Ultrastructure of oesophageal melanocytosis.

Four examples of an endoscopically detected oesophageal melanotic lesion were examined by light microscopy, light microscope histochemistry and transmission electron microscopy, and were compared with 13 control samples of normal oesophageal epithelium. By light microscopy, pigmented melanocytes lacking atypia and mitoses were observed amongst the keratinocytes in the basal layer of the oesophageal mucosa. Junctional activity was absent. The mechanism of pigmentation was studied and found to consist of: an increase in the number of melanocytes in the basal layer of the mucosa, an increase in the quantity of melanin in these melanocytes, transfer of melanin from melanocytes to keratinocytes and to macrophages and fibroblasts in the tunica propria. Since all the lesions demonstrated increased numbers of both melanocytes and melanosomes, the term oesophageal melanocytosis rather than melanosis is suggested, to emphasise the essential character of the lesion as a cellular proliferation. The value of sampling these pigmented lesions during endoscopy is emphasised as a means of obtaining well-preserved material for the evaluation of a lesion which some authorities have viewed as a possible precursor for oesophageal malignant melanoma.