Normal and metastatic melanin in the temporal bone

Malignant melanoma is known to metastasize to the temporal bone. However, melanocytes exist in the normal inner ear and may be difficult to distinguish from metastatic melanotic cells. This study describes distribution of normal melanin in the ear and metastatic melanoma to the temporal bone.

Normal melanin distribution is described in 48 temporal bones from White (18), Native-American (19), and African-American (11) individuals and metastatic melanoma to the temporal bone is described in four cases (seven temporal bones). Temporal bones were removed at autopsy, fixed in 10% buffered formalin, and processed for routine celloidin embedding. Sections were cut at a thickness of 20 microns and every tenth section was stained with hematoxylin-eosin for light microscopic evaluation.

Normal melanin was found in the inner ear, mainly around terminal neural structures and blood vessels, and occurred in greater quantities in African-American individuals. Metastatic melanotic cells reached the temporal bone by hematological dissemination, and by neural invasion from the central nervous system. No correlation was found between histopathological findings and clinical symptoms of patients.

Metastatic melanoma to the temporal bone may be seen in the same areas as normal melanin. They may also be observed in bone marrow cells of the petrous bone and along the course of nerves of the internal auditory canal and cochlear vestibular labyrinth, either by following neural sheaths or blood vessels that run along the nerve. Metastatic disease to the temporal bone is often asymptomatic, or it may present with uncharacteristic symptoms that may delay diagnosis.