Primary omental gastrointestinal stromal tumour (GIST) presenting with a large abdominal mass and spontaneous haemoperitoneum.

A 60-year-old Indonesian woman presented with a 9-day history of increasing abdominal distension, pain and tiredness. Physical examination revealed significant pallor with a palpable mass in the abdomen. CT of the abdomen reported a 22 cm complex mass in the peritoneal cavity with free intra-abdominal fluid. Laboratory results showed anaemia with a raised serum CA 125 level. At laparotomy a large haemorrhagic tumour with blood filled cystic cavities was found attached to both greater omentum and the transverse mesocolon with 2.2 L of blood in the peritoneal cavity. There was no invasion of any part of the stomach or intestines and there were no metastases seen. Histopathology of the resected specimen was consistent with that of a gastrointestinal stromal tumour arising from the omentum. Immunohistochemical studies revealed the tumour to be strongly positive for discovered on GIST-1 (DOG1) but negative for both CD117 and CD34. Platelet-derived growth factor receptor α (PDGFRA) exon 18 mutation D842V was detected.