Struma ovarii mimicking ovarian malignancy: a case report.

Struma ovarii is a rare form of monodermal ovarian teratoma composed predominantly of mature thyroid tissue. Although benign in most cases, it can present with ascites and elevated serum CA125 levels, mimicking ovarian carcinoma. We report the case of a 38-year-old woman with a complex ovarian mass, ascites, and an elevated CA125 level-an initial presentation highly suggestive of malignancy that was ultimately diagnosed as benign struma ovarii following surgical intervention. This case underscores how struma ovarii, though uncommon, can masquerade as ovarian cancer and may even be discovered incidentally in an asymptomatic, premenopausal patient.