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
Cock's peculiar tumour is: September 2007 
Select and explain. 
A. Infected sebaceous cyst, B. Osteomyelitis of skull, C. Cyst in the skull, D. Tumour of the skull
A: Infected sebaceous cyst
Answer: A: Infected sebaceous cyst 
Explanation: Ans. A: Infected sebaceous cyst Cock's peculiar tumour is a sebaceous cyst linked growth. One form of sebaceous cyst is the trichilemmal cyst; these are thought to arise from the hair follicle epithelium and are most commonly found on the scalp. Usually they are multiple but occasionally there can be a proliferating trichilemmal cyst which grows to a large size and ulcerates. These can resemble a squamous cell carcinoma (both clinically and histologically) and these ulcerating solitary cysts are called Cock's peculiar tumour.