Vascular Anatomy of the Brain - A Simplified Guide

The brain comprises only 2% of body mass but receives nearly 15% of total blood supply. A sophisticated network of blood vessels delivers oxygen, energy, and nutrients to the brain for optimal functioning. Here is a simplified guide to the brain’s vascular anatomy – the arteries and veins that regulate blood flow to and from the brain — and several diseases that can affect it.

The brain receives oxygen-rich blood from the heart via two paired arteries. The large carotid arteries can be felt pulsating on the sides of your neck, while the smaller vertebral arteries travel upwards but behind the carotid arteries through bony openings in the spine. Although the carotid arteries start supplying blood to the front of the brain and the vertebral arteries do so from the back, they eventually branch off and connect through many other named blood vessels.

Below is a list of named vessels that you may hear about, with their names broken down by their respective meanings to help give you a sense of where they are located. “Cerebral” refers to anything related to the brain, and “communicating” usually refers to a thin, smaller artery that connects two larger ones together.

• Internal carotid artery: The large carotid artery actually splits into two arteries, the internal and external carotid arteries, as they ascend in the neck. The internal carotid artery is the main artery supplying blood to the brain.
• Anterior cerebral artery: Large branch of the internal carotid artery supplying blood to the front (anterior) parts of the brain, along with other deep structures.
• Anterior communicating artery: A short and slender artery that connects the two anterior cerebral arteries, serving as a bridge between the left and right-sided circulation. Brain aneurysms most commonly occur at the anterior communicating artery.
• Middle cerebral artery: Largest branch of the internal carotid artery that supplies blood to a significant portion of the brain, particularly in the central regions.
• Posterior communicating artery: A thin artery that connects the posterior cerebral arteries to the internal carotid arteries on the left and right side. It also gives branches that supply blood to deep structures.
• Vertebral artery: One of the main arteries that supplies blood to the brain. It enters the bottom of the skull and travels up along the brainstem. It also gives rise to the anterior spinal artery, which supplies blood to a large portion of the spinal cord.
• Basilar artery: The artery that forms when the left and right vertebral arteries join together. It runs along the pons, a structure in the midportion of the brainstem.
• Posterior cerebral artery: These paired arteries are located more towards the back (posterior) part of the brain and arise at the top of the basilar artery. They supply parts of the brain that are located closer to the back of the head.

Veins carry deoxygenated blood and other wastes back to the heart. Venous blood in the brain eventually travels to special larger veins called sinuses, which drain downwards into veins of the neck. They are categorized into 4 types: 

The superficial veins mostly drain the cerebral cortex and are located on the surface of the brain. They include: 

• Superior cerebral veins
• Inferior cerebral veins
• Superficial middle cerebral vein
• Superior anastomotic (connecting) vein
• Inferior anastomotic (connecting) vein 

Deep veins of the cerebrum drain the brain’s internal structures, including the thalamus, hypothalamus, internal capsule, corpus callosum, corpus striatum, and brainstem. They include: 

• Internal cerebral veins 
• Basal veins of Rosenthal
• Great cerebral vein of Galen

The cerebellum is a structure located at the back of the brain, underneath the main cerebral hemispheres. It is drained by the following veins: 

• Superior cerebellar veins
• Inferior cerebellar veins

All of the veins draining blood from the brain converge into large-caliber vessels known as dural venous sinuses. From these sinuses, blood continues its course into the internal jugular veins. The venous sinuses are:

• Cavernous sinus
• Sphenoparietal sinuses
• Superior sagittal sinus
• Inferior sagittal sinus
• Straight sinus
• Occipital sinus
• Superior petrosal sinuses
• Inferior petrosal sinuses
• Transverse sinuses
• Sigmoid sinuses

A cerebral angiogram is a diagnostic procedure used to visualize blood vessels in the brain. It can help to detect abnormal blood flow and vessel structures. A digital subtraction angiogram (DSA) is a specific type of cerebral angiogram that uses digital imaging technology to enhance the visualization of blood vessels in the brain. 

During the procedure, a thin flexible tube called a catheter is inserted into a blood vessel, usually in the groin area or the arm. With the help of X-rays, the catheter is gently guided through the blood vessels until it reaches the brain. Once the catheter is in the right place, a contrast dye is injected into the bloodstream. This dye highlights blood vessels on the X-ray, and images can be taken to investigate any abnormalities in detail.

Cerebral angiograms can help to detect any problems in the blood vessels, such as narrowing, blockages, aneurysms, arteriovenous malformations, and other vascular issues in the brain. It can also provide important information to help diagnose and plan treatment for conditions such as stroke and brain tumors. In some cases, it may even be used to monitor the progression of vascular diseases or the effectiveness of treatment interventions over time.

While an angiogram may seem complex, it is performed by trained medical professionals in a hospital setting, and they take every precaution to ensure the patient's safety and comfort during the procedure.

To access the major vessels in the brain, doctors can use two main pathways: the radial pathway and the femoral pathway. These pathways refer to the locations where a catheter can be inserted into the body to reach the blood vessels.

• Radial Pathway: The radial pathway involves inserting the catheter through a blood vessel in the wrist, specifically the radial artery. The wrist is numbed with a local anesthetic, and a small incision is made to access the artery. The catheter is carefully guided through the radial artery and advanced towards the brain's blood vessels.
• Femoral Pathway: The femoral pathway involves inserting the catheter through a blood vessel in the groin area, known as the femoral artery. The patient lies down on their back, and the groin area is cleaned and sterilized. Local anesthesia is applied to numb the area. Then, a small incision is made to access the femoral artery. The catheter is threaded through the artery and carefully directed toward the brain's blood vessels.

Both pathways have their advantages and risks. The radial pathway, accessed through the wrist, may offer quicker recovery, less bleeding, and lower risk of complications compared to the femoral pathway. However, the radial pathway has size limitations and may not be suitable for everyone, and requires that the arm remains still during the procedure.

The femoral pathway, accessed through the groin, allows for larger catheters to be used, which can be beneficial for more complex procedures. However, it may involve a slightly longer recovery period, and there is a small risk of bleeding and infection at the incision site.

The choice of which pathway depends on various factors, including the specific procedure being performed, the patient's condition, and the expertise of the medical team. The medical professionals involved will assess the individual situation and determine the most appropriate pathway to safely access the major vessels in the brain.

Cerebrovascular diseases are the leading causes of neurological-related deaths and life-threatening events. Here is an overview of the most common cerebrovascular diseases: 

• Ischemic stroke: An ischemic stroke occurs when blood flow is blocked to a portion of the brain, causing loss of neurological function. A stroke can be thought of as similar to a heart attack, but instead it is a “brain attack.” Rapid treatment is needed to reduce the risk of permanent problems.
• Hemorrhagic stroke: A hemorrhagic stroke is a “brain bleed” which causes reduction of blood flow to a portion of the brain, resulting in loss of neurologic function. This usually occurs in a deep part of the brain called the basal ganglia.
• Transient ischemic attack (TIA): Often referred to as a “mini-stroke”, TIA is a temporary disruption of blood flow to the brain, resulting in stroke-like symptoms that typically resolve within 24 hours. While TIAs do not cause permanent brain damage, they are warning signs of an increased risk of stroke.
• Carotid artery stenosis: Carotid stenosis refers to the narrowing of the carotid arteries, limiting the supply of oxygen-rich blood to the brain. It is caused by cholesterol and fat buildup and is a risk factor for transient ischemic attacks and strokes. 
• Brain aneurysms: An aneurysm is a weakened area in the wall of a blood vessel leading to an abnormal bulge or ballooning. Cerebral aneurysms are most common in arteries and rarely develop in veins. Most aneurysms occur in the anterior communicating artery (30 – 35%), internal carotid artery and its branches (30%), and the middle cerebral artery (22%). Aneurysms of the posterior circulation are less common (8 – 10%) with those occurring at the tip of the basilar artery being the most frequent among them.  
• Vascular malformations: Vascular malformations refer to the abnormal development and layout of the brain’s blood vessels. There are different kinds of malformations varying in severity. Examples include arteriovenous malformations and cavernous malformations.

• The brain has a complex blood supply system, composed of numerous arteries and veins.
• Arteries deliver oxygen- and nutrient-rich blood to the brain, while veins carry away deoxygenated blood and waste products.
• Cerebral angiogram is a diagnostic procedure used to visualize the blood vessels in the brain.
• The brain’s blood vessels are vulnerable to various cerebrovascular diseases, including stroke, aneurysms, and other conditions.

• National Institute of Neurological Disorders and Stroke
• American Association of Neurological Surgeons (AANS): Cerebrovascular Disease
• Brain Aneurysm Foundation
• American Association of Neurological Surgeons (AANS): Cerebral Aneurysm
• American Brain Foundation (ABF)