Histocytologic diagnosis of neuroendocrine tumors in the liver: a retrospective study of 23 cases.

A series of 23 needle biopsies of neuroendocrine tumors occurring in the liver is described. Aspirate smears, core biopsies, and touch preparations were examined. Eighteen of the 23 patients had been previously diagnosed: 9 patients had been correctly identified as having a neuroendocrine tumor, and 9 patients had been originally misdiagnosed. Five of the patients in this series had no previously identified neoplasia. Immunohistochemical staining confirmed the neuroendocrine nature of the tumors in each of the cases. On the basis of cytomorphology, these cases were subtyped as either round cell type, spindle cell type, or polygonal cell type. The polygonal cell type of neuroendocrine tumor, as well as rare examples of the round cell type, demonstrated features similar to well-differentiated hepatocellular carcinoma and adenocarcinomas, and may present a diagnostic dilemma. Characteristic cytologic attributes of the polygonal cell type of neuroendocrine tumor which aid in its distinction from well-differentiated hepatocellular carcinoma include eccentrically located "plasmacytoid" nuclei and cellular discohesion. Findings on core needle biopsy which further identify the neuroendocrine tumors are thick fibrous stroma or small "nests" of tumor cells. The additional use of immunohistochemical staining provides reliable evidence of the cell of origin in confusing cases. Attention to these considerations will aid in the cytologic diagnosis of neuroendocrine tumors.