Chiari II Malformation

Overview

Chiari II malformation, also called Arnold-Chiari malformation, is a structural abnormality at the base of the brain. In this condition, parts of the lower brain, the brainstem and the lower portion of the cerebellum, are displaced downward through the opening at the base of the skull into the upper spinal canal. This crowding can interfere with the normal flow of cerebrospinal fluid and with nerve function.

Chiari II is distinct from the more common Chiari I malformation because it almost always occurs together with spina bifida, specifically the open form called myelomeningocele. It is therefore considered part of the same group of neural tube developmental problems. Many children with Chiari II also develop hydrocephalus, a buildup of fluid in the brain. Care is coordinated by a team and tailored to each child's symptoms.

Symptoms

Symptoms vary with age and severity. Some children have few problems, while others have significant difficulties, especially as infants:

• Trouble swallowing, feeding difficulties, or gagging
• Noisy or difficult breathing, including pauses in breathing
• A weak or hoarse cry
• Weakness or stiffness in the arms
• Poor head control or balance problems
• In older children: headaches, neck pain, or worsening coordination

Warning signs such as breathing difficulty, choking, or rapid worsening of symptoms need urgent medical attention, because brainstem compression can be serious.

Causes

Chiari II malformation develops during early pregnancy as part of abnormal neural tube formation. It is closely tied to the same processes that cause spina bifida:

• Neural tube developmental abnormality: The open spinal defect of myelomeningocele is thought to alter pressure and fluid dynamics, contributing to downward displacement of the lower brain.
• Low folic acid (folate): As with other neural tube defects, inadequate folate around conception is a risk factor.
• Genetic and environmental factors: A combination of influences, often without a single identifiable cause.

Risk Factors

• Presence of spina bifida (myelomeningocele), which is almost always associated
• Inadequate folic acid before and during early pregnancy
• A family history of neural tube defects
• A previous pregnancy affected by a neural tube defect
• Poorly controlled maternal diabetes

Diagnosis

Chiari II is often identified before or shortly after birth because of its link with spina bifida:

• Prenatal ultrasound and fetal MRI: Can reveal the malformation and associated spina bifida before birth.
• MRI of the brain and spine: The key test after birth, showing the position of the brainstem and cerebellum and any associated hydrocephalus.
• Clinical evaluation: Assessment of breathing, swallowing, movement, and development.

Treatment

Treatment depends on whether symptoms are present and how severe they are.

• Monitoring: Children with few or no symptoms may be followed closely without immediate surgery.
• Treating hydrocephalus: A shunt or other procedure drains excess fluid from the brain, which can itself relieve some symptoms.
• Decompression surgery: When the brainstem is compressed and causing significant problems, surgery to create more space at the base of the skull may be performed.
• Supportive care: Help with feeding, breathing, and therapies for movement and development as needed.

Because Chiari II accompanies spina bifida, care is part of an overall, lifelong management plan.

Prevention

Chiari II cannot be prevented once it has formed, but reducing the risk of the underlying neural tube defect lowers the chance of the condition:

• Take a daily folic acid supplement before conception and in early pregnancy
• Eat folate-rich foods such as leafy greens, beans, and fortified grains
• Control diabetes before becoming pregnant
• Review medications with a doctor before pregnancy
• Seek genetic counseling if you have a history of neural tube defects

When to See a Doctor

Children with Chiari II are followed by a specialist team. Seek urgent or emergency care if a child develops:

• Difficulty breathing, pauses in breathing, or choking
• Trouble swallowing, persistent gagging, or feeding problems
• New or worsening weakness, stiffness, or poor head control
• Severe headache, vomiting, or unusual sleepiness, which may signal worsening hydrocephalus

Breathing or swallowing difficulties in an infant with Chiari II should be treated as an emergency.

Related Topics

Frequently Asked Questions

References

1. National Institute of Neurological Disorders and Stroke (NINDS). Chiari Malformation.
2. MedlinePlus, U.S. National Library of Medicine. Chiari malformation.
3. Centers for Disease Control and Prevention (CDC). Spina Bifida.
4. March of Dimes. Neural tube defects.