In the 21st Century, the diagnoses of Syringomyelia (SM) and Chiari Malformation (CM) have become more frequent, in part due to the improvements in brain and spine imaging by MRI. MRI is a radiology study that does not use x-rays, but instead applies magnetic fields to image any part of the body. To date there are no scientific studies that show exposure to magnetic fields from MRI is dangerous to a person’s health, provided the patient doesn’t have certain kinds of metallic implants. The definition and detail provided by MRI is unsurpassed by any other technology currently available and is the “gold standard” for the diagnosis of a CM or SM. Patients with SM and CM will undergo an MRI of their brain and spine during their evaluation. MRI is a more expensive test than a CAT scan (CT), but it provides the physician the best chance of making an accurate diagnosis. An MRI requires a patient to lie very still in a tunnel-shaped tube for approximately 20-30 minutes. This can be very difficult for some patients, especially if they are claustrophobic and fear confined spaces. Such patients should request sedation, such as valium or another anti-anxiety drug, prescribed by their doctor prior to entering the “tunnel.” Children less than five years of age often need IV or oral sedation to lie still. Young children should be scanned only at MRI centers that can provide nurses or physicians experienced in monitoring these during the sedation process. In the case of infants who need general anesthesia, one should seek a hospital experienced in providing general anesthesia to pediatric patients.
An MRI of the brain and spine will tell whether or not a patient has CM and/or SM, or any other abnormality of the brain that may cause similar descent of the cerebellar tonsils approximately 3-5mm or more below the opening in the bottom of the skull. A physician is also looking for other potentially treatable causes of CM, such as hydrocephalus. Hydrocephalus is a rare finding in Chiari I malformations but a very common finding in Chiari II malformation, such as patients with myelomeningocle/spina bifida. Hydrocephalus is a condition in which there is too much cerebrospinal fluid (CSF) in the brain, causing the fluid-filled cavities in the brain (ventricles) to enlarge and thus compress the brain. Other causes of tonsillar descent include mass lesions in the brain such as brain tumors or craniofacial abnormalities. Fortunately, these other causes of Chiari malformation are relatively rare. A “screening” MRI of the spine is important because it can establish the diagnosis of SM, which is associated with CM I in 10-60% of patients in recent surgical series. SM, which is a cavitation in the spinal cord, can be associated with CM, in both children and adults. A screening spine MRI should be taken in every patient with CM. Children with an unusual scoliosis (curvature of the spine) may come to a physician’s attention when the scoliosis rapidly progresses on exam and/or plain x-ray films. The early and timely treatment of a Chiari malformation in a child with progressive scoliosis can yield a good result, in terms of halting the progression of the spine deformity. These children should also have an MRI of the spine to assist in ruling out SM, which may be contributing to the progressive spine deformity.
Patients who have had a traumatic spine injury in the past and who begin to note worsening of their symptoms or deterioration of their neurological function should have an MRI of the spine to assess whether or not they have SM. The imaging diagnosis of CM is often, but not always, straightforward. However, these studies should always be interpreted by a physician in the context of the patient’s symptoms and neurological exam. An MRI is a powerful tool, but it is just one objective test used by the treating physician to secure the diagnosis and direct appropriate treatment. Thus, surgical treatment of CM and SM requires an experienced neurosurgeon to put the patient’s symptoms together with the neurological examination, prior to recommending surgery. The experienced neurosurgeon looks at the three tools available to him/her before recommending surgical intervention. Each tool provides the patient with confidence in the diagnosis, just as the presence of each of the three legs in a three-legged stool provides improved stability to the stool.
The three legs for appropriate diagnosis and treatment of CM and SM are: 1) the patient’s history of the specific characteristic symptoms that brought them to the neurosurgeon, 2) the patient’s examination that shows signs consistent with CM and/or SM and 3) a head and spine MRI demonstrating the characteristic anatomy of CM and/or SM. One leg alone or two legs of this three-legged stool does not uniformly provide the neurosurgeon with enough data to recommend surgery with certainty. Descent (herniation) of the cerebellar tonsils on the MRI 3-5 mm or more below the level of the foramen magnum (skull opening) constitutes the generally accepted radiological diagnosis is of CM. [2, 4-8] When tonsillar descent is 5 mm or more and there is associated SM of the spinal cord, the diagnoses of CM/S are easily secured. Patients with CM and tonsillar descent of more than 5 mm often show compression and deformation of the tonsils. In fact, the tonsils may be peglike and also may compress the brainstem and spinal cord, which helps confirm the diagnosis of CM. However, patients may have tonsillar descent of less than 5 mm, without SM. In these patients, symptoms such as persistently severe headache at the back of the head that are aggravated by exercise or straining help improve the certainty of the diagnosis of a symptomatic CM. There are certainly “gray” areas in the diagnosis of CM, which engender controversy on this subject and may confuse.
A very small number of patients may have minimal or almost no tonsillar descent on the MRI, but may have SM. This is called “Chiari 0”. The original description of this entity included 5 patients, each with a syrinx but no hindbrain herniation. Chiari 0 patients may also have all the symptoms of a CM I. When this extremely rare and relatively new diagnosis is entertained, a patient may benefit from a posterior fossa decompression that results in subsequent collapse of associated SM. In CM patients or in any patient suspected of a CM, a special test called a cine-MRI (or cine MRI CSF flow study) can be performed to help improve the certainty of their diagnosis. The cine MRI is a dynamic picture of the brain that shows the movement of CSF around the brain in the region under question, the cerebellar tonsils. It also shows the piston like movement of the cerebellar tonsils. It is essentially a movie of all the MRI pictures taken on a patient. The series of MRI pictures is arranged in a movie format that shows the obstruction of movement of CSF caused by the peg like cerebellar tonsils.
In addition, the cine MRI in a CM patient will show the piston like movement of the cerebellar tonsils in the posterior fossa obstructing the normal flow of CSF through the foramen magnum from the brain into the space around the spinal cord. It takes slightly more time for the patient than a standard MRI, and requires special computer software and physicians with experience viewing and interpreting this type of MRI. Many but not all MRI facilities possess the ability to perform a cine MRI. In some patients, the cine MRI may show a “tight” posterior fossa and obstruction or diminished flow of CSF flow at foramen magnum. Since all the variations of the operations to treat a CM I attempt to correct the “tight” or small posterior fossa and improve CSF flow in the back of the cerebellum, the cine MRI is yet another modern tool that helps guide the physician and improve the certainty of the diagnosis.After a successful decompression, the cine-MRI often shows return of near normal CSF flow behind the cerebellum. Not all neurosurgeons use the cine MR for diagnosis. Some institutions use the cine MRI to follow patients postoperatively. In the successful postoperative state for a patient, the cine MRI shows improvement in the CSF flow compared to the obstructed preoperative situation. In patients whose operation for CM and/or SM has failed or just has not improved all the symptoms, a cine MRI is a very useful tool to figure out whether obstruction to CSF flow or compression of the brain persists. A full spine MRI should be requested in a patient with CM and/or SM. Some physicians prefer that the brain and spine study be performed with contrast (gadolinium) to improve the quality of the exam. The neurosurgeon is trying to rule out a mass lesion such as a tumor (rare) or a tethered cord (less uncommon). A tethered cord is a congenital Cine MRI: A child with severe breathing problems and syringomyelia with minimal tonsillar descent, consistent with the diagnosis of Chiari 0. condition in which the spinal cord ends too low in the spinal canal, i.e., below the mid body of lumbar level 1 instead of above that level. The mechanical stretch from a true tethered cord causes stretch on the brain thus contributing to the descent of the cerebellar tonsils. Tethered cord is a rare and controversial cause or associated finding in patients with CM. The treatment of such patients often entails cutting the filum terminale which is the connection holding the cord too tightly, prior to treating the Chiari malformation. Another test called a myelogram occasionally may be used in the diagnosis of SM. Although this test has been largely replaced by the MRI, it still may be useful in patients with difficult to treat SM, or in patients who cannot have an MRI due to metallic implants such as certain artificial joints. A myelogram is an invasive test performed by a skilled radiologist, who injects contrast into the CSF space around the spinal cord, usually by a lumbar puncture. The test is safe but can be uncomfortable. The patient often receives local anesthetic and sometimes IV sedation prior to performing the lumbar puncture. The contrast agent is water-soluble and mixes with the CSF and goes everywhere the CSF flows. X-rays as well as a CT scan are performed after the contrast agent is injected to see how and where the contrast agent has flowed. This test can show where there is a block of contrast agent and thus CSF flow, and what structure is causing this block. Thus, the myelogram and CT scan pictures can guide surgical treatment of this area of flow obstruction. Scarring of the nerve roots (arachnoiditis) can also be diagnosed by this test, or by MRI, and may be of use in deciding whether or not a patient with isolated SM may benefit from surgery.[8, 13] In summary, if a physician is considering the diagnosis of CM and/or SM, an MRI of the brain and spine is indicated. The interpretation of this test by an experienced radiologist and neurosurgeon is essential prior to any surgical treatment. In addition, these tests must always be viewed in the context of the patient’s complaints and neurological deficits in order to decide whether or not surgery is required.
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