Dandy-Walker syndrome is a rare brain malformation present at birth that affects the cerebellum, the part of the brain responsible for movement and coordination. It occurs in roughly 1 in 25,000 to 30,000 live births and is slightly more common in females. The condition involves underdevelopment of the middle portion of the cerebellum (called the vermis), an enlarged fluid-filled space at the back of the brain, and often a buildup of fluid in the brain known as hydrocephalus.
What Happens in the Brain
During fetal development, the cerebellum normally forms a structure in the back of the skull called the posterior fossa. In Dandy-Walker syndrome, the cerebellar vermis, a strip of tissue that connects the two halves of the cerebellum, either fails to develop fully or is missing altogether. This leaves the fourth ventricle, one of the brain’s fluid-filled chambers, abnormally large. The expansion of this chamber creates a cyst-like space in the back of the skull.
The cerebellum plays a central role in coordinating movement, balance, and posture, so its underdevelopment has wide-reaching effects. But the cerebellum also contributes to language processing and certain cognitive functions, which is why Dandy-Walker syndrome can affect thinking and speech as well as physical coordination.
Causes and Genetic Links
In most cases, the exact cause of Dandy-Walker syndrome is unknown. Researchers have identified mutations in a few genes linked to the condition, but these account for only a small number of cases. One gene called FOXC1, located on chromosome 6, is required for normal cerebellar development and is a major contributor when that chromosomal region is affected. Deletions of two other linked genes, ZIC1 and ZIC4, have also been identified in some patients.
Beyond single-gene mutations, Dandy-Walker syndrome has been associated with many chromosomal abnormalities. It most often appears alongside trisomy 18 (an extra copy of chromosome 18) but can also occur with trisomy 13, trisomy 21 (Down syndrome), or trisomy 9. Deletions or duplications of pieces of various chromosomes have been linked to the condition as well. Most cases, however, occur sporadically with no clear inherited pattern.
Signs in Infants
Most children with Dandy-Walker syndrome show symptoms during their first year of life, and the earliest sign is typically a rapidly growing head. An unusually large head size affects 90% to 100% of patients in their first months. This happens because fluid buildup puts pressure on the skull bones, which haven’t yet fused in infants.
Hydrocephalus is the most common complication. About 75% of affected infants develop it by 3 months of age, and the number eventually reaches close to 90%. Signs of increased pressure inside the skull include irritability, vomiting, sleepiness, and a bulging soft spot on the top of the head. Without treatment, hydrocephalus associated with Dandy-Walker syndrome is life-threatening: 50% of untreated children die before age three.
Motor delays often become apparent as the infant grows. Babies may be slow to sit up, crawl, or walk because of the cerebellar abnormalities affecting coordination and muscle control.
Symptoms in Older Children and Adults
In older children, the presentation shifts. Balance problems and poor coordination become more noticeable as the child attempts more complex movements. Double vision can develop. Cognitive and intellectual disabilities, speech and language impairments, and behavioral challenges are common and add significant complexity to daily life.
In rare cases, Dandy-Walker syndrome is not diagnosed until adolescence or adulthood, when milder forms of the malformation cause balance difficulties, headaches, or problems with fine motor skills that were previously attributed to other causes.
How It Is Diagnosed
Dandy-Walker syndrome can sometimes be detected before birth through routine prenatal ultrasound, which may reveal the enlarged fluid space in the back of the fetal brain. However, prenatal imaging has limitations. Certain features that help confirm the diagnosis, such as the precise structure of the cerebellar vermis and the position of surrounding brain tissue, are more reliably assessed after birth with MRI.
On MRI, the key findings that define Dandy-Walker syndrome include underdevelopment of the lower portion of the cerebellar vermis, a widened angle between the brainstem and the vermis, and displacement of a membrane and blood vessel structure that normally sits close to the cerebellum. Notably, recent research published in the American Journal of Neuroradiology has refined the diagnostic criteria, concluding that the size of the posterior fossa and the position of certain skull landmarks, once considered important, should no longer be used as defining features.
Treatment for Hydrocephalus
There is no cure for the underlying brain malformation, so treatment focuses on managing hydrocephalus and its complications. The primary approach is surgical placement of a shunt, a thin tube that drains excess fluid from the brain into the abdominal cavity, where the body can absorb it. Two types are commonly used: a ventriculoperitoneal shunt, which drains from the brain’s ventricles, and a cystoperitoneal shunt, which drains directly from the cyst in the posterior fossa.
In some cases, a procedure called endoscopic third ventriculostomy (ETV) may be considered. This involves creating a small opening in the floor of a brain ventricle to allow fluid to bypass the blockage and drain naturally. The success rate of ETV varies depending on the child’s age and the specific anatomy of the blockage, and it tends to be less reliable in very young infants. Many children require shunt revisions over the course of their lives as they grow or if the shunt becomes blocked or infected.
Beyond surgery, children with Dandy-Walker syndrome typically benefit from a team approach that includes physical therapy for motor delays, speech therapy for language development, and educational support for cognitive challenges.
Long-Term Outlook
The prognosis for Dandy-Walker syndrome varies widely. About half of all patients develop normal intellectual function. A study of 20 patients (average age around 15 years) found that the structure of the cerebellar vermis was the strongest predictor of cognitive outcome. All 14 patients in that study who had normal intellectual development also had a normally structured vermis and no additional brain abnormalities above the cerebellum. Among the six patients with intellectual disability, three had an abnormally formed vermis along with underdevelopment of the corpus callosum, the band of nerve fibers connecting the two brain hemispheres.
In practical terms, this means two things matter most for long-term outcomes: how fully the cerebellar vermis developed and whether there are additional brain abnormalities beyond the posterior fossa. Children whose malformation is limited to the back of the brain, with a relatively well-formed vermis, have the best chance of typical cognitive development. Those with more extensive brain involvement face greater challenges with learning, language, and daily independence.
Early and consistent treatment of hydrocephalus also plays a critical role. Uncontrolled fluid buildup causes progressive damage to surrounding brain tissue, so timely surgical intervention can meaningfully change a child’s developmental trajectory.