Ultrastructure of cerebellar capillary hemangioblastoma. II. Mast cells and angiogenesis.

The topographic distribution, population density, and ultrastructural features of mast cells were studied in six cases of cerebellar capillary hemangioblastoma. The vascular area of tumor tissue contained large numbers of mast cells (6.3 cells/high power field, X 400) in comparison with hyalinized area (0.3 cell) and adjacent cerebellar tissue (less than 0.1 cell). Close association of mast cells with endothelial cells and stromal cells was found. The morphology of mast cell granules and their degranulation through dissolution of granule contents and exocytosis were illustrated. The findings suggest that an increased number of mast cells may represent one of the characteristic histological features of capillary hemangioblastoma, and continuous degranulation of mast cell granules with release of heparin may play an important pathophysiologic role in the vascular proliferation and expansion of the tumor.