Brain Aneurysm, PCOM Involvement

A brain aneurysm in the posterior communicating artery (PCOM) refers to an abnormal bulge in the artery at the base of the brain, often associated with specific neurological symptoms and an increased risk of rupture compared to other locations.

Key Clinical Features

• PCOM aneurysms often cause acute third cranial nerve (CN III) palsy with ipsilateral pupil dilation; this clinical picture is highly suspicious for a PCOM aneurysm until proven otherwise.

• Symptoms can include sudden headache, visual changes, ptosis (drooping of the eyelid), and facial pain that may mimic trigeminal neuralgia.

• Unlike other causes of CN III palsy (such as from diabetes), pupil involvement is usually present in PCOM aneurysms since the aneurysm compresses the pupillomotor fibers.

Diagnosis and Risk Factors

• Diagnosis typically requires neuroimaging, such as CT angiography, when neurological deficits are present.

• PCOM aneurysms that are irregular, multilobed, or have a higher height/width ratio are at greater risk of rupture.

• Patients tend to be middle-aged, with risk factors including hypertension, diabetes, and smoking.

• The five-year risk of rupture for a 7–12mm PCOM aneurysm can be as high as 14.5%, with ruptures potentially causing subarachnoid hemorrhage and significant morbidity.

Management Strategies

• Emergent neurosurgical intervention, such as surgical clipping or coil embolization, is indicated for symptomatic or large aneurysms to prevent rupture and relieve symptoms.

• Blood pressure control is critical in acute management to decrease the risk of rupture.

Takeaway Points

• PCOM aneurysm should be suspected in patients with acute CN III palsy and ipsilateral pupil dilation.

• Clinical vigilance and detailed neuro-ophthalmic examination are crucial for timely diagnosis and treatment.

• Neuroimaging is warranted for new-onset headaches or cranial nerve findings to rule out life-threatening vascular lesions like PCOM aneurysms.

For anatomical context, the posterior communicating artery sits at the base of the brain and is a known site for aneurysm formation due to its location in the Circle of Willis.