The ultra-structure of a melanotic schwannoma of the skin.

The case is described of a 53-year-old female with a pigmented tumour of the skin of the foot. The light and electron-microscopic findings established that the tumour was a melanotic Schwannoma. The ultra-structural features indicated that the Schwann cells, which contained melanosomes in varying stages of maturation, were producing melanin. A second type of cell within the tumour with features of a mesenchymal cell also contained melanosomes. The interrelationships of nerve sheath tumours, their relationship to pigment cells of neural crest origin and to other pigmented tumours of uncertain histogenesis, is discussed in the light of the findings described in the paper.