Pigmented epidermal cysts.

There are few reports documenting the presence of melanin or melanocytes in epidermal cysts. One hundred and twenty five epidermal cysts from Indian patients were analyzed for the presence of melanin pigment and their sites were noted. A Masson's Fontana stain and immunohistochemistry for S-100 protein and HMB 45 was performed for localization of melanin and melanocytes within the epidermal cysts. Seventy-nine (63%) of the epidermal cysts showed presence of melanin pigment or melanocytes to a variable extent. Melanin was not present in epidermal cysts occurring along lines of fusion of skin folds during embryonogenesis (e.g., ventral midline, inner canthus, nose, upper lip and in the distal most parts like leg and foot and also scrotum). Ten of the 79 epidermal cysts showed extensive accumulation of melanin pigment and infiltration with melanophages in the cyst wall. Four of these patients gave history of trauma and the follow-up was uneventful in two of them. Pigmentation of epidermal cysts thus follows a definite anatomic pattern and is dependent on the natural skin color. Large amount of pigment accumulation within epidermal cysts occurs after cyst rupture and is not associated with hemochromatosis as was believed in the past.