Polymicrogyria is a brain malformation in which the surface of the cerebral cortex develops too many folds that are abnormally small and shallow. The name itself spells out the problem: “poly” (many), “micro” (small), “gyria” (folds). It is one of the most common malformations of cortical development, and a population-based study in Stockholm found a prevalence of roughly 2.3 per 10,000 children.1PubMed Central. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort The condition ranges from a small patch affecting one part of one hemisphere to widespread involvement across both sides of the brain, and that range largely determines how mild or severe the symptoms are.
How Polymicrogyria Develops
During normal brain development, neurons generated deep inside the brain migrate outward toward the cortical surface and arrange themselves into a layered sheet. The surface of that sheet folds into ridges (gyri) and grooves (sulci) in a pattern that, while complicated, is remarkably consistent from person to person. In polymicrogyria, something disrupts the late stages of this process, particularly the organization of neurons once they reach the cortex. The result is a cortex with an excessive number of tiny, poorly formed folds separated by unusually shallow grooves.2PubMed Central. The Genetic Landscape of Polymicrogyria On an MRI, these areas look strikingly different from typical brain tissue, sometimes appearing as an irregularly thickened ribbon of cortex.
The disruption can happen at different points during fetal brain development, roughly between the 16th and 24th weeks of gestation, and can be triggered by a range of causes. Because the timing and the underlying trigger vary, the appearance of polymicrogyria on imaging is more diverse than researchers once assumed, and advances in MRI have revealed that it may represent a broader family of related malformations rather than a single uniform condition.3PubMed Central. Current concepts of polymicrogyria
Genetic Causes
Genetics plays a substantial role. In the Stockholm cohort, genetic testing was performed on 90 patients and revealed clearly disease-causing variants in about a third of them.1PubMed Central. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort Mutations in a growing list of individual genes have been linked to the condition, including GPR56, TUBB2B, SRPX2, PAX6, WDR62, and several others.2PubMed Central. The Genetic Landscape of Polymicrogyria Many of these genes are involved in the construction of microtubules, the tiny structural scaffolding that neurons rely on to migrate and organize themselves. When a gene like TUBB2B is mutated, the microtubule machinery malfunctions, and cortical development goes awry.4PubMed Central. A mutation in Tubb2b, a human polymicrogyria gene, leads to lethality and abnormal cortical development in the mouse Mutations in TUBB2B specifically were identified in about 2% of a cohort of patients with diffuse, symmetrical cortical abnormalities.5PubMed Central. Symmetric polymicrogyria and pachygyria associated with TUBB2B gene mutations
Beyond single-gene mutations, larger chromosomal changes can also be responsible. The 22q11.2 deletion syndrome (sometimes called velocardiofacial syndrome or DiGeorge syndrome) is one well-recognized example. More than 30 patients with both this deletion and polymicrogyria have been described in the literature, and the malformation in these cases tends to cluster around the perisylvian region, often with an asymmetric pattern that favors the right hemisphere.6PubMed. Bilateral polymicrogyria as the indicative feature in a child with a 22q11.2 deletion Other reports have documented similar findings, reinforcing that a 22q11 deletion should be considered in a child found to have polymicrogyria.7PubMed. Polymicrogyria in chromosome 22 delection syndrome The relationship also runs the other direction: finding polymicrogyria on a brain scan can sometimes be the clue that leads clinicians to diagnose the underlying chromosomal deletion.8European Journal of Paediatric Neurology. Unilateral hemispheric polymicrogyria in a child with 22q11 deletion syndrome
Non-Genetic Causes
Not every case of polymicrogyria has a genetic explanation. Environmental insults during fetal development account for a significant portion of cases, particularly disruptions to blood supply and prenatal infections.
Congenital cytomegalovirus (CMV) infection is the most studied infectious cause. CMV is a common virus that usually causes no problems in healthy adults, but when a pregnant person is infected for the first time and the virus crosses the placenta, it can devastate the developing brain. In one series of children with confirmed congenital CMV, two-thirds had polymicrogyria or abnormal gyral patterns on imaging.9PubMed. Congenital cytomegalovirus infection and brain clefting The presence of polymicrogyria in a baby with congenital CMV has significant clinical implications: a recent cohort study found that infants with both CMV and polymicrogyria were dramatically more likely to develop epilepsy, with an odds ratio of about 35 compared to CMV-affected infants without this malformation.10PubMed Central. Polymicrogyria in infants with symptomatic congenital cytomegalovirus at birth is associated with epilepsy The malformation has also been documented in fetuses exposed to CMV as early as mid-pregnancy.11PubMed Central. Congenital cytomegalovirus infection with brainstem hemorrhage and polymicrogyria
Vascular disruptions, meaning interruptions to blood flow in the developing brain, are another recognized cause. These can result from events like twin-to-twin transfusion syndrome, maternal trauma, or placental insufficiency. When a region of the fetal brain loses its blood supply at a critical window, the cortex in that area may develop the characteristic small, abnormal folds of polymicrogyria rather than forming normally.
Where Polymicrogyria Appears in the Brain and Why It Matters
Polymicrogyria can affect virtually any part of the cortex, but the perisylvian region, the area flanking the Sylvian fissure (the deep groove running along the side of each hemisphere), is by far the most common location. In a large multi-center study of patients with polymicrogyria-related epilepsy, about three-quarters had perisylvian involvement, and the majority of those were bilateral, meaning both hemispheres were affected.12PubMed Central. Polymicrogyria-associated epilepsy: a multi-center phenotypic study from the Epilepsy Phenome/Genome Project
The location and extent of the malformation strongly shape the clinical picture. Patients with perisylvian polymicrogyria typically have problems with speech, swallowing, and tongue movement because the perisylvian cortex controls oral and motor-speech functions.13American Journal of Neuroradiology. Syndromes of Bilateral Symmetrical Polymicrogyria People with bilateral frontal polymicrogyria, by contrast, tend to present with more severe motor impairment (weakness in all four limbs) but relatively milder cognitive delays. Those with polymicrogyria limited to the parietal or parieto-occipital regions may have only minor motor difficulties.13American Journal of Neuroradiology. Syndromes of Bilateral Symmetrical Polymicrogyria
A milder variant, bilateral posterior parietal polymicrogyria, illustrates the spectrum well. In one study comparing seven patients with this pattern to ten patients with more diffuse perisylvian involvement, the posterior parietal group had only minor speech difficulties and none had epilepsy. The diffuse group, by contrast, had pseudobulbar palsy (severe difficulty controlling the muscles of the face and throat) and higher rates of epilepsy.14PubMed. Bilateral posterior parietal polymicrogyria: a mild form of congenital bilateral perisylvian syndrome?
Epilepsy and Seizures
Epilepsy is one of the defining challenges of living with polymicrogyria. In the Stockholm population-based cohort, about 54% of patients were diagnosed with epilepsy, and among those, seizures often began early in life: 44% had their first seizure before age one.1PubMed Central. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort The seizure types vary. Most patients present with focal epilepsy, but some have generalized seizures or a combination of both. Among those with generalized seizure patterns, infantile spasms are particularly common. Generalized polymicrogyria, where the malformation is widespread across the cortex, tends to produce seizures earlier (median onset around 8 months) and more frequently comes with developmental delay that predates the seizures themselves.12PubMed Central. Polymicrogyria-associated epilepsy: a multi-center phenotypic study from the Epilepsy Phenome/Genome Project
A particular seizure-related pattern worth noting is electrical status epilepticus during slow sleep (ESES), a condition in which near-continuous abnormal electrical activity occurs in the brain during deep sleep and can erode cognitive abilities over time. In one study of children with unilateral multilobar or hemispheric polymicrogyria, roughly two-thirds showed this pattern on overnight EEG monitoring.15PubMed Central. Clinical features of unilateral multilobar and hemispheric polymicrogyria (PMG)-related epilepsy and seizure outcome with different treatment options That same study found that about 87% of the cohort had hemiparesis (weakness on one side of the body). Patients with polymicrogyria limited to one hemisphere generally had a better seizure prognosis than those with bilateral involvement, and some were able to maintain relatively favorable cognitive development when seizures were controlled.16PubMed. Childhood-onset epilepsy associated with polymicrogyria
Cognitive and Developmental Impact
Neurodevelopmental difficulties are the rule rather than the exception. In the Stockholm cohort, 94% of individuals with polymicrogyria had at least one neurodevelopmental disorder. About 72% had some form of cognitive impairment, with more than half of those meeting criteria for intellectual disability and the remainder having learning difficulties or developmental delay. Autism spectrum disorder and attention deficit hyperactivity disorder were each diagnosed in about 15% of the group. Two or more neurological conditions beyond epilepsy co-occurred in 65% of patients.1PubMed Central. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort
That said, the common assumption that everyone with polymicrogyria has severe intellectual disability is overstated. A detailed neuropsychological study of patients with bilateral perisylvian polymicrogyria found that only a minority had extremely low intelligence. Frontal lobe function and memory were relatively well preserved, and the cognitive profiles correlated with the specific areas of cortical disruption rather than reflecting global brain dysfunction alone. Patients with more extensive cortical involvement and earlier seizure onset tended to have lower performance scores, but some retained meaningful cognitive strengths.17PubMed. Cognitive functioning in bilateral perisylvian polymicrogyria (BPP): clinical and radiological correlations
Speech and Language Difficulties
Because the perisylvian cortex is so frequently affected, speech and language problems are among the most visible symptoms. A systematic review of speech and language in bilateral perisylvian polymicrogyria found that both expressive and receptive language impairment are frequent, with expressive deficits typically more severe. Oral structural and functional problems, including difficulty coordinating the muscles needed for clear speech, are common. Studies that formally assessed speech disorders in these patients identified dysarthria (slurred or effortful speech caused by weak or poorly controlled muscles) as a major feature. More diffuse cortical involvement predicted more severe language impairment.18PubMed Central. Speech and language in bilateral perisylvian polymicrogyria: a systematic review
In extreme cases, speech may be entirely absent. One case study described a patient with bilateral perisylvian polymicrogyria who had no speech at all, with extensive cortical thickening in motor and auditory-language regions. Interestingly, despite the profound cortical changes, the motor network and some speech-related white matter pathways were partially intact, suggesting that the cortex itself was the primary bottleneck rather than a total disconnection of the underlying wiring.19ScienceDirect / Cortex. Functional dysregulation of the auditory cortex in bilateral perisylvian polymicrogyria For families, this distinction matters: it means that some patients may benefit from augmentative communication strategies that work around the cortical impairment rather than assuming the entire language system is destroyed.
How Polymicrogyria Is Diagnosed
MRI is the cornerstone of diagnosis. The characteristic appearance of thickened, irregularly folded cortex is visible on high-quality brain scans, though it can be missed if the imaging is low resolution or if the clinician is not specifically looking for cortical malformations. In the Stockholm study, 18 individuals initially flagged for possible polymicrogyria were excluded upon re-evaluation because their MRIs actually showed different conditions such as pachygyria (a related malformation with abnormally broad, flat folds) or schizencephaly (a cleft in the brain).20Brain Communications. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort – Section: Materials and methods Getting the imaging right matters because these conditions, while sometimes overlapping, carry different prognoses and treatment considerations.
Prenatal detection is possible in some cases. Fetal MRI has been used to identify features suggestive of polymicrogyria as early as 24 weeks of gestation, with the diagnosis confirmed on follow-up imaging later in pregnancy and after birth.21PubMed Central. Early prenatal MR imaging diagnosis of polymicrogyria Prenatal ultrasound, however, is generally not sensitive enough to detect the condition, so fetal MRI is typically pursued only when there is already a reason for concern, such as a known CMV infection, a family history of cortical malformation, or an abnormality noticed on routine ultrasound.
Genetic testing is increasingly a standard part of the workup. As noted earlier, pathogenic variants were found in about a third of patients who underwent testing. Identifying a specific genetic cause can inform genetic counseling for families considering future pregnancies and, in some cases, connect a child to a broader syndrome with other medical features that need monitoring.
Treatment of Epilepsy in Polymicrogyria
There is no treatment that can reverse or repair the malformed cortex. Medical management focuses on controlling seizures and optimizing development. Anti-seizure medications are the first line, but the sobering reality is that epilepsy in polymicrogyria is frequently drug-resistant. In the Stockholm cohort, 56% of those with epilepsy required more than two anti-seizure medications, which is a standard marker for pharmacoresistant epilepsy.1PubMed Central. Polymicrogyria: epidemiology, imaging, and clinical aspects in a population-based cohort
For patients whose seizures do not respond to medication, surgery can be a consideration. The evidence here is encouraging for well-selected candidates. In one study comparing surgical and non-surgical management of drug-resistant epilepsy in polymicrogyria, about 52% of the surgical group achieved seizure freedom over a mean follow-up of nearly four years, while none of the patients in the non-surgical group became seizure-free.22PubMed. Seizure outcome in drug-resistant epilepsy in the setting of polymicrogyria The type of surgery depends on how much brain is affected. When polymicrogyria involves an entire hemisphere and the child already has significant weakness on the opposite side of the body, functional hemispherectomy (disconnecting the affected hemisphere from the rest of the brain) can dramatically reduce or eliminate seizures. For more localized polymicrogyria, targeted removal of the affected cortex is an option, though seizure outcomes tend to be better when the entire malformation can be resected rather than only a portion.23American Epilepsy Society. Surgical Outcomes of Children with Polymicrogyria and Drug-Refractory Epilepsy
The decision to pursue surgery involves careful weighing of risks and benefits. Detailed presurgical evaluation, including advanced MRI, video-EEG monitoring to localize where seizures originate, and sometimes invasive electrode recordings, helps the surgical team determine whether a patient is a good candidate.24PubMed Central. Surgical management of medically refractory epilepsy in patients with polymicrogyria
Supportive Therapies and Daily Life
Beyond seizure management, children and adults with polymicrogyria usually need a team of specialists. Speech-language therapy is critical for the majority, given how commonly the condition affects oral motor control and language. Because expressive difficulties are often more severe than receptive ones, therapists may work simultaneously on strengthening mouth and tongue coordination while introducing augmentative communication tools, such as picture boards, speech-generating devices, or sign language, for children whose verbal output is limited or absent.
Physical and occupational therapy address motor impairments. Many children with polymicrogyria have some degree of weakness, ranging from mild clumsiness in a hand to hemiparesis or full-body involvement, and early intervention can help maximize independence in daily activities like feeding, dressing, and mobility. Educational support, including individualized learning plans, is often necessary given the high rate of cognitive impairment and associated conditions like ADHD and autism.
For families, a polymicrogyria diagnosis can feel overwhelming precisely because it sits on such a broad spectrum. Some children attend mainstream school with modest support; others require intensive daily care. The condition is not degenerative, meaning the brain malformation itself does not worsen over time, though seizures and their treatment can influence developmental trajectory. Gaining seizure control, especially early in life, appears to be one of the most important modifiable factors in preserving cognitive potential.
Prenatal Screening and Genetic Counseling
For families who already have a child with polymicrogyria, the question of recurrence risk looms large. When a specific genetic cause has been identified, a genetic counselor can provide a clearer picture of whether future pregnancies carry a similar risk. Some of the genes implicated follow autosomal recessive inheritance, meaning both parents carry one copy of a mutation without being affected, and each pregnancy carries a one-in-four chance of the child inheriting both copies. Others arise as new (de novo) mutations, which are unlikely to recur. Without a known genetic cause, recurrence counseling is harder, and families are generally quoted a low but non-zero empirical risk.
Prenatal testing through amniocentesis or chorionic villus sampling can detect known chromosomal deletions like 22q11.2 or specific gene mutations. Fetal MRI, as mentioned earlier, can sometimes identify the cortical malformation directly, but it has limitations: the brain’s folding pattern does not mature enough to detect many cases of polymicrogyria until well into the second half of pregnancy, and small or focal areas of abnormal folding may be missed entirely. For infections like CMV, maternal screening and early detection are the primary prevention strategy, though no vaccine is yet widely available.