Treating Chiari Malformations

Chiari malformations are structural defects in which a small portion of the back of the brain descends into the spinal column, where it can impede the flow of cerebrospinal fluid (CSF). There are four types of Chiari malformations. Types 2, 3 and 4 can usually be identified at birth. Type 1, our focus here, develops as the skull and brain grow throughout childhood and often cannot be diagnosed until late childhood or adolescence. Treatments for Chiari type 1 malformation (CM1) vary depending on the size and shape of the cranial malformation responsible for the descending brain tissue and the intensity of the symptoms. If the condition is diagnosed early enough and treated properly, most young patients will recover fully and lead normal lives. Lucile Packard Children’s Hospital Stanford is a national destination center for CM1. Patients and their families travel here for the best available diagnosis, treatment and follow-up care, and we are constantly working to improve our patients’ experience and quality of life.


Diagnosing CM1 can be challenging because many of the condition’s most obvious symptoms are also symptoms of other disorders, including headaches in the back of the head that worsen with straining or when performing the Valsalva maneuver, neck pain, dizziness, difficulty swallowing, fatigue and depression. Other, sometimes subtler, symptoms can also tip physicians off to the possibility of CM1, including impairment of fine motor skills; numbness in the hands, arms or legs; blurred vision or diminished hearing; and trouble sleeping. Problems with balance and muscle weakness are also indicative of CM1 but may not always be present.

The lower rear portion of the brain is called the cerebellum, and the lowermost parts of the cerebellum are called the cerebellar tonsils. The cerebellar tonsils usually rest on top of the hole in the bottom of the skull, called the foramen magnum, where the spinal column passes into the back of the skull and through which CSF flows on its route through the central nervous system. In children with CM1, the cerebellar tonsils push through the foramen magnum and into the spinal column.

Symptoms of CM1 typically arise from blocked flow of CSF, compression of the brainstem or the formation of fluid-filled sacs, called syrinx, either in the spinal cord (where they are called syringomyelia) or in the brainstem (where they are called syringobulbia). The CM1 team may have to address one, two or all three of these problems with any single child.

No single test can determine precisely what is causing a CM1 patient’s symptoms or predict whether that child would benefit from surgery. Collaborative examination by an experienced team of specialists is the only way to zero in on the proper diagnosis and optimal course of treatment. CM1 is defined by the descent of the cerebellar tonsils into the brainstem, but the intensity of its symptoms can vary from patient to patient. Sometimes the tonsils may drop down far but the child remains asymptomatic. In other cases, the tonsils may remain largely above the foramen magnum, yet the child has multiple and intense symptoms. Before we can chart the best course forward for a CM1 patient, physicians must conduct a complete neurological exam to look for symptoms of cerebellar dysfunction, including repetitive, uncontrolled horizontal eye movements (called nystagmus), gait abnormalities, trouble swallowing and an exaggerated response to reflex stimulation. Imaging specialists also must analyze images of the brain, brainstem, spinal cord and the flow of CSF. 

Treatment for CM1

If symptoms are mild, it may be possible to sufficiently treat them with anti-inflammatory and headache medications. In such cases, children are closely tracked so that doctors can quickly intervene should their condition worsen. Even children with mild or asymptomatic cases of CM1 are vulnerable to the compression of brain tissue between the spinal column and the skull, and so they should avoid chiropractic therapy, roller coasters, trampolines and other activities that could result in whiplash. We follow many more children than we treat surgically since the natural history of a child with CM1 is still unknown and CM1 is much more common than previously thought.

Cases in which symptoms are intensifying or are already disabling do require surgery to fix and halt the progress of the structural problems underlying the disorder. 

Surgery for CM1 is called posterior fossa decompression surgery, or sometimes just Chiari decompression. It begins with the removal of a portion of the skull bone (craniectomy) on the lower part of the back of the skull to take pressure off the herniated cerebellum and restore the unimpeded flow of CSF. The surgeon then removes a part of the arched, bony roof of the spinal canal, called C1, to make more room and relieve pressure on the spinal cord. Sometimes the surgeon will then round out the cerebellar tonsils to further improve CSF flow. Finally, using a microscope, the surgeon sews a flexible, durable patch over the area to protect the underlying tissue while allowing room for the cerebellar tonsils and aiding the free flow of CSF. The surgery typically takes between two and three hours.

Most children who have Chiari decompression surgery experience improvement in their symptoms within a week or two of the surgery. While most children only need one surgery to correct their CM1, some children require subsequent surgical procedures to treat their CM1. In very young children, for example, removed bone can grow back and compress the cerebellum again, or the lower portions of the cerebellum may again fall below the foramen magnum and impede the flow of CSF. Syrinx may also reform, necessitating surgical treatment with a repeat Chiari decompression or the installation of a shunt into the syrinx. The goal of surgery is to maximize the quality of life for the child so he or she can be a kid again.

Associated hydrocephalus and benign intracranial hypertension

In some cases, impeded CSF flow can cause hydrocephalus, which must be treated with the surgical placement of a shunt or, alternatively, an endoscopic third ventriculostomy to divert the CSF underneath the brain.

After Chiari decompression surgery, elevated CSF pressures can worsen and result in benign intracranial hypertension or pseudotumor cerebri, causing symptoms (most notably a frontal headache) that are sometimes mistaken as indication of a tumor. Often, this condition can be simply treated with medication that decreases the production of CSF, but a spinal tap and eye exam may be required for diagnosis. Some more extreme cases may require surgical introduction of a shunt that redirects excess CSF out of the brain.

Recovery is quick and often complete

The time it takes to fully recover from Chiari decompression varies from child to child, but most patients will typically spend three to four days in the hospital and two to three weeks at home before returning to school. Patients may experience some intermittent frontal headaches and post-surgical neck pain during recovery, but these usually pass. Most of the children we treat surgically can expect to return to all normal activities and can enjoy just being kids again.

The Lucile Packard Children's Hospital Stanford advantage

Even after recovery, our team of specialists remains an important lifelong resource for our CM1 patients and their families. Our research program includes long-term tracking and follow-up visits with our Chiari 1 patients. This guides us in the best possible treatment for the patient at the time and helps us anticipate complications that may arise for individual patients in the future. Toward this end, we have developed a novel quality-of-life metric, specific to Chiari I, which allows us to track and evaluate children with the disorder over time. Once validated here at Stanford, our researchers will widely disseminate the findings to push back the frontiers of treatment not only for our own patients but for children with CM1 everywhere.

As a destination site for the treatment of CM1, we see patients from around the world. Our surgeons have decades of experience treating this patient population, and our state-of-the-art surgical facilities equip us to offer the best available treatment for whatever surgical challenges a patient brings to us. Our multidisciplinary team of experts also includes pediatric neurologists; sleep medicine experts; ear, nose and throat specialists; and an integrated pain team. Together, we treat our young patients in the most comprehensive fashion possible so they can return to living full, happy and healthy lives.


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