Imaging of the pediatric thymus: Clinicoradiologic approach

Table 1 Significance of imaging the thymus in various clinical settings

Clinical setting	Possible imaging finding(s)
Myasthenia gravis	Thymoma
	Thymic hyperplasia
Suspected immunodeficiency disorder	Thymic hypoplasia
	Thymic aplasia
Incidental detection while imaging for other causes	Thymic cyst
	Thymic hyperplasia
	Lymphangioma
	Vascular malformation
	Castleman’s disease
	Thymolipoma
Fever evaluation	Lymphoma
	Abscess
Detected during evaluation of other multisystem disorders	Lymphoma
	Langerhans cell histiocytosis

Table 2 Classification of thymic disorders according to the imaging appearance

Appearance/size of thymus	Diseases
Small thymus	Physiological
	Age related involution
	Treatment related atrophy
	Ectopic thymus
	Immunodeficiency disorders
	Hypoplasia
	Aplasia
Large thymus	Hyperplasia
	True hyperplasia
	Follicular hyperplasia
	Masses
	Cystic
	Thymic cyst
	Lymphatic malformation
	Germ cell tumor
	Solid
	Mild/moderate enhancement
	Lymphoma
	Thymoma
	Thymolipoma
	Thymic carcinoma
	Intense enhancement
	Hemangioma
	Castleman’s disease
	Thymic carcinoid
	Mixed
	Infections (abscess/ tuberculosis)
	Germ cell tumor
	Langerhans cell histiocytosis

Table 3 Key morphologic features for differentiation of thymic hyperplasia from a thymic mass

Morphologic criteria	Hyperplasia	Mass
Enlargement	Diffuse, symmetric	Focal, asymmetric
Symmetrical
Contour	Smooth	Nodular
Vessels	Normal	Random branching, encased
Necrosis	Absent	Maybe present
Calcification	Absent	May be present
Microscopic fat (on chemical shift MRI)	Present	Absent