This chapter is addressed to the description of the forms of caudal herniation through the foramen magnum different from Chiari type I malformation, which is largely the most common variant of hindbrain herniation. Prompt decompression of a meningomyelocele in patients under the age of 2 years can lead to a significant reduction in mortality and morbidity. Studies suggest that early surgery in type II malformation results in a better outcome. Chiari-related syringomyelia can be treated successfully with surgery.Patients most likely to benefit from surgery are those with reproducible neurological signs - eg, nystagmus, absent gag reflex, and demonstrably abnormal CSF flow in the hindbrain on cine MRI.Management of hydrocephalus alone is often sufficient and may obviate decompression, although a significant proportion of patients will still need both procedures. It may be effective as a primary treatment.
However, endoscopic third ventriculostomy provides a suitable alternative. A shunt is usually inserted in the presence of a large syrinx with or without hydrocephalus.Decompression of the foramen magnum gives good results in terms of arresting deterioration.Suboccipital craniectomy and upper cervical laminectomy to decompress the malformation at the foramen magnum are usually required with cord drainage and institution of drainage of the fourth ventricle, if necessary.A decision regarding surgery should be taken on reviewing these opinions together with the imaging results.A multidisciplinary assessment is helpful, with neurologists, neurosurgeons and rheumatologists all giving an opinion about the patient.How does the malformation relate to physical symptoms?Ī decision on whether to proceed to surgery should be based on the following approach:.The main issues to be determined in the management of a patient with a Chiari I malformation are: Various abnormalities of the skull and upper vertebrae are found in 25-50%.Symptoms include central cord syndrome, impaired sensation, impaired motor control, gait disturbance, torticollis, bowel and/or bladder symptoms, neuropathic joints, trophic phenomena and pain. Problems of the spinal cord present in about 95% of patients with syringomyelia and two thirds of those without it.Compression of the hindbrain can cause weakness, paraesthesia, ataxia, cranial nerve palsies, dysphagia, dysphasia, palpitations, syncope, apnoea and sudden death.Dizziness, vertigo, disturbance of hearing and nystagmus may develop.Bilateral hearing loss has been reported.Pain behind the eyes, visual disturbances, diplopia and photophobia can occur.The hydrodynamics of the cerebrospinal fluid (CSF) are upset, possibly causing caudal to cranial flow and this is a contributor to symptoms. The presentation of this condition depends upon the severity of the herniation and associated other features. Only found in association with myelomeningocele. Chiari type II (Arnold-Chiari malformation) It tends to present earlier if there is syringomyelia. Retrospective investigation of brain MRIs has found a prevalence of 1 in 1,280 individuals. Some authors have added a severe form of cerebellar hypoplasia without displacement of brain through the foramen magnum and called it Chiari IV malformation.Ī case of acquired Chiari malformation secondary to skull hyperostosis has been described. He also described a single case of cervical spina bifida with herniation of the cerebellum through the foramen magnum, now called Chiari III malformation. About 25% have distension of the central or paracentral canal of the cervical spinal cord, causing hydromyelia or syringomyelia. 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. It is now called the Chiari type II, or Arnold-Chiari malformation. Abnormalities of the skull and upper vertebrae are common in this type.įive years later he reported a complex congenital malformation of the brain, nearly always associated with myelomeningocele. This is now called the Chiari type I malformation.
He first described an abnormality of elongated peg-like cerebellar tonsils that are displaced into the upper cervical canal through the foramen magnum. Hans Chiari was a German pathologist who, between 18, described various anomalies of the caudal cerebellum and brain stem from post-mortem studies.
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