Olfactory neuroepithelioma in a domestic carp (Cyprinus carpio).

A well-differentiated olfactory neuroepithelioma was found protruding from the left olfactory fossa of a 6-year-old domestic multicolored carp, Cyprinus carpio. Following diagnostic biopsy the neoplasm continued to grow. At necropsy, the tumor was found to extend beyond the olfactory chamber into the intracranial portion of the olfactory bulb, but no distant metastases could be detected. Histologically, the neoplasm had a remarkably organoid appearance, being composed of imperfect reproductions of the normal olfactory organ including olfactory membrane, axonal bundles, and glial tissue. Electron microscopy demonstrated the presence of numerous ciliated olfactory sensory cells as well as sustentacular, mucous, and basal cells within the neoplastic simulations of olfactory membrane. These observations, together with those from two previous case reports of olfactory neuroepitheliomas in teleosts, suggest that this type of tumor tends to be more highly differentiated than are neoplasms of similar origin in mammals.