Light and electron microscopic studies of malignant melanoma of conjunctiva and palpebra

The authors experienced one case of malignant melanoma of the superior palpebral conjunctiva and the inferior palpebral skin, originating from benign acquired melanosis of the bulbar conjunctiva which developed in a 48-year-old man. Orbital exenteration including superior and inferior palpebrae was performed, and the removed tissue was examined by light and electron microscopy. In the temporal bulbar conjunctiva, melanocytes containing abundant fine melanin granules proliferated over almost the whole area of the epithelial layer. Cellular atypia and karyomitosis were not observed. The basement membrane remained intact with no proliferation of melanocytes in the substantia propria. However, in the perivascular area, in addition to the moderately prominent infiltration by lymphocytes and plasma cells, infiltration by melanophages was observed relatively frequently. Based on these findings, it was confirmed that the primary lesion of the bulbar conjunctiva was an acquired melanosis of Stage IB as classified by Zimmerman. The black nodular tumors of the superior palpebral conjunctiva and inferior palpebral skin consisted of melanoma cells showing markedly prominent cellular and nuclear atypia. The nuclei showed indentations in the membrane with electron-lucent karyoplasm, each having one nucleolus. The cytoplasm contained many round or elongated melanosomes in various developmental stages, with sizes of about 0.7 micron. Scattered among melanoma cells were a number of melanophages which had phagocytized many melanosomes at various stages of maturity.(ABSTRACT TRUNCATED AT 250 WORDS)