[Case of abdominal wall malignant peripheral nerve sheath tumor which is difficult to distinguish from a urachal disease].

Malignant peripheral nerve sheath tumors (MPNST) are highly malignant soft tissue sarcomas. It is very rare for MPNST to arise in the abdominal wall. We report a case of abdominal wall MPNST that was difficult to distinguish from a urachal disease. A 72-year-old woman found a mass of the umbilicus in October 2011. She visited a digestive surgery department in November because it gradually enlarged. Diagnostic imaging suggested a urachal tumor. She was then referred to our clinic. Contrast enhanced CT showed that the 5-cm cystic tumor extended from the umbilicus to abdominal wall. The tumor showed low uptake value in PET-CT. We diagnosed her with a urachal cyst, but could not deny urachal carcinoma. Therefore, we performed surgical resection in January 2012. The pathological diagnosis was MPNST. She has not experienced recurrence for 9 months. MPNST mostly occur in the retroperitoneum close to the spine, extremities, head, and neck. It is very rare for them to occur in the abdominal wall. This is the sixth case including overseas reports. In addition, this is the first case in which it was difficult to distinguish from a urachal disease.