Ultrastructure of mast cells in growing and involuting stages of hemangiomas.

Mast cells from 11 patients with growing strawberry (capillary) hemangiomas and cellular hemangiomas and from ten patients with involuting stages of strawberry hemangiomas were investigated electron microscopically. Two types of mast cells were evident: numerous elongated, fibroblastic cells and a few round, classic cells. The mast cells in growing hemangiomas contained many small, simple-type granules in various stages of development. It is possible that, owing to the immaturity of these granules, mast cells have different, probably weaker, functional activities. Mast cells in involuting stages of hemangiomas were filled primarily with compound-type granules, showing typical parallel, concentric lamellae or crystalloid structures, which were similar to the mature mast cells in normal skin.