Melanotic schwannoma of the orbit. Immunohistochemical and ultrastructural study of a case and survey of the literature.

Light microscopical, immunohistochemical and ultrastructural study of a case of melanotic (pigmented) schwannoma in the left orbit of a 22-year-old man is presented. The tumour caused exophthalmus for three months and was located under the eyeball. Partial removal resulted in recurrence after three years. The recurrent tumour with extension to the nasal cavity and maxillary sinus was extirpated without loss of vision, and a year later the patient was without symptoms. The tumour tissue was Fontana positive, could be bleached, and showed immunoreactivity for S-100, vimentin and HMB 45. Ultrastructurally, the tumour cells, particularly the pigment loaded cells, showed a varying amount of basal lamina at the surface, melanosomes in varying stages of melanization, fine cytoplasmic filaments and micropinocytotic vesicles. Survey of the literature and discussion of the melanogenesis in Schwann's cells are presented.