A Case of Solitary Fibrous Tumor with Tumor Rupture during the Waiting Period for Elective Surgery

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that most commonly arises in the pleura but can occur at virtually any anatomical site, including the abdominal cavity. Although rupture of SFT has occasionally been reported, most such cases involve intrathoracic tumors presenting with hemorrhage, and peritonitis caused by rupture of an intra-abdominal SFT is exceedingly rare.

A man in his 70s was referred to Hokkaido University Department of Gastroenterological Surgery II after contrast-enhanced CT revealed a 12 × 9-cm heterogeneous pelvic mass with poor enhancement accompanied by ascites. Endoscopic US-guided fine-needle aspiration had been performed at the previous hospital but failed to yield a definitive diagnosis, and elective tumor resection was planned. One week after the initial visit, the patient was brought to our hospital with abdominal pain. Emergency CT showed slight enlargement of the tumor, intratumoral fluid collection, and increased fat stranding around the tumor. Conservative management with intravenous antibiotics was initiated because there were no overt signs of generalized peritonitis. However, inflammatory markers worsened and fever developed, prompting emergency surgery on hospital day 2. Laparotomy revealed partial rupture of the tumor wall with leakage of contaminated intratumoral fluid into the peritoneal cavity. The tumor pedicle was identified at the base of the sigmoid mesocolon, and complete resection was achieved. The operative time was 124 min, and the estimated blood loss was 1100 mL. Histopathological examination revealed a patternless proliferation of spindle cells within a fibrous stroma with staghorn-like vasculature. Immunohistochemistry showed nuclear positivity for signal transducer and activator of transcription 6 and positivity for CD34, confirming the diagnosis of SFT. According to the modified Demicco model, the tumor was classified as intermediate risk. The patient was discharged on POD 31.

When managing a large intra-abdominal tumor whose growth rate cannot be reliably assessed, the possibility of rupture should be kept in mind, and emergency surgery should not be delayed when abdominal findings worsen. Although the prognostic impact of tumor rupture in SFT remains unclear, this event may justify closer postoperative surveillance than that indicated by existing risk classification schemes.