Intrathyroidal ectopic thymus in children: A benign lesion

Area of Science:

• Pediatric Imaging
• Endocrinology
• Head and Neck Surgery

Background:

• Incidental thyroid and neck lesions are increasingly detected with widespread ultrasound use.
• Ectopic thymus is a rare congenital anomaly that can mimic other neck masses.

Purpose of the Study:

• To determine the prevalence of ectopic thymus in pediatric patients.
• To describe the natural course and sonographic characteristics of ectopic thymus.

Main Methods:

• Retrospective review of neck/thyroid ultrasounds in 690 children (<18 years) from January 2014 to June 2017.
• Ectopic thymus defined as a hypo- to iso-echoic lesion with vascularity, unconnected to the mediastinal thymus.
• Analysis of lesion location, size, and changes on follow-up ultrasound.

Main Results:

• Sixteen children (2.3%) were diagnosed with ectopic thymus.
• The most common location was the inferior left thyroid lobe; median size was 22.5 mm.
• Follow-up ultrasounds showed stability in 3 cases and decreased size in 1 case.

Conclusions:

• Ectopic thymus is an uncommon but important incidental finding in pediatric neck ultrasounds.
• Its benign nature and stable or decreasing size on follow-up warrant reassurance for parents.
• Consideration of ectopic thymus in the differential diagnosis of pediatric neck lesions is crucial.