What Is Cerebral Hyperperfusion Syndrome?

Cerebral hyperperfusion syndrome (CHS) is a rare complication that can occur after undergoing a surgical procedure known as carotid arterial revascularization. The aim of revascularization is to prevent strokes caused by the narrowing of the carotid artery (the blood vessel which carries oxygenated blood to the brain).

The term hyperperfusion is used to describe the increased arterial blood pressure that is characteristic of the syndrome. If not treated properly, CHS can lead to severe brain swelling (edema), intracranial bleeding, and even death. 

How CHS Happens

Internal carotid artery stenosis is characterized by the narrowing of the artery, which gradually cuts off the flow of blood and oxygen to the brain.

Unlike a hemorrhagic stroke, which happens when a vessel ruptures, this type of stroke is considered ischemic, meaning that the brain is deprived of oxygen due to the restriction or blockage of blood flow.

If diagnosed, doctors will often perform either one of two procedures aimed at ensuring the blood supply is uninterrupted:

• Endarterectomy, a procedure used to remove any blockage from within the vessel
• Stenting, the insertion of a mesh tube to keep the blood vessel open

While both procedures are effective in treating arterial stenosis, they can sometimes be too effective. When the blood flow is suddenly and fully restored, the network of smaller vessels and capillaries may be unable to cope, particularly if they've experienced narrowing and hardening themselves.

This sudden rush of blood can cause an enormous spike in pressure that can disrupt the vascular tissue, causing leakage and localized swelling. In some cases, the blood vessels can entirely rupture, causing a massive hemorrhagic stroke—the very thing the surgery was meant to prevent.

Risk Factors Associated With CHS 

Of the two procedures, carotid endarterectomy is considered the gold standard approach to treating arterial stenosis. The risk of stroke following an endarterectomy is estimated to be around 5% and is most often caused when a piece of arterial plaque breaks off during surgery and blocks a vessel in another part of the brain.

Even if the procedure goes off without a hitch, anywhere between 9-14% of patients will experience hyperperfusion. All told, less than 3% of carotid endarterectomies result in symptomatic CHS. 

Symptoms of CHS

Symptoms of CHS are most likely to occur in persons who experience a greater than 100% increase in blood flow to the brain following surgery. They can range in severity from mild and transient to potentially life-threatening and include:

• Headaches
• Nausea 
• Vomiting
• Dizziness 
• Faintness
• Blurred vision
• Seizures
• Stroke
• Coma

Depending on where the swelling or bleeding occurs, any number of other neurological symptoms can develop, including memory loss, speech impairment, breathing irregularities, and motor problems.

Prevention of CHS 

The greatest single risk factor for CHS is postoperative hypertension. It is, therefore, important that anyone undergoing an endarterectomy be closely monitored to identify the problem early. Imaging options include the transcranial Doppler, a form of ultrasound which measures the velocity of blood through the brain.

Ultimately, early intervention and blood pressure control are central to managing or mitigating any symptoms of CHS.