Highly differentiated follicular carcinoma of ovary: Use of imprint cytology at intraoperative consultation.

Highly differentiated follicular carcinoma of ovary (HDFCO) is a rare entity known to arise in struma ovarii. Clinical presentation and radiological features mimic other cystic ovarian neoplasm. Thus, intraoperative diagnosis of this entity can be challenging. We hereby report a HDFCO case of a 52-year-old woman, who presented with significant abdominal bloating for 3 months. Imaging showed a 11.7 cm left adnexal-mixed cystic and solid mass, adhering to the bowel with ascites. The mass was examined intraoperatively and showed multilocular cysts filled with straw or red brown-colored gelatinous fluid. Microscopically, the tumor consisted of small and large follicles with proteinous material and bland-looking cuboidal cells, suspicious for struma ovarii or granulosa cell tumor with extensive cystic changes, while imprint cytology slides showed watery colloid with cracking artifact favoring the former. However, the adherence to the bowel suggested HDFCO, and prompted surgical staging. The histology of the ovarian mass in the permanent section resembled goiterous thyroid tissue with invasion of endocervical stroma, uterine wall and colonic serosa, and presence of tumor nodules in omentum leading to the diagnosis of HDFCO. Due to striking resemblance of HDFCO to benign thyroid goiter, searching for invasive and metastatic foci is crucial for correct diagnosis. In addition, intraoperative imprint cytology revealing colloid with cracking artifact is helpful for differentiating struma ovarii and/or HDFCO from other ovarian lesions.