What is the appropriate management for an adult patient with an infundibular origin of the left posterior communicating artery (PCOM), considering the risk of cerebral aneurysm formation and cerebrovascular events?

Management of Infundibular Origin of Left PCOM

An infundibular origin of the left posterior communicating artery requires serial imaging surveillance with MRA or CTA at yearly intervals, particularly if the infundibulum measures ≥3 mm in diameter, as these lesions can progress to true aneurysms with rupture risk. 1, 2

Understanding the Clinical Entity

An infundibulum is a funnel-shaped symmetrical enlargement at the origin of a cerebral artery, most commonly occurring at the PCOM-ICA junction, and is found in 7-25% of normal angiograms. 3 While traditionally considered a benign anatomical variant, documented cases demonstrate progression from infundibulum to saccular aneurysm formation with subsequent rupture. 1, 2, 3

Risk Stratification for Progression

High-risk features requiring more aggressive surveillance include:

• Infundibulum diameter ≥3 mm - this threshold warrants mandatory follow-up imaging 1
• Presence of other intracranial aneurysms - significantly increases risk of infundibulum-to-aneurysm progression 1
• History of de novo aneurysm formation - indicates predisposition to aneurysm development 1
• Family history of intracranial aneurysms - genetic susceptibility factor 1
• Uncontrolled hypertension - hemodynamic stress accelerates progression 2
• Well-developed PCOM with large ICA-PCOM angle - creates increased hemodynamic stress 2

Surveillance Protocol

For infundibula ≥3 mm or with high-risk features:

• Perform baseline MRA or CTA to establish morphology and exact measurements 1
• Repeat imaging at yearly intervals to detect early aneurysm formation 1
• More stringent follow-up (potentially every 6 months) is warranted in patients with multiple aneurysms, documented de novo aneurysm formation, or familial aneurysm occurrence 1
• Serial imaging should specifically assess for development of asymmetric outpouching or saccular projection from the infundibular wall 2

For infundibula <3 mm without high-risk features:

• Consider baseline imaging and extended interval surveillance (every 2-3 years) given the lower but documented risk 1, 3

Medical Management

Aggressive cardiovascular risk factor modification is essential:

• Blood pressure control is critical, as hypertension accelerates hemodynamic stress and aneurysm formation from infundibula 2
• Standard atherosclerotic risk factor management including lipid control, smoking cessation, and diabetes management 4
• Consider antiplatelet therapy (aspirin 75-325 mg daily) given the posterior circulation location and potential for thromboembolic complications 4

When to Intervene

Treatment becomes indicated when:

• Documented progression to saccular aneurysm - any asymmetric outpouching or saccular projection requires treatment consideration 1, 2, 3
• Development of symptoms (third nerve palsy, mass effect) - indicates growth and warrants urgent treatment 5
• Aneurysm formation in posterior circulation location - even small posterior circulation aneurysms (<7 mm) carry 2.5% annual rupture risk compared to near 0% for anterior circulation 6

Treatment Modality Selection

If progression to true aneurysm occurs:

• Endovascular coiling is preferred for posterior circulation aneurysms when technically feasible, based on improved functional outcomes 6
• Surgical clipping remains an option for lesions not amenable to endovascular treatment 2
• Both endovascular and neurosurgical evaluation should be obtained 6

Critical Pitfalls to Avoid

• Do not dismiss infundibula as purely benign variants - documented cases of rupture exist, with fatal outcomes reported 3
• Do not rely on single imaging study - progression occurs over years (documented cases show 7-year evolution), requiring serial surveillance 1
• Do not use ultrasound alone - MRA or CTA provides superior visualization of posterior circulation anatomy 4
• Do not delay treatment once aneurysm formation is documented - rupture can occur from small aneurysms originating from infundibula (documented rupture of 1.5 mm aneurysm) 2

Patient Counseling

Patients should be informed that while most infundibula remain stable, documented progression to aneurysm formation and rupture exists, necessitating long-term surveillance. 1, 3 The importance of blood pressure control and adherence to imaging follow-up should be emphasized. 2