The Chiari Malformation (also called the Arnold Chiari Malformation) is a developmental anomaly at the base of the brain which results in the downward displacement of some of the brain's structures into the spinal canal.
It is characterized by a small or misshapen posterior fossa (the compartment in the back of the skull where the brain normally joins to the spinal cord). It is the largest of many such openings in the skull base. These openings serve as passageways through which nerves leaving the brain and blood vessels going to and from the brain can pass.
When a Chiari Malfunction occurs there is a reduction in cerebrospinal fluid pathways and a protrusion of the cerebellar tonsils through the bottom of the skull (foramen magnum) into the spinal canal. The tonsils would normally be round but often become elongated as they protrude down the spinal canal. Diagnosis can be difficult because not all patients will have the classical sign of deeply herniated tonsils.
Chiari Malformations are also known as herniation of the cerebellar tonsils, cerebellar ectopia, hindbrain herniation and Arnold-Chiari malformations.
A German pathologist, Professor Hans Chiari, first described abnormalities of the brain at the junction of the skull with the spine in the 1890's.
These malformations have been subdivided to reflect the degree of displacement as well as the varying etiology of the malformations.
malformations consist of a downward displacement of the cerebellar tonsils (two pegs of tissue which hang off the inferior surface of the cerebellum at the base of the brain) out the inferior opening of the skull into the spinal canal. No other structures of the brain are displaced. There is frequently (30-75%) an associated accumulation of fluid within the interior of the spinal cord.
malformations have greater displacement of brain structures into the spinal canal. In addition to the cerebellum's tonsils there is also displacement of the inferior vermis (bundle of tissue connecting the two halves of the cerebellum), fourth ventricle, choroid plexus and medulla. The displacement is variable but quite frequently can extend down to the mid portion of the neck. Type II malformations are typically part of a larger developmental syndrome associated with myelodysplasia (spina bifida).
malformation is a special type of myelodysplasia where there is a spina bifida (division or defect in the posterior portion of the bony spine) in the neck with an associated herniation of a fluid sac into the overlying defect in tissue closure. Lower structures of the brain herniate into this fluid sac. Type III is the most severe and fortunately the rarest type. It has all the characteristics of the Type II but with additional complications .
Occasionally one hears of a malformation. This refers to a hypoplasia (incomplete development) or aplasia (lack of development) of a portion of the cerebellum and, in fact, is not a hind brain herniation at all in contrast to Types I-III.
Many people with the Chiari Malformation experience no symptoms. When symptoms are present they depend to a certain extent upon the Type of the malfunction present and they may not appear until adolescence or early adulthood. Sometimes, however, they can be seen in young children.
Because of the complexity of the disorder, the symptoms can be as varied as the individual him/herself. Many people experience no symptoms. For others the symptoms are present for months to several years prior to diagnosis.
When symptoms are present they depend to a certain extent upon the Type of the malfunction present. The initial symptoms may be vague and variable. Subjective symptoms may be slowly progressive, leading to misdiagnoses such as multiple sclerosis, myasthenia gravis, or psychiatric disorders.
There are certain general principles that are common to all four types of Chiari Malformation. First, a compression of the brain stem and cerebellum by the bony structures of the skull and upper spinal column will be noticed. Secondly, the spinal fluid will be restricted. The spinal fluid may back up into the other three ventricles causing them to dilate producing a condition called hydrocephalus (or water on the brain). Adhesions around the brain stem and cerebellum caused by scar tissue can further aggravate the situation by creating a strangling effect on the brain stem and cerebellum.
The majority of patients complain of severe head and neck pain. The headache which is associated with Chiari malformation generally begins in the neck, or the skull base area. The pain is generally described as sharp, throbbing or pulsating. Pain radiates throughout the back of the head, into the frontal areas and often around or behind the eyes. The headache may be brought on by cough, sneeze, bending forward or straining. The headache can last from minutes to hours. The headache may be associated with nausea, but usually not vomiting.
Persons may report difficulty swallowing either liquids or solid foods, or a feeling of "catching" in the throat when attempting to swallow. The progression of this symptom may be rapid, suggesting the possibility of aspiration if undetected. If you have this symptom, your health care provider should be notified as soon as possible.
Persons may also complain of neck or upper extremity (arm) pain. Often, the pain is worse with exertion, fatigue, or lifting. Pain can be described as dull and aching, or shooting and stabbing. Pain on one side is more commonly reported than pain on both sides equally. Along with the pain, some patients experience weakness of the hand or arm, or incoordination of fine movements of the hand.
Changes in voice character and timbre is a common complaint. Hoarseness is often noted first by the person's friends or family members. Some persons will report inability to modulate the voice for singing or speaking loudly. Slurred speech has been reported, however, this is a less common complaint.
Tingling, numbness or pins and needles (proprioceptive disturbances)sensation can also accompany the pain, usually in the same areas as the pain. Again, the numbness is generally on one side only. Numbness can progress over months to years to involve the lower extremities and trunk.
Although some persons do not report any visual changes, others may complain of disturbances from blurred to double vision (diplopia). Physical examination may reveal nystagmus (involuntary eye movements). This is often described by the person as "bobbing" of the eyes when looking downward or to the side. Difficulty driving or reading may be reported by the person, due to "blind spots" in the eyes. Some patients experience difficulty in tracking objects or a hypersensitivity to bright lights.
This gait disturbance can be described as unsteadiness, or listing to one side. Persons may report falling, or bumping into walls or doors when walking. Infrequently, patients may present with spasticity (stiffness) of the lower extremities, which results in gait disturbance.
Episodes of passing out or loss of consciousness are reported in the literature, however, this is a less common complaint. The episodes are unpredictable and brief, lasting from 30 seconds to 2 minutes, associated with loss of consciousness, and prompt, complete recovery. Drop attacks have been also been reported in the literature, however, less commonly in the adult population. There are generally no symptoms of seizure and no state of confusion after the event. Persons may also complain of occasional vertigo, without loss of consciousness.
Various other symptoms may occur, which may include nausea, vomiting, dizziness, dysequilibrium, muscle weakness, nosebleeds, fast or slow heart beat, high or low blood pressure, ringing in the ears, hearing loss, depression, shortness of breath, fatigue and balance problems. There may also be excessive drooling, irritability during feedings, slow intake, pouching, gaging or vomiting, vocal paralysis, sleep apnea and/or failure to gain weight.
In early infancy the initial symptom is intermittent apnea (cessation of breathing). Progressive weakness of the upper extremities, trunk and lower extremities frequently follows and the infant becomes floppy and limp. If treatment is not instituted promptly, the situation may disintegrate into a ventilator-dependent vegetative state or death.
The Chiari Malformations may also be associated with other disorders such as hydrocephalus (build up of fluid in the ventricles of the brain) or Syringomyelia. Hydrocephalus, when it occurs, can further displace the brain stem and cerebellum stretching one or more cranial nerves.
It is not unusual for the Chiari Malformations to have an associated accumulation of fluid within the interior of the spinal cord, forming a cavity known as a syrinx. This condition is termed or . The condition ultimately results in progressive formation intramedullary (referring to the interior of the spinal cord or brainstem) cyst associated with progressive neurological deficits. While there are other reasons for cysts to occur within the spinal cord (trauma, tumor), the bulk of cysts which occur in the spinal cord are due to anomalies in the anatomy at the skull base. It is recommended that patients diagnosed with a Chiari Malformation have the entire spine imaged to rule out the presence of a syrinx, since it may be a consideration in treatment and prognosis.
When a patient presents to the doctor with findings suggesting the presence of a Chiari malformation, the next step is to perform diagnostic tests to confirm the diagnosis. The test most frequently used is the MRI scan. Bony changes in the skull and upper spine seen on X-rays are often diagnostic of the malformation. Asymptomatic malformation should be left alone.
The object of treatment is to stop progression and hopefully relieve symptoms. This may be accomplished by: 1) decompression of the neural structures, the brain stem and cerebellum and 2) re-establishment of spinal fluid circulation if it is affected. Decompression is achieved by removing the bony structures compressing the brain stem and cerebellum. Re-establishment of spinal fluid circulation may be established in a variety of ways. Treatment of the different disorders are diverse but generally involve a posterior decompression, a shunt, or a combination of both.
Techniques are quite diversified amongst neurosurgeons, and patient responses vary greatly. A successful surgery will alleviate pressure on the neural elements and may result in an improvement of symptoms.
The decision to treat a Chiari Malformation surgically requires careful consultation between patient and physician. Factors to be considered are the patient's current neurological condition and progression of symptoms over a period of time.
Research into the risk of inheritance for the Type I Chiari Malformation is still in its early stages. In some families, more than one member has been documented to have the Type I Chiari Malformation. Familial recurrences are suggestive of a possible genetic component of the condition, but unfortunately there is no conclusive answer to the question of inheritance at this time. It is currently recommended that only those relatives experiencing symptoms commonly associated with the Type I Chiari Malformation need undergo investigational procedures.