The finding is a structure in the left side of the neck with a thin wall and fluid density contents. It is located anterior to the left sternocleidomastoid muscle, lateral to the carotid artery and jugular vein, and posterior to the submandibular gland. This is the typical location and appearance of a 2nd branchial cleft cyst.

Branchial cleft abnormalities arise from remnants of the branchial apparatus of embryonic life. The second, third and fourth branchial clefts form a depression lined with ectoderm, the cervical sinus of His. Branchial cleft anomalies are believed to result from incomplete obliteration of this structure or from buried epithelial rests. The vast majority of branchial cleft abnormalities arise from the second branchial cleft, and most of these are cysts. Less commonly, a fistula or sinus tract may develop. The cysts gradually enlarge over time, and are often discovered between 10-40 years of age as a painless fluctuant neck mass near the angle of the mandible.

Ultrasound may demonstrate an anechoic cystic mass, or may demonstrate a cyst with fine internal echoes representing debris. CT scan shows sharply circumscribed low density mass with a thin wall if no infection has occurred. If infection supervenes, the wall may become thicker and enhance.

Treatment is surgical excision due to the likelihood of infection.