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 (cerebrospinal fluid) outflow.
Terminology
Some sources use the term “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 the term “Arnold Chiari” is that the term “Chiari’s Syndrome” can refer to Budd-Chiari syndrome a hepatic conditon also named after Hans Chiari
What is Chiari Malformation?
An image showing a brain affected the chiari malformation image courtesy braincatalognucleusinc.com
Chiari Malformations (CMs) are structural defects in the cerebellum, the part of the brain that controls balance. When indented bony space at the lower rear of the skull is smaller than normal, the cerebellum and brainstem can be pushed downward. The resulting pressure on the cerebellum can block the flow cerebrospinal fluid (the liquid that surrounds and protects the brain and spinal cord) and can cause a range of symptoms including dizziness, muscle weakness, numbness, vision problems, headache and problems with balance and coordination. There are three primary types of CMs:- Type I :- Most common. It may not cause symptoms and is often found by accident during an examination for another condition. Type II :-Also called Arnold Chiari Malformation is usually accompanied by a myelomeningocele- a form of spina bifida that occurs when the spinal canal and backbone donot close before birth, causing the spinal cord to protrude through an opening in the back. This can cause either partial or complete paralysis below the spinal opening in the back. Type III :- This is the most serious form of CM, and causes severe neurological defects. Other conditons sometimes associated with CM include hydrocephalus, syringomyelia and spinal curvature.
History
Hans chiari, an austrian pathologist first described these hindbrain malformations in the 1890s Image courtesy weborionpharma.se
An Austiran pathologist, Hans Chiari, first described these hindbrain malformations in the 1890s. A colleague of Professor Chiari, Dr. Julius Arnold, later contributed to the definiton of the condition, and students of Dr. Arnold (Schwalbe and Gredig) suggested the term “Arnold – Chiari Malformation” to henceforth refer to the condition. Between 1891 and 1896, German pathologist Hans Chiari described a series of anomalies of the caudal cerebellum and brainstem on the basis of autopsy observations. In 1891, he described an anomaly consisting of elongated peglike cerebellar tonsils that are displaced into the upper cervical canal through the foramen magnum. This is now designated as the Chiari Type I malformation. Five years later, he published a further report on a hindbrain anomaly, now known as the Chiari type II malformation. He also reported a single case of cervical spina bifida associated with herniation of the cerebellum through the foramen magnum, which has since been called Chairi III malformation. Some authors have added a form of severe cerebellar hypoplasia without displacement of brain through the foramen magnum, the so-called Chiari IV malformation. The Chiari II is a complex congenital malformation of the brain, nearly always associated with myelomeningocele. This condition includes downward displacement of the medulla, fourth ventricle and cerebellum into the cervical spinal canal as well as elongation of the pons and fourth ventricle probably due to a relatively small posterior fossa
Mortality / Morbidity
Neonatal Chiari II malformation continue to result in significant morbidity and mortality. Hindbrain dysfunction is the major cause of the mortality. The mortality rate is 15% in first years of life among the patients with Chiari II malformation. Symptomic Chiari II malformation is the leading cause of mortality in the myelodysplastic population. One third of the patients with myelomeningocele develop brainstem dysfunction by the age of 5 years. Of these one third die in infancy. Cranial nerve and brainstem dysfunction are the most serious and potentially life threatening problems. Respiratory difficulties occur in about 29-76 percent of patients; which are the most common and leathal manifestation of the conditon.
Preferred Examination
The Chiari II malformation is a complex anomaly with skull, dural, brain, spinal and spinal cord maifestations. Traditionally, when suggestions and symptoms were suggestive of a Chiari II malformation, plain radiography of the head or spine was performed, followed by myelography. Because myelography is a invasive procedure, clinicians were reluctant to perform the test until the severity of the symptoms warranted it. The introduction of modern imaging techniques, specifically, MRI, has radically changed the evaluation of symptoms referable to the brain and spinal cord. MRI is usually used for the detailed evaluation of lesions and complications due to Chiari II malformations. Chiari II malformations are also diagnosed with the help of CT scan and UltraSonography. CT is especially useful after the neonatal period in following up obstructive hydrocephalus in infants who have undergone a ventriculoperitoneal shunt procedure. Ultrasonography or US, is routinely used during gestation for screening purposes and in the neonatal period for diagnosis and follow up of hydrocephalus
Treatment
Once symptomatic onset occurs, a common treatment is decompression surgery in which a nuerosurgeon usually removes the first and part of the second and sometimes third crevical 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 recognised and accepted. Medications may ease certain symptoms, such as pain but surgery is the only treatment.
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