OC13.01: Ovarian Malignant Mesothelioma with Peritoneal Carcinomatosis in a Woman with Previous Gastric Cancer: a Case Report

A 73-year-old pluriparous Caucasian woman was referred to our Center after an incidental finding of pelvic masses. She had a previous gastrectomy due to a gastric cancer and a right salpingo-oophorectomy for a benign ovarian cyst. Transvaginal and transabdominal ultrasound examinations showed an irregular solid mass of 70 × 43 × 40 mm in size with inhomogeneous echostructure and richly vascularisation, localised in the pouch of Douglas and a left irregular solid mass of 72 × 47 × 65 mm in size. Free pelvic fluid and pelvic carcinomatosis were also visualised. Other two irregular solid masses of 48 × 36 × 54 mm and 44 × 26 × 35 mm in size respectively, with inhomogeneous echostructure and poorly vascularised were identified in the upper abdomen. Serum levels of oncological markers were: CA125 34.56 U/ml, CA 19.9 4.66 U/ml, CA15.3 15.26 U/ml, CEA 0.22 ng/ml. An abdominal Computed Tomography (CT) confirmed the ultrasound findings. Applying the IOTA Simple Rules, the mass (left mass was considered as target lesion) was classified as malignant for the presence of three M-Rules (M1, irregular solid tumour; M2, presence of ascites; M5, very strong blood flow - colour score 4). According to IOTA ADNEX model, the risk of malignancy was 92.4%, with the highest Relative Risk (8.5) for metastatic cancer to the adnexa- 0-RADS 5 (High Risk). The ultrasound examiner was uncertain to the diagnosis: the first hypothesis was a metastatic tumour due to the personal history, bilateral tumours and negative CA 125. However, a primary ovarian carcinoma could not be excluded. At laparoscopy, ascites, abdominal and pelvic carcinomatosis were detected. Peritoneal biopsy was performed and the final histology report was positive for ovarian malignant mesothelioma. Malignant mesothelioma is an uncommon tumour that can be difficult to diagnose and there are no studies describing the ultrasound feature of ovarian malignant mesothelioma.