BACKGROUND
The thymus originates around 6 weeks of gestation from the paired third pharyngeal pouches together with the inferior parathyroid glands.1 Fusion of the bilateral primordial thymus occurs around the 8th week of gestation. The thymus then migrates caudally along the line of embryological descent to enter into the anterior mediastinum. Ectopic cervical thymus (ECT) is a rare lesion caused by the abnormal descent of the thymus gland into the mediastinum and represents less than 1% of neck lesions in children.2 The lesion can be solid, partially or predominantly cystic, with the latter accounting for majority (76-92%) of cases.3 The presentation is generally with an asymptomatic lateral neck lump. Symptoms can occur as a result of infection, airway obstruction or, in neonates and infants, feeding difficulties in large ECT.4-9 The diagnosis can be suspected with ultrasound scan (USS).10-12 However, magnetic resonance imaging (MRI) has the added benefits of clarifying the anatomy, especially the relation with neck vascular structures, documenting additional ectopic thymic tissue in the neck and the presence of a normal mediastinal thymus.13 Fine needle aspiration cytology (FNAC) may also be helpful in the diagnosis although might not always be accurate.14-16 Surgical excision might be indicated in large symptomatic masses. Nevertheless, in children, conservative management might be appropriate in asymptomatic cases and in the absence of a normal mediastinal thymus; this is to prevent rendering a child athymic and subsequently immuno-incompetent.9, 17, 18 We herein describe a case report of a 10-year old girl with a right neck ECT which was initially misdiagnosed as branchial cyst. We also performed a systematic review of the paediatric literature in the last 20 years. We aim to clarify the management of ECT in children.