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': 'Which of the following regarding branchial cyst is true? \nSelect and explain. \nA. Seen deep to lower 1/3rd of sternocleidomastoid, B. Wall consists of lymphoid tissue, C. Filled with keratinized fluid, D. Presents at birth', 'role': 'user'}, {'content': "Answer: B \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\nSix branchial arches with five pharyngeal pouches (endoderm lining) inside and five pharyngeal clefts (ectoderm lining) outside are present.\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.\nIn 3% cases, it is bilateral; it can be familial also.\nUsually painless unless it is infected.\xa0\nIt contains cholesterol crystals which is from the lining of mucous membrane which contains sebaceous gland. Cheesy toothpaste like material is typical.\nHistologically, it is lined by squamous epithelium. Occasionally it contains ciliated columnar epithelium. Cyst wall shows plenty of lymphoid tissue.\xa0\n\nKey Concept:\nHistologically, it is lined by squamous epithelium. Occasionally it contains ciliated columnar epithelium. Cyst wall shows plenty of lymphoid tissue. Epithelial infusion within lymph node may be the\xa0 cause as branchial cyst contains lymphoid tissues in their wall.\xa0\nReference: SRB's Manual of Surgery, 5th ed, page no 431", 'role': 'assistant'}]