Primary hepatic carcinoid tumor with a paranuclear clear zone: a case report.

Carcinoid tumors having distinct paranuclear clear zones seen on hematoxylin and eosin stain are rare and few cases have been reported in the literature. Furthermore, primary hepatic carcinoid tumor with a paranuclear clear zone is extremely rare. We recently experienced a case from a 48-year-old man who presented a large single mass, 12 cm in largest diameter, in the right lobe of the liver. Histologically, the tumor revealed characteristic organoid pattern with central hyaline degeneration. The tumor cells had a prominent paranuclear vacuolated dear zone. On immunohistochemistry, tumor cells were diffusely positive for synaptophysin and focally stained for chromogranin A. Ultrastructural examination revealed paranuclear aggregation of intermediate filaments and membrane-bound clear vesicles, which corresponded to the paranuclear vacuolated clear zone.