The specimen consists of a rounded dark tan-dark red lesion measuring in maximum dimensions 3 x 3 x 2.8 cm. It is subsequently painted in black ink and serially sliced. The cut surfaces show a hemorrhagic dark tan lesion with cyst formation. Small representative fragments in the centre of the lesion are placed in 2.5% glutaraldehyde. The remainder of the slices are submitted consecutively in blocks A1-A10 with A1 and A10 being the tips of the lesion, which are sectioned perpendicular to the remaining slices. Block A2 is used for Oil Red O stains, prior to processing for paraffin embedding.
Sections show the lesion is comprised of numerous small vessels, between which there are small round cells with eosinophilic cytoplasm, round nuclei with a minimal degree of pleomorphism. In some regions, these cells are arranged in sheets with little intervening blood vessels. Some large-diameter blood vessels are present in the lesion, some of which are thrombosed. Hemosiderin-laden macrophages are seen in some areas, which are sclerotic. Oil Red O stains on A2 show lipid droplets in some of the cells arranged in sheets. Immunohistochemistry shows that the tumor is negative for epithelial membrane antigen and keratin. Numerous CD31-positive blood vessels are seen within the lesion. Cerebellar tissue are seen adjacent to the lesion. This show varying degrees of gliosis, rarefaction of the granular layer, loss of Purkinje cells, and thinning of the molecular layer.