Imaging of the pediatric thymus: Clinicoradiologic approach

Abstract

The thymus is a lymphatic organ that undergoes dynamic changes with age and disease. It is important to be familiar with these physiological changes in the thymus gland to be able to identify pathology and make an accurate diagnosis. The thymus may be involved in multisystem disorders or show focal isolated lesions. The aim of this article is to review the radiological anatomy of the thymus, normal variants, and pathology including hyperplasia and benign/malignant lesions involving the thymus gland in the pediatric age group. We also propose an algorithmic approach for imaging evaluation of a suspected thymic mass on the basis of morphologic features.

Challenges in diagnosing ectopic thymus tissue in children

“…Thymic cysts commonly have a homogeneous low attenuation on CT imaging, and the i njection of gadolinium contrast enhances their smooth, thin, regular walls 20. In-phase and opposed-phase T1-weighted MRI does not clearly distinguish cysts from solid or cellular material unless the cystic lesion is homogeneously T1-hyperintense 21. With increased proteinaceous content during infection or bleeding, they mimic solid lesions as attenuation increases and T1-isointense, with an intermediate signal, or T1-hyperintense images can be seen 18.…”

“…With increased proteinaceous content during infection or bleeding, they mimic solid lesions as attenuation increases and T1-isointense, with an intermediate signal, or T1-hyperintense images can be seen 18. Solid lesions can vary from mild enhancement, such as lymphomas, to intense enhancement in the case of haemangiomas 21. Therefore steady-state free precession T2-weighted imaging, and precontrast and postcontrast dynamic contrast enhanced MRI with postprocessed subtraction are the most helpful MR pulse sequences to distinguish between cystic and solid lesions 21.…”

“…Solid lesions can vary from mild enhancement, such as lymphomas, to intense enhancement in the case of haemangiomas 21. Therefore steady-state free precession T2-weighted imaging, and precontrast and postcontrast dynamic contrast enhanced MRI with postprocessed subtraction are the most helpful MR pulse sequences to distinguish between cystic and solid lesions 21. As opposed to the thymus of an adult, where fatty atrophy takes place, the growing thymus of a child limits the value of in-phase and out-of-phase chemical shift MRI , making differential diagnosis of solid components more difficult.…”

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

“…However, it is known that when the involution starts, the epithelial component of the thymus atrophies, resulting in scattered small lymphocytes in abundant adipose tissue (18,19,22). LFH, also known as autoimmune thymitis, is characterized by a normal size and weight of the thymus with chronic inflammation and proliferation of lymphoid follicles, active germinal centers and increased numbers of lymphocytes and epithelial cells (23,24). The symptoms of MG, including the impairment of ocular (extra-ocular muscles, eyelids), bulbar (ingestion function, voice/speech function, respiratory function, facial muscles) and limb-axial muscles (arms, legs and neck), always improve after thymectomy in patients with thymoma or LFH thymus (5)(6)(7)(8).…”

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

“…It becomes triangular in shape with straight or concave margins as age increases. Thymus density on computed tomography (CT) decreases with age in children (from 80 to 56 Hounsfield unit (HU)) due to fatty replacement [5].…”