This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ovary, Subject name: Gynaecology & Obstetrics
All of the following ovarian tumours usually occur bilaterally. Except - 
Select and explain. 
A. Metastatic mass, B. Dysgerminoma, C. Adenoma of ovary, D. Dermoid cyst
B: Dysgerminoma
Answer: B: Dysgerminoma 
Explanation: Ans. is 'b' > 'd' Dysgerminoma (more than Dermoid cyst) (Ref Shaws, 13/e, p 361 (12/e, p 317)).Two option b & d seem to be correct in this question (b is the better option to go with).About dysgerminoma Shaw's states "It is usually unilateral."About dermoid cyst Shaw states that "Dermoid cyst is bilateral" in 10-15% cases. "Ovarian adenomas are bilateral in 50% cases and.Metastasis to ovary is always bilateral.