What is a PCom aneurysm?

A posterior communicating artery aneurysm (PCOM) is a bulge or swelling 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 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 site for an aneurysm within this circle of Willis, accounting for approximately 30 percent of cerebral aneurysms. The most common causes of a PCOM aneurysm include hypertension, atherosclerosis, congenital malformations, and trauma. Structurally, there are three classifications of aneurysms: saccular, fusiform, and dissecting.

Researchers estimate that one to six percent of people will develop brain aneurysms. Brain aneurysms can occur at any age, but are more common in adults, with women being affected more than men. Aneurysms can 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 internal opening of the aneurysm often contains a blood clot.

A PCOM aneurysm may have no symptoms at all. Prior to aneurysm rupture, patients may report severe headache, stiff neck, nausea, vomiting, and visual impairment. In some cases, the patient may lose consciousness. The rupture of the aneurysm causes bleeding in the brain or the lining of the brain with sudden onset of symptoms. The risk of aneurysm rupture is about 1.3 percent per year in the United States.

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

Treatment for a ruptured PCOM aneurysm primarily involves stabilizing the patient's breathing and decreasing pressure on the brain. In addition to medical treatment, doctors may proceed with surgical clipping of the aneurysm or placement of a coil within the aneurysm to plug it and minimize the risk of repeated bleeding. Coil placement allows for a quicker recovery for the patient, but is associated with a slightly higher recurrence rate than trimming. The risks of both procedures occur at about the same rate.

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