We report the case of a 51-year-old woman referenced to our hospital with complaints of slowly enlarging abdominal volume for over a year. The patient also reported increased bowel movements in the weeks before the admission. She denied additional symptoms, including surfeit, pain, vomiting and dyspnoea. Clinical examination revealed a mobile abdominal and pelvic tumour, palpable up to 3 cm below the xiphoid process.
The patient did not have adequate gynaecological surveillance and took oral contraceptives for several years until the previous 7 months. There was no significant personal nor familial history reported. The laboratory results presented as follows: CA-125, 118 U/mL; CEA < 0.5 ng/mL; and CA 19-9, 6 U/mL.
A pre- and post-contrast abdominal and pelvic MDCT on portal venous phase reported a large intraperitoneal mixed tumour with few solid components (Figs. 1, 2, 3, 4, 5, 6 and 7), mostly located in the upper abdomen (Figs. 2, 3 and 4). It measured up to 30 × 12 × 26 cm in longitudinal, anteroposterior and transversal axes, respectively. The tumour compressed the surrounding structures, particularly the kidneys and the small bowel, the latter located predominantly in the upper left abdominal quadrant (Figs. 2 and 3). Despite these findings, no dilatation of the urinary tract nor the digestive tract was noted. The vascular pedicle of the lesion was not accurately identified, although several enlarged vessels could be seen converging to the superior mesenteric vein and the vesical peritoneum (Figs. 2, 3, 5, 6 and 7).
Even though the origin of this tumour was not clear, the most probable differential diagnoses included an ovarian neoplasm and an intraperitoneal desmoid. An ovarian tumour was the most likely diagnosis given the demographics and the morphological features, although the serum tumoral marker (CEA) was not elevated. Desmoid tumours are rare benign neoplasms most frequently found in women. They are well-circumscribed and enhancing masses that may be found in the mesentery, but are usually more homogeneous and predominantly solid.
The patient underwent subsequent diagnostic laparotomy, whose operative data reported a cystic and lobulated tumour with 30 cm. It was adherent to the greater curvature of the stomach and the vesical peritoneum. There were no abnormalities involving the uterus and the ovaries.
The intraoperative pathological evaluation reported a fusocellular tumour with no cytological features of malignancy. The final pathological assessment depicted a gastrointestinal stromal tumour (GIST) with extragastrointestinal location (presumably peritoneal), of mixed subtype.