Peripheral primitive neuroectodermal tumor of the small bowel mesentery: a case showing perforation at onset.

A case of peripheral primitive neuroectodermal tumor of the small bowel mesentery with an uncommon clinical onset is reported. A 40-year-old man was admitted to hospital because of acute severe abdominal pain. Chest X-ray revealed a free air sign beneath the diaphragm. At emergency surgery a mass measuring 11.0 x 8.0 cm with perforation was located in the jejunal mesenteric region. Histologically the resected lesion consisted of sheets of undifferentiated small round cells forming abortive Homer Wright rosettes. Some spindle-shaped cells showed perivascular pseudorosettes. Immunohistochemical study revealed that the tumor cells expressed positivity against CD99 (MIC2), neuron-specific enolase, synaptophysin and vimentin. To the authors' knowledge this is the first documentation of peripheral primitive neuroectodermal tumor of the small bowel mesentery with perforation at onset.