Chiari Malformation & Syringomyelia

What are Chiari malformation and syringomyelia?

An anatomical variation at the back of the brain that in some children is asymptomatic, while in others it causes pain, neurological symptoms, or scoliosis.

Chiari malformation type I is defined as descent of the cerebellar tonsils ≥ 5 mm below the foramen magnum into the upper cervical spinal canal. This can disrupt the normal circulation of cerebrospinal fluid (CSF) between the skull and the spine.

Syringomyelia refers to the formation of a CSF-filled cavity within the spinal cord (a syrinx), most commonly in the cervical or thoracic region. It is frequently associated with Chiari I, but may also occur in other conditions (trauma, tumors, arachnoid adhesions).

Chiari malformation type II occurs in children with spina bifida and is characterized by downward displacement of the cerebellar vermis, fourth ventricle, and brainstem, almost always accompanied by hydrocephalus. Management is part of the comprehensive treatment of spina bifida.

How common are they and at what ages do they occur?

Chiari type I is more frequent than previously thought and is often discovered incidentally on CT or MRI.

In large pediatric series, the prevalence of Chiari type I is approximately 3.6%, with nearly one quarter of these children also having syringomyelia. In adult studies, prevalence is reported at approximately 0.9%.

In children, Chiari type I is commonly identified:

• as an incidental finding on MRI performed for headaches or trauma,
• or during evaluation of scoliosis, sensory disturbances, or weakness.

The natural history varies: many children remain stable and never require surgery; others develop progressive symptoms; and in rare cases spontaneous improvement has been reported. For this reason, structured long-term surveillance is critical.

How do they develop? What is the pathophysiology?

The fundamental problem is impaired cerebrospinal fluid flow at the level of the foramen magnum.

Chiari I – small posterior fossa & downward displacement

In many children with Chiari type I, the posterior cranial fossa is relatively small or anatomically constricted, causing the cerebellum to be crowded and displaced downward. The cerebellar tonsils become impacted at the foramen magnum, creating a mechanical obstruction to normal CSF flow.

Syringomyelia – how the syrinx forms

When CSF flow is obstructed at the cranio-cervical junction, pressure gradients develop between the cranial and spinal compartments. CSF may be forced into the central pathways of the spinal cord, gradually forming a fluid-filled cavity (syrinx). Although no single theory fully explains this process, all models converge on abnormal CSF hydrodynamics.

Chiari II – association with spina bifida & hydrocephalus

In Chiari type II, myelomeningocele and congenital spinal malformations exert downward traction on the spinal cord and brainstem. Severe hydrocephalus, skull base anomalies, and additional congenital abnormalities are common.

What are the typical symptoms?

From “benign” headaches and subtle clumsiness to progressive weakness and scoliosis.

Symptoms of Chiari type I

• Occipital or neck pain, often exacerbated by coughing, sneezing, or straining (Valsalva-induced headache).
• Weakness or numbness in the upper and/or lower extremities, a sense of heaviness or instability.
• Balance disturbances, clumsiness, difficulty with fine motor skills.
• Scoliosis, frequently at a relatively young age, often with an atypical curve pattern.
• In more advanced cases: dysphagia, hoarseness, nystagmus, dizziness.

Symptoms of syringomyelia

• Classically, loss of pain and temperature sensation in a “cape-like” distribution across the shoulders and trunk, with relative preservation of light touch.
• Weakness or stiffness of the upper or lower extremities.
• Rapidly progressive scoliosis, particularly when the syrinx is asymmetric.
• Less commonly: hand deformities, neurogenic arthropathy, urinary disturbances.

Chiari II in spina bifida

Children with Chiari II may present with swallowing difficulties, apnea, worsening hydrocephalus, or changes in neurological status. In this population, the first consideration is always potential shunt malfunction.

How is the diagnosis made?

Magnetic resonance imaging is the diagnostic modality of choice; evaluation of the entire spine is often required.

• Brain & cervical spine MRI: demonstrates tonsillar descent, posterior fossa morphology, and CSF flow obstruction.
• Whole-spine MRI: essential to detect or exclude syringomyelia and other causes (tumors, adhesions, tethered cord).
• Cine MRI (CSF flow studies): in selected cases, helps assess the degree of functional CSF obstruction at the foramen magnum.
• Plain radiographs or CT: not diagnostic on their own, but useful for evaluating bony anomalies or cranio-cervical instability.

Imaging must always be correlated with clinical symptoms: the presence of tonsillar descent > 5 mm does not, by itself, mandate surgical intervention.

What are the potential consequences and risks?

Early diagnosis and appropriate monitoring help prevent irreversible neurological injury.

If left unmonitored or untreated, a child may develop:

• Progressive syringomyelia with permanent sensory or motor deficits.
• Worsening scoliosis, potentially requiring extensive spinal surgery.
• Chronic pain, headaches, and reduced quality of life.
• Rarely, severe brainstem symptoms (respiratory compromise, dysphagia).

When is treatment or surgery required?

We do not operate on imaging findings alone—we operate on the symptomatic patient, considering the entire clinical picture.

Surgery is usually not required when:

• Chiari type I is completely asymptomatic,
• there is no syringomyelia or the cavity is very small and stable,
• there is no progressive scoliosis or neurological deterioration.

Indications for surgical decompression

• Persistent or progressive occipital/neck pain with imaging features of Chiari malformation.
• Neurological deficits (weakness, sensory loss, gait disturbance).
• Presence or progression of syringomyelia.
• Progressive scoliosis associated with a syrinx.
• Brainstem or cranial nerve symptoms (dysphagia, apnea).

How is surgery performed and what other treatments exist?

The primary goal is to restore normal cerebrospinal fluid circulation at the foramen magnum.

Posterior fossa decompression

• A limited suboccipital craniectomy.
• Removal of the posterior arch of the C1 vertebra (and rarely C2) when indicated.
• Depending on the case, opening of the dura and duraplasty using autologous or synthetic graft material.
• Lysis of adhesions, possible reduction of the cerebellar tonsils, and confirmation of restored CSF flow.

Additional therapeutic options

• Rarely, when the underlying cause cannot be corrected, syrinx shunting may be considered as a secondary or tertiary option.
• In complex cases with osseous abnormalities (instability, retroflexed odontoid), cranio-cervical stabilization may be required in conjunction with decompression.

What is the prognosis?

When indications are appropriate and surgery is performed at an experienced center, outcomes are typically excellent.

In most children with symptomatic Chiari type I and/or syringomyelia, posterior fossa decompression results in:

• Improvement or complete resolution of headaches,
• gradual reduction or disappearance of the syrinx on follow-up MRI,
• stabilization or improvement of neurological function,
• decreased risk of scoliosis progression, particularly when intervention is timely.

Less favorable outcomes are observed when permanent neurological deficits are already established prior to surgery. For this reason, early diagnosis and optimal timing of intervention are of paramount importance.

How is long-term follow-up organized?

MRI and clinical evaluation continue over time to ensure durable results.

• Postoperative MRI typically at 3–6 months to assess decompression and syrinx evolution.
• Repeat spinal MRI every 1–2 years or more frequently, depending on the clinical course.
• Regular neurological examinations, assessing strength, sensation, and gait.
• Follow-up with a pediatric orthopedist when scoliosis is present, including periodic radiographs.

Practical guidance for parents and children

Accurate information reduces anxiety about both the condition and the surgical and recovery process.

• Many children with Chiari type I never require surgery; management is individualized.
• After successful decompression, most children can gradually return to daily activities and school.
• Caution is advised with high-impact contact sports, particularly during the first postoperative months; this is discussed in detail with each family.
• Parents should be aware of warning signs: new weakness, abrupt changes in gait, severe headaches, or sudden progression of scoliosis.