Q: What is the difference between a brain aneurysm (which Emilia Clarke from Game of Thrones survived twice) and a stroke?

A: Both aneurysms and strokes are diseases that affect the blood vessels in the brain. Both can lead to serious neurological deficits or even death. They share similar risk factors and preventive strategies. However, they are fundamentally different diseases. Each has unique symptoms and distinct treatment procedures.

A stroke is a “brain attack.” It is comparable to a heart attack. During a stroke, the blood supply to a specific area of the brain is either interrupted or severely reduced. When the brain doesn’t receive enough blood, there is not sufficient oxygen and nutrients for the brain cells to carry on normal activities. Cells begin to die. The symptoms depend on the location of the affected brain cells. Symptoms can include weakness, numbness, difficulty with speech, vision loss, and balance issues.

Interruption in blood supply to the brain can be progressive or it can be sudden. Blood vessels leading to the brain, including the carotid arteries in the neck, can narrow over time. A blood clot causes a sudden blockage of a blood vessel in the brain. A clot can originate in the brain, heart, legs, or other parts of the body. That clot travels to the brain, gets lodged in one of the small vessels, and stops the blood flow. In either case, there is usually time between the onset of symptoms and the death of the affected brain cells. This window is when treatment is most likely to prevent permanent damage and/or death.

The above describes an ischemic stroke. It is the most common type of stroke and happens about 87 percent of the time, according to a report by the American Heart Association.

The other type of stroke is a hemorrhagic stroke, in which a small blood vessel inside the brain leaks blood inside the brain tissue, permanently damaging it. Uncontrolled high blood pressure is a common cause of hemorrhagic strokes. Blood-thinning medications can increase the risk of brain hemorrhages.

Aneurysms occur when an arterial wall weakens, creating a distension, or bulge. They can happen anywhere in the body. Brain aneurysms result in a bulge on a brain artery. A saccular aneurysm looks like a berry hanging on one side of an artery. A fusiform aneurysm appears as a bulge on all sides of the blood vessel.

Aneurysms usually cause symptoms only when they rupture. The weak, bulged-out side of the artery bursts open, leaking blood. That blood fills the space between the surface of the brain and the arachnoid, a thin layer that covers the brain. This bleeding is called a subarachnoid hemorrhage. Patients experience what they describe as “the worst headache of my life.” This singular, severe headache is the main feature that can differentiate a ruptured aneurysm from a stroke, which is usually painless. Patients with ruptured aneurysms might also experience nausea, vomiting, light sensitivity, confusion, seizures, or loss of consciousness.

Strokes are much more common than subarachnoid hemorrhages; however, a ruptured aneurysm is more lethal. Nationally, about 40 percent of ruptured aneurysms are fatal. Of those who survive, about 66 percent suffer some permanent neurological deficit, according to the Brain Aneurysm Foundation.

If you suspect you or a loved one is having an aneurysm or stroke, call 911 immediately.

Jorge Eller, M.D., is a cerebrovascular and endovascular surgeon at AtlantiCare Neurosciences Institute, co-medical director of AtlantiCare Stroke Program, and clinical professor in the department of neurological surgery at Jefferson Neurosciences at AtlantiCare Regional Medical Center in Atlantic City.