Second branchial cleft cyst
Branchial cleft anomalies are the second most common type of congenital neck mass and present as cartilaginous remnants, sinuses, fistulas, or cysts due to the failure of the branchial apparatus to obliterate. The most common are second branchial cleft anomalies, representing 95% of these cases. Second branchial cleft anomalies are usually located along the anterior border of the sternocleidomastoid muscle on the left side of the neck.
Differential diagnoses include thyroglossal duct cyst, neck abscess, cystic hygroma, cervical lymphadenopathy, metastatic lymph nodes, and cat scratch disease.