Benign schwannoma of the liver with cystic changes misinterpreted as hydatid disease.

The rare event of a benign mesenchymal tumor of the liver is described since its cystic transformation resembled hydatid disease through the presence of Echinococcus. Ultrasound and computerized tomography showed a cystic mass within the liver of a 57 year-old woman with upper abdominal pain. This was interpreted as hydatid disease and an evacuation procedure was performed. The histopathology of a minute specimen was interpreted as consistent with chronic inflammation in a cyst wall. Five years later, a recurrence of the parasite was suspected, and complete excision of the mass and resection of a bile fistula was performed. The histopathological examination revealed a large benign schwannoma with regressive cystic changes, proven by positive immunoreaction for the neurogenic marker S-100 protein. Revision of old paraffin blocks of tissue taken during the first operation was able to retrospectively confirm the identical tumor by the same markers. Occurrence of schwannomas in parenchymatous organs or the retroperitoneum is extremely rare and may lead to asymptomatic growth with cystic changes, causing considerable difficulties in imaging procedures. Overall, the primary complete excision of cystic masses within the liver seems to be the best approach in discovering their real nature and to ultimately cure them.