Introduction/Background Ovarian sex cord-stromal tumours (SCTs) are a group of benign and malignant neoplasms that develop from different types of cells, mostly specialized in the production of steroid hormones. In contrast to the more common epithelial ovarian malignant neoplasms, most patients with malignant SCTs are diagnosed with early-stage disease. Histology is generally low grade, lymph node metastases are rare and prognosis is usually good.

Methodology To present a clinical case of an unexpected diagnosis of an adult granulosa cell tumour of the ovary with review of the literature.

Results A 37-year-old woman was admitted to the emergency department with abdominal pain. The patient did not have any relevant medical history. As a contraceptive method, she used the subcutaneous implant with etonogestrel. On physical examination, she had pain and tenderness on the right iliac fossa. The transvaginal ultrasound demonstrated a 6 cm ovarian cyst on the right side (with regular walls and anechoic content) but with decreased doppler flow. The blood work revealed light leucocytosis. Faced with a possible diagnosis of adnexal torsion, the patient was then proposed for diagnostic laparoscopy. She was submitted to a diagnostic laparoscopy that had to be converted to laparotomy due to extensive pelvic adhesions – the surgery confirmed the adnexal torsion and she underwent right adnexectomy and left salpingectomy. The anatomopathological examination of the surgical specimen confirmed that it was an adult granulosa cell tumour of the ovary. As the patient didn´t want any more children, she was latter submitted to total hysterectomy + contralateral oophorectomy and surgical staging.

Conclusion With the presentation of this case, the authors intend to emphasize that even in the face of ultrasound aspects of an adnexal mass suggestive of benignity, we must always bear in mind the possibility that we are facing a borderline or malignant tumor.