Paraffin-embedded sections stained with hematoxylin and eosin showed a richly vascular neoplasm composed of uniform cells with finely granular, eosinophilic cytoplasm, discrete cell borders, and round to oval nuclei with "salt-and-pepper" chromatin and indistinct nucleoli. A nested pattern was focally discernable and cells showed an orderly relationship to blood vessels. Blood vessels were frequently sinusoidal and occasionally thick-walled and hyalinized. The tumor was surrounded by a thin, focally calcified fibrous capsule. Immunohistochemical stains showed strong, diffuse cytoplasmic staining for synaptophysin and little GFAP positivity. Dense core neurosecretory granules were identified by electron microscopy.