Primary carcinoid tumor of the orbit. A clinicopathologic study with histochemical and electron microscopic observations.

A patient with a primary carcinoid tumor of the orbit is described. No other tumor had been found during the 15-year interval since the onset of unilateral proptosis. Symptoms of the carcinoid syndrome were absent, and the urinary levels of 5-hydroxyindoleacetic acid were normal. Histologically, the bulky, noninfiltrating tumor compressed but did not invade the optic nerve. The argyrophilic cells were arranged in solid lobules and formed abundant, rosettelike structures. Pleomorphic neurosecretory granules were demonstrated by transmission electron microscopy.