Chiari II Malformation

What Chiari II malformation is

The back of the skull (posterior fossa) normally holds the cerebellum and brainstem. In Chiari II malformation the posterior fossa is small, and the cerebellum, the fourth ventricle and part of the brainstem are pushed down through the foramen magnum, the large opening at the base of the skull, into the upper spinal canal.

The leading theory is that the open spinal defect in myelomeningocele lets cerebrospinal fluid (CSF) leak out during development. The fluid spaces of the brain do not expand normally, so the posterior fossa stays small and the hindbrain is drawn downward.

For the more common adult form, see Chiari malformation.

Associated conditions

• Spina bifida (myelomeningocele): an open defect in the spine with exposed spinal cord, causing leg weakness or paralysis, bladder and bowel problems and loss of sensation.
• Hydrocephalus: blocked CSF flow causes fluid buildup in the brain. Historically, 80 to 90 in 100 babies with myelomeningocele needed a shunt. Fetal surgery has lowered this.
• Syringomyelia: a fluid-filled cavity in the spinal cord.
• Tethered cord syndrome after spina bifida repair.
• Other brain differences, such as an underdeveloped corpus callosum.

Symptoms

Many children with Chiari II malformation have no symptoms from it. Symptomatic Chiari II is the leading cause of death in infants with myelomeningocele, so warning signs matter.

In babies

• stridor: high-pitched noisy breathing, often from vocal cord paralysis
• apnea: pauses in breathing, especially during sleep
• swallowing problems: choking, gagging, slow feeding, milk coming out the nose, aspiration pneumonia
• weak or hoarse cry
• arm weakness and floppiness
• abnormal eye movements

In older children and adults

• headaches at the back of the head, worse with coughing or straining
• neck pain
• arm weakness, numbness or stiffness
• balance and coordination problems
• swallowing difficulty and sleep apnea
• scoliosis

Many of these symptoms can also be caused by a blocked shunt, which is always checked first.

Diagnosis

• Prenatal: the routine anatomy scan at 18 to 22 weeks often shows signs of spina bifida and Chiari II, such as the "lemon sign" (a scalloped skull) and the "banana sign" (a curved cerebellum). Raised alpha-fetoprotein on maternal blood screening can also prompt testing. Fetal MRI confirms the findings.
• After birth: MRI of the brain and spine shows the hindbrain herniation, hydrocephalus and any syrinx.
• Additional tests: swallow studies, sleep studies, and a scope exam of the vocal cords for breathing or feeding problems.

Treatment

Spina bifida repair

• Fetal surgery: closing the spinal defect before birth, typically between 19 and 26 weeks, reduces the need for a shunt and often reverses the hindbrain herniation. It increases risks for the pregnancy, such as preterm birth, so it is offered at specialized centers to selected families.
• Postnatal repair: closure within the first 48 hours after birth to prevent infection.

Hydrocephalus management

• Ventriculoperitoneal (VP) shunt: a tube draining fluid from the brain to the belly.
• Endoscopic third ventriculostomy (ETV), sometimes with choroid plexus cauterization, as an alternative in some babies.

Making sure the shunt works is the first step whenever Chiari II symptoms appear.

Posterior fossa decompression

If symptoms persist with a working shunt, surgeons may perform a decompression: removing bone at the back of the skull and upper spine to relieve pressure on the brainstem. Infants with severe breathing problems may also need a tracheostomy and a feeding tube.

Long-term care

A multidisciplinary spina bifida clinic coordinates neurosurgery, urology, orthopedics, physical therapy, and developmental and educational support.

Outlook

Outlook depends mainly on the severity of the spina bifida and on whether brainstem symptoms develop. Many children with Chiari II lead active lives, attend school and reach adulthood. Infants with severe brainstem symptoms, especially vocal cord paralysis and apnea, face higher risk and need intensive care.

Prevention

The risk of neural tube defects, and therefore Chiari II, is reduced by taking 400 micrograms (mcg) of folic acid daily before conception and in early pregnancy, as recommended by the CDC. People who have had a pregnancy affected by a neural tube defect are usually advised to take a higher dose prescribed by their doctor.

Frequently asked questions

What is Chiari II malformation?

It is a birth defect in which the cerebellum and brainstem extend down through the base of the skull into the spinal canal. It occurs almost only in babies with myelomeningocele, a severe form of spina bifida, and usually comes with hydrocephalus.

What are the symptoms of Chiari II malformation in babies?

Symptoms include noisy, high-pitched breathing (stridor), pauses in breathing, choking or difficulty swallowing, a weak or hoarse cry, and arm weakness. Many babies have no symptoms. Any of these signs need urgent assessment.

How is Chiari II different from Chiari I?

Chiari I involves only the lower tips of the cerebellum, is not linked to spina bifida, and is usually found in older children or adults. Chiari II involves more of the hindbrain, is present from before birth and is almost always linked to spina bifida.

Can Chiari II malformation be treated before birth?

Yes, indirectly. Fetal surgery to close the spina bifida defect during pregnancy can reduce the hindbrain herniation and the need for a shunt. It is offered at specialized centers to selected pregnancies.

Can Chiari II malformation be prevented?

The best prevention is taking folic acid before and during early pregnancy, which reduces the risk of spina bifida and the Chiari II malformation linked to it. Folic acid fortification of foods has also lowered rates.