RESUMO
BACKGROUND: Desmoid tumors, also known as aggressive fibromatosis, are extremely rare, accounting for less than 3% of soft-tissue sarcomas and less than 0,03% of all neoplasms. The diagnosis is usually delayed because of the lack of specific symptoms, and can sometimes lead to serious and, even fatal complications. CASE PRESENTATION: We report the case of a 27-year-old male patient presenting with the clinical picture of acute appendicitis. During the operation, we found a tumor in the jejunum with a necrotic zone and perforation on its surface, causing hemorrhagic effusion into the abdominal cavity and subsequent peritonitis. The tumor was removed with negative margins via resection of the small bowel. The final histological result showed aggressive fibromatosis. CONCLUSIONS: Aggressive fibromatosis remains a serious problem with the possibility of locally aggressive behavior with high rates of recurrence. Sometimes, its clinical and macroscopic recognition can be immensely tricky. As shown by our patient, on rare occasions, desmoid tumors can lead to acute surgical abdomen requiring an emergency operation.