Anatomy of the Cerebral Structure

Introduction

The vascular system of the human brain differs significantly, both anatomically and physiologically, from that of other organs. Although it accounts for only 2% of the body weight, the brain receives 15% of the cardiac output and consumes 20% of the body's oxygen supply in the basal state. Unlike other arteries, the cerebral arteries are little influenced by sympathetic nervous activity, but they respond dramatically to changes in carbon dioxide and oxygen levels.

Depending on their location, obstructive lesions of the intracranial and extracranial arteries supplying the brain can cause a wide array of neurologic symptoms. The extent of clinical symptoms is strongly dependent on the presence and extent of the collateral circulation to the brain because these collaterals can help minimize the effects of arterial occlusions, decreased cerebral perfusion, and the ensuing neurologic deficit. Therefore understanding the normal and collateral anatomy of the brain circulation can help in the diagnosis of obstructive disease of the cerebrovascular system and help plan interventions.

This chapter reviews the vascular anatomy of the brain and touches on the physiologic adaptations that can help maintain cerebral perfusion and prevent permanent neurologic deficits. There is great variability in this vascular anatomy that partly explains the brain's ability to compensate for alterations in cerebral blood flow.

As new treatment modalities become available for both extracranial and intracranial pathologies, a basic appreciation of normal anatomy, congenital variations, and collateral vascular pathways is extremely important. Endovascular treatment with angioplasty and stenting of carotid stenosis, coiling for aneurysm disease, and thrombolysis for acute intracerebral occlusions are now routinely used to treat intracranial atherosclerotic disease. Successful implementation of these interventions is helped by the knowledge of the extracranial and intracranial vascular anatomy.