Can Chiari Malformation Cause Seizures?

Seizures do occur in people with Chiari malformation, but whether the malformation itself directly causes them is far from settled. The best available evidence suggests that when epilepsy and Chiari coexist, the seizures are more likely driven by associated brain abnormalities than by the herniated cerebellar tonsils alone. That distinction matters for treatment, for prognosis, and for the thousands of patients and families trying to understand why seizures showed up alongside a Chiari diagnosis.

How Often Seizures Show Up in Chiari Patients

Seizures are not among the hallmark symptoms of Chiari malformation type 1 (the most common form). Headaches at the back of the skull, neck pain, balance problems, and tingling in the hands are far more typical. But seizures do appear in a meaningful minority of patients. In one institutional review spanning seven years, roughly 13% of 30 Chiari type 1 patients had epilepsy.¹ Other reports describe epileptic seizures as “occasionally reported” in Chiari type 1 patients, showing up both in people with classic Chiari symptoms and in people whose malformation was only discovered incidentally during a workup for seizures.²

In fact, seizures are one of the most common reasons brain imaging gets ordered in the first place, and that imaging sometimes reveals a previously unknown Chiari malformation. One study of children with incidentally discovered Chiari type 1 found that about 15% of the initial MRIs had been ordered to evaluate seizures.³ This raises a tricky question: if the Chiari was found because someone was already having seizures, does the malformation explain the seizures, or are they two separate problems that showed up in the same scan?

Why a Direct Causal Link Is Hard to Prove

Chiari malformation type 1 involves the lower part of the cerebellum extending down through the opening at the base of the skull. The cerebellum coordinates movement and balance; it does not generate the kind of cortical electrical storms that produce epileptic seizures. That anatomical fact is the core reason researchers remain skeptical of a direct cause-and-effect relationship. A 2022 review in the Journal of Clinical Medicine put it plainly: to date, there is no evidence that Chiari type 1 or the syringomyelia that sometimes accompanies it can affect the brain’s electrical activity enough to cause seizures.⁴

What complicates the picture is that Chiari malformation rarely travels alone. Many patients, especially children, have additional brain anomalies that are each independently capable of causing seizures. In people with Chiari type 2, which is associated with spina bifida, structural brain differences are the rule rather than the exception. One study found that among patients with spina bifida, about 7% had epilepsy, and the vast majority also had ventriculomegaly, abnormalities in the corpus callosum, and other developmental differences.⁵ Any of those associated anomalies could be the seizure generator, making it nearly impossible to pin the blame on the Chiari malformation itself.

Even in genetic syndromes where Chiari type 1 and epilepsy appear together, such as PTEN hamartoma tumor syndrome and SETD2-related neurodevelopmental disorders, the seizures seem to stem from associated brain tumors, vascular malformations, or enlarged ventricles rather than from the cerebellar herniation.⁴ Researchers have looked for a “pure” association between Chiari type 1 and epilepsy, one where no other brain abnormality could explain the seizures, and so far have not found it.

A Shared Developmental Origin

If Chiari malformation does not cause seizures on its own, why do the two keep showing up together? One hypothesis is that they share a common developmental root. Some researchers have proposed that the combination of Chiari type 1, seizures, speech delay, and intellectual disability may represent a distinct neurodevelopmental pattern rather than a coincidence of unrelated problems.⁶ Under this model, a disruption during early brain development could simultaneously produce the posterior fossa crowding that defines Chiari and subtle cortical malformations that later generate seizures.

Evidence from SPECT imaging adds some weight to this idea. When researchers used blood-flow scans to study Chiari type 1 patients who had seizures, they found areas of reduced blood flow in the brain that matched up with the regions producing abnormal electrical activity on EEG. Those underperfused zones may represent areas of cortical microdysgenesis, meaning tiny structural irregularities in brain tissue that formed during fetal development. In some patients, reduced blood flow also appeared in the cerebellum, hinting at functional or structural involvement beyond the cortex.⁷ If this hypothesis holds up, Chiari and epilepsy would not have a simple cause-and-effect relationship. Instead, they would be sibling symptoms of the same underlying developmental disruption.

What the Seizures Look Like

When epilepsy does occur alongside Chiari type 1, the seizures tend to follow recognizable patterns. In a clinical and EEG study, most seizures were classified as the complex partial type, with the abnormal electrical activity concentrated over the frontal and temporal regions of the brain.⁸ Complex partial seizures involve altered awareness and can include staring spells, repetitive movements like lip-smacking or hand-rubbing, and confusion before and after the episode. The frontal and temporal lobe localization is consistent with what you would expect from a cortical abnormality rather than from cerebellar pathology, which supports the view that the seizure focus lies upstream of the Chiari malformation itself.

Children with Chiari type 1 are increasingly being evaluated not just for the classic posterior fossa symptoms but also for developmental delay, behavioral concerns, and seizures. One comparison of pediatric and adult Chiari patients found that developmental delay appeared in over a third of children, along with seizures and abnormal swallowing, while adults more often presented with sensory disturbance and motor weakness.⁹ The broader clinical profile in children reflects both the higher rates of associated brain anomalies in younger patients and the growing tendency to image children for developmental red flags, catching Chiari malformations that might have gone undiagnosed in earlier decades.

When Seizure-Like Episodes Are Something Else Entirely

One of the biggest diagnostic traps with Chiari malformation is that it can produce episodes that look remarkably like seizures but are not. These events go by several names, and understanding them matters because the treatment is entirely different.

The most well-described of these mimics is the “cerebellar fit,” a sudden attack that can involve drop episodes, abnormal extensor posturing (the body going rigid), and pauses in breathing. In one series of 13 children with Chiari type 1, about 70% had previously been evaluated for suspected cortical epilepsy or heart-related fainting before the correct diagnosis was made. Cerebellar fits were being mistaken for epileptic seizures or cardiac syncope, sometimes for years, because the episodes superficially resembled both conditions.¹⁰ The key difference is that cerebellar fits originate from pressure on the brainstem and cerebellum rather than from abnormal cortical electrical discharges. Anti-seizure medications, unsurprisingly, do not help. Surgical decompression of the posterior fossa does.

Another mimic involves cough-triggered syncope and convulsions brought on by hyperventilation. In one reported case of Chiari 1.5 malformation (a variant where the brainstem, not just the tonsils, is displaced), forced hyperventilation during an EEG provoked brief generalized clonic jerking. The movements looked like a seizure, but the EEG showed no epileptic patterns at all. Consciousness was preserved throughout, and the episode was attributed to brainstem-mediated mechanisms rather than cortical seizure activity.¹¹ These findings underscore why EEG monitoring is so important in Chiari patients who have episodic neurological events. The treatment for epilepsy and the treatment for brainstem compression head in very different directions, and misdiagnosis can delay appropriate care by years.

How Imaging and EEG Help Sort Things Out

Distinguishing true epilepsy from Chiari-related mimics typically requires both brain imaging and EEG, and sometimes more specialized functional scans. MRI shows the anatomy: the degree of tonsillar herniation, whether a syrinx is present in the spinal cord, and whether any additional brain malformations (cortical dysplasia, enlarged ventricles, heterotopias) might independently explain seizures. EEG shows the electrical activity: if classic epileptic discharges appear, the episodes are likely true seizures; if the EEG is clean during an episode, brainstem compression or syncope becomes the more likely explanation.

In some cases, the EEG findings themselves are ambiguous. Children with Chiari type 1 can show nonspecific EEG abnormalities, such as intermittent rhythmic delta activity or focal spikes, even when they do not have obvious clinical seizures. In a small series, children with apparently asymptomatic Chiari type 1 displayed a range of EEG irregularities that did not clearly fit a typical epilepsy pattern.¹² These findings were linked to impaired flow of cerebrospinal fluid, and intriguingly, surgical decompression normalized the EEG abnormalities in those patients. That observation raises the possibility that obstructed CSF flow contributes to abnormal brain electrical activity without necessarily producing clinical epilepsy, and that restoring flow can resolve the problem.

Functional imaging adds another layer. As noted earlier, SPECT scans in Chiari patients with seizures have identified regions of reduced blood flow that correspond with EEG abnormalities.⁷ When standard MRI looks normal but a patient keeps having seizures, SPECT can sometimes reveal subtle functional abnormalities that MRI misses, helping clinicians locate the seizure focus and decide on appropriate treatment.

Does Surgery Help with Seizures?

Posterior fossa decompression is the standard surgical treatment for symptomatic Chiari malformation, and it reliably improves classic symptoms like headache, neck pain, and swallowing difficulty. Its effect on seizures is less clear-cut, which makes sense given that the seizures probably do not originate from the cerebellar herniation in most cases.

The EEG normalization observed after surgery in children with impaired CSF flow is promising but comes from very small case series.¹² It suggests that, at least in a subset of patients, restoring normal CSF dynamics can eliminate the conditions that produce abnormal brain electrical activity. Whether this translates to seizure freedom for patients with established epilepsy is a different and largely unanswered question. If a patient’s seizures stem from cortical microdysgenesis or another fixed structural abnormality, decompressing the posterior fossa would not be expected to help with the epilepsy, even if it improves other Chiari symptoms.

For the seizure-like episodes that are actually cerebellar fits, the picture is more straightforward. Since those events arise from brainstem compression, decompression surgery directly addresses the cause and can eliminate the episodes entirely.¹⁰ Getting the diagnosis right beforehand is what matters most: anti-seizure drugs will not resolve cerebellar fits, and unnecessary surgery will not cure epilepsy caused by a cortical malformation.

What We Can Learn from Dogs

An unexpected window into this question comes from veterinary neurology. Cavalier King Charles spaniels are prone to a condition called Chiari-like malformation that closely parallels Chiari type 1 in humans. These dogs also have high rates of seizures, which prompted researchers to investigate whether the malformation or the ventriculomegaly that often accompanies it could explain the epilepsy. In a study of 85 Cavalier King Charles spaniels with Chiari-like malformation, 27 of which had seizures, no statistical association was found between the malformation (or its associated ventriculomegaly) and seizure occurrence.¹³ Most seizures were classified as having partial onset, and the researchers suspected a separate familial epilepsy in the breed. The finding is consistent with the human literature: even in a population where Chiari-like anatomy is nearly universal, the malformation itself does not appear to drive the seizures.

Practical Takeaways for Patients and Families

If you or your child has a Chiari malformation and seizures, the first priority is determining whether the episodes are true epileptic seizures or one of the mimics that Chiari can produce. An EEG during or shortly after an episode is the most direct way to make that distinction. If the EEG shows epileptic activity, the seizure focus is almost certainly cortical, and standard anti-seizure medication is the appropriate starting point. Additional imaging, sometimes including SPECT or high-resolution MRI, can help identify whether an associated brain abnormality is responsible.

If the episodes look like seizures but the EEG is clean, brainstem compression should be considered. Cerebellar fits, cough-related syncope, and hyperventilation-triggered convulsions are all known to occur in Chiari patients and can be misidentified as epilepsy for years before the correct diagnosis is reached.¹⁰ In these cases, posterior fossa decompression may resolve the problem.

A Chiari diagnosis does not automatically explain seizures, and seizures do not automatically mean Chiari surgery is needed. The relationship between the two conditions remains an active area of research, and the honest state of the science is that no one has yet proven a direct causal pathway from cerebellar tonsillar herniation to epileptic seizure activity. What clinicians do know is that the two conditions overlap more often than chance would predict, that shared developmental origins probably account for much of that overlap, and that careful diagnostic workup is the only way to figure out what is actually happening in any individual patient.

1
Journal of Pediatric Neurology and Neuroscience. A Possible Association between Arnold-Chiari Type I Malformation and Epilepsy: Case Series and Review
2
PubMed. Epilepsy in type 1 Chiari malformation
3
SpringerLink / Springer Nature (Child’s Nervous System). Long-term outcomes for children with an incidentally discovered Chiari malformation type 1: what is the clinical significance?
4
PubMed Central. Chiari 1 Malformation and Epilepsy in Children: A Missing Relationship
5
SpringerLink / Childs Nervous System. Prevalence of epilepsy and structural brain anomalies in spina bifida aperta
6
PubMed. Association of Chiari I malformation, mental retardation, speech delay, and epilepsy: a specific disorder?
7
PubMed. Seizures in paediatric Chiari type I malformation: the role of single-photon emission computed tomography
8
PubMed. Seizures in Chiari I malformation: a clinical and electroencephalographic study
9
PubMed. Clinical Characteristics, Imaging Findings and Surgical Outcomes of Chiari Malformation Type I in Pediatric and Adult Patients
10
Neurosurgical Focus. Cerebellar fits in children with Chiari I malformation
11
PubMed. Cough syncope and hyperventilation-induced convulsion in Chiari 1.5 malformation
12
PubMed. Surgery removes EEG abnormalities in patients with Chiari type I malformation and poor CSF flow
13
PubMed. The association between Chiari-like malformation, ventriculomegaly and seizures in cavalier King Charles spaniels