A weak portion of a blood vessel (usually occurring at the point it branches out) that leads to bulging or other abnormal distention of that vessel is known as an aneurysm. Whereas they are most common in older individuals—and particularly in women—aneurysms can occur at any time in a person’s life and can rupture or break open without warning.

For cerebral aneurysms, the typical location is at the base of the brain and just inside the skull, where they can develop up to one inch in size. These aneurysms can be congenital in that they exist from birth or may develop as we age. Infections and injuries can and do weaken the walls of blood vessels, sometimes leading to the condition, and genetic factors are also considerations. However, unlike other conditions that are bodies cannot prevent or fight, there are steps we can take to prevent the development of aneurysms, including controlling high blood pressure and diabetes and avoiding alcohol and smoking.

Aneurysms can exist in an unruptured state forever, or they may rupture at any time. If they do burst, an individual may experience a severe and localized headache; nausea and vomiting; neck pain; vision problems that include a sensitivity to light; and a loss of sensation in one or more parts of their body. When an aneurysm is unruptured, most individuals will not experience any signs at all, whereas others may suffer from nerve palsy; see double; have dilated pupils; experience pain behind the eyes; and have a worsening weakness throughout the body.

Physicians have many tools at their disposal to diagnosis cerebral aneurysms: with different types of angiography, a dye injected into the blood and accompanying x-rays or CT scans detect the weak blood vessels and determine their size. Doppler ultrasound, on the other hand, uses sound waves to find abnormal conditions in the veins. And with a magnetic resonance angiogram, images taken of the brain can show physicians the existence of aneurysms and well as any abnormal blockages within the brain’s arteries.

Because smaller aneurysms very rarely rupture, treatment for them is often not necessary. With other larger yet unruptured aneurysms, a doctor may be proactive and treat it surgically—which requires a craniotomy—in order to prevent a future rupture, which can cause serious and life-threatening problems.

While under general anesthesia, a patient’s head is secured to prevent movement during the craniotomy. A surgeon begins by making an incision and pushes away skin and muscle structures. One or possibly more small holes are drilled into the bone of the skull, and a saw is used to cut between the holes and remove a section known as the bone flap. The outermost membrane covering the brain—the dura—is now visible and accessible, and the surgeon cuts through this layer to reach the brain itself.

Once the blood vessel with the aneurysm is found, the surgeon isolates it from the surrounding brain tissue and attaches a metal clip that blocks the flow of blood to the weakened portion of the vessel. The dura is closed and the bone flap is returned to its original position and secured in place by plates and screws, and the skin is restored and sutured or stapled shut.

Post-craniotomy, a patient will typically be taken to an intensive care unit for monitoring and recovery from anesthesia, and they may be placed on a ventilator to assist with breathing. Once the patient is awake, physicians will check for normal breathing ability and that body movements are intact, and that there are no physical or mental complications as result of the surgery. A hospital stay lasts a few days, and patients will most likely receive some form of rehabilitation to help them return to normal daily activities.