Does a 2mm posterior communicating artery (p-comm) infundibulum or aneurysm warrant a neurosurgery consult?

Management of 2mm Posterior Communicating Artery Infundibulum or Aneurysm

A 2mm posterior communicating artery (PComm) infundibulum or aneurysm does not warrant a neurosurgery consult unless there are specific risk factors or symptoms present. 1

Understanding Small Aneurysms and Infundibula

• Aneurysms smaller than 5mm have an extremely low risk of rupture, with annual rupture rates estimated at approximately 0.05% 1, 2
• Small aneurysms (≤5mm) are associated with very low surgical morbidity rates (approximately 3%) when treatment is necessary 1
• Infundibular dilations are funnel-shaped widenings at the origin of cerebral arteries, most commonly at the posterior communicating artery, and are generally considered normal anatomic variants 3

Risk Assessment for Small PComm Lesions

Low-Risk Features (Conservative Management Recommended):

• Size less than 5mm (especially ≤3mm) 1, 2
• Asymptomatic presentation 1
• No documented growth on serial imaging 1
• No family history of aneurysmal subarachnoid hemorrhage 2

High-Risk Features (Consider Neurosurgical Consultation):

• Evidence of growth on follow-up imaging 1, 4
• Development of symptoms, particularly cranial nerve palsy (CN3) 1, 5
• Previous history of subarachnoid hemorrhage from another aneurysm 2, 6
• Family history of aneurysmal subarachnoid hemorrhage 2

Evidence for Conservative Management

• Guidelines generally advocate treatment only for aneurysms ≥5mm in diameter, as this ensures that 99% of aneurysms that should be treated will have treatment offered 1
• The risk of rupture for aneurysms smaller than 5mm is extremely low, with morbidity rates of less than 3% reported in studies 1
• Most infundibula in the context of subarachnoid hemorrhage were associated with an actual aneurysm either on or near the infundibulum, not from the infundibulum itself 3

Monitoring Recommendations

• For asymptomatic 2mm PComm infundibula or aneurysms, periodic imaging surveillance is recommended rather than immediate intervention 2
• Mid-term and long-term follow-up MRI (e.g., in yearly intervals) is advised for infundibula with a diameter of 3mm or more 4
• More frequent monitoring may be warranted in patients with:
  • Multiple aneurysms 4
  • Previous de novo aneurysm formation 4
  • Family history of aneurysms 4

Important Caveats and Pitfalls

• While rare, progression from infundibulum to true aneurysm has been documented in case reports, with development occurring over periods of 7-10 years 4, 6, 7
• The risk of infundibulum-to-aneurysm progression appears higher in patients with other risk factors such as hypertension, multiple aneurysms, or previous subarachnoid hemorrhage 4, 7
• Symptoms such as new onset of third nerve palsy ipsilateral to a PComm lesion should prompt immediate reevaluation, as this may indicate growth and increased risk of rupture 1, 5
• Treatment decisions should be made at high-volume centers with experienced neurovascular teams, as surgical experience significantly influences outcomes 1

Conclusion

For a 2mm PComm infundibulum or aneurysm without symptoms or risk factors, conservative management with periodic imaging surveillance is the appropriate approach. Neurosurgical consultation should be reserved for cases showing growth, development of symptoms, or presence of other significant risk factors for rupture.