Brain vessels

The brain is supplied with blood by two pairs of large arteries that branch off from the aortic arch - the carotid and vertebral arteries. The area supplied by the carotid arteries is also called the carotid, or anterior vascular basin, and the area supplied by the vertebral arteries is called the vertebrobasilar, or posterior vascular basin.

The bifurcation zone of the common carotid artery into the internal and external carotid arteries is located near the angle of the mandible. The internal carotid artery goes up without giving off branches until it enters the cranial cavity. After perforating the dura mater, the first branch, the ophthalmic artery (a. ophthalmica), departs from it. It has already been mentioned that amaurosis fagax occurs as a result of occlusion of this artery, the terminal branch of which is the central retinal artery. Thus, loss of vision in one eye is characteristic of pathology of the carotid artery or heart.

The internal carotid artery divides at the base of the brain into the anterior and middle cerebral arteries. The anterior cerebral artery(ACA) follows medially and supplies the internal part of the cerebral hemisphere. Since the area of the cortex where the legs are represented is located most medially, with occlusion of the ACA, leg function is affected to a greater extent than arm or face function. Since cortical representation is contralateral to the body, stroke often affects the side of the body contralateral to the lesion: for example, with damage to the right hemisphere, weakness occurs in the left limbs.

The middle cerebral artery(MCA) runs in the Sylvian fissure from the base of the brain to the outer surface of the cerebral hemisphere. In the Sylvian fissure, it gives rise to penetrating vessels, the lenticulostriate arteries, which supply the internal capsule, the basal ganglia, and part of the thalamus. Occlusion of these vessels causes lacunar syndromes, the most important of which is isolated hemiparesis ("pure motor stroke"), most often caused by a small infarction in the internal capsule. Small infarctions in the basal ganglia often remain asymptomatic.

After leaving the Sylvian fissure, the MCA bifurcates or divides into branches that supply the outer surface of the cerebral hemisphere. Occlusion of these branches causes extensive wedge-shaped cortical infarctions, the clinical manifestations of which depend on whether they involve the motor or somatosensory areas of the cortex. When the optic radiation is affected, there is a limitation of the visual fields. Cognitive impairment, such as aphasia, is most often observed with occlusion of the branches of the MCA.

In proximal occlusion of the MCA, the entire blood supply zone is affected, including both deep and cortical structures. In this case, loss of both motor and sensory functions develops, involving the face, arm, and leg. Even if the ACA basin is not affected, if the internal capsule is affected, the function of the leg is impaired. Occlusion of the carotid artery often leads to partial or complete involvement of the zone supplied by the MCA, due to the peculiarities of collateral blood flow.

The posterior vascular basin is supplied by the vertebral arteries, which merge at the junction of the medulla oblongata with the pons to form the basilar (main) artery. Accordingly, each half of the medulla oblongata (and the caudal part of the cerebellum) is supplied by only one vertebral artery. The basilar artery supplies the pons. At the level of the midbrain, it again divides into two posterior cerebral arteries(PCA). Both PCA encircle the midbrain, following posteriorly along the base of the cerebral hemispheres. Penetrating branches extend from the vertebral, basilar, and posterior cerebral arteries, supplying the brainstem.

Penetrating branches from the PCA supply the posterior parts of the cerebral hemispheres, including the medial parts of the frontal lobes and the occipital lobes. The dual blood supply to the central visual cortex prevents its damage when one of the arteries is occluded, which is why central vision often remains intact in strokes involving the visual cortex.

Syndromes that are out of keeping with the vascular anatomy of the brain indicate that the brain damage may be caused by diseases other than stroke. Although brain tumors, whether primary or metastatic, may present acutely, there are usually other signs that indicate that the sudden onset of symptoms has been occurring over a longer period of time. A stroke-like acute onset of symptoms may occur with hemorrhage into the tumor or rapid tumor growth. A sudden onset of symptoms that mimics a stroke may also occur in multiple sclerosis. Neuroimaging techniques can reveal characteristic changes that cause the sudden onset of neurological symptoms in both tumors and multiple sclerosis.