Histopathological studies of temporal bones of patients with malignant melanoma

Although malignant melanoma is known to metastasize to various sites including the temporal bones, there have been few studies on temporal bone histopathology in malignant melanoma. Here we describe the temporal bone histopathology of 5 patients (10 temporal bones) who died of malignant melanoma with multiple metastasis to many internal organs and bones. We investigated the temporal bone based on the following three points: 1) the presence of metastatic lesions in the temporal bone, 2) inner ear pathology, and 3) the distribution of melanin in the inner ear. Normal melanin distribution was also studied in 35 temporal bones of patients without malignant melanoma. Metastatic malignant melanoma was observed in 5 temporal bones from 3 patients, in two of whom the internal auditory canal was involved bilaterally by melanoma cell infiltration. In the remaining patient (one ear), metastatic melanoma was found along the dura mater of the posterior cranial fossa to the mastoid air cells. In the former two patients, the inner and outer hair cells as well as the stria vascularis showed degenerative changes to various extents. In particular, the inner ear changes were severe in the ear with the decongestion of the inner ear vessels. Melanin was found in the modiolus, stria vascularis, osseous spiral lamina, membranous labyrinth, and endolymphatic sac, as previously reported. The amount of melanin in the inner ear increased with age in the control patients, but was greater than in the controls, in all of the cases of malignant melanoma except one, in which metastatic lesions were present in the internal auditory canal with marked congestion of the inner ear vessels.