Malignant Struma Ovarii: A Blinded Study of 86 Cases Assessing Which Histologic Features Correlate With Aggressive Clinical Behavior

Context.—Struma ovarii exhibiting malignant histology are uncommon, and an aggressive clinical course in the form of initial extraovarian spread or recurrence is even more exceptional for these tumors. Objective.—To determine whether specific histologic features have predictive value in distinguishing clinically benign from clinically malignant struma ovarii. Design.—Blinded analysis of 19 histologic characteristics of thyroid tumors was performed in 60 clinically benign and 26 clinically malignant struma ovarii cases, with long-term follow-up. Results.—Except for lack of fibrosis and macrofollicular pattern, which were more common in biologically malignant tumors (P  =  .04 and P  =  .008, respectively), and trabecular pattern, which was associated with a benign clinical course (P  =  .03), none of the other histologic features was found to be correlated with clinical behavior. The presence of the following features was similar in the biologically benign and malignant tumors: papillae, pseudo-papillae, p...