Chiari malformation is a herniation of the lower part of the brain, called the tonsils, through the space at the base of the skull into the spinal canal. The herniated tissue affects the circulation of cerebrospinal fluid and causes symptoms. This is characterized by the accumulation of cerebrospinal fluid in the brain or spinal cord.
Chiari malformation is analyzed in 3 categories. This categorization is based on the level at which the cerebellum descends into the spinal canal and which tissues are anatomically located in the spinal canal. The treatment of Chiari malformation varies according to its form, the complaint it causes and the neurological symptoms of the patient. Follow-up or surgical treatment method is applied.
What are the Symptoms of Chiari Disease?
Headache is among the primary symptoms of Chiari malformation. Apart from this, we can list the symptoms as follows;
- Neck pain
- Headache
- Difficulty swallowing
- Weakness in the arms
- Difficult to feel pain and heat
Depending on the type and degree of Chiari malformation, sometimes very serious problems can arise.
What are the Diagnostic Methods for Chiari Disease?
Since bony anomalies such as basilar invagination, Klippel-Feil, occipitalization of the atlas can be found at the craniocervical junction in 25% of cases, the craniovertebral junction should be evaluated with direct radiographs and computed tomography. MRI is the imaging modality of choice because it is reliable, specific, noninvasive and can show both tonsillar herniation and anomalies at the craniovertebral junction, such as hydro syringomyelia, which is associated in approximately 30% of cases. In type I malformation, cerebellar tonsillar herniation is the main finding and the cerebellar tonsils are herniated more than 3 mm from the foramen magnum into the upper cervical canal, while the vermis, IV ventricle and bulbus show normal or minimal deformation. Measurement of ventricular dimensions in Chiari I cases is important in terms of detecting hydrocephalus in rare cases and affects the treatment protocol.
How is Chiari Disease Treated?
Clinical findings in Chiari I cases progress slowly but progressively. The aim of the surgical approach is to correct the clinical picture and syringomyelic cavity, if present. The presence of hydrocephalus, ventral brainstem compression and congenital cervical instability should be investigated before surgery.
The methods used in the treatment of Chiari I have changed in parallel with physiopathologic studies. Decompression of the posterior fossa and expansion of the cisterna magna with dura graft is the most commonly used technique in recent years. Cervical laminectomy can be combined with posterior fossa decompression depending on the level of herniation. Since the main task is to release the tonsils from compression, the level of herniation of the cerebellar tonsils should be evaluated well before the operation. Dural graft is performed to provide more space for existing structures such as tonsils and bulbus.
The physiopathologic mechanism of syrinx cavity formation in cases with uncomplicated posterior fossa decompression and duraplasty is the impaired CSF circulation in the posterior fossa and the expansion of the cavity by the piston effect of the cerebellar tonsils. Thus, in addition to explaining the formation of a syrinx cavity when the obex is closed, it also suggests that the cavity may not be communicating. In the literature, it has been reported that sagittal and horizontal longitudinal septa may be present in the cavity of the cirrhincter and therefore, its coexistence should be investigated preoperatively with endomyelography.
In addition to the function of the syrinx cavity, syrongostomy (fenestration, usually using the dorsal root entry area DREZ, with or without the use of a stent or shunt), terminal ventriculostomy, and opening of the foramen magendi if obstruction is present may be performed in the same session or in a second operation. There are even some who argue that in cases with a large syrinx cavity, it is more accurate to apply syringosubarachnoid shunt without decompression of the posterior fossa.
In unsuccessful cases, in addition to posterior fossa decompression and dural grafting, Gardner's operation, which consists of removal of intraarachnoidal adhesions and closure of the obex with muscle and Teflon, has been advocated to be sufficient. There are also those who argue that fibrous adhesions between the dura, arachnoid and tonsils should be removed. At this stage, attention should be paid to the posterior inferior cerebellar artery and its branches.
Partial resection of the cerebellar tonsils with decompression of the posterior fossa and closure of the obex may be beneficial, although there have been reports that closure of the obex does not affect the outcome of treatment. It has also been reported that resection of the cerebellar tonsils is not beneficial for enlargement of the cisterna magna, i.e. normalization of CSF circulation.
The cases with good surgical results are those with mild weakness, pain and scoliosis in the preoperative period. The results are not encouraging in patients with prolonged complaints, sensory deficits due to posterior cord involvement, muscle atrophy and orthopedic deformities of the foot.
Good results are seen in patients with cerebellar syndrome. Important postoperative complications include progressive cervical kyphosis, instability due to congenital bone anomalies, aseptic meningitis, pseudomeningocele, sleep apnea, lung bleeding and postoperative pain in the occipital region.
The degree of herniation of the cerebellar tonsils, possible concomitant syringohydromyelia, hydrocephalus and craniovertebral junction anomalies should be well evaluated with direct radiographs, CT, MRI, Cine MRI, endomyelography and correlated with the complaints in Chiari I cases in the preoperative period.
Although reported in different ways in the literature, the first surgical approach to Chiari I cases is basically posterior fossa decompression and dural grafting. The aim is improvement in the clinical picture and disappearance of syringomyelic cavity, if any. Accordingly, radiologically defined Chiari I cases should be followed up with posterior fossa decompression and dural grafting if asymptomatic and syringomyelic cavity is present. If hydrocephalus is present in symptomatic patients, a V-P shunt should be inserted; if the syrinx is present in symptomatic patients without hydrocephalus, posterior fossa decompression, dural grafting and drainage of the syrinx (fenestration, stent or shunt) should be performed. In symptomatic patients without hydrocephalus, if the syrinx is absent, posterior fossa decompression and dural grafting should be performed classically and followed clinically and radiologically. If symptomatic patients with ventral compression are present, transoral decompression should be performed.