Imaging of the pediatric thymus: Clinicoradiologic approach

Incontinentia pigmenti underlies thymic dysplasia, autoantibodies to type I IFNs, and viral diseases

Human inborn errors of thymic T cell tolerance underlie the production of autoantibodies (auto-Abs) neutralizing type I IFNs, which predispose to severe viral diseases. We analyze 131 female patients with X-linked dominant incontinentia pigmenti (IP), heterozygous for loss-of-function (LOF) NEMO variants, from 99 kindreds in 10 countries. Forty-seven of these patients (36%) have auto-Abs neutralizing IFN-α and/or IFN-ω, a proportion 23 times higher than that for age-matched female controls. This proportion remains stable from the age of 6 years onward. On imaging, female patients with IP have a small, abnormally structured thymus. Auto-Abs against type I IFNs confer a predisposition to life-threatening viral diseases. By contrast, patients with IP lacking auto-Abs against type I IFNs are at no particular risk of viral disease. These results suggest that IP accelerates thymic involution, thereby underlying the production of auto-Abs neutralizing type I IFNs in at least a third of female patients with IP, predisposing them to life-threatening viral diseases.

[Morphology of Hassall's corpuscles and their microenvironment in neonates with increased thymus weight]

OBJECTIVE

To study morphological features of Hassall's corpuscles (HC) and their microenvironment in newborns with increased thymus mass.

MATERIAL AND METHODS

The study was carried out on autopsy material of children of the first month of life. Based on the thymic index (TI), 2 groups were identified: with normal (conditional norm) and increased TI value (increased thymus weight). The standard method of histological staining and immunohistochemical methods with antibodies to Pan-CK, CK19, CD68, CD3 and p53 were used in the study. The classification proposed by A.G. Beloveshkin (2013) was used to determine the degree of maturity of HC. Nonparametric Mann-Whitney test was used to determine statistically significant differences in the groups.

RESULTS

In the group of children with increased thymus weight, the number of HC decreased by 20%. It was found that the proportion of progressive and mature corpuscles in this group was reduced by 2.3 and 1.6 times, respectively, compared to the group of children with normal thymus weight, while the proportion of regressive corpuscles increased almost 2-fold. In the HC microenvironment, there is an increase in the total number of thymocytes, combined with a decrease in the expression of CD68, CD3 and p53 in them. A sharp decrease in CK19-expressing cells in this group is accompanied by a disruption in the formation of reticular structures characteristic of the comparison group.

CONCLUSION

In the thymus with increased mass, the structural and functional organization changes: along with an increase in the total number of thymocytes in the cortical layer and a decrease in the number of macrophages, epithelial cells and HC (with a predominance of regressive corpuscles), disturbances in the processes of maturation, apoptosis and negative selection of lymphocytes occur, which can lead to development of immunogenesis disorders.

Computed Tomographic Features of Thymus in Dogs: Correlation with Age, Gender, Breed and Body Fat Content

BACKGROUND

The thymus is the first lymphoid organ formed to regulate a newborn's immunity. It reaches its maximum size during puberty, after which it undergoes an atrophic procedure called involution, but its ability to grow again in response to some stresses, such as infections, neoplasia, surgeries, chemotherapy, and radiotherapy is maintained. There is no comprehensive study on computed tomographic features of thymus in dogs. So, the goal of the present study is to gain better insight into the thymus using computed tomography as a non-invasive method.

METHODS

One hundred and fifty dogs classified in five age groups and five breed groups were recruited to this study and the thymus was evaluated using a 2-slice computed tomography machine. The inclusion criteria for the present study were having a normal complete blood count, plain and post-contrast CT scan examination of the thoracic region and no history of neoplasia, chemotherapy or radiotherapy. The visibility, density, enhancement, grade, size, volume, shape, borders and lateralization of the thymus were evaluated and statistical analysis was performed. The effect of obesity on thymic grade and volume was also investigated.

RESULTS

The visibility, density, dorsal length, volume and grade decreased with increasing age. The thymic shape and lateralization were mostly wedge shaped and left sided, respectively. The borders became concave with aging and increasing body fat content caused an increase in the fatty degeneration of the thymus.

CONCLUSIONS

Declining thymic density, grade, size and volume with aging are related to thymic involution and fatty degeneration was accelerated by increasing body fat content. Females and males were different only in thymic shape and small and large breeds were different only in thymic volume. The thymus was visible in some geriatric dogs with no underlying disease. We expect that the present work can be used by radiologists in reading thoracic computed tomography but investigation of thymic characteristics in dogs with neoplasia and history of chemotherapy, radiotherapy and thoracic surgeries can complete this study.

Massive true thymic hyperplasia with osseous metaplasia

True thymic hyperplasia is defined as an increase in both the size and weight of the gland, while maintaining a normal microscopic architecture. Massive true thymic hyperplasia is a rare type of hyperplasia that compresses adjacent structures and causes various symptoms. Limited reports address the imaging findings of massive true thymic hyperplasia. Herein, we report a case of massive true thymic hyperplasia in a 3-year-old girl with no remarkable medical history. Contrast-enhanced CT revealed an anterior mediastinal mass with a bilobed configuration containing punctate and linear calcifications in curvilinear septa, which corresponded to lamellar bone deposits in the interlobular septa. To our knowledge, this is the first report of massive true thymic hyperplasia with osseous metaplasia. We also discuss the imaging features and etiology of massive true thymic hyperplasia with osseous metaplasia.

Mediastinal lesions in children

The mediastinum is where thoracic lesions most frequently occur in young patients. The histological spectrum of diseases caused by the presence of several organs in the mediastinum is broad. Congenital lesions, infections, benign and malignant lesions, and vascular diseases are examples of lesions. Care should be taken to make the proper diagnosis at the time of diagnosis in order to initiate therapy promptly. Our task is currently made simpler by radiological imaging techniques.

Abnormal Locations of Thymic Tissue as an Uncommon Cause of Neck Masses in Children: A Practical Approach

Background: The thymus gland is a lymphoid organ normally located in the anterior mediastinum. Location abnormalities of the thymus, such as ectopic thymus or the superior herniation of a mediastinal thymus, could be responsible for the occurrence of cervical masses in pediatric patients, raising concerns among clinicians. The knowledge of these conditions is essential for a thorough differential diagnosis and for preventing unnecessary invasive procedures. Methods: Descriptive retrospective series of three patients with a cervical mass, that was later diagnosed as ectopic thymic tissue. Results: The thymus has a unique and distinctive ultrasound appearance that is the keystone to detecting thymic parenchyma in locations other than anterior mediastinum. In selected patients, an accurate ultrasound could be conclusive for the diagnosis, with no need for further and potentially risky procedures. Conclusions: This case series supports the use of ultrasound in both diagnosis and follow-up of thymus location abnormalities, advocating a minimal invasive and conservative approach.

The Role of Thoracic Ultrasound for Diagnosis of Diseases of the Chest Wall, the Mediastinum, and the Diaphragm-Narrative Review and Pictorial Essay

The diagnostic capabilities of ultrasound extend far beyond the evaluation of the pleural space and lungs. Sonographic evaluation of the chest wall is a classic extension of the clinical examination of visible, palpable, or dolent findings. Unclear mass lesions of the chest wall can be differentiated accurately and with low risk by additional techniques such as color Doppler imaging, contrast-enhanced ultrasound, and, in particular, ultrasound-guided biopsy. For imaging of mediastinal pathologies, ultrasound has only a complementary function but is valuable for guidance of percutaneous biopsies of malignant masses. In emergency medicine, ultrasound can verify and support correct positioning of endotracheal tubes. Diaphragmatic ultrasound benefits from the real-time nature of sonographic imaging and is becoming increasingly important for the assessment of diaphragmatic function in long-term ventilated patients. The clinical role of thoracic ultrasound is reviewed in a combination of narrative review and pictorial essay.

Characterizing Differences in Thymic Function in Women With and Without Vulvodynia: A Community-Based Study

OBJECTIVE

The aim of the study was to evaluate the association between vulvodynia and thymic function.

MATERIALS AND METHODS

In this case-control study of 200 clinically confirmed cases of vulvodynia and 205 general population controls residing in the Minneapolis/Saint Paul metropolitan area, we used DNA extracted from whole blood to measure levels of signal joint T-cell receptor excision circles (sjTRECs), a measure of thymic output. We used logistic regression to evaluate the association between vulvodynia and thymic function.

RESULTS

In 405 participants (aged 18-40 years), we observed an association between decreasing thymic function and increasing age. Women with vulvodynia had a steeper decline in sjTREC values across age categories compared with women without vulvodynia. In addition, at younger ages, women with vulvodynia had higher sjTREC values compared with women without vulvodynia. In older women, those with vulvodynia had lower sjTREC than those without vulvodynia. When accounting for recency of vulvar pain onset, women with a shorter time since pain onset had higher thymic function compared with women with a longer time since vulvar pain onset.

CONCLUSIONS

These findings suggest that at younger ages, women with vulvodynia have higher thymic output and a more precipitous decline of thymic function than those without vulvodynia. It also seems that a strong immune inflammatory response is present proximate to the onset of vulvar pain and may wane subsequently over time.

Ultrasound Monitoring of Thymus Involution in Septic Mice

Thymus involution is characterized by a progressive regression of thymus size and contributes to immunosuppression in sepsis. High-frequency ultrasonography is a non-invasive monitoring system in multiple organs, including the thymus, in mice. However, thymus involution has not been studied using ultrasonography in septic mice. This study reports ultrasound approaches to monitoring septic thymus involution in mice. Sepsis was induced by cecum ligation and puncture (CLP). Mice were euthanized at three time points: baseline and days 3 and 10 after CLP. Thymus areas and volumes were measured using 2-D and 3-D ultrasound approaches. Thymus weights were measured ex vivo. Compared with values at baseline, both thymus area and volume decreased significantly at days 3 and 10. In addition, thymus areas and volumes correlated positively with thymus weights. In conclusion, ultrasonography provides reliable thymus measurements and is an optimal technique for monitoring thymus involution in septic mice.

Cervical Extension of the Normal Thymus in Children and Adolescents: Sonographic Features and Prevalence

OBJECTIVE

This study aims to confirm the prevalence of incidental cervical extension of normal thymus in children and adolescents undergoing neck ultrasound and describe the ultrasound appearance to minimize future misdiagnosis.

MATERIALS AND METHODS

This retrospective study was conducted in a single institution. Thyroid and lower neck ultrasound images of the consecutive pediatric subjects between January 1, 2011 and September 30, 2017 were independently reviewed by 2 radiologists for the presence of cervical thymus. When identified on sonographic images, cervical thymus was described on the basis of echogenicity, location, and shape.

RESULTS

In 278 consecutive cases, the 2 reviewers identified 105 (37.8%) and 103 (37.1%) cases respectively as having sonographically visible tissue in the expected location of cervical extension of the thymus. The internal echotexture was variable with 38.1% of cases being hypoechoic, 37.1% mixed, and 24.8% hyperechoic. Cervical extension of the thymus was most commonly (65.0%) to the left of the trachea or (30.9%) bilateral/anterior to the trachea; isolated right paratracheal thymus was uncommon. Thymic shape was variable: quadrilateral (30.9%), oval (29.9%), triangular (25.8%), and other (13.4%). The logistic regression model including age, gender, and BMI z-scores showed that, when controlled for sex and BMI z-scores, younger age was a predictor for the presence of cervical thymic extension (p < .001).

CONCLUSION

Cervical thymic extension is sonographically visible as a soft tissue mass of variable appearance in about a third of children and adolescents undergoing neck ultrasonography with decreasing prevalence with age. Sonographically visible cervical thymic tissue is more common in younger patients.

Respiratory Failure Due to a Large Mediastinal Mass in a 4-year-old Female with Blast Cell Crisis: A Case Report

INTRODUCTION

Symptomatic leukostasis is an exceptionally atypical presentation of blast crisis; and when coupled with an enlarged neoplastic mediastinal mass in a four-year-old female, an extremely rare and challenging pediatric emergency arises.

CASE REPORT

We present a unique case of a four-year-old female who arrived via emergency medical services in cardiopulmonary arrest with clinical and radiographic evidence suggestive of bilateral pneumothoraces, prompting bilateral chest tube placement. Further evaluation revealed a large mediastinal mass and a concurrent white blood cell count of 428,400 per milliliter (/mL) (4,400-12,900/mL), with a 96% blast differential, consistent with complications of T-cell acute lymphoblastic leukemia.

CONCLUSION

This case highlights how pulmonary capillary hypoperfusion secondary to leukostasis, coupled with a ventilation/perfusion mismatch due to compression atelectasis by an enlarged thymus, resulted in this patient's respiratory arrest. Furthermore, the case highlights how mediastinal masses in pediatric patients present potential diagnostic challenges for which ultrasound may prove beneficial.

Role of different imaging modalities in the evaluation of normal and diseased thymus

Background

The appearance of the thymus on imaging studies showed great variability. Thymus imaging is a great challenge. This cross-sectional prospective study investigated the diagnostic value of different imaging modalities in the evaluation of normal and diseased thymus. Chest X-ray was done as a primary survey. Chest computed tomography (CT) was done for 82 patients, chest magnetic resonant imaging (MRI) was done for 40 patients, and 18 flurodeoxy glucose positron emission tomography (18 FDG-PET) was done for 2 patients. Ultrasonography (US) of the anterior mediastinum was done for 2 pediatric patients. Histopathological assessment was done for all cases with diseased thymus.

Results

The study included 158 patients divided into 2 groups: group A, 79 patients with normal thymus for age and group B, 79 patients with thymic lesions detected by one or more of the used modalities. The large-sized thymus was in 79 patients, who were subcategorized to patients with myasthenia gravis (12 patients) and patients with mediastinal masses (67 patients). Imaging findings in normal and diseased thymus gland were compared and lesion analysis by various modalities displayed with histopathological correlation.

Conclusion

There are different imaging modalities for thymus gland evaluation. CT is beneficial for primary assessment giving the morphology and density, and MRI is the imaging modality of choice in diseased thymus owing to functional assessment of the gland; however, X-ray may be helpful as a primary survey tool before CT and MRI. Chest ultrasound could be a suitable primary assessment tool in pediatrics before MRI because it is an easy bedside test.

Challenges in diagnosing ectopic thymus tissue in children

The presentation of a fast-growing cervical mass necessitates prompt attention due to risk of the mass effect on vital structures and requires preferential screening for infections, bleeding and malignancies in an extensive list of differential diagnoses. This case report describes a 4.5-year-old boy with a fast-growing, unilateral lesion in the neck, with clinical features in keeping with malignant characteristics. Surgical excision with pathocytological examination revealed an exceptional diagnosis of haemorrhage in an ectopic cervical thymic cyst. Thymic cysts are a rare cause of unilateral masses in the neck, usually presenting as an asymptomatic, painless, slow-growing or stable mass anywhere along the thymopharyngeal duct. Spontaneous haemorrhages in thymic tissue can occur, often due to coagulation defects. Treatment of symptomatic thymic cysts is based on surgical excision. Partial resection of the thymus should be encouraged if possible, since clinical consequences of removing all thymic tissue in children are still unclear.

Thymic lesions of the paediatric age group: a comprehensive review of non-neoplastic and neoplastic etiologies

Thymus is an important part of the immune system of the paediatric age group. Thymic lesions are rare causes of anterior mediastinal pathology. Their occurrence in children is rarer, nevertheless, knowledge about their pathologies help in clinching the correct diagnosis. All lesions both non-neoplastic as well as neoplastic are found in children, however, they differ from adults not only in the clinical presentation but also in the pathogenesis and natural history of the disease. Thymic hyperplasia may not actually be true if age is taken into consideration. Similarly, a type B thymoma may be mistakenly diagnosed as a lymphoblastic lymphoma especially on small biopsies. This review has been carried out after extensive search of literature using the Google and Pubmed search engines. An attempt has been made to comprehensively cover all aspects of thymic pathology of the paediatric age group having historical significance as well as the recent updates.

Ultrasound of the pediatric chest

Cross-sectional imaging modalities like MRI and CT provide images of the chest which are easily understood by clinicians. However, these modalities may not always be available and are expensive. Lung ultrasonography (US) has therefore become an important tool in the hands of clinicians as an extension of the clinical exam, which has been underutilized by the radiologists. Reinforcement of the ALARA principle along with the dictum of "Image gently" have resulted in increased use of modalities which do not require radiation. Hence, ultrasound, which was earlier being used mainly to confirm the presence of pleural effusion as well as evaluate it and differentiate solid from cystic masses, is now being used to evaluate the lung as well. This review highlights the utility of ultrasound of the paediatric chest. It also describes the normal and abnormal appearances of the paediatric lung on ultrasound as well as the advantages and limitations of this modality.

Comparative study of computed tomography of normal and lymphoid follicular hyperplasia thymus in myasthenia gravis patients

The aim of the present study was to evaluate the thymuses of non-thymomatous myasthenia gravis (MG) patients by computed tomography (CT) for differentiating lymphoid follicular hyperplasia (LFH) thymus from normal/involuted thymus in order to assist surgeons in determining whether a non-thymomatous MG patient requires an operation. In the present retrospective review over 10 years, 80 patients who received CT scan and thymectomy at the Affiliated General Hospital of Tianjin Medial University (Tianjin, China) were included. According to the pathological records, 54 of the cases initially detected on CT were confirmed as LFH thymus. Thymic measurements, including anteroposterior and transverse dimensions, width (the longest axis of the lobe on a transverse scan) and thickness (the largest dimension perpendicular to the long axis of the lobe) and CT attenuation of the thymus region, adipose tissue and chest wall musculature in each CT slice were included to assess differences between the LFH group and the normal/involuted thymus group. Although a negative association between patient age and the CT attenuation of the thymus region was identified (r=-0.779, P<0.05, Pearson's correlation test), the LFH thymus group featured nodular changes on CT, while no such changes were observed in the normal/involuted thymus group. The mean age of disease onset in the LFH thymus group was significantly lower than that in the normal thymus group (40.2±17.3 vs. 59.2±9.3 years). Furthermore, significant differences in CT attenuation were identified between the LFH group and the normal/involuted thymus group [-41.21±54.42 vs. -108.23±8.72 Hounsfield units (HU) on unenhanced CT; -25.57±58.65 vs.-117.40±6.22 HU on contrast-enhanced CT]. In the LFH group, the difference in mean CT attenuation between the thymus region and adipose tissue was significant, while no significant difference was observed in the normal/involuted thymus group. In conclusion, CT may be used to distinguish LFH thymus from normal/involuted thymus in MG patients.

Late Relapse of Ovarian Germ Cell Tumour

BACKGROUND

Malignant ovarian germ cell tumours typically require multimodal therapy including surgery and systemic platinum-based chemotherapy. Most patients are cured, with survival rates exceeding 95%.

CASE

This report describes an unusual case of ovarian germ cell tumour (GCT) recurring 15 years after surgery and manifesting as metastatic disease to the liver, lung, and retroperitoneal lymph nodes.

CONCLUSION

Thymic hyperplasia was a confounding finding in this case, and it should be considered in the differential diagnosis of a mediastinal mass in heavily treated patients with GCT.