EP453 Fibrothecomas masquerading as ovarian malignancy; a review of pre-operative imaging

Introduction/Background Ovarian fibrothecomas are the most common benign solid ovarian tumour, accounting for approximately 4–5% of all ovarian tumours. Imaging can aid diagnosis of fibrothecoma pre-operatively, with its correct interpretation reducing radiological misdiagnosis as an ovarian malignancy. This could decrease physical, psychological, and social costs of placing patients on the cancer pathway unnecessarily. This is a retrospective review correlating radiological diagnosis with final histological diagnosis of fibrothecoma. Methodology Over a six-year period from 2013 to 2018, we identified patients with a radiological/histological diagnosis of fibrothecoma from the radiology and histology databases, and multi-disciplinary team (MDT) notes at a Cancer Unit and Centre. Pre-operative imaging, MDT outcomes, operative notes, use of frozen section, and final histology were analysed. Results 660 patients with suspicious adnexal masses were discussed at the MDT over the six-year period, of which 31 patients had fibrothecoma. Of this group, the median age was 65(range 29–88), and 27/31(87%) post-menopausal. CA125 was documented in over 90% (28/31), with a risk of malignancy index (RMI) >250 in 42% (13/31). 7 patients (23%) underwent one imaging modality (ultrasound, CT, or MRI), 17(55%) had two modalities, and 7 patients (23%) had all three. In those who underwent ultrasound imaging (19/31(86%)), 26% had a documented U-score. Imaging reports suggested fibrothecoma in 24% (9/31), and 56% (5/9) of these underwent surgery. All 31 patients were discussed at the MDT, and 65% (20/31) underwent surgery at the Cancer Centre, all requiring frozen section. The operative morbidity rate was 33%, and median length of hospital stay 3 days (range 1–10). Conclusion This study highlights that we can improve the pre-diagnostic pathway for our patients, and avoid unnecessary surgery. We endeavor to achieve this through the implementation of standardized radiological reporting for suspected fibrothecoma. Disclosure Nothing to disclose.