Thymic Hyperplasia with Lymphoepithelial Sialadenitis (LESA)-Like Features: Strong Association with Lymphomas and Non-Myasthenic Autoimmune Diseases

Making an accurate diagnosis of anterior mediastinal lesions: a proposal for a new diagnostic algorithm from the BTOG Thymic Malignancies Special Interest Group

Due to the rising demand in cross-sectional thoracic imaging, anterior mediastinal lesions are being identified with increasing frequency. Following iterative and multidisciplinary discussions, the BTOG Thymic Malignancies Special Interest Group have developed an algorithm to standardise the diagnostic approach for these relatively uncommon but important conditions which span from benign (thymic remnant, thymic hyperplasia and thymic cysts) to suspected localised thymomas to suspected more aggressive malignancy (thymic carcinoma, lymphoma and germ cell tumours). For each condition, we provide a brief description, an overview of the key radiological findings and a description of the proposed algorithm including the rationale behind the recommendations. We also highlight the role of magnetic resonance (MR) imaging for the characterisation of anterior mediastinal masses in specific indications when the necessary local resources and expertise exist. In addition, we hope this provides the rationale for service development in MR of the anterior mediastinum where current resource and expertise requires development. Through this standardised pathway, we hope to drive improvements in patient care by rationalising surveillance schedules, avoiding unnecessary resections of benign entities with their associated morbidity and optimising the diagnostic work-up prior to the appropriate treatment of anterior mediastinal malignancies.

Benign lesions of the mediastinum

Mediastinal tumours represent a heterogeneous group of entities derived from the manifold structures located in or adjacent to the mediastinum. Due to the occurrence of some of these tumours in characteristic mediastinal compartments, an anatomical subdivision of the mediastinum in the prevascular (anterior), visceral (middle), and paravertebral (posterior) is helpful for the differential diagnosis. Benign anterior mediastinal tumours linked to an enlargement of the thymic gland mainly consist of thymic cysts and several types of thymic hyperplasia: true thymic hyperplasia, rebound hyperplasia, lymphofollicular hyperplasia, and so-called thymic hyperplasia with lymphoepithelial sialadenitis (LESA)-like features. Mature teratomas, ectopic (para)thyroid tissue, and benign thymic tumours such as thymolipoma or thymofibrolipoma represent further typical tumours of the anterior mediastinum. Pericardial, bronchogenic, or oesophageal duplication cysts predominate in the middle mediastinum, whereas neurogenic tumours and myelolipomas are characteristic findings in the posterior compartment. Vascular tumours, lipomas, adenomatoid tumours, Castleman disease, or mediastinitis are further examples of less frequent tumours or tumorous lesions affecting the mediastinum. This review focuses on benign mediastinal lesions with an emphasis on benign tumours of the thymus. Besides histology, characteristic epidemiological and clinical aspects prerequisite for the correct diagnosis and patient management are discussed.

Development and validation of a contrast-enhanced CT-based radiomics nomogram for differentiating mass-like thymic hyperplasia and low-risk thymoma

PURPOSE

To explore the efficiency of a contrast-enhanced CT-based radiomics nomogram integrated with radiomics signature and clinically independent predictors to distinguish mass-like thymic hyperplasia (ml-TH) from low-risk thymoma (LRT) preoperatively.

METHODS

135 Patients with histopathology confirmed ml-TH (n = 65) and LRT (n = 70) were randomly divided into training set (n = 94) and validation set (n = 41) at a ratio of 7:3. The least absolute shrinkage and selection operator (LASSO) algorithm was used to obtain the optimal features. Based on the selected features, four machine learning models, support vector machine (SVM), logistic regression (LR), extreme gradient boosting (XGBOOST), and random forest (RF) were constructed. Multivariate logistic regression was used to establish a radiomics nomogram containing clinically independent predictors and radiomics signature. Receiver operating characteristic (ROC), DeLong test, and calibration curves were used to detect the performance of the radiomics nomogram in training set and validation set.

RESULTS

In the validation set, the area under the curve (AUC) value of LR (0.857; 95% CI: 0.741, 0.973) was the highest of the four machine learning models. Radiomics nomogram containing radiomics signature and clinically independent predictors (including age, shape, and net enhancement degree) had better calibration and identification in the training set (AUC: 0.959; 95% CI: 0.922, 0.996) and validation set (AUC: 0.895; 95% CI: 0.795, 0.996).

CONCLUSION

We constructed a contrast-enhanced CT-based radiomics nomogram containing clinically independent predictors and radiomics signature as a noninvasive preoperative prediction method to distinguish ml-TH from LRT. The radiomics nomogram we constructed has potential for preoperative clinical decision making.

Thymic hyperplasia with lymphoepithelial sialadenitis (LESA)-like features: a case report and literature review

BACKGROUND

Thymic hyperplasia with lymphoepithelial sialadenitis-like features (LESA-like TH) is a rare form of thymic hyperplasia, characterized by a prominent expansion of the thymic medulla containing hyperplastic lymphoid follicles with germinal centers, while an almost total absence of thymic cortex. Since the first report in 2012, only a few cases of LESA-like TH have been reported in the literature to date. Due to the rarity of LESA-like TH and the tumor-like morphology, it is easy to be misdiagnosed as other common diseases of the thymus in routine practice, such as thymoma and lymphoma.

CASE PRESENTATION

Herein, we present a case report of a 52-year-old Chinese female patient with LESA-like TH, without any discomforting symptoms. Computer-tomography imaging revealed a cystic solid mass in the anterior mediastinum, with well-defined boundaries and multiple internal septa. Histologically, prominent features were florid lymphoid follicles containing germinal centers, as well as hyperplasia of thymic epithelial cells and proliferation of Hassall bodies. However, the thymic cortex rich in immature T cells was almost completely absent. Furthermore, mature plasma cells, lymphoepithelial lesions, and cholesterol clefts were frequently seen.

CONCLUSION

We made a diagnosis of LESA-like TH and performed a literature review to better understand the clinicopathological features of LESA-like TH and reduce misdiagnosis.

Thymic Hyperplasia With Lymphoepithelial Sialadenitis-Like Features Arising in a Patient With Immunoglobulin G4-Related Disorders: A Case Report

Thymic hyperplasia with lymphoepithelial sialadenitis-like features is characterized by thymic hyperplasia with lymphocytic infiltrates in the thymic epithelium. The lesion differs from other forms of thymic hyperplasia, including true and follicular thymic hyperplasia, in that it presents at an advanced age and has been reported to be unassociated with autoimmune diseases. We report a case of thymic hyperplasia with lymphoepithelial sialadenitis-like features in a 55-year-old male patient with a history of an immunoglobulin G4 (IgG4)-related disorder. Histologically, the resected mediastinal mass showed features consistent with those of thymic hyperplasia with lymphoepithelial sialadenitis-like features. In addition, the IgG4/IgG ratio was elevated in the polyclonal plasmacytoid infiltration. Thymic hyperplasia with lymphoepithelial sialadenitis-like features has not been reported to be associated with IgG4-related disorders; however, as shown in our report, it is crucial to include it in the differential diagnosis of a mediastinal mass in a patient with IgG4-related disorders.

GTF2I Mutation in Thymomas: Independence From Racial-Ethnic Backgrounds. An Indian/German Comparative Study

Thymomas are the most frequent adult mediastinal cancers. Their etiology is unknown and their pathogenesis poorly understood. Racial, ethnic and environmental factors influence tumorigenesis in many cancers, but their role in thymomas remains unclear to date. In this study that included pretreatment thymoma cases from India and Germany (n = 37 and n = 77, respectively) we compared i) the prevalence of the thymoma-specific chromosome 7 c.74146970T > A mutation of the GTF2I gene in type A and AB thymomas; ii) epidemiological features; and iii) the frequency of myasthenia gravis (MG). Due to a known predominance of GTF2I mutation in A and AB histotypes, we included only a marginal number of type B thymomas as a control group in both cohorts. While the distribution of histological types between the cohorts was similar (p = 0.1622), Indian patients were strikingly younger (p < 0.0001; median age 50 vs. 65 years) and showed significantly lower tumour stage (Masaoka-Koga stage I) at primary diagnosis (p = 0.0005) than the German patients. In patients with known MG status (n = 17 in Indian and n = 25 in German cohort), a clear trend towards more frequent MG was observed in the Indian group (p = 0.0504; 48 vs. 82%). The prevalence of the GTF2I mutation (analysed in n = 34 Indian and n = 77 German patients) was identical in the two cohorts. We conclude that racial-ethnic and environmental factors do not significantly influence the most common molecular feature of thymomas but may have an impact on the timing of clinical presentation.