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Anatomic Aspects of Cerebral Circulation
The brain and meninges are supplied by arteries derived from the common carotid artery (CCA) and vertebrobasilar system ( Fig. 14.1 ). The right CCA usually originates from the brachiocephalic trunk, whereas the left CCA originates directly from the aortic arch. Both vertebral arteries (VAs) originate from the subclavian arteries. The morphologic variants of the CCA and VAs usually are not clinically significant.
Arteries to Brain and Meninges.
The CCA bifurcates at approximately the level of the sixth cervical vertebrae into the external and internal carotid arteries. The external carotid artery (ECA) supplies the neck, face, and scalp. The internal carotid artery (ICA) and its branches are mostly responsible for the arterial supply of the anterior two-thirds of the cerebral hemispheres (anterior circulation).
The vertebrobasilar and posterior cerebral arteries (PCAs) supply blood to the brainstem, cerebellum, occipital lobes, and posterior portions of the temporal and parietal lobes (posterior circulation).
The Carotid Artery System
External Carotid Artery
At its origin, the ECA deviates anteriorly and medially in relation to the ICA in the neck and provides many branches to the neck (superior thyroid, ascending pharyngeal arteries) and face (lingual and facial arteries). As the artery ascends, occipital and posterior auricular branches supply the scalp in their named areas. However, the occipital artery also has several meningeal branches that supply the posterior fossa and dura. Within the substance of the parotid gland, the ECA divides into its two terminal branches: the superficial temporal and maxillary arteries. The superficial temporal artery is the main supply to the scalp over the frontoparietal convexity and its underlying muscles. The more proximal branches also supply the masseter muscle. The superficial temporal artery is commonly involved in giant cell arteritis, an important consideration in the elderly with headaches, and can be palpated anterior to the tragus and in the temporal area (see Chapter 21 ).
The maxillary artery supplies the face and, through its middle meningeal branch, provides most of the blood supply to the dura mater covering the brain. The middle meningeal artery is often implicated in the formation of epidural hematomas in patients with temporal or parietal bone skull fractures (see Chapter 19 ).
The ECA occasionally has an important role in supplying collateral flow for ICA occlusive disease through anastomoses between its facial, maxillary, and superficial temporal branches and the ophthalmic artery.
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