Brain Vasculature

Objectives List vessels found in brain region Identify the locations of and relationships between brain vasculature Differentiate between brain scans performed with and without the injection of contrast media. After completing this topic, you should be able to: List vessels found in the brain region Identify the locations of and relationships between brain vasculature Differentiate between brain scans performed with and without the injection of contrast media.

Brain Imaging Brain scans are the most routine CT exams. These exams are often completed to evaluate for trauma or CVA. Similar to other exams, the scan begins with a scout image. Reference lines are placed to identify exam slices through the brain. Scan lines are angled away from the lenses of the eyes to reduce radiation exposure to this radiosensitive organ. The scan begins inferiorly below the skull base and extends superiorly through the vertex of the head.

Brain with vs. without Contrast Brain CT scans are primarily completed without contrast. This is the case when evaluating a CVA to differentiate between a hemorrhagic versus an ischemic stroke. When scans are performed for post traumatic injury, no intravenous contrast is administered. Intravenous contrast media is administered when evaluating for a primary brain tumor. Brain edema or swelling around a primary tumor has a darker appearance. Following the injection of contrast, brain tumors frequently enhance with contrast appearing bright white on the image. Lung and breast cancer commonly metastasize to the brain. Contrast media is injected to evaluate for brain metastases. Abscesses are another pathology that occur in the brain. An abscess may form following chronic infection or in AIDS patients. When an abscess is the reason for a brain scan, intravenous contrast media is injected.

Brain Vasculature Internal Carotid Arteries Vertebral Arteries Circle of Willis Dural Sinuses When learning brain vasculature, it is important to separate the vessels into anterior and posterior circulation. The internal carotid arteries are responsible for the anterior brain circulation. The internal carotid arteries have two main branches including the anterior and middle cerebral arteries. The anterior cerebral arteries provide blood supply to the forebrain while the middle cerebral arteries extend laterally to the cerebral hemispheres and insula. The posterior brain circulation begins with the vertebral arteries. The vertebral arteries ascend up the neck through the transverse foramina located in the cervical spine. At the level of the clivus, on the skull base, the vertebral arteries merge together to form the basilar artery. The basilar artery continues into the posterior cerebral arteries. The Circle of Willis provides collateral blood flow to the brain and the dural sinuses are responsible for venous drainage. These vessels will be discussed further in this presentation.

Posterior Brain Circulation The posterior circulation of the brain begins with the vertebral arteries. The vertebral arteries merge together forming the basilar artery as seen in the image above.

This image is scanned more superiorly than the previous image and a reference line demonstrates the exact placement of the CT slice. The basilar artery is centrally located in this image. Superiorly, the air-filled maxillary sinuses are demonstrated with the 4th ventricle seen inferior to the basilar artery on this axial image. The ventricular system in the brain holds cerebral spinal fluid. When a subarachnoid hemorrhage occurs, typically when an aneurysm bursts, blood will fill the ventricles.

The Circle of Willis is shown on this image The Circle of Willis is shown on this image. Specifically, the middle cerebral and internal carotid arteries are identified. An important structure to recognize on this image is the midbrain. The medulla oblongata, pons, and midbrain comprise the brain stem structures.

Circle Of Willis The Circle of Willis has a spiderlike appearance in the brain. The middle cerebral arteries extend to the lateral aspect of the brain. The anterior cerebral artery supplies the frontal lobe and forebrain with arterial blood supply. Posterior circulation is provided by the posterior cerebral arteries. Below the Circle of Willis is the midbrain. The midbrain resembles a heart in its appearance. The dark, 4th ventricle is seen as a midline structure filled with cerebral spinal fluid.

Circle Of Willis A reconstructed Circle of Willis image is visualized with this image. The Circle of Willis is formed from the following vessels: the internal carotids, the anterior cerebral, anterior communicating, posterior cerebral, and posterior communicating arteries. The middle cerebral arteries are lateral branches extending on each side from the Circle of Willis. Inside of the Circle of Willis is the pituitary gland.

This image provides a lateral view of neck and brain vasculature This image provides a lateral view of neck and brain vasculature. It is a good review of the anterior and posterior brain circulation with its respective branches.

These are reconstructed images of brain vasculature beginning with the aortic arch. Brachiocephalic, left common carotid, and left subclavian arteries are demonstrated as branches coming directly from the aortic arch. The right and left common carotid arteries are seen branching into the internal and external carotid arteries in these images.

The dural sinuses are responsible for venous brain drainage The dural sinuses are responsible for venous brain drainage. The dural sinuses in the brain include: superior sagittal sinus, inferior sagittal sinus, straight sinus, transverse sinus, sigmoid sinus and the confluence of sinuses. The dural sinuses empty into the internal jugular vein which descends down the neck into the thorax.

In this image, the transverse sinuses are visualized In this image, the transverse sinuses are visualized. Other anatomy labeled includes the lateral fissure also called the Sylvian fissure. The lateral or Sylvian fissure separates the frontal and parietal lobes from the temporal lobe which is identified on this image.

The straight sinus emptying into the confluence of sinuses is well demonstrated on this image. These dural sinuses are highlighted from the injection of contrast media. Other anatomy visualized includes the right and left lateral ventricles with the choroid plexus located within the ventricles. The choroid plexus is responsible for producing cerebral spinal fluid.

On this image, the superior sagittal sinus is demonstrated On this image, the superior sagittal sinus is demonstrated. The superior sagittal sinus is the most superiorly placed dural sinus responsible for the brain venous drainage.