Ectopic thymus presenting as a right-side cervical mass in an infant

Abstract

A 3-cm, soft, nontender and mobile mass was detected in the right mandibular angle of a 7-week-old boy. A right parapharyngeal mass (Fig. 1, arrows) was discovered on MR imaging, isointense to muscle on T1-W images and hyperintense on T2-W and post-contrast images. It was isointense to thymus (Fig. 1, arrowheads) on all sequences. A core-needle biopsy showed thymic tissue. Ectopic cervical thymus is a rare cause of a neck mass during infancy [1]. During its descent a remnant of thymus remains along the thymopharyngeal duct. It is often located between the superior vena cava, the brachiocephalic vessels and the aorta; rarely, it is within the posterior mediastinum [2]. This resultant “mass” can be mistaken for a pathologic process. The differential diagnosis of a lateral cervical mass in an infant includes various congenital cysts, lymphatic malformation, branchial cleft anomalies, lymphadenopathy, and inflammatory or neoplastic lesions.