SOME OBSERVATIONS ON THE PATHOGENESIS AND NATURAL HISTORY OF INTRACRANIAL ANEURYSMS

The purpose of this paper is to present an account of the development of intracranial aneurysms and to describe the way in which they grow and rupture. It is hoped that this account and the coloured illustrations which accompany it will be of interest and use to the clinicians and radiologists working in this field who cannot obtain such a good view of the lesions as can the pathologist. The observations which follow are based on the personal dissection, using a simple dissecting microscope, of 163 ruptured cerebral aneurysms and of some 40 unruptured aneurysms. The photographs have been made by using the macro-attachment for the Vicker's projection photomicrography equipment, with Kodak "ektachrome" as the colour film. The specimens, after careful cleaning under the dissecting microscope, were suspended across a metal ring by threads attached to the arteries and were illuminated by oblique incident beams from below, and the photographs taken at linear magnifications varying between three and eight times. Depth of focus was obtained by cutting down the lens aperture to f22 and increasing exposure time accordingly. This method of illumination may give an unpleasant irregular lighting to the background, but this aesthetic blemish is amply repaid by the detailed delineation of the contours of the subject which are obtained. The aneurysms which form this series have all arisen in close relationship to the angles of branching and anastomosis in, or close to, the circle of Willis. The distribution of the ruptured aneurysms is listed in Table J. In 20 instances (1233% of the cases) a second unruptured aneurysm was present. Only with aneurysms arising in the angle between the posterior communicating artery and the internal carotid artery, which were four times more common on the right than on the left side, was any significant difference between the two sides found.