Abstract
Branchial cleft cysts (BCCs) are a congenital malformation most commonly seen in children and adolescents. BCCs are usually incidental findings and are benign in nature. In this report, we present a case of a 13-year-old female with syncope as a rare complication of a fluid-filled second BCC. The patient initially presented with a unilateral non-tender swelling on the right side of the neck and submandibular region, which was suspicious of an inflammatory process. After initial lab investigations came back negative, imaging studies of the neck with computed tomography (CT) with intravenous contrast revealed a hypodense lesion with a uniform density, which lay beneath the sternocleidomastoid muscle and abutted the carotid sheath. The cyst was surgically excised, and histopathological studies of the cyst wall and the analysis of the fluid contained within the cyst confirmed that it was indeed a branchial cleft cyst. We propose that the syncopal episodes she experienced most likely occurred due to the proximity of the cyst wall to the carotid sheath, which caused a mass effect leading to carotid sinus syndrome (CSS). This is the first case of CSS due to a BCC to be reported in the pediatric population.