| Arnold-Chiari | |
| Classification and external resources | |
 | |
|---|---|
| A T2-weighted sagittal MRI scan, from a patient with Chiari-like symptomatology, demonstrating tonsillar herniation less than 3 mm | |
| ICD-10 | Q07.0 |
| ICD-9 | 741.0 |
| OMIM | 207950 |
| DiseasesDB | 899 |
| MeSH | D001139 |
Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla[1] through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow [2]. The cerebrospinal fluid outflow being caused by phase difference in outflow and influx of blood in the vasculature of the brain.
Contents |
Terminology
Chiari malformation is the most frequently used term for these types of malformations. The use of the term Arnold-Chiari malformation has fallen somewhat out of favor over time, although it is used by some to refer to the type II malformation. Some sources use "Chiari malformation" to describe four specific grades of the condition, reserving the term "Arnold-Chiari" for type II only.[3] Some sources use "Arnold-Chiari" for all four types.[4] This article uses the latter convention.
Chiari malformation or Arnold-Chiari malformation should not be confused with Budd-Chiari syndrome,[5] 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.[6]
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.[7]
Incidence
The incidence of Chiari 1 malformation, defined as tonsilar herniations of 3 to 5 mm or greater, is approximately 1 in 1,200.[citation needed] The incidence of symptomatic Chiari is less but unknown.
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.[8]
| Type | Presentation | Other notes |
|---|---|---|
| I | Is generally asymptomatic during childhood, but often manifests with headaches and cerebellar symptoms. Herniation of cerebellar tonsils.[9][10] | The most common form. |
| II | Usually accompanied by a myelomeningocele[11] leading to partial or complete paralysis below the spinal defect. Abnormal development of the cerebellar vermis and medulla oblongata occur, and they both descend into the foramen magnum. Hydrocephalus is also nearly always present. | |
| III | Causes severe neurological defects. It is associated with an encephalocele.[12] | |
| IV | Involves a failure of brain development.[13] |
Other conditions sometimes associated with Chiari Malformation include hydrocephalus,[14] syringomyelia, spinal curvature, and connective tissue disorders[15] 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 Valsalva maneuvers, such as yawning, laughing, crying, coughing, sneezing or straining. Chiari also includes muscle weakness, facial pain, hearing problems, and extreme fatigue. 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,[16] 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.
Prognosis
The prognosis differs dependent on the type of malformation (i.e., type I, II, III, or IV). Types I and II are generally adult-onset variations and, while not curable, are treatable and non-fatal. Types I and II sufferers may also develop syringomyelia. Types III and IV are extremely rare and patients generally do not survive past the age of two or three.[17]
History
An Austrian pathologist, Hans Chiari, first described these hindbrain malformations in the 1890s.[18] A colleague of Professor Chiari, Dr. Julius Arnold, later contributed to the definition of the condition,[19] and students of Dr. Arnold (Schwalbe and Gredig)[20] suggested the term "Arnold-Chiari malformation" to henceforth refer to the condition.[21][22]
Some sources credit the characterization of the condition to Cleland[23][24] or Cruveilhier.[25]
Notable people with the malformation
Research
Considerable research has been directed towards improving methods used to diagnose Arnold-Chiari malformation. In particular, the traditional diagnosis method quantifying a 5 mm descent of the lower cerebellar tonsils through the foramen magnum may be insufficient for diagnosis in some patients. Research has been conducted to investigate the importance of cerebrospinal fluid velocities, other geometric parameters of the cranium, the importance of cranial and spinal canal compliance, and thickening of the filum terminale in assessment of Arnold-Chiari malformation.