Primary malignant melanoma of the vagina: Case presentation with special references to electron microscopic findings

Abstract

A case of primary malignant melanoma which presumably developed from pre-existing pigmented nevi (so-called lentigo maligna) in the vagina is presented. The electron microscopic findings of the tumor itself and of the pigmented nevi surrounding the tumor were of particular significance. Atypical melanocytes were seen in the areas of pigmented nevi, showing a number of dendrites, intracytoplasmic melanosomes and premelanosomes. The premelanosomes exhibited various stages of maturation and those in advanced stages had a definite inner structure with striae made of laterally associated and cross-linked fibrils. The Golgi apparatus was generally prominent and often occupied several sites within a single cell. Lipid droplets, vacuolation and nuclear inclusion bodies were also encountered. On the other hand, the melanoma cells were built up mainly with melanophages containing autophagosomes which were formed with aggregated melanosomes enveloped in a layer of limiting membrane. The cells filled with autophagosomes contained relatively few organelles. Premelanosomes were much rarer than in the pigmented nevi. The cytoplasm occasionally showed clusters of minute granules thought to be glycogen, as well as myelinoid corpuscles and a centriol. The primary occurrence of maligant melanoma in the vagina is discussed with specific reference to histopathological ultrastructure.