Some Observations on the Natural History of Intracranial Aneurysms

The histories, radiographs and, where relevant, the operation notes and pathological findings in 197 cases of intracranial aneurysm have been reviewed in order to throw light on the natural history of the disease. It is concluded that the earliest changes of atherosclerosis are closely associated with the formation of aneurysms and that their subsequent history depends upon a balance between healing processes and advanced atheroma. Grounds are given for discounting the importance of defects in the muscular coat of intracranial arteries in this disease. Sudden (sometimes silent) changes in size and shape may be demonstrated as well as slower ones. Some emphasis is placed upon the benign course of the disease in a proportion of patients and the possibility of permanent healing in others after subarachnoid haemorrhage. The serious significance of loculation is underlined. There are sex differences not only in the demonstration of symptom-producing aneurysms, but also in the natural history of the disease. At first equally proportioned between the sexes or perhaps commoner in men, aneurysms become both commoner and less stable in women in early middle age. This instability manifesting itself by loculation and/or haemorrhage persists through the next three decades. On the other hand large aneurysms with their rather different natural history (fewer subarachnoid haemorrhages, but greater tendency to brain damage) are less uncommon in men.