Neurovascular Anatomy I: General
Neural tissue depends on continuous arterial blood supply and the adult brain requires 750 milliliters (almost a quart) of oxygenated blood every minute to maintain normal activity. Of the total amount of oxygen delivered to the body tissues by the arteries, 20 percent is consumed by the brain alone. Delivery of blood to the brain is accomplished by two arterial systems which enter the skull: the carotid arteries (anterior circulation) and vertebral (vertebro-basilar system) arteries (posterior circulation). A series of anastomotic chanells lying at the base of the brain, known as the Circle of Willis, permits communication between these two systems.
The largest systemic artery, the aorta, leaves the base of the heart in a sweeping arch to supply the entire body with oxygenated blood. The aortic arch lies anterior to the formation of the paired primary bronchi from the bifurcation of the trachea at the level of the fourth thoracic vertebra. The left common carotid and left subclavian arteries arise directly from the apex of the aortic arch slightly to the left of midline. To the right of the midline, the aortic arch gives off a large vessel, the brachiocephalic artery (there is no left brachiocephalic artery), which runs a short distance rostrally and laterally before dividing to form the more central right common carotid artery and the more lateral right subclavian artery. The right and left common carotid arteries ascend in the neck, each lateral to the trachea, sharing a common sheath with the internal jugular vein and vagus nerve. At the level of the laryngeal prominence (Adam's apple) of the thyroid cartilage (C5 vertebrae), each common carotid artery bifurcates (divides) into the external and internal carotid arteries.
The internal carotid artery enters the skull on either side without branching, through the carotid canal located in the petrous portion of the temporal bone, enters the carotid foramen (foramen lacerum), ascends anteriorly through the petrous portion of the temporal bone (petrous part) forming a s-shaped curve (carotid siphon) that lies within the cavernous (venous) sinus (cavernous part) and turns rostrally into the middle cranial fossa (cranial part). As the artery leaves the cavernous sinus, it pierces the cranial dura and arachnoid to enter the subarachnoid space at the base of the brain.
At this position, distal to the cavernous segment within the subarachnoid space and caudal to the optic nerve, the cavernous part of the internal carotid artery gives rise to the ophthalmic artery, an importnatn anastomotic communication artery, which enters the orbit along the optic nerve to supply the orbital structures, including the eyeball. The internal carotid artery also gives rise to the posterior communicating and anterior choroidal arteries. The posterior communicating artery connects the internal carotid artery to the posterior cerebral artery. The internal carotid also gives off the posterior communicating and anterior choroidal arteries which supplies the ipsilateral internal capsule and portion of the basal ganglia.
The terminus of the carotid artery divides into its major terminal branches, the anterior cerebral and middle cerebral arteries. The anterior communicating artery can be seen connecting the paired anterior cerebral arteries. The anterior cerebral and middle cerebral arteries, can be seen at the base of the brain. The anterior cerebral arteries are connected to each other by the small anterior communicating artery and continues midline between the two hemispheres to supply blood to their medial surfaces. The middle cerebral artery courses laterally between the temporal and frontal lobes and emerges from the insula between the frontal and temporal lobes, where its branches spread over and supply blood to the lateral surface of the hemisphere.
The internal carotid artery and its major branches:
1 The cervical segment extends from the bifurcation of the common carotid (into the external and internal carotid arteries) to where it enters the carotid canal
2 The intrapetrosal segment courses through the petrous portion of the temporal bone
3 The intracavernous segment courses through the cavernous sinus, a venous structure overlying the sphenoid bone
4 The cerebral segment extends to where the internal carotid artery bifurcates into the anterior and middle cerebral arteries. The intracavernous and cerebral portions form the carotid siphon, an important radiological landmark.
Branches emerging directly from the cerebral segment of the internal carotid artery, in caudal to rostral order are:
1 the opthalmic artery, which supplies the optic nerve and the inner portion of the retina
2 the posterior communicating artery, which primarily nourishes diencephalic structures, and
3 the anterior choroidal artery, which supplies diencephalic and subcortical telencephalic structures
An additional, significant source of blood (25%) is carried to the brain by two vertebral arteries which arise as first branches of the superior surface of the left and right subclavian arteries. Each vertebral artery dives deep toward the lower cervical vertebrae, medial and posterior to the scalene muscles, three muscles found on each side of the neck spanning between the transverse processes of the cervical vertebrae and upper two ribs, and lateral and posterior to the common carotid artery. It enters and ascends through the transverse foramina (in the transverse processes) of the rostral six cervical vertebrae. In its passage through the transverse foramina, the vertebral artery gives one or two branches to the spinal cord. The two vertebral arteries are often of unequal caliber, one being dominant.
After passing through the atlas (C1), it bends sharply medial to approach the foramen magnum and turns upward to pass through to enter the subarachnoid space at the cranial cavity (skull) at the ventrolateral surface of the medulla subsequently joining at the caudal border of the pons to form the basilar artery. In its rostral course along the brain stem, the basilar artery gives off important branches: the anterior and posterior inferior cerebellar arteries (AICA & PICA), superior cerebellar artery and multiple median and paramedian perforators. The basilar artery terminates at the caudal midbrain by bifurcating into the left and right posterior cerebral arteries. The posterior communicating arteries usually arise as branches of the posterior cerebral arteries and join those vessels with the internal carotid arteries to complete the circle of Willis. Branches from these arteries normally provide the sole arterial supply to the occipital lobe, under the surface of the temporal lobe, thalamus, midbrain, pons, cerebellum, medulla, and portions of the cervical spinal cord.
At the base of the brain, surrounding the optic chiasm and pituitary stalk, anastomotic connections occur between the internal carotid and vertebral basilar arterial systems. This ring-like series of vessels is called the circle of Willis and consists of the anterior communicating artery, which unites the two anterior cerebral arteries, and the posterior communicating arteries, which join the internal carotid arteries with the posterior cerebral arteries.
The brain is provided with blood from the anterior, middle and posterior cerebral arteries. The anterior cerebral artery supplies the medial surface of the cerebrum and the superior border of the frontal and parietal lobes. The middle cerebral artery supplies most of the lateral surface of the cerebral hemispheres, including the lateral portions of the frontal lobe, the superior and lateral portions of the temporal lobes, and the deep structures of the frontal and parietal lobes. The posterior cerebral artery and medial portions of the temporal lobe. The deeper structures of the cerebral hemispheres are supplied by penetrating branches of the larger arteries. Of notable importance are the perforating lenticulostriate arteries, which supply the basal ganglia and internal capsule, and the perforating branches of the posterior cerebral artery, which supply the thalamus.
Blood leaves the head by way of venous drainage of the cerebral hemispheres is divided into superficial and deep systems that converge into large channels, the venous sinuses, contained within the layers of the dura mater. The cerebral cortex and other half of the white matter drain into the superficial system of veins located over the convexity of the brain in the subarachnoid space. The superficial veins of the superior half of the brain drain into the superior sagittal sinus those from the interior half drain into the lateral sinuses, the most prominent of the sinuses which run longitudinally from ventral to dorsal in the falx cerebri between the hemispheres. The deep white matter and deep nuclei of the brain drain into the deep venous system, which includes the great cerebral vein of Galen, inferior sagittal sinus, and straight sinus. The major venous channels merge in the occipital region and blood empties into the transverse sinuses, the sigmoid sinuses, jugular foramen and jugular veins. Veins on the inferior surfaces of the cerebrum terminate directly or indirectly in the cavernous sinus, an important dural structure located on either side of the pituitary fossa containing the carotid artery and cranial nerves III, IV, V and VI.
The largest systemic artery, the aorta, leaves the base of the heart in a sweeping arch to supply the entire body with oxygenated blood. The aortic arch lies anterior to the formation of the paired primary bronchi from the bifurcation of the trachea at the level of the fourth thoracic vertebra. The left common carotid and left subclavian arteries arise directly from the apex of the aortic arch slightly to the left of midline. To the right of the midline, the aortic arch gives off a large vessel, the brachiocephalic artery (there is no left brachiocephalic artery), which runs a short distance rostrally and laterally before dividing to form the more central right common carotid artery and the more lateral right subclavian artery. The right and left common carotid arteries ascend in the neck, each lateral to the trachea, sharing a common sheath with the internal jugular vein and vagus nerve. At the level of the laryngeal prominence (Adam's apple) of the thyroid cartilage (C5 vertebrae), each common carotid artery bifurcates (divides) into the external and internal carotid arteries.
The internal carotid artery enters the skull on either side without branching, through the carotid canal located in the petrous portion of the temporal bone, enters the carotid foramen (foramen lacerum), ascends anteriorly through the petrous portion of the temporal bone (petrous part) forming a s-shaped curve (carotid siphon) that lies within the cavernous (venous) sinus (cavernous part) and turns rostrally into the middle cranial fossa (cranial part). As the artery leaves the cavernous sinus, it pierces the cranial dura and arachnoid to enter the subarachnoid space at the base of the brain.
At this position, distal to the cavernous segment within the subarachnoid space and caudal to the optic nerve, the cavernous part of the internal carotid artery gives rise to the ophthalmic artery, an importnatn anastomotic communication artery, which enters the orbit along the optic nerve to supply the orbital structures, including the eyeball. The internal carotid artery also gives rise to the posterior communicating and anterior choroidal arteries. The posterior communicating artery connects the internal carotid artery to the posterior cerebral artery. The internal carotid also gives off the posterior communicating and anterior choroidal arteries which supplies the ipsilateral internal capsule and portion of the basal ganglia.
The terminus of the carotid artery divides into its major terminal branches, the anterior cerebral and middle cerebral arteries. The anterior communicating artery can be seen connecting the paired anterior cerebral arteries. The anterior cerebral and middle cerebral arteries, can be seen at the base of the brain. The anterior cerebral arteries are connected to each other by the small anterior communicating artery and continues midline between the two hemispheres to supply blood to their medial surfaces. The middle cerebral artery courses laterally between the temporal and frontal lobes and emerges from the insula between the frontal and temporal lobes, where its branches spread over and supply blood to the lateral surface of the hemisphere.
The internal carotid artery and its major branches:
1 The cervical segment extends from the bifurcation of the common carotid (into the external and internal carotid arteries) to where it enters the carotid canal
2 The intrapetrosal segment courses through the petrous portion of the temporal bone
3 The intracavernous segment courses through the cavernous sinus, a venous structure overlying the sphenoid bone
4 The cerebral segment extends to where the internal carotid artery bifurcates into the anterior and middle cerebral arteries. The intracavernous and cerebral portions form the carotid siphon, an important radiological landmark.
Branches emerging directly from the cerebral segment of the internal carotid artery, in caudal to rostral order are:
1 the opthalmic artery, which supplies the optic nerve and the inner portion of the retina
2 the posterior communicating artery, which primarily nourishes diencephalic structures, and
3 the anterior choroidal artery, which supplies diencephalic and subcortical telencephalic structures
An additional, significant source of blood (25%) is carried to the brain by two vertebral arteries which arise as first branches of the superior surface of the left and right subclavian arteries. Each vertebral artery dives deep toward the lower cervical vertebrae, medial and posterior to the scalene muscles, three muscles found on each side of the neck spanning between the transverse processes of the cervical vertebrae and upper two ribs, and lateral and posterior to the common carotid artery. It enters and ascends through the transverse foramina (in the transverse processes) of the rostral six cervical vertebrae. In its passage through the transverse foramina, the vertebral artery gives one or two branches to the spinal cord. The two vertebral arteries are often of unequal caliber, one being dominant.
After passing through the atlas (C1), it bends sharply medial to approach the foramen magnum and turns upward to pass through to enter the subarachnoid space at the cranial cavity (skull) at the ventrolateral surface of the medulla subsequently joining at the caudal border of the pons to form the basilar artery. In its rostral course along the brain stem, the basilar artery gives off important branches: the anterior and posterior inferior cerebellar arteries (AICA & PICA), superior cerebellar artery and multiple median and paramedian perforators. The basilar artery terminates at the caudal midbrain by bifurcating into the left and right posterior cerebral arteries. The posterior communicating arteries usually arise as branches of the posterior cerebral arteries and join those vessels with the internal carotid arteries to complete the circle of Willis. Branches from these arteries normally provide the sole arterial supply to the occipital lobe, under the surface of the temporal lobe, thalamus, midbrain, pons, cerebellum, medulla, and portions of the cervical spinal cord.
At the base of the brain, surrounding the optic chiasm and pituitary stalk, anastomotic connections occur between the internal carotid and vertebral basilar arterial systems. This ring-like series of vessels is called the circle of Willis and consists of the anterior communicating artery, which unites the two anterior cerebral arteries, and the posterior communicating arteries, which join the internal carotid arteries with the posterior cerebral arteries.
The brain is provided with blood from the anterior, middle and posterior cerebral arteries. The anterior cerebral artery supplies the medial surface of the cerebrum and the superior border of the frontal and parietal lobes. The middle cerebral artery supplies most of the lateral surface of the cerebral hemispheres, including the lateral portions of the frontal lobe, the superior and lateral portions of the temporal lobes, and the deep structures of the frontal and parietal lobes. The posterior cerebral artery and medial portions of the temporal lobe. The deeper structures of the cerebral hemispheres are supplied by penetrating branches of the larger arteries. Of notable importance are the perforating lenticulostriate arteries, which supply the basal ganglia and internal capsule, and the perforating branches of the posterior cerebral artery, which supply the thalamus.
Blood leaves the head by way of venous drainage of the cerebral hemispheres is divided into superficial and deep systems that converge into large channels, the venous sinuses, contained within the layers of the dura mater. The cerebral cortex and other half of the white matter drain into the superficial system of veins located over the convexity of the brain in the subarachnoid space. The superficial veins of the superior half of the brain drain into the superior sagittal sinus those from the interior half drain into the lateral sinuses, the most prominent of the sinuses which run longitudinally from ventral to dorsal in the falx cerebri between the hemispheres. The deep white matter and deep nuclei of the brain drain into the deep venous system, which includes the great cerebral vein of Galen, inferior sagittal sinus, and straight sinus. The major venous channels merge in the occipital region and blood empties into the transverse sinuses, the sigmoid sinuses, jugular foramen and jugular veins. Veins on the inferior surfaces of the cerebrum terminate directly or indirectly in the cavernous sinus, an important dural structure located on either side of the pituitary fossa containing the carotid artery and cranial nerves III, IV, V and VI.