Ultrastructure of giant pigment granules (macromelanosomes) in the cutaneous pigmented macules of neurofibromatosis

Abstract

Electron microscopy was used to elucidate the nature of the giant granules in the light brown, or cafe au lait, macules from 6 patients with neurofibromatosis. It was shown that these giant granules were surrounded by a membrane system similar to that of normal melanosomes in melanocytes and keratinocytes. These giant granules contained several subunits: highly electron dense amorphous material; electron lucent globular bodies (400 Å in diameter), characteristic also of the normal melanosomes in heavily pigmented skin and hair; electron globular bodies (400-500 Å in diameter) with fine grains inside; and fine granular substances, or grains, of moderate to high electron density. Several subtypes were found, suggesting that a morphological sequence may exist in the development of these granules in melanocytes. The giant granules were found also in keratinocytes as a single unit, indicating that they were apparently transferred from melanocytes to keratinocytes as a single unit after their maturation. Because of many similarities with normal melanosomes, it is suggested that these giant granules be called 'macromelanosomes'. In addition to these macromelanosomes, small ellipsoidal melanosomes that were normal and small spherical granular melanosomes like those found in melanosomes were also found in the cafe au lait lesions.