Thymopharyngeal duct cyst: an unusual variant of cervical thymic anomalies.

BACKGROUND: The thymus develops from the third pharyngeal pouch and descends from the neck into the anterior-superior mediastinum. Thus, it is possible to have thymic remnants in the neck, which most often present as a cervical mass during childhood. One type of cystic thymic remnant is the thymopharyngeal duct cyst, a remnant of one of the paired tracts of embryological thymic descent. Thymopharyngeal duct cysts are rare lesions that can have a similar presentation to more commonly encountered childhood neck masses.
OBJECTIVES: To review the embryological development of cervical thymic remnants and to report our experience with the thymopharyngeal duct cyst.
DESIGN: Case series.
SETTING: Tertiary care center. PATIENTS: Two children who presented with asymptomatic neck masses that were caused by cystic remnants of the thymopharyngeal duct.
RESULTS: Both patients underwent preoperative computed tomography, which revealed a multiloculated mass coursing adjacent to the carotid sheath. Surgical treatment was the definitive therapy for both patients, although neither patient had a definitive preoperative diagnosis. In both cases, the mass was approached through an incision anterior to the sternocleidomastoid muscle, and dissection proceeded along the length of the carotid sheath. A fibrous cord extending into the mediastinum was found in both patients. There were no postoperative complications. Histopathologic evaluation revealed the presence of mature thymic elements within the wall of a multiloculated cyst.
CONCLUSIONS: Thymopharyngeal duct cysts must be considered in the differential diagnosis of pediatric neck masses. Computed tomography is helpful to delineate the relationship to the carotid sheath. Complete surgical excision is the appropriate therapy in a majority of cases, with minimal morbidity when careful attention is paid to vital structures.