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Prof. Dr.Adalet Demir, Thoracic Surgery

The thymus gland is a small organ located in the anterior part of the chest, under the sternum bone, in the anterior mediastinum.

The thymus gland is the primary organ that forms the defense system until puberty, protects our body against foreign antigens, and is responsible for the production and maturation of immune cells (production of T-lymphocytes). The thymus gland is large in children, and with the development of the immune system, the thymus gland gradually loses its function, shrinks, and remains a residue. Within years, the epithelial component of the thymus atrophies, and eventually, small lymphocytes remain dispersed within the adipose tissue. T-lymphocytes are produced in the bone marrow.

Thymus Hyperplasia; is an increase in the size or weight of the thymus gland. It can be histopathological and morphological.

  • Histopathological hyperplasia is real hyperplasia (increase in size and weight of the thymus gland).
    • Real hyperplasia may present without any cause.
    • Among the most common reasons for thymus hyperplasia is as follows: hyperthyroidism, cortisone therapy, radiotherapy, and some blood diseases.
    • It is more common in men.
  • Morphological hyperplasia is follicular hyperplasia (presence of germinal-centered lymphoid follicles)
    • The weight and size of the thymus may be normal or increased.
    • Autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and scleroderma are among the most common causes.
    • It is more common in women.

 We recommend that patients with thymus hyperplasia consult their doctors in the neurology, endocrine, and rheumatology departments to discover the etiology of thymus hyperplasia.

Diagnosis of Thymus Hyperplasia

  • It may be asymptomatic in some cases.
    • The most common symptoms are; cough, shortness of breath, and lung infections.
  • PA chest X-ray
    • Detects Mediastinal expansion
  • Thorax CT
    • Diffuse enlargement of the thymus gland region in the mediastinum and soft contours are observed as fat or lymphoid tissue.
    • The thymus reaches its greatest size in the first two years of life and typically fills the anterior mediastinum.
    • The thymus gland begins to shrink at five and takes a rectangular shape.
    • The thymus gland involutes with age, and its density gradually decreases in CT.
    • Thymic hyperplasia's characteristics are diffuse and symmetrically enlarged thymus tissue with smooth borders. Asymmetric enlargement is a sign of thymoma (Picture 1)
  • Thorax MRI
    • The normal thymus has a muscle-like signal intensity on both T1- and T2-sequences. After childhood, the glandular structures in the thymus atrophy are replaced by fat infiltration, increasing the signal intensity in both sequences.
  • PET-CT
    • Although FDG uptake accompanying thymic hyperplasia in PET-CT is variable, it is often diffuse and homogeneous.
    • Thymic hyperplasia does not have a threshold value that can make the differential diagnosis of thymus tumors. When the uptake pattern is heterogeneous, we should consider diseases other than thymus hyperplasia.

Conclusion: We do not prefer biopsy and surgical removal in Thymus Hyperplasia unless it is accompanied by myasthenia gravis disease. The important thing here is to make a differential diagnosis of thymic hyperplasia from benign and malignant masses in the anterior mediastinum (thymoma, lymphoma, etc.). Here, a good radiologist and MRI with Dual echo (In and out phase) of coronal and sagittal sections of the mediastinum are essential.

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