This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': 'Most frequent site of branchial cyst is at \nSelect and explain. \nA. Upper third of posterior border of sternocleidomastoid, B. Lower third of anterior border of sternocleidomastoid, C. Upper third of anteromedial border of sternocleidomastoid, D. Supraclavicular fossa', 'role': 'user'}, {'content': 'Answer: C \nExplanation: BRANCHIAL CYST\n\nIt arises from the remnants of second branchial cleft. Normally, 2nd, 3rd, 4th clefts disappear to form a smooth neck. Persistent 2nd cleft is called as cervical sinus (of His) which eventually gets sequestered to form branchial cyst.\xa0\nSwelling in the neck beneath the anterior border of upper third of the sternomastoid muscle. It is smooth, soft, fluctuant, often transilluminant with a sensation of ‘Half-filled double hot water bottle’.\nIt is equal in both sexes. Even though congenital, it is seen in late adolescents and early 3rd decade.\nIt contains cholesterol crystals which is from the lining of mucous membrane which contains sebaceous gland. Cheesy toothpaste like material is typical.', 'role': 'assistant'}]