What is a PCom Aneurysm?

A posterior communicating artery (PCOM) aneurysm is a bulging or ballooning of the arterial wall in an area of focal weakness. The posterior communicating artery branches off the internal carotid artery as it enters the brain, and the junction area of the PCOM and the internal carotid artery is the most common site for a PCOM aneurysm. Interconnecting with other vessels to form an arterial circle at the base of the brain, the PCOM is the second most common place for an aneurysm within this circle of Willis, accounting for about 30 percent of brain aneurysms. The most common causes for a PCOM aneurysm include hypertension, atherosclerosis, congenital malformations, and trauma. Structurally, there are three classifications of aneurysms — saccular, fusiform, and dissecting.

Investigators estimate one to six percent of people will suffer brain aneurysms. Brain aneurysms may occur at any age, but they are more common in adults, with women being affected more than men. Aneurysms may occur more frequently in connection with medical conditions such as polycystic kidney disease, connective tissue disorders, and fibromuscular dysplasia. When aneurysms are examined under a microscope, the arterial wall lacks the normal middle, muscular layer, called the media. The inner bore of the aneurysm often contains a blood clot.

A PCOM aneurysm may have no symptoms at all. Preceding rupture of an aneurysm, patients may report severe headache, stiff neck, nausea, vomiting, and vision impairment. In some cases, the patient may lose consciousness. Aneurysm rupture results in bleeding into the brain or the lining of the brain with sudden onset of symptoms. The risk of aneurysm rupture is about 1.3 percent annually in the United States.

Oculomotor nerve palsy is a notable sign specific to this type of aneurysm. The oculomotor nerve provides the nerve supply to the muscles that lift the eyelid and move the eye up, down, and inward. Additionally, the nerves that constrict the pupil in bright light travel with the oculomotor nerve. If a patient has an oculomotor palsy, he will have a droopy upper eyelid, double vision, a deviated eye that moves improperly, and, possibly, a large unresponsive pupil. Patients experiencing these symptoms should undergo immediate brain imaging to search for a PCOM aneurysm.

Treatment for a ruptured PCOM aneurysm primarily involves stabilizing the patient’s respiration and lowering the pressure on the brain. In addition to medical management, physicians may proceed with surgical clipping of the aneurysm or placement of a coil within the aneurysm to plug it and minimize the risk of repeat bleeding. Coil placement allows a speedier recovery for the patient, but it is associated with a slightly higher recurrence rate than clipping. The risks of both procedures occur at approximately the same rate.