Intrachoroidal microvascular abnormality: A previously unrecognized form of choroidal neovascularization

Purpose. The goal of this study was to evaluate the histopathological and histochemical characteristics of intrachoroidal microvascular abnormality (ICMA) in diabetic subjects. Method. Six human eyes ranging in age from 58 to 91 years were analysed in this study. Five subjects had type I diabetes mellitus and one had type II diabetes mellitus. One patient had proliferate diabetic retinopathy, four had background retinopathy and one subject had no retinopathy. Choroids were processed for alkaline phosphatase (APase) flat-embedding as previously described (McLeod and Lutty, /OVS 35:3799, 1994). Vascular patterns were examined and documented en bloc and subsequent serial sectioning was performed to analyse vessel structure. Result. ICMA had the most prominent APase reaction product of choroidal vessels. They were ameboid or cobweb-like vascular networks (0.05 to 4.6 mm² in area) in the choroidal stroma external to the choriocapillaris. They appeared as both singular or groups of formations in the posterior pole region in all subjects. ICMA was found in 6 of 34 subjects screened (24 diabetics, 10 nondiabetics), and all 6 subjects were diabetic. ICMA was connected with all levels of choroidal vasculature. Microaneurysms were observed within ICMA formations in most subjects, but not in other choroidal vessels of these subjects. Conclusions. These results suggest that ICMA is a form of intrachoroidal neovascularization. This neovascularization has features similar to intraretinal microvascular abnormalities found in diabetic subjects and seemed to form independent of the status of retinopathy. The presence of aneurysms in ICMA and not other choroidal vessels suggests that aneurysms may be aborted attempts at neovascularization.