An unusual presentation of presentation of a branchial cleft cyst.

Branchial cleft cysts are congenital anomalies that arise from the aberrant embryological development of the branchial apparatus. The location of a branchial cleft cyst is determined by which branchial cleft failed to obliterate during embryological development, with the second branchial cleft cyst being the most commonly recognized lesion. Although the most common location for branchial cleft cysts is between the external auditory canal and the level of the clavicle, the literature does describe unusual locations. We present a case a 15-year-old boy who had an enlarging lesion on his back that had been present since birth. A presumptive radiologic diagnosis of lymphangioma circumscriptum was made. Upon excision of the lesion and pathologic examination, it was determined to be a branchial cleft cyst. The patient had an uneventful postoperative course, and no recurrence was noted after a 2-year follow-up. Our clinical report demonstrates a lesion on the posterior thorax that proved to be a branchial cleft cyst and should always be part of the differential diagnosis for soft tissue masses of the thorax.