Difficult diagnosis of a large cystic retroperitoneal tumor mimicking a hepatic origin.

Schwannomas are rare tumors, usually benign, originating from the nerve sheath, and found only infrequently in the retroperitoneal space. We report on a 67-year-old woman who was initially misdiagnosed and treated for a liver hydatid cyst. After incomplete resection and recurrence of the tumor, we were able to diagnose a large retroperitoneal schwannoma that completely displaced the liver to the left abdomen. The patient underwent surgical resection of the schwannoma; pathological evaluation revealed a cystic tumor measuring 18.5 × 18 × 12.5 cm, with tumor cells staining strongly positive for S-100. Retroperitoneal schwannomas may mimic cystic hepatic tumors and should, therefore, be considered as a differential diagnosis in such cases. We describe the diagnostic modalities and difficulties in the approach of a cystic liver tumor.