This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous ENT, Subject name: ENT
The most frequent site of branchial cyst is at 
Select and explain. 
A. Upper third of posterior border of sternocleidomastoid, B. Upper third of anteromedial border of sternocleidomastoid, C. Supraclavicular fossa, D. Lower third of anterior border of sternocleidomastoid
B: Upper third of anteromedial border of sternocleidomastoid
Answer: B: Upper third of anteromedial border of sternocleidomastoid 
Explanation: The branchial cyst is common in the second decade of life but can occur at any age with equal frequency in both sexes. Cyst presents as a swelling in the upper pa of the neck anterior to the sternocleidomastoid muscle. Mass is smooth, round, fluctuant, non-tender and not transilluminate. A painful increase in size at the time of upper respiratory infection can occur. Anomalies of the second branchial arch are the most common. A brachial cyst maybe associated with sinus or fistula. A second arch brachial sinus has an external opening at junction of lower and middle of the anterior border of sternomastoid and may exude mucoid discharge. It may have an internal opening in the tonsillar fossa. Treatment involves surgical excision along with its tract of the present. (Ref: Textbook of diseases of ENT, PL Dhingra, 7th edition, pg no. 446,447)