Chiari, Part 2 of 6: The Chiari I Malformation
Chiari I is very likely an acquired problem, that is, it is not present at birth but develops sometime later. The descent of the tonsils may actually fluctuate by several mm on any given day. Chiari I may also result from increased pressure within the skull itself, perhaps caused by hydrocephalus or tumor. These problems are usually obvious and in such a case the Chiari I will resolve following their treatment and without specific Chiari decompression surgery.
Symptoms associated with Chiari I vary from nothing at all (asymptomatic), to nonspecific headaches, to more ominous clumsiness or tingling in the hands. Occasionally, a person will have trouble with swallowing or gagging when eating, but these are unusual. Idiopathic scoliosis may be caused by Chiari I when advanced syringomyelia is present. Syringomyelia will be discussed in another section of this monograph.
Chiari I is a relatively common diagnosis, though whether or not treatment is necessary in a given situation may be controversial. If there is associated headache, it is usually suboccipital in location (across the back of the head), and worsens with coughing, sneezing, and sometimes straining at stool. The upper neck may be sore.
Headache is very common in the general population and Chiari I is very often asymptomatic. Lots of people have headache, a few people have Chiari I, and occasionally the two groups overlap. This does not mean they are associated and in the absence of other symptoms, the headache should be treated symptomatically (with medications, etc.) without surgical intervention. Very often the headaches will resolve and the Chiari is considered incidental and need not be treated.
To be specific: headache is a very nonspecific symptom and when present with Chiari I does not in and of itself mandate surgical treatment.
Some patients with Chiari I complain of clumsiness in the hands, +/- tingling. On MRI (the definitive imaging study for all forms of Chiari) such patients generally demonstrate crowding at the level of the foramen magnum, as well as decent of the tonsils greater than 5 mm. The degree of crowding is important, as it may indicate a degree of chronic brainstem compression, which can be detrimental over time. In fact, decent of the tonsils without any significant crowding at the level of the foramen magnum is probably not a serious affair.
Pressure on the brainstem is likely responsible for the clumsiness in the hands and, when present, for the trouble swallowing. I have had one teenage patient who was entirely unable to eat or drink without significant gagging over a period of four years. He could not even sip water from a fountain at school. After treating him with a Chairi decompression (described later), these symptoms resolved entirely.
Chronic crowding at the level of the foramen magnum seems to interfere with the normal circulation of CSF at the skull base, creating a differential between the spinal canal and the intracranial space. This differential leads to forces within the spinal cord and brainstem which, over time, can enlarge the normally microscopic central canal. This situation leads to syringomyelia, a potential serious condition in which the function of the spinal cord slowly deteriorates with time.
Note that Chiari I is not associated with spinal abnormalities like tethered cord or myelomeningocele. Nor is hydrocephalus generally present, though it can be and if so should be treated in lieu of the Chiari I. The Chiari I is likely to resolve with effective treatment of the hydrocephalus.
As a rule, Chiari I is not associated with cognitive difficulties. Patients have normal thinking and are not developmentally delayed.
Next time: The Chiari II Malformation