ODP423 Postmenopausal Virilization Secondary to A Rare Left Ovarian Androgen-Secreting Leydig Cell Tumor Localized Using Ovarian Vein Sampling

INTRODUCTION: Postmenopausal virilization can be caused by androgen-secreting tumours from either the adrenal glands or ovaries. Ovarian androgen-secreting tumours are rare, accounting for <0.2% of all cases of hyperandrogenism, and <1% of ovarian tumours. Leydig cell tumours account for <0.1% of all ovarian tumours and may represent a diagnostic challenge given their small size and difficulty to visualize radiologically. CLINICAL CASE: A 57-year-old female with a past medical history of hypertension presented with a 10-year history of hirsutism, and a 4-year history of virilization. She denied exogenous testosterone or supplement use. Examination was significant for voice deepening, excessive hair growth on her face, back, chest, and upper leg (Ferriman-Gallwey score of 20), male pattern baldness, and clitoromegaly. Investigations revealed markedly elevated total testosterone 11.5nmol/L (reference range (RR)=0.3-1.3) and bioavailable testosterone 7.19nmol/L (RR=0.1-0.6). DHEAS was normal at 4. 0umol/L (RR=0.8-4.9). TSH, prolactin, 17-OH-progesterone, ACTH, IGF-1 and GH were normal, and cortisol suppressed to <50nmol/L after 1-mg dexamethasone. Abdominal and transvaginal ultrasound, and adrenal and pelvic MRI did not identify adrenal or ovarian masses. Given normal DHEAS, there was a high suspicion for an ovarian source despite unremarkable imaging, thus ovarian vein sampling was undertaken. This revealed lateralization to the left gonad with total testosterone level of 780nmol/L (RR=0.3-1.8) and right gonadal testosterone level of 18.6nmol/L (RR=0.3-1.3). Left-to-right ovarian ratio was 41.94 (>15 is a strong lateralization to the left ovary as the likely source). After discussion with Gynecology, the patient underwent bilateral salpingo-oopherectomy given she was postmenopausal. The ovarian pathology revealed a left ovarian Leydig cell tumour with normal right ovarian pathology. Post-operatively, her total testosterone normalized to 0.4nmol/L, and the patient's virilizing symptoms improved. CONCLUSION AND IMPLICATIONS FOR PRACTICE: This case illustrates the importance of considering rare androgen-secreting ovarian tumours in the differential diagnosis of post-menopausal virilization. It also demonstrates the diagnostic challenge associated with such tumours particularly given their difficulty to visualize radiologically. This demonstrates the importance of considering ovarian vein sampling as a diagnostic tool for localization when there is a high suspicion for an ovarian tumour, even when not identified on imaging studies. Presentation: No date and time listed