Masked tumor: A rare presentation of struma ovarii disguised under features imitating malignancy

Aim: To present a rare case of struma ovarii in a 46-year-old lady presenting with features pointing toward malignancy. Background: Struma ovarii is a specialized or monodermal teratoma, which is predominantly composed of mature thyroid tissue. It accounts for less than 5% of all ovarian teratomas. It is mostly benign, and malignant changes are extremely rare. Most patients are asymptomatic or may present with mild signs and symptoms. Although the vast majority are benign, they may rarely present mimicking malignancy. Case description: A 46-year-old lady presented with a large complex abdominopelvic mass with ascites and elevated CA-125 levels, thus arising suspicion of malignancy. Postoperatively, histopathology revealed a benign struma ovarii, which was further confirmed by immunohistochemistry. Conclusion: Struma ovarii can imitate ovarian malignancy clinically, especially if it is complex and found in combination with ascites and an elevated CA-125 level. There is paucity of literature about such cases, and hence, it makes an accurate and timely diagnosis difficult. Clinical significance: This case is one of the very few that provide a description of an atypical presentation of a rare tumor, struma ovarii. A high level of clinical suspicion may help with better preparedness before surgery and prevent extensive laparotomies in such patients.