Arnold-Chiari malformation overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Fahimeh Shojaei, M.D.

Arnold-Chiari malformation was first described by Cleland in 1883 in a child with spina bifida. Hans Chiari, an Austrian pathologist was the first person who described type 2 Arnold-Chiari malformation. Hans Chiari also described different classification of Arnold-Chiari malformation into 4 groups.

Arnold chiari malformation may be classified according to herniation content into 4 subtypes. Type 1 has herniation of cerebellar tonsils. Type 2 has herniation of cerebellar tonsils and vermis. Type 3 has herniation of cerebellar tonsil and vermis and lower brain stem. Type 4 has cerebellar hypoplasia with brain stem in posterior fossa.

The exact pathogenesis of Arnol-Chiari malformation is not fully understood but It is thought that Arnol-Chiari malformation is the result of bone developmental abnormalities or mesodermal growth and differentiation abnormalities. Genes involved in the pathogenesis of Arnold-Chiari malformation include PAX1, PAX2, PAX3, PAX6, FGF2, TBX6, HOX gene, Noggin gene, and EFNB1. Conditions associated with Arnold-Chiari malformation include hydrocephalus, syringomyelias,Tethered spinal cord syndrome, neurofibromatosis type 1, Noonan syndrome, Pierre Robin sequence, Klippel-Feil syndrome, Albright hereditary osteodystrophy, x-linked aqueductal stenosis, Goldenhar syndrome, Williams syndrome, Shprintzen- goldberg syndrome, achondroplasia, familial osteosclerosis, velocardiofacial syndrome, and connective tissue disorders.

The cause of Arnold Chiari malformation include craniosynostosis, osteopetrosis, vitamin D deficiency and genetic mutations.

On the basis of seizure, visual disturbance, and constitutional symptoms, Arnold-Chiari malformation must be differentiated from astrocytoma, oligodendroglioma, meningioma, hemangioblastoma, pituitary adenoma, schwannoma, primary CNS lymphoma, medulloblastoma, ependymoma, craniopharyngioma, pinealoma, AV malformation, brain aneurysm, bacterial brain abscess, tuberculosis, toxoplasmosis, hydatid cyst, CNS cryptococcosis, CNS aspergillosis, and brain metastasis.

The prevalence of Arnold Chiari malformation is unknown since most of the cases are accidentally found. The mortality rate of Arnold Chiari malformation depends on the subtype but type 3 has the highest mortality rate as a result of respiratory failure in infancy. Arnold Chiari malformation commonly affects adolescence and adulthood, but also has been seen in younger children. There is no racial predilection to Arnold Chiari malformation.

Common risk factors in the development of Arnold-Chiari malformation include lumbar-peritoneal shunt and multiple lumbar puncture.

There is insufficient evidence to recommend routine screening for Arnold-Chiari malformation.

MRI is the gold standard test for the diagnosis of Arnold Chiari malformation. Cerebellar tonsillar herniation, wedge shaped tonsils, syringohydromyelia, small posterior fossa, obstructive hydrocephalus, and brainstem anomalies.

Patients with Arnold-Chiari malformation may have a positive history of lumbar puncture, lumbar-peritoneal shunt, hydrocephalus, syringomyelias,Tethered spinal cord syndrome, neurofibromatosis type 1, Noonan syndrome, Pierre Robin sequence, Klippel-Feil syndrome, Albright hereditary osteodystrophy, x-linked aqueductal stenosis, Goldenhar syndrome, Williams syndrome, Shprintzen- goldberg syndrome, achondroplasia, familial osteosclerosis, velocardiofacial syndrome, and connective tissue disorders. The most common symptoms of Arnold-Chiari malformation is headache, arm pain and weakness, neck pain, nausea and vomiting, balance problem, dizziness and ear ringing.

Patients with Arnold Chiari malformation usually appear normal. Physical examination of patients with Arnold Chiari malformation is usually remarkable for impaired coordination, sensory/ motor deficit, abnormal gait, nystagmus, scoliosis, and autonomic dysfunction.

There are no diagnostic laboratory findings associated with Arnold Chiari malformation.

There are no ECG findings associated with Arnold Chiari malformation.

There are no ultrasound findings associated with Arnold-Chiari malformation.

CT scan may be helpful in the diagnosis of Arnold Chiari malformation. Findings on CT scan diagnostic of Arnold Chiari malformation depends on the subtype and include herniation of cerebellar tonsils, vermis, and lower brain stem, underdeveloped cerebellum and crowded foramen magnum.

MRI may be helpful in the diagnosis of Arnold-Chiari malformation. Findings on MRI diagnostic of Arnold-Chiari malformation include cerebellar tonsillar herniation, wedge shaped tonsils, syringohydromyelia, small posterior fossa, obstructive hydrocephalus, and brainstem anomalies.

There are no other imaging findings associated with Arnold-Chiari malformation.

There are no other diagnostic studies associated with Arnold-Chiari malformation.

There are no established measures for the primary prevention of Arnold-Chiari malformation.

There are no established measures for the secondary prevention of Arnold-Chiari malformation.

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