carcinoma of the thymus. This case highlights the critical importance of differential diagnosis in mediastinal lesions, especially those presenting with multilocular thymic cysts on chest CT. The subxiphoid video-assisted thoracoscopic surgery enabled complete tumor resection with minimal trauma and favorable postoperative outcomes. The patient opted against further radiotherapy or chemotherapy and she has survived for over eight months without recurrence. This case report contributes to the growing understanding of thymic basaloid carcinoma, a rare and potentially aggressive thymic carcinoma subtype. It emphasizes the necessity for precise surgical techniques and enhanced diagnostic acumen among cardiothoracic surgeons and oncologists.

Development and Validation of Contrast-Enhanced CT-Based Deep Transfer Learning and Combined Clinical-Radiomics Model to Discriminate Thymomas and Thymic Cysts: A Multicenter Study

RATIONALE AND OBJECTIVES

This study aims to evaluate the feasibility and effectiveness of deep transfer learning (DTL) and clinical-radiomics in differentiating thymoma from thymic cysts.

MATERIALS AND METHODS

Clinical and imaging data of 196 patients pathologically diagnosed with thymoma and thymic cysts were retrospectively collected from center 1. (training cohort: n = 137; internal validation cohort: n = 59). An independent external validation cohort comprised 68 thymoma and thymic cyst patients from center 2. Region of interest (ROI) delineation was performed on contrast-enhanced chest computed tomography (CT) images, and eight DTL models including Densenet 169, Mobilenet V2, Resnet 101, Resnet 18, Resnet 34, Resnet 50, Vgg 13, Vgg 16 were constructed. Radiomics features were extracted from the ROI on the CT images of thymoma and thymic cyst patients, and feature selection was performed using intra-observer correlation coefficient (ICC), Spearman correlation analysis, and least absolute shrinkage and selection operator (LASSO) algorithm. Univariate analysis and multivariable logistic regression (LR) were used to select clinical-radiological features. Six machine learning classifiers, including LR, support vector machine (SVM), k-nearest neighbors (KNN), Light Gradient Boosting Machine (LightGBM), Adaptive Boosting (AdaBoost), and Multilayer Perceptron (MLP), were used to construct Radiomics and Clinico-radiologic models. The selected features from the Radiomics and Clinico-radiologic models were fused to build a Combined model. Receiver operating characteristic curve (ROC), calibration curve, and decision curve analysis (DCA) were used to evaluate the discrimination, calibration, and clinical utility of the models, respectively. The Delong test was used to compare the AUC between different models. K-means clustering was used to subdivide the lesions of thymomas or thymic cysts into subregions, and traditional radiomics methods were used to extract features and compare the ability of Radiomics and DTL models to reflect intratumoral heterogeneity using correlation analysis.

RESULTS

The Densenet 169 based on DTL performed the best, with AUC of 0.933 (95% CI: 0.875-0.991) in the internal validation cohort and 0.962 (95% CI: 0.923-1.000) in the external validation cohort. The AdaBoost classifier achieved AUC of 0.965 (95% CI: 0.923-1.000) and 0.959 (95% CI: 0.919-1.000) in the internal and external validation cohorts, respectively, for the Radiomics model. The LightGBM classifier achieved AUC of 0.805 (95% CI: 0.690-0.920) and 0.839 (95% CI: 0.736-0.943) in the Clinico-radiologic model. The AUC of the Combined model in the internal and external validation cohorts was 0.933 (95% CI: 0.866-1.000) and 0.945 (95% CI: 0.897-0.994), respectively. The results of the Delong test showed that the Radiomics model, DTL model, and Combined model outperformed the Clinico-radiologic model in both internal and external validation cohorts (p-values were 0.002, 0.004, and 0.033 in the internal validation cohort, while in the external validation cohort, the p-values were 0.014, 0.006, and 0.015, respectively). But there was no statistical difference in performance among the three models (all p-values <0.05). Correlation analysis showed that radiomics performed better than DTL in quantifying intratumoral heterogeneity differences between thymoma and thymic cysts.

CONCLUSION

The developed DTL model and the Combined model based on radiomics and clinical-radiologic features achieved excellent diagnostic performance in differentiating thymic cysts from thymoma. They can serve as potential tools to assist clinical decision-making, particularly when endoscopic biopsy carries a high risk.

Contrast-enhanced CT-based radiomics differentiate anterior mediastinum lymphoma from thymoma without myasthenia gravis and calcification

AIM

To explore the value of a radiomics model based on enhanced computed tomography (CT) in differentiating anterior mediastinal lymphoma (AML) and thymoma without myasthenia gravis (MG) and calcification.

MATERIALS AND METHODS

The present study analysed patients who were diagnosed histologically with AML and thymoma in three independent institutions. All pre-treatment patients underwent enhanced CT. In the training group of patients from institutions 1 (the First Affiliated Hospital of Kunming Medical University) and 3 (the Yunnan Cancer Hospital), two radiologists independently analysed the enhanced CT images and performed manual segmentation of each tumour. Radiomics features were screened using interobserver interclass coefficient (ICC) analysis, feature correlation analysis, and L1 regularisation. The discriminative efficacy of the logistic regression model was evaluated using receiver operating characteristic (ROC) analysis. Validation group of patients from institution 2 (the Second Affiliated Hospital of Zhejiang University School of Medicine) was used to validate the proposed models.

RESULTS

A total of 114 patients were enrolled in this study and 1,743 radiomics features were extracted from the enhanced CT images. After feature screening, the remaining 37 robust radiomics features were used to construct the model. In the training group, the AUC of the model was 0.987 (95% confidence interval [CI]: 0.976-0.999), the sensitivity, specificity, and accuracy were 0.912, 0.946, and 0.924, respectively. In the validation group, the AUC of the model was 0.798 (95% CI: 0.683-0.913), the sensitivity, specificity, and accuracy were 0.760, 0.700, and 0.743, respectively.

CONCLUSION

The radiomics model created provided effective information to assist in the selection of clinical strategies, thus reducing unnecessary procedures in patients with AML and guiding direct surgery in patients with thymoma to avoid biopsy.

A diagnostic model based on 18F-FDG PET/CT parameters in improving the differential diagnosis of invasive thymic epithelial tumors and anterior mediastinal lymphomas

BACKGROUND

Accurately distinguishing between invasive thymic epithelial tumors (TETs) and anterior mediastinal lymphoma before surgery is crucial for subsequent treatment choices. But currently, the diagnosis of invasive TET is sometimes difficult to distinguish from anterior mediastinal lymphoma.

OBJECTIVE

To assess the application of fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography/computer tomography (PET/CT) in the differential diagnosis of TETs and anterior mediastinal lymphomas.

METHODS

18F-FDG PET/CT images of 133 invasive TETs and anterior mediastinal lymphomas patients were retrospectively analyzed. In particular, the tumor's longest diameter and maximum standardized uptake value (SUVmax) were evaluated. The SUVmax and longest diameter values of the two groups were analyzed by using the receiver operating characteristic (ROC) curve to determine the optimal threshold and diagnostic efficiency.

RESULTS

Age, myasthenia gravis, SUVmax and tumor longest diameter differed significantly between invasive TETs and anterior mediastinal lymphomas patients. The tumor location, calcification, relationship with adjacent vessels and distant metastasis differed significantly between the groups. The ROC analysis showed an AUC for SUVmax and tumor longest diameter of 0.841 and 0.737. Respectively, the cutoff values with the best diagnostic performance were 9.65 (sensitivity: 77.78%, specificity: 81.97%) and 6.65 (sensitivity: 80.56%, specificity: 62.30%) for SUVmax and tumor longest diameter. The diagnostic model of SUVmax, calcification, relationship with surrounding blood vessels, lymph node metastasis and lung metastasis in the highest AUC of 0.935 (sensitivity: 90.16%, specificity: 88.89%). In addition, we incorporated splenic involvement and metastatic sub-diaphragmatic lymph node into Model 2 as a new predictive model 3 for differential diagnosis and found a significant improvement in the diagnostic performance of Model 3.

CONCLUSION

The diagnostic model composed of 18F-FDG PET parameters is improving the differential diagnosis of invasive TETs and anterior mediastinal lymphomas.

Histogram analysis based on unenhanced CT for identifying thymoma and lymphoma among prevascular mediastinal incidentalomas

OBJECTIVE

To determine whether histogram analysis based on unenhanced CT can play a role in the differential diagnosis of thymoma and lymphoma from thymic hyperplasia and cyst (mean CT attenuation > 10 HU).

MATERIALS AND METHODS

This retrospective study included consecutive asymptomatic participants who have prevascular mediastinal lesions incidentally detected by unenhanced CT between December 2013 and August 2020, and with definitive diagnosis by pathology or additional radiologic work-ups. A total of thirteen histogram parameters on enhanced CT were calculated for each lesion, then were compared between tumor (thymoma + lymphoma) and non-tumor (hyperplasia + cyst). Receiver operating characteristic analysis was conducted to investigate the performance of histogram parameter for identifying tumor.

RESULTS

The study population included 192 patients (106 men and 86 women) with a mean age of 50.5 years at the time of CT examination. Of them, 94 patients have tumor (87 thymomas and 7 lymphoma) and 98 have non-tumor (48 thymic hyperplasia and 50 cysts). Nine of the thirteen histogram parameters revealed significant difference between the two groups, including median, minimum, range, 10th percentile, 90th percentile, kurtosis, skewness, uniformity and entropy. No significant difference was observed in the mean CT attenuation between groups. Higher median was found to be independent predictors for distinguishing tumor from non-tumor, and can achieve an area under the curve (AUC) of 0.785 (95% confidence interval [95% IC], 0.720-0.841).

CONCLUSIONS

Histogram analysis based on unenhanced CT may be able to provide some help in the differential diagnosis of incidental lesions in prevascular mediastinal.

GRAND SUPPORT

This study was sponsored by Natural Science Foundation of Shanghai (No. 21ZR1459700).

The thymus: what's normal and what's not? Problem-solving with MRI

Anterior mediastinal masses can be difficult to characterise on computed tomography (CT) due to the wide spectrum of normal appearances of thymic tissue as well as the challenge of differentiating between benign and malignant pathologies. Additionally, attenuation of cystic mediastinal lesions can be misinterpreted on CT due to varying attenuation values. Anecdotally, non-vascular magnetic resonance imaging (MRI) of the thorax is underutilised across radiology departments in the UK, but has been shown to improve diagnostic certainty and reduce unnecessary surgical intervention. T2-weighted MRI is useful in confirming the cystic nature of lesions, whereas chemical shift techniques can be utilised to document the presence of macroscopic and intra-cellular fat and thus help distinguish between benign and malignant pathologies. In this review article, we present a practical approach to using MRI for the characterisation of anterior mediastinal lesions based on our clinical experience in a UK district general hospital.

Differentiating thymic epithelial tumors from mediastinal lymphomas: preoperative nomograms based on PET/CT radiomic features to minimize unnecessary anterior mediastinal surgery

PURPOSE

Clinical feasibility nomograms were developed to facilitate the differentiation between thymic epithelial tumors (TETs) and mediastinal lymphomas (MLs), aiming to minimize the occurrence of non-therapeutic thymectomy.

METHODS

A total of 255 patients diagnosed with TETs or MLs underwent pre-treatment 18F-FDG PET/CT. Comprehensive clinical and imaging data were collected, including age, gender, lactate dehydrogenase (LDH) level, pathological results, presence of myasthenia gravis symptoms, B symptoms, mass size, location, morphology, margins, density, and metabolic parameters derived from PET/CT. Radiomic features were extracted from the region of interest (ROI) of the primary lesion. Feature selection techniques were employed to identify the most discriminative subset of features. Machine learning methods were utilized to build candidate models, which were subsequently evaluated based on their area under the curve (AUC). Finally, nomograms were constructed using the optimal model to provide a clinical tool for improved diagnostic accuracy. The performance of the radiomic models was evaluated by their calibration, discrimination, and clinical utility.

RESULTS

Several independent risk factors were identified for distinguishing TETs from MLs, including average standardized uptake value (SUVavg), LDH, age, mass size, and radiomic score (rad-score). Significance was observed in differentiating the two types of tumors based on these factors. The best clinical efficacy was demonstrated by the combined model, with an impressive AUC of 0.954. Decision curve analysis and calibration curves indicated that the combined model was clinically advantageous for discriminating TETs from MLs. Besides, the results of external validation showed a sensitivity of 0.8 and a specificity of 0.78.

CONCLUSION

Preoperatively, the differentiation of TETs from MLs can be facilitated by the utilization of the combined clinical information and radiomics model. This approach holds promise in minimizing the occurrence of unnecessary anterior mediastinal surgeries.

ERS/ESTS/ESTRO/ESR/ESTI/EFOMP statement on management of incidental findings from low dose CT screening for lung cancer

BACKGROUND

Screening for lung cancer with low radiation dose computed tomography has a strong evidence base, is being introduced in several European countries and is recommended as a new targeted cancer screening programme. The imperative now is to ensure that implementation follows an evidence-based process that will ensure clinical and cost effectiveness. This European Respiratory Society (ERS) task force was formed to provide an expert consensus for the management of incidental findings which can be adapted and followed during implementation.

METHODS

A multi-European society collaborative group was convened. 23 topics were identified, primarily from an ERS statement on lung cancer screening, and a systematic review of the literature was conducted according to ERS standards. Initial review of abstracts was completed and full text was provided to members of the group for each topic. Sections were edited and the final document approved by all members and the ERS Science Council.

RESULTS

Nine topics considered most important and frequent were reviewed as standalone topics (interstitial lung abnormalities, emphysema, bronchiectasis, consolidation, coronary calcification, aortic valve disease, mediastinal mass, mediastinal lymph nodes and thyroid abnormalities). Other topics considered of lower importance or infrequent were grouped into generic categories, suitable for general statements.

CONCLUSIONS

This European collaborative group has produced an incidental findings statement that can be followed during lung cancer screening. It will ensure that an evidence-based approach is used for reporting and managing incidental findings, which will mean that harms are minimised and any programme is as cost-effective as possible.

ERS/ESTS/ESTRO/ESR/ESTI/EFOMP statement on management of incidental findings from low dose CT screening for lung cancer

BACKGROUND

Screening for lung cancer with low radiation dose computed tomography has a strong evidence base, is being introduced in several European countries and is recommended as a new targeted cancer screening programme. The imperative now is to ensure that implementation follows an evidence-based process that will ensure clinical and cost effectiveness. This European Respiratory Society (ERS) task force was formed to provide an expert consensus for the management of incidental findings which can be adapted and followed during implementation.

METHODS

A multi-European society collaborative group was convened. 23 topics were identified, primarily from an ERS statement on lung cancer screening, and a systematic review of the literature was conducted according to ERS standards. Initial review of abstracts was completed and full text was provided to members of the group for each topic. Sections were edited and the final document approved by all members and the ERS Science Council.

RESULTS

Nine topics considered most important and frequent were reviewed as standalone topics (interstitial lung abnormalities, emphysema, bronchiectasis, consolidation, coronary calcification, aortic valve disease, mediastinal mass, mediastinal lymph nodes and thyroid abnormalities). Other topics considered of lower importance or infrequent were grouped into generic categories, suitable for general statements.

CONCLUSIONS

This European collaborative group has produced an incidental findings statement that can be followed during lung cancer screening. It will ensure that an evidence-based approach is used for reporting and managing incidental findings, which will mean that harms are minimised and any programme is as cost-effective as possible.

Risk factor analysis for major mediastinal vessel invasion in thymic epithelial tumors based on multi-slice CT Imaging

Objective

To explore the characteristics and risk factors for major mediastinal vessel invasion in different risk grades of thymic epithelial tumors (TETs) based on computed tomography (CT) imaging, and to develop prediction models of major mediastinal artery and vein invasion.

Methods

One hundred and twenty-two TET patients confirmed by histopathological analysis who underwent thorax CT were enrolled in this study. Clinical and CT data were retrospectively reviewed for these patients. According to the abutment degree between the tumor and major mediastinal vessels, the arterial invasion was divided into grade I, II, and III (< 25%, 25 - 49%, and ≥ 50%, respectively); the venous invasion was divided into grade I and II (< 50% and ≥ 50%). The degree of vessel invasion was compared among different defined subtypes or stages of TETs using the chi-square tests. The risk factors associated with TET vascular invasion were identified using multivariate logistic regression analysis.

Results

Based on logistic regression analysis, male patients (β = 1.549; odds ratio, 4.824) and the pericardium or pleural invasion (β = 2.209; odds ratio, 9.110) were independent predictors of 25% artery invasion, and the midline location (β = 2.504; odds ratio, 12.234) and mediastinal lymphadenopathy (β = 2.490; odds ratio, 12.06) were independent predictors of 50% artery invasion. As for 50% venous invasion, the risk factors include midline location (β = 2.303; odds ratio, 10.0), maximum tumor diameter larger than 5.9 cm (β = 4.038; odds ratio, 56.736), and pericardial or pleural effusion (β = 1.460; odds ratio, 4.306). The multivariate logistic model obtained relatively high predicting efficacy, and the area under the curve (AUC), sensitivity, and specificity were 0.944, 84.6%, and 91.7% for predicting 50% artery invasion, and 0.913, 81.8%, and 86.0% for 50% venous invasion in TET patients, respectively.

Conclusion

Several CT features can be used as independent predictors of ≥50% artery or venous invasion. A multivariate logistic regression model based on CT features is helpful in predicting the vascular invasion grades in patients with TET.

Differentiation between rebound thymic hyperplasia and thymic relapse after chemotherapy in pediatric Hodgkin lymphoma

BACKGROUND

Rebound thymic hyperplasia (RTH) is a common phenomenon caused by stress factors such as chemotherapy (CTX) or radiotherapy, with an incidence between 44% and 67.7% in pediatric lymphoma. Misinterpretation of RTH and thymic lymphoma relapse (LR) may lead to unnecessary diagnostic procedures including invasive biopsies or treatment intensification. The aim of this study was to identify parameters that differentiate between RTH and thymic LR in the anterior mediastinum.

METHODS

After completion of CTX, we analyzed computed tomographies (CTs) and magnetic resonance images (MRIs) of 291 patients with classical Hodgkin lymphoma (CHL) and adequate imaging available from the European Network for Pediatric Hodgkin lymphoma C1 trial. In all patients with biopsy-proven LR, an additional fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT was assessed. Structure and morphologic configuration in addition to calcifications and presence of multiple masses in the thymic region and signs of extrathymic LR were evaluated.

RESULTS

After CTX, a significant volume increase of new or growing masses in the thymic space occurred in 133 of 291 patients. Without biopsy, only 98 patients could be identified as RTH or LR. No single finding related to thymic regrowth allowed differentiation between RTH and LR. However, the vast majority of cases with thymic LR presented with additional increasing tumor masses (33/34). All RTH patients (64/64) presented with isolated thymic growth.

CONCLUSION

Isolated thymic LR is very uncommon. CHL relapse should be suspected when increasing tumor masses are present in distant sites outside of the thymic area. Conversely, if regrowth of lymphoma in other sites can be excluded, isolated thymic mass after CTX likely represents RTH.

Thymic Parenchymal Hyperplasia

Thymic hyperplasia is a rare condition generally caused by lymphoid follicular hyperplasia associated with autoimmune disorders. True thymic parenchymal hyperplasia unassociated with lymphoid follicular hyperplasia is extremely rare and may give rise to difficulties in diagnosis. We have studied 44 patients with true thymic hyperplasia (38 females and 6 males) aged 7 months to 64 years (mean, 36 years). Eighteen patients presented with symptoms of chest discomfort or shortness of breath; in 20 patients, the lesions were discovered incidentally. Imaging studies demonstrated enlargement of the mediastinum by a mass lesion suspicious for malignancy. All patients were treated with complete surgical excision. The tumors measured from 3.5 to 24 cm (median, 10 cm; mean, 10.46 cm). Histologic examination showed lobules of thymic tissue displaying well-developed corticomedullary architecture, with scattered Hassall corpuscles separated by mature adipose tissue and bounded by a thin fibrous capsule. No cases showed evidence of lymphoid follicular hyperplasia, cytologic atypia, or confluence of the lobules. Immunohistochemical studies showed a normal pattern of distribution for keratin-positive thymic epithelial cells against a background rich in CD3/TdT/CD1a+ lymphocytes. Twenty-nine cases had an initial clinical or pathological diagnosis of thymoma or thymoma vs thymic hyperplasia. Clinical follow-up in 26 cases showed that all patients were alive and well between 5 and 15 years after diagnosis (mean, 9 years). Thymic parenchymal hyperplasia causing significant enlargement of the normal thymus that is sufficient to cause symptoms or worrisome imaging findings should be considered in the differential diagnosis of anterior mediastinal masses. The criteria for distinguishing such lesions from lymphocyte-rich thymoma are presented.

Diagnostic approach for mediastinal masses with radiopathological correlation

PURPOSE

Mediastinal masses have various histopathological and radiological findings. Although lymphoma is the most common type of tumor, thymic epithelial and neurogenic tumors are common in adults and children, respectively, but several other types are difficult to distinguish. No previous review has simply and clearly shown how to differentiate mediastinal masses.

METHOD

We conducted a review of the latest mediastinal classifications and mass differentiation methods, with a focus on neoplastic lesions. Both older and recent studies were searched, and imaging and histopathological findings of mediastinal masses were reviewed. Original simple-to-use differentiation flowcharts are presented.

RESULTS

Assessing localizations and internal characteristics is very important for mediastinal mass differentiation. The mass location and affected organ/tissue should be accurately assessed first, followed by more qualitative diagnosis, and optimization of the treatment strategy. In 2014, the International Thymic Malignancy Interest Group presented a new mediastinal clinical classification. In this classification, mediastinal masses are categorized into three groups according to location: prevascular (anterior)-, visceral (middle)-, and paravertebral (posterior)-compartment masses. Then, the internal characteristics and functional images are evaluated.

CONCLUSIONS

Differentiation of mediastinal masses is very difficult. However, if typical imaging findings and clinical characteristics are combined, reasonable differentiation is possible. In each patient, proper differential diagnosis may contribute to better treatment selection.

CT Characteristics of the Thymus in Adult Dogs with Non-Thymic Neoplasia Compared to Young Dogs

The thymus is a lymphatic mediastinal organ that is largely subject to changes with age. In human patients, the CT characteristics of the thymus in children and adults is well described. Furthermore, it is known in human medicine that stress can lead to a reduction in the size of the thymus, followed by a phase of hyperplasia (called the ‘rebound effect’). The visualization of thymic tissue in the cranial mediastinum of adult dogs with neoplasia is possible and could be related to a similar effect. In this study, we aimed to describe the CT characteristics of the thymus in adult dogs with neoplasia and to compare the aspect of the thymus in these dogs to juvenile dogs with a presumed normal thymus. A total of 11 adult dogs with neoplasia and 20 juvenile dogs were included. Several CT features of the thymus were evaluated, including the size, shape, and pre- and post-contrast attenuation values. The overall appearance was lobulated in all of the adult dogs and homogeneous in all of the juvenile dogs; it was left-sided in all of the adult dogs, while it was located in the midline in a few of the juvenile dogs (right-sided only in one). The thymus was less attenuating in adult dogs, in some cases with negative minimum pre-contrast attenuation values. In some dogs with neoplasia, the thymus can be detected at CT examination despite their age.

Massive Thymic Hyperplasia Masquerading as Cancer: A Case Report and Review of the Literature

A 34-year-old woman presenting with abdominal pain, chest pressure, weight loss, and tachycardia was found to have an 11.4-cm anterior mediastinal mass associated with intrathoracic lymphadenopathy on chest computed tomography (Fig. 1A). Core needle biopsy was concerning for a type B1 thymoma. During this patient's initial workup, she was found to have both clinical and laboratory evidence of Graves' thyroiditis, raising diagnostic suspicion for thymic hyperplasia rather than thymoma. The case discussed here highlights the unique challenges that arise in the evaluation and management of thymic masses and serves as a prudent reminder that both benign and malignant disorders may present with mass-like changes.

Clinical radiomics-based machine learning versus three-dimension convolutional neural network analysis for differentiation of thymic epithelial tumors from other prevascular mediastinal tumors on chest computed tomography scan

Purpose

To compare the diagnostic performance of radiomic analysis with machine learning (ML) model with a convolutional neural network (CNN) in differentiating thymic epithelial tumors (TETs) from other prevascular mediastinal tumors (PMTs).

Methods

A retrospective study was performed in patients with PMTs and undergoing surgical resection or biopsy in National Cheng Kung University Hospital, Tainan, Taiwan, E-Da Hospital, Kaohsiung, Taiwan, and Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan between January 2010 and December 2019. Clinical data including age, sex, myasthenia gravis (MG) symptoms and pathologic diagnosis were collected. The datasets were divided into UECT (unenhanced computed tomography) and CECT (enhanced computed tomography) for analysis and modelling. Radiomics model and 3D CNN model were used to differentiate TETs from non-TET PMTs (including cyst, malignant germ cell tumor, lymphoma and teratoma). The macro F1-score and receiver operating characteristic (ROC) analysis were performed to evaluate the prediction models.

Result

In the UECT dataset, there were 297 patients with TETs and 79 patients with other PMTs. The performance of radiomic analysis with machine learning model using LightGBM with Extra Tree (macro F1-Score = 83.95%, ROC-AUC = 0.9117) had better performance than the 3D CNN model (macro F1-score = 75.54%, ROC-AUC = 0.9015). In the CECT dataset, there were 296 patients with TETs and 77 patients with other PMTs. The performance of radiomic analysis with machine learning model using LightGBM with Extra Tree (macro F1-Score = 85.65%, ROC-AUC = 0.9464) had better performance than the 3D CNN model (macro F1-score = 81.01%, ROC-AUC = 0.9275).

Conclusion

Our study revealed that the individualized prediction model integrating clinical information and radiomic features using machine learning demonstrated better predictive performance in the differentiation of TETs from other PMTs at chest CT scan than 3D CNN model.

MRI-Based Stepwise Approach to Anterior Mediastinal Cystic Lesions for Diagnosis and Further Management

As the majority of incidentally detected lesions in the anterior mediastinum is small nodules with soft tissue appearance, the differential diagnosis has typically included thymic neoplasm and prevascular lymph node, with benign cyst. Overestimation or misinterpretation of these lesions can lead to unnecessary surgery for ultimately benign conditions. nonsurgical anterior mediastinal lesions. The pitfalls of MRI evaluation for anterior mediastinal cystic lesions are as follows: first, we acknowledge the limitation of T2-weighted images for evaluating benign cystic lesions. Due to variable contents within benign cystic lesions, such as hemorrhage, T2 signal intensity may be variable. Second, owing to extensive necrosis and cystic changes, the T2 shine-through effect may be seen on diffusion-weighted images (DWI), and small solid portions might be missed on enhanced images. Therefore, both enhancement and DWI with apparent diffusion coefficient values should be considered. An algorithm will be suggested for the diagnostic evaluation of anterior mediastinal cystic lesions, and finally, a management strategy based on MRI features will be suggested.

Intrathymic growing bronchogenic cyst mimicking thymoma: A case report

Intrathymic bronchogenic cysts are extremely rare lesions, and the differential diagnosis with a banal thymic cyst or a solid tumor can be problematic. Thymic carcinomas arising within thymic cysts have also been reported. We report a case of radical thymectomy for a slowly growing small thymic cyst. The pathological finding revealed a bronchogenic cyst rather than a thymic neoplasm.

The diagnostic value of magnetic resonance imaging compared to computed tomography in the evaluation of fat-containing thoracic lesions

Intrathoracic fat-containing lesions may arise in the mediastinum, lungs, pleura, or chest wall. While CT can be helpful in the detection and diagnosis of these lesions, it can only do so if the lesions contain macroscopic fat. Furthermore, because CT cannot demonstrate microscopic or intravoxel fat, it can fail to identify and diagnose microscopic fat-containing lesions. MRI, employing spectral and chemical shift fat suppression techniques, can identify both macroscopic and microscopic fat, with resultant enhanced capability to diagnose these intrathoracic lesions non-invasively and without ionizing radiation. This paper aims to review the CT and MRI findings of fat-containing lesions of the chest and describes the fat-suppression techniques utilized in their assessment.

Machine-learning classifiers based on non-enhanced computed tomography radiomics to differentiate anterior mediastinal cysts from thymomas and low-risk from high-risk thymomas: A multi-center study

Background

This study aimed to investigate the diagnostic value of machine-learning (ML) models with multiple classifiers based on non-enhanced CT Radiomics features for differentiating anterior mediastinal cysts (AMCs) from thymomas, and high-risk from low risk thymomas.

Methods

In total, 201 patients with AMCs and thymomas from three centers were included and divided into two groups: AMCs vs. thymomas, and high-risk vs low-risk thymomas. A radiomics model (RM) was built with 73 radiomics features that were extracted from the three-dimensional images of each patient. A combined model (CM) was built with clinical features and subjective CT finding features combined with radiomics features. For the RM and CM in each group, five selection methods were adopted to select suitable features for the classifier, and seven ML classifiers were employed to build discriminative models. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic performance of each combination.

Results

Several classifiers combined with suitable selection methods demonstrated good diagnostic performance with areas under the curves (AUCs) of 0.876 and 0.922 for the RM and CM in group 1 and 0.747 and 0.783 for the RM and CM in group 2, respectively. The combination of support vector machine (SVM) as the feature-selection method and Gradient Boosting Decision Tree (GBDT) as the classification algorithm represented the best comprehensive discriminative ability in both group. Comparatively, assessments by radiologists achieved a middle AUCs of 0.656 and 0.626 in the two groups, which were lower than the AUCs of the RM and CM. Most CMs exhibited higher AUC value compared to RMs in both groups, among them only a few CMs demonstrated better performance with significant difference in group 1.

Conclusion

Our ML models demonstrated good performance for differentiation of AMCs from thymomas and low-risk from high-risk thymomas. ML based on non-enhanced CT radiomics may serve as a novel preoperative tool.

Thymic cyst: Is attenuation artifactually increased on contrast-enhanced CT?

Background

Thymic cysts are often misinterpreted as thymomas or lymph nodes, then leading to unnecessary thymectomy. The purpose of this study was to investigate how the adjacent large vessels artifactually affected attenuation values of thymic cysts on contrast–enhanced CT (CE-CT).

Methods

In this retrospective study, a total of 84 patients were included with pathological diagnosis of thymic cysts and preoperative CE-CT. Quantitative measurements of the size, CT attenuation of thymic cysts and CT attenuation of adjacent large vessels were performed on preoperative CE-CT. According to the absolute change in attenuation of the cysts between contrast-enhanced and nonenhanced CT, the patients were classified into the groups of artifactual hyper-density, unchanged density, and artifactual hypo-density. CT characteristics were compared between the three groups. Furthermore, multivariable logistic regression analysis was performed to determine the independent factors for artifactual hyper-density.

Results

The group of artifactual hyper-density had smaller short diameter of the cysts, higher postcontrast attenuation values and lower nonenhanced attenuation values of the adjacent large vessel. Furthermore, the multivariable logistic analysis showed that artifactual hyper-density of thymic cysts was negatively associated with nonenhanced attenuation of adjacent large vessel, and positively associated with postcontrast attenuation of adjacent large vessel and postcontrast attenuation of cysts.

Conclusions

Most cases with &gt;20 HU nonenhanced CT attenuation in surgically resected cases. Artifactual hyper-density─pseudo-enhancement phenomenon of thymic cysts was more apparent in higher increasing attenuation of adjacent large vessels on CE-CT. A well understanding of this phenomenon can help reduce preoperative misdiagnosis and unnecessary thymectomy.

Added Value of Magnetic Resonance Over Computed Tomography in Distinguishing Nonneoplastic Complex Thymic Cysts From Malignant Cystic Thymic Neoplasms

PURPOSE

The aim of the study was to evaluate cystic thymic masses by using computed tomography (CT) and magnetic resonance (MR) scoring systems to differentiate nonneoplastic thymic cysts from cystic thymic neoplasms.

METHODS

This retrospective multisite study included adult patients who underwent CT and MR imaging of the chest between 2007 and 2020 with any of the following impressions on cross-sectional imaging studies: "thymic mass with cystic component," "unilocular or multilocular cystic thymic lesion," "complex thymic cyst," "thymic cyst with hemorrhage." Two blinded radiologists reviewed and recorded specific imaging features as well as overall impressions on both CT and MR using a Likert scale scoring system. Data were analyzed, and diagnostic accuracy of CT and MR was compared using areas under the receiver operating characteristic curves (AUC).

RESULTS

Fifty-six patients were included, of which 45 (80%) had benign masses. Total of 21 patients (38%) had indeterminate scores on CT of which 3 (14%) were malignant, while only 6 (11%) had indeterminate scores on MR and 1 was malignant. Magnetic resonance scoring system (AUC, 0.95) performed better than CT scoring system (AUC, 0.86) in distinguishing benign versus malignant lesions (P = 0.06). Lack of enhancement within the mass was completely predictive of benign etiology (P < 0.001). Wall thickness of an enhancing cyst was predictive of malignancy, with AUC 0.93.

CONCLUSIONS

Magnetic resonance yielded higher specificity allowing a larger number of lesions to be confidently assigned a benign diagnosis. This could help in averting unnecessary follow-up, biopsies, or surgery. The authors recommend follow-up imaging with MR for prevascular masses, even those appearing "solid" on CT.

Development and Validation of a CT-Based Radiomics Nomogram in Patients With Anterior Mediastinal Mass: Individualized Options for Preoperative Patients

Background

To improve the preoperative diagnostic accuracy and reduce the non-therapeutic thymectomy rate, we established a comprehensive predictive nomogram based on radiomics data and computed tomography (CT) features and further explored its potential use in clinical decision-making for anterior mediastinal masses (AMMs).

Methods

A total of 280 patients, including 280 with unenhanced CT (UECT) and 241 with contrast-enhanced CT (CECT) scans, all of whom had undergone thymectomy for AMM with confirmed histopathology, were enrolled in this study. A total of 1,288 radiomics features were extracted from each labeled mass. The least absolute shrinkage and selection operator model was used to select the optimal radiomics features in the training set to construct the radscore. Multivariate logistic regression analysis was conducted to establish a combined clinical radiographic radscore model, and an individualized prediction nomogram was developed.

Results

In the UECT dataset, radscore and the UECT ratio were selected for the nomogram. The combined model achieved higher accuracy (AUC: 0.870) than the clinical model (AUC: 0.752) for the prediction of therapeutic thymectomy probability. In the CECT dataset, the clinical and combined models achieved higher accuracy (AUC: 0.851 and 0.836, respectively) than the radscore model (AUC: 0.618) for the prediction of therapeutic thymectomy probability.

Conclusions

In patients who underwent UECT only, a nomogram integrating the radscore and the UECT ratio achieved good accuracy in predicting therapeutic thymectomy in AMMs. However, the use of radiomics in patients with CECT scans did not improve prediction performance; therefore, a clinical model is recommended.

I-131 false-positive uptake in a thymic cyst with expression of the sodium-iodide symporter: A case report

RATIONALE

I-131 radioiodine false-positive findings in postoperative patients with differentiated thyroid cancer (DTC) should be recognized to avoid unnecessary therapies.

PATIENT CONCERNS AND DIAGNOSES

A 50-year-old man underwent I-131 therapy 3 times, including the initial ablative therapy after total thyroidectomy for papillary thyroid cancer. The initial I-131 posttherapeutic whole-body scintigraphy showed 2 cervical and one superior mediastinal focal I-131 positive uptake lesions. The serum thyroglobulin level was negative every time when the radioiodine therapy was performed. Although the 2 cervical positive uptake lesions disappeared after the second therapy, the superior mediastinal I-131 positive uptake persisted even after the third therapy, and this lesion was suspicion of I-131 therapy-resistant node metastasis.

INTERVENTIONS AND OUTCOMES

The lesion was resected, and the pathological diagnosis with immune-histochemical analysis was a thymic cyst with thymic epithelial cells having a weak expression of the sodium-iodide symporter (NIS).

LESSONS

The false-positive result may be attributed to the NIS expression in the thymic cyst epithelial cells. It is necessary to include a thymic cyst in the differential diagnosis, when I-131 uptake is noted in the superior mediastinal region on I-131 posttherapeutic scans of patients with postoperative DTC. Although the I-131 positive uptake in a thymic cyst may be influenced by the I-131 administered dose and scan timing after I-131 administration, the NIS expression may be essential to the false-positive uptake in a thymic cyst.

Computed Tomography-Based Radiomics for Differentiation of Thymic Epithelial Tumors and Lymphomas in Anterior Mediastinum

Objective

To investigate the differential diagnostic performance of computed tomography (CT)-based radiomics in thymic epithelial tumors (TETs) and lymphomas in anterior mediastinum.

Methods

There were 149 patients with TETs and 93 patients with lymphomas enrolled. These patients were assigned to a training set (n = 171) and an external validation set (n = 71). Dedicated radiomics prototype software was used to segment lesions on preoperative chest enhanced CT images and extract features. The multivariable logistic regression algorithm was used to construct three models according to clinico-radiologic features, radiomics features, and combined features, respectively. Performance of the three models was compared by using the area under the receiver operating characteristic curves (AUCs). Decision curve analysis was used to evaluate clinical utility of the three models.

Results

For clinico-radiologic model, radiomics signature model, and combined model, the AUCs were 0.860, 0.965, 0.975 and 0.843, 0.961, 0.955 in the training cohort and the test cohort, respectively (all P<0.05). The accuracies of each model were 0.836, 0.895, 0.918 and 0.845, 0.901, 0.859 in the two cohorts, respectively (all P<0.05). Compared with the clinico-radiologic model, better diagnostic performances were found in the radiomics signature model and the combined model.

Conclusions

Radiomics signature model and combined model exhibit outstanding and comparable differential diagnostic performances between TETs and lymphomas. The CT-based radiomics analysis might serve as an effective tool for accurately differentiating TETs from lymphomas before treatment.

Dual-energy CT perfusion imaging for differentiating invasive thymomas, thymic carcinomas, and lymphomas in adults

AIM

To evaluate the role of dual-energy computed tomography perfusion (DECTP) imaging in differentiating invasive thymomas (ITs), thymic cancers (TCs), and lymphomas in adults.

MATERIALS AND METHODS

Ninety-five patients with solid masses in the prevascular mediastinum who underwent DECTP examinations were enrolled in this study. The perfusion parameters (blood flow, BF; blood volume, BV; mean transit time, MTT; permeability surface, PS) and spectral parameters (water concentration, WC; iodine concentration, IC; normalised iodine concentration, NIC; the slope of spectral radiodensity [Hounsfield units] curve, λ_HU) of the lesions were analysed.

RESULTS

There were no differences in the MTT or WC values among ITs, TCs, and lymphomas (all p>0.05). The IC, NIC, and λ_HU values in the optimal arterial and venous phases and PS values of TCs were higher than those of ITs and lymphomas (all p<0.05), and there were no differences between ITs and lymphomas (all p>0.05). The BF and BV values of lymphomas were lower than those of ITs and TCs (all p<0.05), and there were no differences between ITs and TCs (all p>0.05). The cut-off values for BF and BV used to differentiate lymphomas from ITs and TCs were 42.83 ml/min/100 g and 4.66 ml/100 g, respectively (area under the receiver operating characteristic curve: 0.847 and 0.839; sensitivity, 80.6% and 82.1%; specificity, 75% and 71.4%; accuracy, 78.9% and 81.1%).

CONCLUSIONS

The perfusion and spectral parameters of DECTP imaging help to identify ITs, TCs, and lymphomas, and BF and BV values help to differentiate lymphomas from ITs and TCs.

Magnetic resonance imaging of the pediatric mediastinum: updates, tips and tricks

Magnetic resonance imaging (MRI) of the pediatric mediastinum is challenging for the practicing radiologist. Many confounding factors add to the complexity of pediatric mediastinal MRI including small patient size, broad spectrum of mediastinal pathologies, motion artifacts and the need for sedation in a significant portion of children. However, with special attention to motion-reduction techniques and knowledge of pediatric-specific considerations, pediatric radiologists can help to provide accurate and timely diagnosis and also prevent multimodality imaging where MRI might be all that is needed. The purpose of this paper was present a practical review of pediatric mediastinal MRI with particular emphasis on diseases where MRI is the primary imaging modality of choice. Additionally, the author addresses those mediastinal processes for which MRI serves as a secondary problem-solving imaging tool.

Special Computed Tomography Imaging Features of Thymic Cyst

OBJECTIVE

To explore the features and diagnostic value of computed tomography (CT) imaging in cases of thymic cysts.

METHODS

A total of 24 cases of the thymic cysts (confirmed by postoperative pathology) were retrospectively analyzed. The location, morphology, and density of the thymic cysts were summarized, and the changes in CT value of the region of interest (ROI) in the thymic cysts between noncontrast enhanced and enhanced chest scans were compared and classified.

RESULTS

The average long-axis dimension was 17.50 ± 6.00 mm, the CT value range across the 24 cases was 5-81 HU, and the average CT value of the noncontrast enhanced scans was 39.75 ± 20.66 HU. The CT value in the noncontrast enhanced scan was >20 HU in 79% of the sample cases. The CT value in the ROI of the thymic cysts under enhanced scan showed a significant decrease in 15 cases, a significant increase in 5 cases, and an insignificant change in 4 cases.

CONCLUSION

The CT values of the thymic cysts in the enhanced scans were generally lower than in the noncontrast enhanced scans, which might be a valuable finding for thymic cysts diagnosis.

Diagnostic Test Accuracy of 18F-FDG PET or PET/CT for Characterization of Histologic Type of Thymic Epithelial Tumor: A Meta-analysis

PURPOSE

This study investigated diagnostic accuracies of 18F-FDG PET or PET/CT for characterization of histologic type of thymic epithelial tumors (TETs) through a systematic review and meta-analysis.

PATIENTS AND METHODS

The PubMed, Cochrane database, and EMBASE database, from the earliest available date of indexing through August 31, 2020, were searched for studies evaluating diagnostic performance of 18F-FDG PET or PET/CT for characterization of TET. We determined the sensitivities and specificities, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic curves.

RESULTS

The pooled sensitivity of 18F-FDG PET or PET/CT was 0.89 (95% confidence interval [CI], 0.80-0.95), and the pooled specificity was 0.77 (95% CI, 0.63-0.87) for differentiation between thymic cancer and thymoma. Likelihood ratio syntheses gave an overall positive likelihood ratio (LR+) of 3.9 and negative likelihood ratio (LR-) of 0.14. The pooled diagnostic odds ratio was 28 (95% CI, 13-63). The pooled sensitivity was 0.90 (95% CI, 0.75-0.96), and the pooled specificity was 0.81 (95% CI, 0.68-0.89) for differential diagnosis of a low-risk or high-risk TET. LR+ was 4.7 and LR- was 0.12. The pooled diagnostic odds ratio was 38 (95% CI, 12-121). In meta-regression analysis, no variable was the source of the study heterogeneity.

CONCLUSIONS

18F-FDG PET or PET/CT has excellent diagnostic performances for characterization of TET. Further large multicenter studies would be necessary to establish the diagnostic accuracy of 18F-FDG PET or PET/CT for differentiation of histologic type of TET.

Imaging of the Chest After Radiotherapy and Potential Pitfalls

Radiotherapy is one of the cornerstones for the treatment of thoracic malignancies. The goal of radiotherapy is to deliver maximal dose to the tumor while minimizing damage to surrounding normal anatomical structures. Although advances in radiotherapy technology have considerably improved radiation delivery, potential adverse effects are still common. Post radiation changes to the chest may include different structures such as the lung, heart, great vessels, and esophagus. The purpose of this manuscript is to illustrate the post radiotherapy changes to these anatomical structures resulting from external beam radiotherapy, as well as discuss imaging pitfalls to prevent radiologist's interpretation errors.

CT-Based Radiomics Nomogram for Differentiation of Anterior Mediastinal Thymic Cyst From Thymic Epithelial Tumor

Objectives

This study aimed to distinguish preoperatively anterior mediastinal thymic cysts from thymic epithelial tumors via a computed tomography (CT)-based radiomics nomogram.

Methods

This study analyzed 74 samples of thymic cysts and 116 samples of thymic epithelial tumors as confirmed by pathology examination that were collected from January 2014 to December 2020. Among the patients, 151 cases (scanned at CT 1) were selected as the training cohort, and 39 cases (scanned at CT 2 and 3) served as the validation cohort. Radiomics features were extracted from pre-contrast CT images. Key features were selected by SelectKBest and least absolute shrinkage and selection operator and then used to build a radiomics signature (Rad-score). The radiomics nomogram developed herein via multivariate logistic regression analysis incorporated clinical factors, conventional CT findings, and Rad-score. Its performance in distinguishing the samples of thymic cysts from those of thymic epithelial tumors was assessed via discrimination, calibration curve, and decision curve analysis (DCA).

Results

The radiomics nomogram, which incorporated 16 radiomics features and 3 conventional CT findings, including lesion edge, lobulation, and CT value, performed better than Rad-score, conventional CT model, and the clinical judgment by radiologists in distinguishing thymic cysts from thymic epithelial tumors. The area under the receiver operating characteristic (ROC) curve of the nomogram was 0.980 [95% confidence interval (CI), 0.963–0.993] in the training cohort and 0.992 (95% CI, 0.969–1.000) in the validation cohort. The calibration curve and the results of DCA indicated that the nomogram has good consistency and valuable clinical utility.

Conclusion

The CT-based radiomics nomogram presented herein may serve as an effective and convenient tool for differentiating thymic cysts from thymic epithelial tumors. Thus, it may aid in clinical decision-making.

Role of quantitative energy spectrum CT parameters in differentiating thymic epithelial tumours and thymic cysts

AIM

To explore the utility of multiple energy spectrum computed tomography (CT) parameters in distinguishing thymic epithelial tumours (TETs) from thymic cysts among lesions <5 cm in diameter.

MATERIALS AND METHODS

Data pertaining to 56 patients with TETs and thymic cysts <5 cm in diameter were assessed retrospectively. All patients underwent surgical resection and the diagnosis was confirmed histopathologically. Thirty-five patients with TETs (average age, 51.97 years) and 21 patients with thymic cysts (average age, 50.54 years) were included. The region of interest for the lesion on the energy spectrum CT was delineated on the post-processing workstation, and multiple parameters of the energy spectrum CT were obtained. The diagnostic efficacies of the parameters were analysed using receiver operating characteristic (ROC) curves.

RESULTS

To distinguish small TETs from thymic cysts, a single-energy CT value of 60 keV showed good differential diagnostic performance in the arterial phase (cut-off value = 68.42 HU; area under the curve [AUC] = 0.978), a single-energy CT value of 70 keV showed good differential diagnostic performance in the venous phase (cut-off value = 59.77 HU; AUC = 0.956). In the arterial and venous phases, effective atomic numbers of 8.065 and 8.175, respectively, were used as cut-off values to distinguish small TETs from thymic cysts (AUC = 0.972 and AUC = 0.961, respectively). Iodine concentrations of 10.99 and 11.05 were used as cut-off values to distinguish small TETs from thymic cysts (AUC = 0.956 and AUC = 0.924, respectively).

CONCLUSION

According to the present study, energy spectrum CT parameters may have clinical value in the differential diagnosis of TETs and thymic cysts.

Differential diagnosis of thymic epithelial neoplasms on computed tomography using the diameter of the thymic vein

Although differentiating benign and malignant thymic epithelial lesions is important to avoid unnecessary treatment and predict prognosis, it is challenging because of overlaps in the chest computed tomography (CT) findings. In this study, we investigated whether the diameter of the thymic vein and other CT findings could differentiate between benign (thymoma and thymic cysts) and malignant (thymic carcinoma, [TCa]) lesions.We conducted a retrospective study across two tertiary referral hospitals in Japan between November 2009 and June 2018. We included 12 patients with TCa, 34 patients with thymomas, and 17 patients with thymic cysts. We analyzed the receiver operating characteristic (ROC) curve to determine the best cut-off values and performed univariate and multivariate analyses of CT findings to distinguish TCa from other benign lesions. Post-hoc analysis was performed for the maximum short axis of the thymic vein using the Mann-Whitney U test, and the number of the maximum short axis of the thymic vein ≥ the cutoff was determined using the Fisher exact test with a family-wise error-correction using Bonferroni's method.ROC analysis showed that a maximum short axis of the thymic vein ≥2 mm was considerably more frequent in TCa than in the other lesions (P < .001 for both), with 83% sensitivity and 86% specificity. Univariate and multivariate analyses revealed the association with TCa of the number of the maximum short axis of the thymic vein ≥2 mm (P = .005, multivariate generalized linear model analysis), ill-defined margin (P = .001), and mediastinal lymphadenopathy (P < .001). Thymic vein diameter was in descendimg order of TCa > thymoma > thymic cysts with statistically significant differences between the groups (Ps < .05).Thymic vein diameter was significantly longer in TCa than in thymoma and thymic cysts. Measurement of the maximum short axis of the thymic vein could be a powerful diagnostic tool to differentiate TCa from thymoma and thymic cysts.

Acute Angle of Multilobulated Contours Improves the Risk Classification of Thymomas

Background: Computed tomography plays an important role in the identification and characterization of thymomas. It has been mainly used during preoperative evaluation for clinical staging. However, the reliable prediction of histological risk types of thymomas based on CT imaging features requires further study. In this study, we developed and validated a nomogram based on CT imaging and included new indices for individualized preoperative prediction of the risk classification of thymomas.

Methods: We conducted a retrospective, multicenter study that included 229 patients from two Chinese medical centers. All the patients underwent cross-sectional CT imaging within 2 weeks before surgery. The results of pathological assessments were retrieved from existing reports of the excised lesions. The tumor perimeter that contacted the lung (TPCL) was evaluated and a new quantitative indicator, the acute angle (AA) formed by adjacent lobulations, was measured. Two predictive models of risk classification were created using the least absolute shrinkage and selection operator (LASSO) method in a training cohort for features selection. The model with a smaller Akaike information criterion was then used to create an individualized imaging nomogram, which we evaluated regarding its prediction ability and clinical utility.

Results: A new CT imaging-based model incorporating AA was developed and validated, which had improved predictive performance during risk classification of thymomas when compared with a model using traditional imaging predictors. The new imaging nomogram with AA demonstrated its clinical utility by decision curve analysis.

Conclusions: Acute angle can improve the performance of a CT-based predictive model during the preoperative risk classification of thymomas and should be considered a new imaging marker for the evaluation and treatment of patients with thymomas. On the contrary, TPCL is not useful as a predictor for the risk classification of thymomas in this study.

Longitudinal CT and MRI Characteristics of Unilocular Thymic Cysts

Background Isoattenuating and hyperattenuating thymic cysts at CT are often misinterpreted as lymphadenopathy or thymic epithelial neoplasms. Purpose To evaluate the longitudinal change in thymic cyst appearance at CT and MRI. Materials and Methods All chest MRI studies showing thymic cysts between July 2008 and December 2019, identified from a retrospective search of a quality assurance database, were included in this study if initial CT depicted a thymic lesion, the patient was referred for follow-up MRI for characterization, and the baseline (ie, index) MRI indicated a cystic lesion. Follow-up CT scans and/or MRI scans were identified through July 2020. Thymic cyst characteristics, such as size, location, and morphologic features, as well as CT and MRI characteristics, were recorded. Change in size, attenuation, and T1-weighted MRI signal was assessed longitudinally. Descriptive statistics of longitudinal change were tabulated. Results A total of 244 chest MRI studies in 140 patients with 142 unique cysts and 392 CT examinations (636 total examinations and 645 thymic cysts-nine examinations with two cysts each) were evaluated. The median follow-up duration was 2.2 years. Thirty-three patients with 34 unique cysts (34 of 142 cysts [24%]) underwent imaging follow-up for more than 5 years. Thymic cysts followed up for more than 5 years were most commonly saccular (189 of 274 cysts [69% axially]) and retrosternal (14 of 34 cysts [41%]). Craniocaudal dimension was larger than transverse and anteroposterior dimensions in 223 of 274 cysts (81%). Mean thymic cyst attenuation was 25 HU (range, 15-100 HU). Five of 31 cysts (16%) exhibited wall calcification. The median cyst wall thickness was 2.0 mm (range, 0.9-3.0 mm). Most thymic cysts changed in volume (31 of 34 cysts [91%]), CT attenuation (15 of 35 cysts [43%]), and T1-weighted MRI signal (12 of 18 cysts [67%]) over time. None developed mural irregularity, nodularity, or septations. Conclusion Unilocular thymic cysts, defined at index MRI, never developed irregular wall thickening, mural nodularity, or septations that would raise concern for malignant transformation. However, these cysts showed mural calcification and change in size, CT attenuation, and MRI signal over more than 5 years of follow-up. © RSNA, 2021 Online supplemental material is available for this article.

Mediastinal thymoma: A difficult diagnosis in the pediatric age

Thymoma is a rare neoplasm of the anterior mediastinum, which originates from the epithelium of the thymic gland; it occurs mainly in middle-aged adults and is much less common in children. The tumor has slow growth and is asymptomatic in most pediatric cases, thus resulting in an accidental discovery; one-third of the young patient presents symptoms related to the compression of the tumor mass on the surrounding anatomic structures and/or related to paraneoplastic syndromes. Surgery is the treatment of choice and complete resection of the thymoma achieves excellent long-term results in terms of disease-free survival. In this article, we report the clinical case of a 21-month-old girl who came to our observation for persistent cough for over a month investigated with a chest X-ray, performed in another hospital. The X-ray showed an extensive opacification of the left hemithorax with contralateral dislocation of the mediastinum. The instrumental investigations carried out in our hospital (ultrasound, computed tomography, and magnetic resonance of the chest) showed a voluminous expansive mass of the left antero-superior mediastinum, which occupied the entire ipsilateral hemithorax and not dissociable from the thymus. At the histologic examination, the mass resulted to be a B1 thymoma with a low degree of malignancy according to the histologic classification of thymic tumors of the World Health Organization.

Limited resection for early-stage thymoma: minimally invasive resection does not mean limited resection

Standard resection for patients with thymoma is resection of thymoma with total thymectomy (TTx) via median sternotomy. Hence, limited resection for thymoma means a lesser extent of resection of normal thymus compared with a standard procedure, i.e. resection of thymoma with partial thymectomy (PTx). In contrast, minimally invasive resection has been defined as resection of thymoma with TTx via a less-invasive approach. However, to date, few studies have precisely evaluated the differences in surgical and oncological outcomes among these three procedures. This report summarizes the differences among these three procedures with a review of studies (January 2000 to December 2020) focusing on the difference in surgical and oncological outcomes and presents current issues in the surgical management of thymoma. In this report, 16 studies were identified; 5 compared standard resection to limited resection, 9 compared standard resection to minimally invasive resection and 2 compared limited resection to minimally invasive resection. Most studies reported that the surgical and oncological outcomes of limited resection or minimally invasive resection were similar to those of standard resection in patients with early-stage thymoma. However, they did not include a sufficient follow-up period. Both limited resection and minimally invasive resection for early-stage thymoma might be reasonable treatment options. However, they are still promising modes of resection. Further studies with a long follow-up period are needed.

ACR Appropriateness Criteria® Imaging of Mediastinal Masses

Mediastinal masses can present with symptoms, signs, and syndromes or incidentally. Selecting the appropriate diagnostic imaging study for mediastinal mass evaluation requires awareness of the strengths and weaknesses of the various imaging modalities with regard to tissue characterization, soft tissue contrast, and surveillance. This publication expounds on the differences between chest radiography, CT, PET/CT, ultrasound, and MRI in terms of their ability to decipher and surveil mediastinal masses. Making the optimal imaging choice can yield diagnostic specificity, avert unnecessary biopsy and surgery, guide the interventionist when necessary, and serve as a means of surveillance for probably benign, but indeterminate mediastinal masses. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.