Cervical thymus

Preschooler

with left neck massTransverse+sagittal US of the neck (above) shows the mass to have a starry sky appearance. Axial+coronal CT with contrast of the neck shows the mass to be inferior to the thyroid and contiguous with the thymus.The diagnosis was cervical thymus.

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CT density of

cervical thymus, in comparison with mediastinal thymus. Transverse (axial) USG sections of thymus in lower neck and upper mediastinum. a–d Images of a 19-year-old male patient shows thymus (arrows) extending from neck to superior mediastinum. e Hypoechoiec thymus (arrow) in a 4-year-old female. f Hyperechoiec starry sky pattern of thymus (arrow) in an 8-year-old male

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CT density of

cervical thymus, in comparison with mediastinal thymus. a, b Non-contrast CT images of neck and thorax of a 15-year-old male patient. c, d Contrast CT images of neck and thorax of a 10-year-old female patient. a Cervical thymus shows density of 35 HU on non-contrast CT. b Mediastinal thymus shows density of 61 HU on non-contrast CT. c Cervical thymus shows density of 46 HU on post-contrast CT. d Mediastinal thymus shows density of 100 HU on post-contrast CT

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Radiopaedia • CC-by-nc-sa 3.0 • de

The cervical thymus (plural: cervical thymi) refers to an ectopic location of the thymus in the neck above the level of the brachiocephalic veins.

Clinical presentation

A cervical thymus usually presents before adolescence as a painless unilateral midline or lateral neck mass.

Pathology

Etiology

Around the 4 to 5 week of gestation, development of the thymus begins from the 3 branchial pouch. Towards the end of the 6 week, the thymus traverses caudomedially into the inferoanterior mediastinum before fusing in the midline.

Location

Ectopic tissue may occur anywhere along this path secondary to failure of or incomplete descent, implantation or persistence of remnant tissue or failure of involution; resulting in a cervically positioned thymus above the brachiocephalic veins.

Radiographic features

Ultrasound

Sonographic characteristics of the parenchyma are the same as normally positioned thymic tissue:

multiple linear hyperechoic septa
discrete homogeneously distributed hyperechoic foci giving a "speckled" appearance

Contiguity with the normally positioned thymus may be seen with the thymopharyngeal duct.

Treatment and prognosis

No intervention is required as normal involution will usually occur with age. Like normal thymic tissue, residual focal thymic tissue may persist throughout life as an anatomic variant.

Differential diagnosis

The clinical differentials for a cervical thymus may include:

However, if the characteristic normal thymic echo pattern is demonstrated, differential diagnoses are usually easy to exclude.