Makindo Medical Notes

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The presence of a fetal PCA may lead to unique cerebral blood flow dynamics, especially during ischaemic events. In individuals with a fetal PCA, the posterior circulation becomes more dependent on the internal carotid artery, which can influence the brain's response to vascular occlusions. If an ischaemic event affects the internal carotid artery, it could compromise blood supply to both the anterior and posterior cerebral territories. Although many individuals remain asymptomatic, this variant can sometimes impact conditions that involve the occipital lobe, including transient ischaemic attacks (TIAs) and stroke events. Additionally, the fetal PCA is associated with a higher risk of posterior ischaemic events in patients with carotid artery disease.

About

• The fetal posterior cerebral artery (PCA) is a cerebral artery variant where the PCA originates directly from the internal carotid artery, rather than from the basilar artery. This alternate origin is part of the fetal circulation pattern, which may persist into adulthood in some individuals, potentially influencing cerebral blood flow dynamics.
• Typically, the basilar artery supplies the posterior cerebral arteries. However, in the fetal PCA variant, the internal carotid artery supplies this region, creating an anatomical connection between anterior and posterior circulation.
• It may be unilateral (one-sided) or bilateral (both sides).

Incidence

• The fetal posterior communicating artery is a well-established variant of the cerebral vasculature, occurring in 4-29% of the population.

Clinical

• Ischaemic Impact: The fetal PCA alters blood flow dynamics, potentially affecting ischaemic events, especially in cases where the internal carotid artery is compromised. Due to the direct supply from the carotid artery, any blockage here can reduce blood flow to the posterior circulation, potentially leading to occipital ischaemia.
• Asymptomatic in Many Cases: Often, individuals with a fetal PCA do not exhibit any symptoms, and the condition is usually discovered incidentally during imaging studies conducted for other reasons.
• Risk in Carotid Artery Disease: For patients with atherosclerosis or other forms of carotid artery disease, a fetal PCA may increase susceptibility to posterior circulation ischaemic events.

Shows the effect of a blocked left internal carotid artery (ICA), which supplies the middle cerebral artery (MCA), anterior cerebral artery (ACA), and PCA on the same side. The likely vascular anatomy is demonstrated here, illustrating how an ischaemic event in the ICA could impact both anterior and posterior cerebral territories.

Variants

While a complete Circle of Willis is defined as the normal anatomy (Figure 1A), a fetal-type PComA is defined as having a hypoplastic P1 segment of the PCA (Figure 1C), whereas, in a true fetal PComA, the P1 segment is absent

Diagnosis: is typically done via imaging studies

• Magnetic Resonance Angiography (MRA): A non-invasive imaging method that provides a detailed view of cerebral blood flow and vascular structures. MRA can identify the origin of the PCA and determine if it arises from the internal carotid artery.
• Computed Tomography Angiography (CTA): CTA offers a clear image of the cerebral vasculature, helping to map out the PCA's origin and its relationship with other cerebral vessels.
• Conventional Angiography: In complex cases, conventional angiography may be performed to gain a detailed view of the cerebral blood flow patterns and arterial connections.

Management

• No specific management is required if the fetal PCA is an incidental finding without associated symptoms. However, if it impacts cerebral blood flow or is present in patients with cerebrovascular risk factors, management strategies might include:
• Regular Monitoring: Monitoring is essential for individuals with risk factors for cerebrovascular disease, particularly those with known carotid artery disease or a history of ischaemic events.
• Stroke Prevention: Preventative measures may include managing hypertension, controlling diabetes, and monitoring cholesterol levels to reduce the risk of atherosclerosis affecting the internal carotid artery.
• Antiplatelet Therapy: In some cases, especially in patients with additional cerebrovascular risks, antiplatelet therapy may be considered to prevent clot formation and reduce stroke risk.

References

• A Fetal-type Variant Posterior Communicating Artery and its Clinical Significance