Anatomical patterns of hypoplastic posterior communicating arteries and their implications for cerebrovascular diseases.

A total of 114 undersized posterior communicating arteries (PCoA-s, external diameter less than 1 mm) and 126 larger ones were investigated histologically. Microscopic examination of hypoplastic PCoA-s revealed five different structural patterns. Two of them showed microscopic appearances characteristic of intracranial arteries seen in adults or newborns without vascular disease. Two other types resembled the histologic picture of Moya Moya disease. The last type was thin-walled and dilated. All PCoA-s larger than 1 mm displayed the adult pattern. The PCoA-s with the Moya Moya-like structure and the thin-walled, dilated pattern contained unusually few reticular fibers. It is supposed that Moya Moya disease may be restricted to the PCoA-s. Further, the types of hypoplastic PCoA-s with reticular fiber deficiency are most probably the source of the so-called unexplained subarachnoid hemorrhage regardless of the presence of infundibular widening. The latter statement stems from the observation that the structure of junctional dilatation does not differ from that of other segments of the artery that exhibit this alteration.