Recent advances in the investigation and management of cerebrovascular disease.

C EREBROVASCULAR ACCIDENTS represent the third most common cause of nontraumatic death in the United States of America. More patients are admitted to hospital wards with major brain stroke than with any other ineurologic disorder. Fortunately, recent advances in our knowledge of the embryology, anatomy and physiology of the cerebral circulation are improving methods of diagnosis and treatment of cerebrovascular disease. EMBRYOLOGY Probably because of better recognition, cerebrovascular accidents due to rupture of congenital aneurysms of the circle of Willis or of arteriovenous malformations of the brain are far more numerous today than 20 years ago. In a series of 200 patients with cerebro-vascular disorders analyzed by Brain,4 16 per cent harbored aneurysms or congenital an-giomas. Reinvestigation of the embryologic construction of the intracranial vascular circulation by Padget26 and others has disclosed the raison d'etre of these developmental anomalies. Faults in the media of arteries, particularly at the points of their bifurcation, failure of complete resorption of primitive vessels of phylogenetic but not ontogenetic importance, inadequate fusion or anastomosis of the carotid and vertebral circulations and incomplete splitting of the three vascular layers (cranial, meningeal and cerebral) of the embryonal head are largely responsible for the presence of intra-cranial circulatory malformations in adult life. Acquired factors such as arteriosclerotic weakening of the internal elastic lamina of arteries and focal necrosis of vessels during angiitis contribute to aneurysmal sacculation and rupture14 which is manifest most often in maturity and not in infancy. ANATOMY Collateral A rtcrial Circulation: Few vessels of the cerebrum and cerebellum are true end-arteries. Utnfortuniately, these lie in the critical fields of supply of the basal ganglia and internal capsule, ponis and the tip of the temporal lobe. Collateral anastomoses are numerous, especially superficially,36 and increase numerically with age. At autopsy of elderly individuals, occlusion of major vessels such as the middle cerebral artery have been found without in-farction, peripheral to the site of thrombosis. Anastomnoses betwveeni the carotid and verte-bral circulations are quite variable, a "normal" circle of Willis being found in only 50 per cent of brains examined. Onily thus can hemiplegia, following unilateral carotid thrombosis in one patient, be reconciled with bilateral occlusion of both carotid arteries (verified by angiog-raphy) without (cliniical aftermath in others. External-internial carotid cross circulation is not a negligible factor in preserving intra-cranial circulation, as demonstrated by angio-graphic filling of the cerebral vessels via the ophthalmic artery after coinplete occlusion of …