Cervical thymic cysts.

Thymic cysts are considered uncommon lesions in the differential diagnosis of pediatric neck masses. They usually present in the 1st decade after the age of 2 years, possibly because the thymus attains its greatest development before puberty. They may be found anywhere along the normal descent route of the thymus gland from the mandible to the sternal notch; 50% extend into the mediastinum. Most patients are asymptomatic, although respiratory complications may occur. A review of the operative records in our hospital over the last 10 years revealed two cases of cervical thymic cysts (CTC) in a 5- and a 9-year-old boy. Both children presented with an atraumatic, painless, enlarging mass in the left side of the neck anterior to the sternocleidomastoid muscle. Neither boy had respiratory problems or swallowing difficulties. Ultrasound and computed tomography showed a lesion consistent with a tentative diagnosis of a branchial cyst in one boy and an extensive cystic hygroma in the other. Both lesions were approached through a transverse cervical incision and, although closely adherent to the internal jugular vein, carotid artery, and vagus nerve, were resected completely. There were no postoperative complications and so far there has been no recurrence. CTCs are uncommon benign lesions that should be considered in the evaluation of neck masses in children. Preoperative diagnosis is unusual and, at this time, there is no preoperative radiologic test that can accurately identify a neck mass as a CTC. Histologic investigation of the excised specimen showing thymic tissue remnants with pathognomonic Hassall's corpuscles and cholesterol clefts in the cyst wall is the only definitive diagnosis. Evolution is benign. Intact, complete surgical excision remains the treatment of choice.