Ultrastructural comparison of capillary and cavernous hemangiomas of the orbit.

Capillary and cavernous hemangiomas are often grouped together as if they were modulations of the same entity. To clarify this nosologic question, three capillary hemangiomas in children and four cavernous hemangiomas in adults were studied by transmission electron microscopy. The capillary hemangiomas consisted of two variably admixed zones, solid cellular zones and zones with open vascular lumens. However, both zones had similar organization. Each vascular unit was composed of endothelial cells and pericytes, which persisted in a tumor three years after its clinical appearance. Macrophages and degenerating cells were found in the interstitium and may be related to the clinical feature of partial spontaneous regression. The cavernous hemangiomas had much larger lumens, and wider and more heavily collagenized trabeculae. The vascular walls were created by multilaminar smooth muscle cells. Therefore, capillary hemangioma is completely different from cavernous hemangioma, which resembles a venous tumor.