The posterior cerebral artery (PCA) is one of the major arteries supplying blood to the posterior part of the brain, particularly the occipital lobe, thalamus, and parts of the temporal lobe. It originates from the basilar artery and forms a crucial part of the brain’s blood supply network.
Location
The posterior cerebral artery is located at the base of the brain, where it arises from the basilar artery near the upper border of the pons. It travels around the midbrain, passing through the ambient cistern and the quadrigeminal cistern, then extends laterally and posteriorly toward the occipital lobe. As it courses along the inferior surface of the brain, the PCA passes through the tentorial notch and supplies the posterior regions of the brain, including parts of the temporal lobe and the visual cortex in the occipital lobe. The artery also connects with the Circle of Willis via the posterior communicating artery, which links it to the internal carotid artery.
Structure and Anatomy
The posterior cerebral artery (PCA) is a key vessel in the brain’s vascular system, supplying the occipital lobe, parts of the temporal lobe, and other important structures. It forms a crucial component of the blood supply to the posterior part of the brain. Below is a detailed description of the anatomy of the PCA.
Origin
The posterior cerebral artery originates from the basilar artery, which forms at the junction of the two vertebral arteries. The basilar artery ascends along the ventral surface of the pons and bifurcates at the upper border of the pons, giving rise to the two posterior cerebral arteries. This bifurcation occurs near the midbrain, where the basilar artery splits to form the left and right posterior cerebral arteries.
Course
After originating from the basilar artery, the posterior cerebral artery follows a complex course around the midbrain and towards the posterior parts of the brain. The artery passes laterally and posteriorly, running through several important anatomical regions:
- Ambient Cistern: Shortly after its origin, the posterior cerebral artery passes through the ambient cistern, a space filled with cerebrospinal fluid located between the midbrain and the temporal lobe. Here, the artery wraps around the midbrain, positioning itself close to the oculomotor nerve (cranial nerve III).
- Quadrigeminal Cistern: As the PCA continues its course, it passes through the quadrigeminal cistern, located posterior to the midbrain. This cistern is situated near the superior and inferior colliculi, two important structures of the midbrain that are involved in visual and auditory reflexes.
- Tentorial Notch: The posterior cerebral artery runs through the tentorial notch, a gap in the tentorium cerebelli (a fold of dura mater separating the cerebellum from the cerebrum). This brings the PCA into proximity with the occipital lobe and portions of the temporal lobe.
The artery then branches as it approaches the posterior part of the brain, terminating by supplying the occipital cortex and other regions.
Relations
- Anteriorly: The posterior cerebral artery is related to the posterior communicating artery, which connects the PCA to the internal carotid artery, forming part of the Circle of Willis. The oculomotor nerve runs near the origin of the PCA as it passes anteriorly to the midbrain.
- Posteriorly: The artery supplies the occipital lobe and extends towards the visual cortex at the posterior part of the brain.
- Laterally: It runs close to the temporal lobe as it passes through the ambient cistern and along the medial edge of the temporal cortex.
- Medially: The artery is closely related to the midbrain and the structures of the thalamus. Small perforating branches arise from the PCA to supply these areas.
Branches
The posterior cerebral artery gives off several important branches as it travels along its course. These branches are responsible for supplying blood to critical areas of the brain, including the occipital and temporal lobes, as well as the thalamus and midbrain.
Cortical Branches: These branches supply the occipital lobe and parts of the temporal lobe.
- Calcarine Artery: This artery supplies the visual cortex located in the occipital lobe, specifically the area responsible for visual processing.
- Parieto-occipital Artery: It supplies portions of the parietal lobe and occipital lobe.
- Temporal Branches: These branches supply the inferior and medial surfaces of the temporal lobe, particularly the fusiform and lingual gyri.
Central or Perforating Branches: These branches arise from the proximal portion of the PCA and supply deep structures of the brain, including the thalamus and midbrain.
- Thalamoperforating Arteries: These small perforating arteries supply the thalamus, which is a critical relay station for sensory information.
- Thalamogeniculate Arteries: These branches supply the geniculate bodies and the posterior portion of the thalamus.
- Quadrigeminal Arteries: These arteries supply the tectum of the midbrain, which includes the superior and inferior colliculi (involved in visual and auditory processing).
Posterior Communicating Artery: While not a branch of the PCA itself, the posterior communicating artery connects the posterior cerebral artery to the internal carotid artery, forming part of the Circle of Willis. This anastomosis is important for collateral circulation within the brain.
Termination
The posterior cerebral artery terminates by dividing into smaller branches that supply the occipital lobe, particularly the calcarine cortex, which processes visual information. The artery also supplies parts of the temporal lobe, including the fusiform gyrus, which plays a role in high-level visual processing such as facial recognition.
Anastomoses
The posterior cerebral artery forms important anastomoses with other arteries in the brain, ensuring a robust collateral circulation:
- The posterior communicating artery connects the PCA to the internal carotid artery, allowing blood to flow between the anterior and posterior circulations of the brain.
- The cortical branches of the PCA anastomose with branches from the middle cerebral artery and the anterior cerebral artery, providing additional routes for blood flow to reach the occipital and temporal lobes.
Variations
There are several anatomical variations in the posterior cerebral artery’s structure. In some individuals, the PCA may have a smaller or larger posterior communicating artery, altering the balance of blood flow between the internal carotid and basilar systems. In rare cases, the PCA may arise directly from the internal carotid artery instead of the basilar artery, a condition known as a fetal-type posterior cerebral artery.
Function
The posterior cerebral artery (PCA) plays a crucial role in providing oxygenated blood to the posterior part of the brain. Its branches supply vital structures such as the occipital lobe, temporal lobe, thalamus, and midbrain, which are involved in vision, memory, sensory processing, and basic autonomic functions. Below is a detailed explanation of the specific functions of the PCA.
Blood Supply to the Visual Cortex (Occipital Lobe)
One of the most critical functions of the PCA is to supply blood to the visual cortex, located in the occipital lobe. The calcarine artery, a branch of the PCA, directly nourishes the calcarine sulcus, which houses the primary visual cortex (V1). This region of the brain is responsible for processing visual information, such as light, color, shape, and motion.
Calcarine Artery: The calcarine artery supplies the primary visual cortex, allowing for the proper interpretation of visual stimuli. Any disruption to this artery or its blood flow can lead to cortical blindness, where the eyes function normally but the brain cannot process visual information.
The PCA ensures the occipital lobe receives a steady supply of oxygenated blood, enabling continuous and efficient visual processing, which is crucial for daily activities like reading, recognizing faces, and navigating environments.
Blood Supply to the Temporal Lobe
The PCA also supplies portions of the temporal lobe, particularly the inferior and medial surfaces. This part of the brain is involved in processing visual stimuli, language comprehension, memory formation, and recognition of complex objects such as faces.
Temporal Branches: These branches of the PCA provide blood to areas such as the fusiform gyrus and lingual gyrus, which are critical for higher-level visual processing, including facial recognition and the identification of objects.
By supplying these regions, the PCA supports essential cognitive functions such as visual memory, recognition, and language comprehension, ensuring the brain can process complex visual information and store memories.
Blood Supply to the Thalamus
The PCA provides blood to the thalamus through its perforating branches, such as the thalamoperforating and thalamogeniculate arteries. The thalamus is a vital relay center in the brain that processes and transmits sensory information to the cerebral cortex, playing a central role in sensory perception, motor control, and alertness.
Thalamoperforating and Thalamogeniculate Arteries: These branches supply the thalamus, which is responsible for relaying sensory signals, including those for vision, hearing, touch, and proprioception, to the appropriate cortical areas.
The blood supply from the PCA ensures that the thalamus can efficiently process sensory inputs, allowing the brain to integrate sensory information and coordinate responses. If this blood supply is compromised, it can result in sensory deficits and motor dysfunction, depending on the affected thalamic region.
Blood Supply to the Midbrain
The PCA also supplies the midbrain, an important part of the brainstem that is involved in controlling eye movements, auditory and visual reflexes, and certain aspects of motor coordination.
Quadrigeminal Artery: A branch of the PCA, this artery supplies the superior and inferior colliculi, structures in the midbrain that process visual and auditory reflexes. The superior colliculi are involved in coordinating eye movements and tracking objects, while the inferior colliculi are part of the auditory pathway.
By supplying blood to these structures, the PCA ensures proper reflexive responses to visual and auditory stimuli, helping to maintain functions such as gaze stabilization and sound localization.
Blood Supply to the Parietal Lobe
The PCA also contributes to the blood supply of the parietal lobe, particularly the posterior parietal cortex, through branches such as the parieto-occipital artery.
Parieto-occipital Artery: This artery supplies portions of the parietal lobe, which plays a role in integrating sensory information from different modalities (e.g., visual, auditory, and tactile) and is involved in spatial awareness and navigation.
The PCA’s supply to this region is essential for maintaining functions like spatial orientation and the integration of sensory inputs, which are critical for tasks such as movement coordination, perception of body position, and visual-motor coordination.
Contribution to the Circle of Willis
The PCA forms an integral part of the Circle of Willis, a circulatory anastomosis that provides collateral blood flow to the brain. This system allows blood from the anterior and posterior circulations to mix, ensuring that oxygenated blood can reach the brain even if one of the main arteries is compromised.
Posterior Communicating Artery: The PCA connects with the internal carotid artery via the posterior communicating artery, forming part of the Circle of Willis. This connection is critical for maintaining cerebral perfusion and protecting the brain from ischemia in case of arterial occlusion.
By being part of the Circle of Willis, the PCA ensures that adequate blood flow reaches the posterior parts of the brain under conditions where other major arteries may be blocked or narrowed, helping to prevent strokes or localized brain ischemia.
Support for Autonomic and Sensory Functions
The PCA, through its branches to the thalamus and midbrain, also supports important autonomic functions and sensory processing. These regions are involved in regulating autonomic responses, such as cardiovascular control and respiratory rhythm, as well as sensory signal transmission.
Thalamus and Midbrain: These regions, supplied by the PCA, are essential for maintaining consciousness, sensory processing, and motor coordination. Blood flow to these structures ensures they can perform their vital roles in autonomic regulation and sensory perception.
Disruption of blood flow to these areas can result in a wide array of deficits, including loss of consciousness, impaired sensation, and motor coordination issues.
Clinical Significance
The posterior cerebral artery (PCA) is clinically significant due to its role in supplying blood to the occipital lobe, temporal lobe, thalamus, and midbrain. Blockage or disruption of blood flow in the PCA can result in posterior cerebral artery stroke, which may lead to various neurological deficits, depending on the affected area.
One of the most common outcomes of PCA stroke is visual disturbances, including cortical blindness, where the eyes remain functional but the brain cannot process visual information due to damage to the primary visual cortex in the occipital lobe. Other possible effects include visual field deficits, such as homonymous hemianopia, where one half of the visual field is lost in both eyes.
Additionally, PCA strokes can affect the thalamus, leading to thalamic pain syndrome, characterized by chronic pain, sensory loss, or abnormal sensations. Damage to the midbrain or temporal lobe can result in memory impairments, auditory processing issues, and motor coordination problems.
