Ectopic cervical thymoma located in the carotid triangle.

Ectopic cervical thymoma is an extremely rare tumor thought to arise from ectopic thymic tissue caused by the aberrant migration of the embryonic thymus. We present the case of a 44-year-old woman with an ectopic cervical thymoma located in the carotid triangle. A computed tomography (CT) scan detected a mass in her right carotid triangle. On an unenhanced scan, the tumor showed homogeneous isodensity compared with muscles, and neither fat nor calcification was detected. A contrast-enhanced CT image obtained during the arterial phase showed intratumoral septa, while an image obtained during the parenchymal phase showed cystic changes within the mass. The patient underwent a surgical resection. A histological study enabled a diagnosis of type AB thymoma in which foci with the features of type A thymoma are admixed with foci rich in lymphocytes. This subtype is a benign tumor with a good prognosis. Ectopic cervical thymoma should be included in the differential diagnosis of solid masses located in the carotid triangle when the CT findings are typical of a thymoma.