Most of the blood supply to the brain comes from paired vessels, the internal carotid and the vertebral arteries ( ). The internal carotid supplies the majority of the brain while the vertebral arteries provide blood to the posterior aspect of the cerebrum, the brain stem, and the cerebellum. A large anastomosis on the inferior surface of the brain, the circle of Willis, connects the anterior and posterior circulation. The blood–brain barrier is a physiological and anatomical system present in the circulatory system of the brain that controls the bidirectional movement of molecules. Superficial and deep cerebral veins drain the brain tissue and empty into dural venous sinuses, which in turn drain into the internal jugular vein and venous plexi.
The anterior circulation of the brain is derived from the internal carotid artery (ICA) (a). The internal carotid originates from the common carotid, which is a branch of the subclavian artery. After ascending through the neck, the ICA enters the carotid canal and begins its intracranial course (b). The pathway of the ICA is commonly divided into four segments:
Fig. 6.2 (a) Internal carotid artery. Left lateral view. (b) The four anatomical divisions of the internal carotid artery. Anterior view of the left internal carotid artery. The internal carotid artery consists of four topographically distinct parts between the carotid bifurcation and the point where it divides into the anterior and middle cerebral arteries. The parts are as follows: (1) Cervical part located in the lateral pharyngeal space; (2) petrous part located in the carotid canal of the petrous bone; (3) cavernous part which follows an S-shaped curve in the cavernous sinus; (4) cerebral part located in the chiasmatic cistern of the subarachnoid space. (c) The petrous part of the internal carotid artery (traversing the carotid canal) and the cavernous part (traversing the cavernous sinus) have a role in supplying extracerebral structures of the head. They give off additional small branches that supply local structures and are usually named for the areas they supply. Of the branches not supplying the brain, of special importance is the ophthalmic artery, which arises from the cerebral part of the internal carotid artery. Note: The ophthalmic artery forms an anastomosis with the artery of the pterygoid canal derived from the maxillary artery. (d) The ICA supplies most of the cerebrum. After giving off the ophthalmic artery, it bifurcates into the anterior and middle cerebral arteries.
(e) Cerebral arteries. Medial view of the right hemisphere. (f) The MCA runs laterally into the lateral sulcus of the brain. (g) After entering the lateral sulcus, the MCA sends branches to the insula. ICA, internal carotid artery; MCA, middle cerebral artery. (a, e, and f: Reproduced with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker. b and 6.2g: Reproduced with permission from Schuenke M, Schulte E, Schumacher U. THIEME Atlas of Anatomy Second Edition, Vol 3. ©Thieme 2016. Illustrations by Markus Voll and Karl Wesker. c: Reproduced with permission from Baker EW. Anatomy for Dental Medicine. Second Edition. © Thieme 2015. Illustrations by Markus Voll and Karl Wesker. e: Modified with permission from Schuenke M, Schulte E, Schumacher U. THIEME Atlas of Anatomy Second Edition, Vol 3. ©Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)
The petrous portion begins in the carotid canal, which is located in the petrous part of the temporal bone. After entering the canal, it curves forward and medially. As it exits, it travels superior to foramen lacerum, which in life is filled with cartilage, and then enters the cavernous sinus.
The cavernous portion lies between layers of dura forming the cavernous sinus. It initially ascends toward the posterior clinoid process, then curves forward along the side of the body of the sphenoid bone, and finally turns upward and ascends alongside the anterior clinoid process. The resulting S-shaped configuration of the ICA, which is made up of the cavernous and, to a smaller extent, the cerebral portion, is referred to as the carotid siphon and is often used as a radiographic landmark.
The cerebral portion begins after the vessel perforates the dura medial to the anterior clinoid process. Here, the ICA passes between the optic and occulomotor nerves and travels toward the lateral cerebral fissure where it gives off its terminal branches, the anterior and middle cerebral arteries.
The ICA supplies the majority of the cerebrum. After giving off the ophthalmic artery, the ICA continues in a superior direction alongside the optic chiasm. Eventually, it will bifurcate into the anterior and middle cerebral arteries but before it does so, the anterior choroidal and posterior communicating arteries are given off (d).