The posterior cerebral artery (PCA) is the main blood supplier to the back of the brain, feeding the visual cortex, parts of the thalamus, the inner surface of the temporal lobe, and portions of the midbrain. When it gets blocked or damaged, the consequences range from sudden vision loss to memory problems to unusual neurological syndromes that can puzzle even experienced clinicians. Because so many critical structures depend on its blood flow, the PCA occupies an outsized role in stroke neurology, neurosurgery, and neuroimaging despite being smaller and less frequently discussed than the middle or anterior cerebral arteries.
Where the PCA Runs and What It Feeds
Each side of the brain has its own PCA. In most people, both originate from the top of the basilar artery, which itself forms from the two vertebral arteries running up through the spine. From that starting point, each PCA curves around the midbrain, passes through a series of deep cisterns (fluid-filled spaces at the base of the brain), and eventually fans out across the underside of the occipital and temporal lobes. Along the way, it sends off small perforating branches that dive into the thalamus, hypothalamus, and midbrain, plus larger cortical branches that supply the visual cortex, the hippocampus, and surrounding structures.
Neurosurgeons and radiologists divide the PCA into segments to describe where along its course a problem sits. The most commonly used scheme labels these P1 through P4, though some authors add a P5 for the very distal branches. P1 is the short stretch from the basilar tip to where the posterior communicating artery (PComA) connects. P2 runs alongside the midbrain through the ambient cistern. P3 courses through the quadrigeminal cistern behind the midbrain. P4 corresponds to the branches running within the calcarine fissure and the parieto-occipital sulcus, where the artery finally reaches the visual cortex.1PubMed Central. Morphology and Variations of the Posterior Cerebral Artery: A Literature Review An earlier anatomical study further subdivided P2 into anterior and posterior halves based on their relationship to the midbrain margin.2Journal of Neurosurgery. Microsurgical anatomy of the posterior cerebral artery
Deep Perforating Branches and the Thalamus
Some of the PCA’s most clinically important branches are the ones you never see on a standard angiogram without high-resolution technique. Tiny perforating arteries shoot off the P1 and P2 segments to supply the thalamus and upper brainstem. The most proximal of these, the paramedian thalamic artery (also called the inferior thalamic artery or paramedian thalamo-subthalamic artery, depending on which textbook you read), feeds the medial thalamic nuclei, parts of the hypothalamus, the subthalamus, the red nucleus, and the substantia nigra.3PubMed Central. Thalamo-mesencephalic Branches of the Posterior Cerebral Artery: a 3D Rotational Angiography Study When one of these tiny arteries gets blocked, the resulting infarct can produce dramatic symptoms out of proportion to the size of the lesion, from sudden coma-like drowsiness (if the reticular formation is involved) to bizarre eye movement disorders.
The thalamic perforators also explain the Dejerine-Roussy syndrome, sometimes called thalamic pain syndrome. Damage to the sensory relay nuclei of the thalamus can initially cause numbness on the opposite side of the body, but weeks or months later, some patients develop agonizing, burning pain in the same area. A study of 30 patients with thalamic vascular lesions and sensory disturbances identified four distinct subtypes, ranging from complete numbness without pain to pure central pain with otherwise normal touch and joint sensation.4JAMA Neurology. Thalamic Pain Syndrome of Dejérine-Roussy: Differentiation of Four Subtypes Assisted by Somatosensory Evoked Potentials Data The pain can be relentless and difficult to treat, making thalamic stroke one of the more feared consequences of PCA territory ischemia.
The Fetal-Type Variant
In early fetal development, the PCA is actually supplied by the internal carotid artery through the PComA, not by the basilar artery. As the fetus matures, the basilar connection usually takes over. In a sizable fraction of adults, though, the fetal configuration persists: the PCA continues to draw most or all of its blood from the internal carotid system instead of the vertebrobasilar system. This is called a fetal-type posterior cerebral artery (FTP or FPCA). Estimates of how common it is range from about 3% to 36% depending on the study and imaging technique, with most recent work placing the prevalence around 20% to 30%.5PubMed. Mechanisms of Stroke in Patients with Fetal Posterior Cerebral Artery6PubMed Central. Evaluating the Prevalence and Clinical Significance of Fetal Posterior Cerebral Artery Variants via Magnetic Resonance Imaging
The fetal variant is usually considered a normal anatomical variation rather than a disease, but it is not entirely benign. People with an FTP tend to have higher rates of other variations in the circle of Willis and carry a moderately increased risk of aneurysms, particularly at the junction of the internal carotid artery and the PComA. One CT angiography study found a moderate association between FTP and aneurysms at that junction, with an odds ratio of about 2.8.7Europe PMC. Is fetal-type posterior cerebral artery a risk factor for intracranial aneurysm as analyzed by multislice CT angiography? The fetal variant also changes the clinical picture of carotid artery disease: if someone with an FTP develops a blockage in their internal carotid, they may lose blood flow not only to the front of the brain but to the visual cortex as well, because the PCA depends on that carotid supply.
Visual Loss After PCA Stroke
The symptom most tightly linked to PCA territory infarction is loss of vision on one side of the visual field, called homonymous hemianopia. Because the PCA’s cortical branches supply the primary visual cortex in the occipital lobe, a stroke here knocks out the opposite visual field. A patient with a right PCA stroke loses the left half of vision in both eyes, and vice versa.
One curious and clinically important feature of PCA strokes is macular sparing: many patients retain central vision even when they lose the peripheral field. The leading explanation is that the occipital pole, where central (macular) vision is processed, sits at the boundary between the PCA’s territory and the middle cerebral artery’s territory. In many people, the middle cerebral artery sends collateral branches to the occipital pole, so even when the PCA is blocked, blood still reaches the most central part of the visual cortex.8PubMed Central. The Mechanism of Macular Sparing The exact boundary between the two arterial territories varies from person to person, but it consistently falls within the region that maps central vision, because the macular representation in the cortex is disproportionately large. An MRI-based study of PCA stroke patients with macular sparing confirmed that preserved tissue at the occipital pole corresponded closely to the spared visual field.9Journal of Neuro-Ophthalmology. Correlation of Macular Sparing and Homonymous Paracentral Scotomas With MRI Lesions in Posterior Cerebral Artery Infarction
The branching pattern of the PCA’s occipital arteries also matters. The artery splits into several named branches, including the calcarine, parieto-occipital, posterior temporal, and common temporal arteries, each supplying variable cortical regions. An anatomical study found these branches in all examined brains, though a smaller branch to the lingual gyrus was present in only about 8% of cases.10PubMed. Distribution of the occipital branches of the posterior cerebral artery. Correlation with occipital lobe infarcts This variability means that two patients with PCA strokes can have quite different patterns of visual loss depending on which branch is affected.
Memory and the Hippocampus
The PCA also feeds the hippocampus and surrounding medial temporal lobe structures through its inferior temporal and posterior choroidal branches. That means PCA strokes can impair memory, sometimes profoundly. A study of 84 patients with PCA territory infarction found that more than 80% had a measurable memory deficit, most often affecting both verbal and visual memory together.11PubMed Central. The amnestic syndrome of posterior cerebral artery infarction Left-sided strokes were more likely to impair verbal memory, while right-sided strokes affected nonverbal (figural) memory, consistent with the general lateralization of memory functions.
MRI studies of hippocampal involvement in PCA stroke have identified distinct patterns of damage depending on which hippocampal subregion loses its blood supply. One study classified lesions into four patterns: complete hippocampal involvement, lateral body and tail involvement, dorsal body and tail involvement, and circumscribed lateral lesions. Interestingly, while hippocampal damage on MRI was common, prominent memory complaints were the leading symptom in only a minority of patients, likely because the accompanying visual field loss and other deficits often overshadowed the memory impairment.12PubMed. Hippocampal lesion patterns in acute posterior cerebral artery stroke: clinical and MRI findings
An earlier analysis of 30 patients with unilateral PCA infarction showed that verbal learning was the most vulnerable memory function in those with left-sided strokes, and that the critical lesion location was the posterior parahippocampal gyrus and the collateral isthmus, a narrow strip of cortex that connects the hippocampus to broader neocortical areas. Damaging this strip effectively disconnects the hippocampus from its input and output pathways, even if the hippocampus itself is partially spared.13Brain. Verbal Memory and Learning in Unilateral Posterior Cerebral Infarction: A Report on 30 Cases
Higher Cognitive Syndromes
Left PCA strokes can produce alexia without agraphia, a striking condition in which a patient loses the ability to read but can still write. The mechanism involves damage to the left visual cortex (preventing visual information from reaching language areas) combined with damage to the splenium of the corpus callosum (blocking the right visual cortex from relaying written-word information to the left hemisphere’s language centers). A case report documented this in a 55-year-old man whose MRI showed a left PCA infarct involving the occipital lobe and splenium.14PubMed. Posterior cerebral artery stroke presenting as alexia without agraphia But alexia without agraphia is really just the most famous item on a broader menu: a systematic neuropsychological study of left PCA infarcts found impairments extending well beyond reading, including deficits in color naming, object naming, and other language-related tasks.15Brain. The Pattern of Neuropsychological Impairment Associated With Left Posterior Cerebral Artery Infarcts
Midbrain Syndromes
Because the PCA’s perforating branches supply the midbrain, occlusion at the right spot can produce classic brainstem stroke syndromes. Weber syndrome results from infarction of the cerebral peduncle on one side, damaging the third cranial nerve (which controls most eye movements and the pupil) and the pyramidal tract (which controls voluntary movement). The result is a drooping eyelid, a dilated pupil, and impaired eye movement on the same side as the stroke, combined with weakness of the arm, leg, and lower face on the opposite side.16Risk Management and Healthcare Policy. A Case of Comorbid Weber Syndrome Following Mechanical Thrombectomy for Middle Cerebral Artery Occlusion
Claude syndrome is a related but distinct midbrain pattern, involving the third nerve plus the cerebellar outflow pathway rather than the pyramidal tract. A patient typically presents with eye movement problems on the stroke side and uncoordinated limb movements on the opposite side, but without the hemiplegia seen in Weber syndrome. A case report described this arising from PCA stenosis in a 61-year-old man with hypertension and smoking history.17PubMed. Claude’s syndrome in association with posterior cerebral artery stenosis
PCA Aneurysms
Aneurysms of the PCA are uncommon compared with those at more typical locations like the anterior communicating artery or the middle cerebral artery bifurcation, but they present unique challenges. A systematic review and meta-analysis pooling 685 patients with 698 PCA aneurysms found that roughly half were saccular (the “berry” type) and half were non-saccular (fusiform, dissecting, or other shapes), and about 54% had ruptured at the time of diagnosis.18PubMed. Natural history and management of posterior cerebral artery aneurysms: a systematic review and meta-analysis of individual patient data
Giant PCA aneurysms (typically exceeding 25 mm) are especially formidable. A review of 55 patients with giant saccular PCA aneurysms found a mean maximum diameter near 38 mm, with about a third presenting after rupture and another quarter presenting with headache. Around 31% had significant brainstem compression from the aneurysm’s mass. Treatment was predominantly microsurgical. Strikingly, the PCA was sacrificed (permanently clipped off) in 40% of these patients without causing severe neurological harm, likely because collateral circulation from neighboring arteries compensated for the lost flow.19Brain and Spine. Review of treatment modalities and clinical outcome of giant saccular posterior cerebral artery aneurysms That tolerance for sacrifice sets the PCA apart from the middle cerebral artery, where permanently blocking the vessel would be devastating.
Treating PCA Strokes With Thrombectomy
Mechanical thrombectomy, the procedure of threading a catheter into the brain’s arteries to physically remove a clot, has transformed stroke care for large-vessel occlusions in the anterior circulation. Its role in PCA occlusions has been less clear, partly because PCA strokes are less common and partly because the visual and cognitive deficits they cause tend to score lower on the standard stroke severity scales used to triage patients for intervention. Nonetheless, emerging evidence suggests that thrombectomy for PCA occlusions is technically feasible and appears safe.
A multicenter case-control study of 184 patients compared thrombectomy with standard medical treatment for PCA occlusion and found early clinical improvement with endovascular treatment, along with acceptable rates of symptomatic bleeding and successful clot removal.20JAMA Neurology. Thrombectomy for Primary Distal Posterior Cerebral Artery Occlusion Stroke: The TOPMOST Study A smaller series of 35 patients who underwent thrombectomy for distal PCA occlusion reported successful recanalization in about 89% of cases, with no procedure-related complications, though the mortality rate was about 23%, reflecting the severity of the underlying strokes.21PubMed. Mechanical thrombectomy of acute distal posterior cerebral artery occlusions
A systematic review comparing thrombectomy to intravenous clot-dissolving drugs (alteplase) in isolated PCA occlusions found that thrombectomy achieved a significantly higher recanalization rate, around 86% versus 53%. Yet the odds of a favorable long-term outcome, the rate of symptomatic brain bleeding, and the mortality rate did not significantly differ between the two approaches.22Journal of NeuroInterventional Surgery. Mechanical thrombectomy versus intravenous alteplase alone in acute isolated posterior cerebral artery occlusion: a systematic review In other words, thrombectomy opens the artery more reliably, but whether that translates to meaningfully better patient outcomes remains an open question. Randomized trials are still needed.
Why the Posterior Circulation Is Vulnerable to PRES
Posterior reversible encephalopathy syndrome (PRES) is a condition that causes headache, seizures, visual disturbances, and confusion, usually triggered by severe hypertension, eclampsia, or certain medications. On brain imaging, the hallmark finding is swelling predominantly in the back of the brain, in territory that overlaps with the PCA’s supply zone. This posterior predilection is thought to reflect a basic difference in the way the posterior circulation is wired: it has less sympathetic nerve innervation than the anterior circulation.23Practical Neurology. Posterior reversible encephalopathy syndrome (PRES): diagnosis and management Without as much sympathetic tone to counter reflex vasodilation, the posterior arteries are more susceptible to the sudden surge in blood pressure that overwhelms the brain’s normal autoregulation, leading to fluid leaking out of capillaries into the surrounding brain tissue.24PubMed Central. Posterior Reversible Encephalopathy Syndrome The condition is usually reversible if the underlying trigger is controlled, but it illustrates how the PCA’s territory can be disproportionately affected even by systemic problems that have nothing to do with a clot or bleed in the artery itself.
Infections That Target the PCA
The PCA can also be damaged by infections, most notably varicella zoster virus (VZV), the same virus that causes chickenpox and shingles. After a primary chickenpox infection, VZV goes dormant in nerve ganglia. If it reactivates and spreads to cerebral blood vessels, it can trigger an inflammatory vasculopathy that narrows or occludes arteries, leading to stroke. The most typical pattern involves the anterior circulation arteries, probably because the virus migrates from the trigeminal ganglia, which are anatomically closer to the carotid system.25PubMed. Ischemic Cerebellar Stroke in a 4-Year-Old Boy After Chickenpox: An Atypical Vascular Involvement But posterior circulation involvement, including the PCA, does occur and can be particularly insidious because VZV vasculopathy sometimes develops weeks to months after the initial infection, when the connection to chickenpox or shingles may not be obvious.
Pathological analysis of VZV-infected arteries reveals a consistent pattern of damage: the internal elastic layer is disrupted, the inner lining thickens with smooth muscle cells (not the normal endothelial cells), and the muscular wall of the artery thins out. The severity of these changes tracks with how long the infection has been active.26PubMed Central. Varicella zoster virus vasculopathy: analysis of virus-infected arteries In children, up to 30% of post-varicella strokes may stem from this mechanism, making it an important and sometimes overlooked cause of pediatric stroke in the posterior circulation.
The PCA Across Species
The PCA exists in some form across most mammals, but its anatomy varies in ways that reflect each species’ brain proportions and blood supply needs. A comparative study measuring the circle of Willis in rhesus monkeys, dogs, sheep, goats, and rabbits found that the basic circular arrangement of arteries at the brain’s base is remarkably conserved. In monkeys, dogs, and rabbits, the circle looks quite similar to the human version, with a few differences: in dogs, rabbits, goats, and sheep, the anterior cerebellar artery branches off the PCA rather than from a separate origin. In goats and sheep, the PCA arises from the posterior communicating artery rather than directly from the basilar, and a longer stretch of the internal carotid contributes to the circle’s formation.27PubMed. Morphology and comparative anatomy of circulus arteriosus cerebri in mammals These variations are not just anatomical curiosities; they matter for researchers using animal models of stroke, because a technique that blocks the PCA in a monkey may produce a very different infarct pattern than the same maneuver in a sheep, simply because the surrounding vascular anatomy is wired differently.