Ectopic cervical thymus in a child: A rare neck mass case report

Ectopic cervical thymus is a rare congenital anomaly caused by aberrant thymic migration. It commonly presents in the pediatric population as a neck mass and is often misdiagnosed due to its nonspecific clinical features.

This report describes a 12-year-old female presenting with a progressively enlarging, painful mass in the left lower cervical region over four months. Clinical examination revealed a firm, mildly tender mass inferior to the left thyroid lobe and medial to the carotid sheath. Laboratory investigations, including complete blood count and thyroid function tests, were normal. Neck US showed a hypoechoic lesion with echogenic foci, with starry sky appearance, consistent with thymic tissue. Contrast-enhanced CT of the neck and chest confirmed a well-circumscribed, homogeneously enhancing 3 × 1 cm mass along the thymopharyngeal tract, medial to the carotid sheath, with the anterior mediastinal thymus present and normal. The patient underwent surgical excision via a transcervical approach, preserving the recurrent laryngeal nerve and parathyroid glands. Histopathology confirmed ectopic thymic tissue with corticomedullary differentiation and Hassall's corpuscles. The postoperative course was uneventful. At 16 months postoperatively, the patient remained asymptomatic, with no evidence of recurrence on clinical examination or imaging.

Ectopic cervical thymus should be considered in the differential diagnosis of pediatric neck masses, particularly those adjacent to the thyroid gland. High-resolution imaging is critical for accurate diagnosis and operative planning. While conservative management may be appropriate in asymptomatic cases, surgical excision is warranted for symptomatic, enlarging, or diagnostically uncertain lesions. Complete resection typically results in excellent outcomes with minimal morbidity.

Although rare, ectopic cervical thymus should be recognized as a potential cause of pediatric neck masses. Surgical excision offers definitive treatment with favorable long-term outcomes and low recurrence risk.