PURPOSE: To evaluate the histopathologic and histochemical characteristics of intrachoroidal microvascular abnormality. METHODS: Forty eyes obtained at autopsy from human donors ranging in age from 20 to 91 years (25 diabetics, 15 nondiabetics) were analyzed. Choroids were processed for alkaline phosphatase flat-embedding. Vascular patterns were examined and analyzed before embedding and serial sectioning. RESULTS: Intrachoroidal microvascular abnormality had the most prominent alkaline phosphatase reaction product of choroidal vessels. These formations appeared as ameboid or cobweb-like vascular networks (area, 0.05 to 4.6 mm2) in the choroidal stroma external to the choriocapillaris. They appeared as both single or groups of formations in the posterior pole and equatorial regions in all subjects. Intrachoroidal microvascular abnormality was found in five subjects with diabetes: four with type I diabetes mellitus, and one with type II diabetes mellitus. One subject had proliferative diabetic retinopathy, three had background retinopathy, and one had no retinopathy. Intra-choroidal microvascular abnormality was connected with all levels of choroidal vasculature. Microaneurysms were observed within intrachoroidal microvascular abnormality formations in most subjects but not in other choroidal vessels. CONCLUSIONS: Intrachoroidal microvascular abnormality is a form of intrachoroidal neovascularization. This neovascularization has features similar to intraretinal microvascular abnormalities found in diabetic subjects but seems to form independently of the status of retinopathy. The presence of microaneurysms in intrachoroidal microvascular abnormalities and not other choroidal vessels supports the view that aneurysms may be aborted attempts at neovascularization.
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