Abstract
BACKGROUND: Retroperitoneal desmoid-type fibromatosis (DF) is an uncommon mesenchymal neoplasm presenting as a firm mass with locally aggressive features. It usually manifests as a well-circumscribed or ill-defined, solid mass on cross-sectional imaging. Cystic changes of DF have been described in the literature in association with prolonged medical treatment or abscess formation. However, spontaneous cystic change is rarely reported. CASE PRESENTATION: Here we report the case of a 46-year-old patient with a DF mimicked a large cystic tumor in the retroperitoneum. Ultrasonography and computed tomography were performed in order to search for localizations and characteristics of the cystic tumor. Radiological findings showed an oval cystic mass with a relatively thick wall, measuring 18.3 × 12.3 × 21.5 cm in the left upper abdomen. Laparoscopic spleen-preserving distal pancreatectomy was performed and histopathological examination by immunohistochemical study enabled us to diagnose a DF invading the pancreatic parenchyma. The patient remained asymptomatic during an 8-month follow up period. CONCLUSIONS: We report an extremely rare case of retroperitoneal DF with spontaneous cystic change. DF can manifest as a mainly cystic mass with a thick wall, as in our case, which makes the correct diagnosis difficult. DF should be included in the preoperative differential diagnosis of a cystic retroperitoneal mass, regardless of its rarity.