|
|
|
|
Arnold-Chiari malformation
|
| |
|
| |
Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of CSF outflow.
sources use "Chiari malformation" to describe four specific grades of the condition, reserving the term "Arnold-Chiari" for type II only. Other sources use "Arnold-Chiari" for all four types.
Discussion
Ask a question about 'Arnold-Chiari malformation' Start a new discussion about 'Arnold-Chiari malformation' Answer questions from other users |
Encyclopedia
Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of CSF outflow.
Terminology
Some sources use "Chiari malformation" to describe four specific grades of the condition, reserving the term "Arnold-Chiari" for type II only. Other sources use "Arnold-Chiari" for all four types. This article uses the latter convention.
One advantage of using "Arnold-Chiari" is that the term "Chiari's syndrome" can refer to Budd-Chiari syndrome, a hepatic condition also named for Hans Chiari.
Diagnosis
Chiari malformations are diagnosed with a sagittal T1 magnetic resonance imaging (MRI) scan of the posterior fossa of the skull. This displays the typical downward herniation of the cerebellar tonsils. A displacement of greater than 5 mm below the foramen magnum is deemed significant and will lead to a patient being diagnosed with Arnold-Chiari malformation. In some instances, MRI CSF flow studies are used to decide if a displacement is causing any damage.
The average age at diagnosis is about 27 and it is more common in women, but is also found in men.
Some characteristics are visible prenatally.
Incidence
The incidence of Arnold-Chiari Malformation (Chiari I malformation) defined as tonsilar herniations of 3 to 5 mm or greater is approximately 1 in 1,200. The incidence of symptomatic Chiari is less but unknown.
A prevalence of approximately 1 in 1000 has been described.
History and classification
The Austrian pathologist Hans Chiari in the late 1800s described seemingly related anomalies of the hindbrain, the so called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation. The scale of severity is rated I - IV, with IV being the most severe. Types III and IV are very rare.
- The most common form of Arnold-Chiari Malformation is Type I, which is generally asymptomatic during childhood, but often manifests with headaches and cerebellar symptoms.
- Type II is usually accompanied by a myelomeningocele leading to partial or complete paralysis below the spinal defect. Abnormal development of the cerebellar vermis and medulla occur, and they both descend into the foramen magnum. Hydrocephalus is also nearly always present.
- Type III causes severe neurological defects. It is associated with an encephalocele.
- Type IV involves a failure of brain development.
Other conditions sometimes associated with Chiari Malformation include hydrocephalus, syringomyelia, spinal curvature, and connective tissue disorders such as Ehlers-Danlos syndrome and Marfan Syndrome.
Symptoms
The brainstem, cranial nerves, and the lower portion of the cerebellum may be stretched or compressed. Therefore, any of the functions controlled by these areas may be affected. The blockage of Cerebro-Spinal Fluid (CSF) flow may also cause a syrinx to form, eventually leading to syringomyelia. Chiari is often associated with major headaches, sometimes mistaken for migraines. Chiari headaches usually include intense pressure in the back of the head, aggravated by laughing, coughing, sneezing or straining. Chiari also includes extreme muscle soreness, facial pain, hearing problems, and low energy levels. It also can cause insomnia cycles of sleep deprivation followed by inabilities to remain awake cycling between them. 15% of patients with adult Chiari malfomation are asymptomatic.
Treatment
Once symptomatic onset occurs, a common treatment is decompression surgery, in which a neurosurgeon usually removes the first and part of the second and sometimes third cervical vertebrae and part of the occipital bone of the skull to allow the flow of spinal fluid and may be accompanied by a shunt. This treatment is well recognized and accepted with many studies published (involving a total of hundreds of patients) in well-respected peer-reviewed medical journals showing that about 80% of patients obtain improvement. Some authors advocate performing a transoral clivus-odontoid resection in cases with ventral brain-stem compression, as they feel these patients may potentially deteriorate with posterior fossa decompression alone.
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.
History
An Austrian pathologist, Hans Chiari, first described these hindbrain malformations in the 1890s. A colleague of Professor Chiari, Dr. Julius Arnold, later contributed to the definition of the condition, and students of Dr. Arnold (Schwalbe and Gredig) suggested the term "Arnold-Chiari malformation" to henceforth refer to the condition.
Some sources credit the characterization of the condition to Cleland or Cruveilhier.
See Also
External links
- (ACT)
- from a father whose son suffered from Chiari Malformation and the emotional roller coaster it created.
|
| |
|
|
