Arnold Chiari Malformation

Definition

Definition of Arnold Chiari Malformation
Arnold–Chiari malformation, or often simply Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness in the head and face, difficulty swallowing, dizziness, nausea, impaired coordination, and, in severe cases, paralysis.

Symptoms

Symptoms of Arnold Chiari Malformation

1. Headaches aggravated by Valsalva maneuvers, such as yawning, laughing, crying, coughing, sneezing or straining
2. Tinnitus (ringing in the ears)
3. Dizziness and vertigo
4. Nausea
5. Nystagmus (irregular eye movements)
6. Facial pain
7. Muscle weakness
8. Impaired gag reflex
9. Restless Leg Syndrome
10. Sleep Apnea
11. Dysphagia (difficulty swallowing)
12. Impaired coordination
13. Increased intracranial pressure
14. Pupillary dilatation

Causes

Causes of Arnold Chiari Malformation
Although the exact cause of Chiari malformation is unknown, it is thought that a problem during fetal development may cause the abnormal brain formation. Chiari malformation may be caused by exposure to harmful substances during fetal development or associated with genetic problems or syndromes that may have a tendency to run in families.

Diagnosis

Diagnosis of Arnold Chiari Malformation
Diagnosis is made through a combination of patient history, neurological examination, and Magnetic Resonance Imaging (MRI). The radiographic criteria for diagnosing a congenital Chiari I Malformation is a downward herniation of the cerebellar tonsils greater than 5 mm below the foramen magnum. Other imaging techniques involve the use of 3-D CT imaging of the brain and cine imaging (a movie of the brain) can be used to determine if the brainstem is being compressed by the pulsating arteries that surround it.

In the Syndrome of Occipitoatlantoaxial Hypermobility, cerebellar tonsillar herniation is typically only evident on an up-right MRI, due to the fact that the Chiari Malformation is gravitationally acquired by means of connective tissue weakness. 3-D CT imaging may aid in the diagnosis of related disorders such as retroflexed odontoid. Invasive cranial traction (lifting of the head off the spine) is often used as a confirmation of the diagnosis.

Treatment

Treatment of Arnold Chiari Malformation
Once symptomatic onset occurs, a common treatment is decompression surgery, in which a neurosurgeon usually removes the lamina of the first and sometimes the second or even third cervical vertebrae and part of the occipital bone of the skull to relieve pressure. The flow of spinal fluid may be accompanied by a shunt. Since this surgery usually involves the opening of the dura mater and the expansion of the space beneath, a dural graft is usually applied to cover the expanded posterior fossa.

A small number of neurological surgeons believe that detethering the spinal cord as an alternate approach relieves the compression of the brain against the skull opening (foramen magnum), obviating the need for decompression surgery and associated trauma. However, this approach is significantly less documented in the medical literature, with reports on only a handful of patients. It should be noted that the alternative spinal surgery is also not without risk.

On April 24, 2009, a young patient with Type 1 Chiari malformation was successfully treated with a minimally invasive endoscopic transnasal procedure by Dr. Richard Anderson at the Columbia University Medical Center Department of Neurosurgery.

Prognosis

Prognosis of Arnold Chiari Malformation
The prognosis differs dependent on the type of malformation (i.e., type I, II, III, or IV). Type I is generally adult-onset and, while not curable, is treatable and rarely fatal. Syndrome of Occipitoatlantoaxial Hypermobility (Ehlers-Danlos syndrome related) is more difficult to treat than the congenital form of the disease. Individuals with this type do not respond well to the decompression surgery and often require an occipitoatlantoaxial fusion for stability. These patients are at risk of experiencing serious heart complications. Types I and II sufferers may also develop syringomyelia. Type II is typically diagnosed at birth or prenatally. Approximately 33% of individuals with Chiari II malformation develop symptoms of brainstem damage within five years; a 1996 study found a mortality rate of 33% or more among symptomatic patients, with death frequently occurring due to respiratory failure. 15% of individuals with Chiari II malformation die within two years of birth. Among children under two who also have myelomeningocele, it is the leading cause of death. Prognosis among children with Chiari II malformation who do not have spina bifida is linked to specific symptoms; the condition may be fatal among symptomatic children when it leads to neurological deterioration, but surgical intervention has shown promise. Types III and IV are extremely rare and patients generally do not survive past the age of two or three.

Prevention

Prevention of Arnold Chiari Malformation
There is no known way to prevent Arnold-Chiari syndrome. Parents of a child with this condition may benefit from genetic counseling.