Sturge-Weber syndrome (SWS) is a rare condition present from birth in which abnormal blood vessels develop in the skin, brain, and eyes. It affects roughly 1 in 20,000 to 1 in 50,000 births in Europe, occurs across all ethnicities, and affects males and females equally. The hallmark sign is a flat, reddish-purple birthmark on the face called a port-wine stain, but the more serious effects come from similar blood vessel abnormalities on the surface of the brain and inside the eye.
What Causes It
SWS is caused by a specific genetic change, a mutation in the GNAQ gene, that happens randomly during early fetal development. This mutation isn’t inherited from a parent and isn’t something that can be passed on to future children. It’s what’s called a somatic mosaic mutation, meaning it occurs in only some of the body’s cells rather than all of them. The timing of when the mutation happens during embryonic development determines which tissues are affected and how severe the condition becomes.
The GNAQ gene normally helps regulate how cells grow and form blood vessels. When the mutation disrupts this signaling, capillaries (the smallest blood vessels) form abnormally and don’t develop the way they should. Because the mutation happens during the earliest stages when the face, brain, and eyes are forming from the same embryonic tissue, all three areas can be involved.
The Port-Wine Stain
The most visible feature of SWS is the port-wine stain, a flat birthmark caused by dilated capillaries just beneath the skin. It typically appears on the forehead and upper eyelid, following the path of the first and second branches of the trigeminal nerve, which supplies sensation to the face. The birthmark is present at birth, starts out pink or light red, and tends to darken to a deeper purple over time as the abnormal blood vessels thicken.
Not every child born with a port-wine stain has Sturge-Weber syndrome. Isolated port-wine stains are far more common. The location matters: birthmarks affecting the forehead and upper eyelid carry the highest risk of brain and eye involvement. Port-wine stains limited to the lower face are less likely to be associated with the full syndrome.
How It Affects the Brain
The neurological effects of SWS stem from a tangle of abnormal blood vessels called a leptomeningeal angioma that forms on the surface of the brain. During normal fetal development, a temporary network of blood vessels around the brain is supposed to regress and be replaced by mature veins. In SWS, this primitive network fails to disappear. The result is that the brain lacks normal venous drainage and instead relies on these malformed vessels, which don’t work efficiently.
This creates a cascade of problems. Blood backs up, raising pressure in the veins around the affected brain tissue. Over time, this venous congestion starves the underlying brain of adequate oxygen and nutrients, a state of chronic low-grade ischemia. The abnormal vessels are also prone to clotting, which worsens the oxygen deficit. Eventually, the affected brain tissue begins to shrink, and calcium deposits form in the damaged areas, a combination of scarring and deteriorating blood vessels that shows up clearly on brain imaging.
Seizures are the most common neurological consequence. The median age of first seizure is around 4.5 months, though onset can happen later in childhood or, less commonly, in adulthood. Seizures tend to worsen the underlying brain damage because they spike the brain’s demand for oxygen and blood flow in tissue that already has almost no reserve capacity. This creates a cycle where seizures cause more damage, which in turn lowers the threshold for more seizures. Standard seizure medications adequately control symptoms in only about half of patients, leaving many with difficult-to-treat epilepsy.
Depending on how much brain tissue is involved, children with SWS may also experience weakness on the side of the body opposite the brain lesion, developmental delays, learning difficulties, or intellectual disability. The severity varies enormously. Some people have mild involvement and live relatively typical lives, while others face significant neurological challenges from infancy.
Eye Problems and Glaucoma
Glaucoma, a condition where increased pressure inside the eye damages the optic nerve, develops in 30 to 70 percent of people with SWS. The abnormal blood vessels that affect the skin and brain also affect the eye, particularly a layer called the choroid that supplies blood to the retina. This vascular malformation raises fluid pressure inside the eye.
The timing follows a distinct pattern. About 60 percent of those who develop glaucoma show signs at birth or in early infancy, while the remaining 40 percent develop it later in childhood or adulthood. Because glaucoma can cause permanent vision loss if untreated, regular eye pressure monitoring starting in infancy is a critical part of managing SWS. Symptoms in babies can include an enlarged eye, excessive tearing, or light sensitivity.
How It’s Diagnosed
A port-wine stain on the forehead or upper eyelid at birth raises the initial suspicion, but confirming brain involvement requires imaging. MRI with a contrast agent is the gold standard. The contrast dye highlights the abnormal leptomeningeal blood vessels on the brain’s surface, making them clearly visible. MRI is more sensitive than CT scanning for detecting these malformations, though CT is sometimes used to identify the characteristic calcifications in older children and adults.
In newborns, the brain abnormalities may not yet be visible on imaging, so a normal MRI in the first weeks of life doesn’t always rule out the condition. Repeat imaging is sometimes needed as the child grows. Specialized MRI techniques that map blood flow patterns in the brain can also help determine how much the affected tissue’s blood supply is compromised, which helps predict seizure risk.
Managing Seizures
Seizure control is the central challenge in SWS. Treatment typically begins with anti-seizure medications, and for about half of patients, these medications keep seizures under reasonable control. For the other half, seizures prove resistant to medication, a situation called refractory epilepsy. In these cases, early and aggressive treatment matters because each prolonged seizure episode can cause additional brain damage in the vulnerable tissue.
When medications fail, epilepsy surgery becomes an option. The most common procedure involves disconnecting or removing the affected portion of the brain. Surgery is generally considered after at least six months of medication failure, though children experiencing severe, catastrophic seizure episodes may be candidates sooner. The outcomes are encouraging: roughly 87 percent of surgical patients are seizure-free at one year, 81 percent at two years, and about 71 percent remain seizure-free at five years. Children who undergo surgery may also experience improvements in motor function and cognitive development once the constant seizure burden is lifted, though outcomes depend on how much brain tissue was damaged before the operation.
Treating the Port-Wine Stain
Pulsed dye laser therapy is the standard treatment for port-wine stains. The laser targets the abnormal blood vessels beneath the skin, causing them to shrink and lightening the birthmark’s color. A large study following 974 children over 20 years found an overall efficacy rate of 65 percent, with results improving after multiple sessions, reaching 84 percent effectiveness after three treatments.
Several factors influence how well laser treatment works. Smaller birthmarks (under 3 square centimeters) respond better, with a 77 percent efficacy rate. Location also matters: port-wine stains on the limbs respond best at nearly 88 percent, while those on the forehead in the area of the ophthalmic nerve, the most common location in SWS, respond least well at about 58 percent. Treatment can begin in infancy, and infant efficacy rates are around 71 percent. While laser therapy rarely eliminates a port-wine stain completely, it can significantly lighten the color and reduce the thickening that tends to develop over time.
Long-Term Outlook
The course of SWS varies widely depending on how much of the brain, skin, and eye are affected. Some people have only a port-wine stain with minimal or no brain involvement and lead fully independent lives. Others face significant challenges from refractory seizures, vision loss, or cognitive disability. The condition is not progressive in the way a degenerative disease is, but the cumulative effects of seizures and chronic blood flow problems can cause gradual worsening if not managed proactively.
Regular monitoring by a team that includes neurology, ophthalmology, and dermatology helps catch complications early. Children with SWS benefit from developmental assessments so that learning support and therapies can begin as soon as gaps are identified. Low-dose aspirin is sometimes used to reduce the risk of blood clots in the brain’s abnormal vessels, though this decision is individualized. The wide spectrum of severity means that each person’s experience with SWS looks different, and management plans are tailored accordingly.