Chiari Malformation & Syringomyelia Program

Chiari malformation is a spectrum of disorders occurring in children with or without myelomeningocele.

Chiari II malformation is the form seen in association with myelomeningocele and is the result of differential growth patterns in the hindbrain (brainstem and cerebellum) and the bones of the posterior fossa presumed due to the loss of cerebrospinal fluid during embryonic life. All large series of myelomeningocele infants report a proportion of infants having brain stem dysfunction. This is presumed due to compression of the Chiari malformation. Work done by the Division has thrown this presumption into question in particular reference to expiratory apnea. For lesser degrees of medullary dysfunction, posterior fossa decompression is used following the establishment of optimal CSF drainage. Partial or complete recovery has been achieved in these patients. Of interest, long term craniocervical instability has not been a problem seen in these patients following decompressive laminectomy or expansion laminoplasty.

Older children with Chiari II malformation may require treatment for hydromyelia, hydrobulbia, progressive cranial nerve dysfunction or quadriparesis. Decompression of the hindbrain hernia and reconstitution of the “cisterna magna” has been used successfully in those children and teenagers who do not have arachnoiditis in the basal cisterns. Shunting of the fourth ventricle to the cervical subarachnoid space may or may not be necessary.

Chiari I malformation is usually found in children without myelomeningocele. This malformation is often associated with syringomyelia/hydromyelia (fluid within the spinal cord), or syringobulbia. Children typically present as teenagers, and the symptoms are variable. They include scoliosis, back pain, numbness in the chest or upper limbs, weakness in the upper and/or lower limbs, unsteadiness, occipital headache, and cranial nerve dysfunction, particularly swallowing difficulties and tongue weakness. The diagnosis is made readily by MR imaging . Sometimes the Chiari malformation is identified on a MR scan done for other reasons, and there are no symptoms related to the malformation.

In situations where the volume of the posterior fossa content can be changed, for example by treating a Vein of Galen arteriovenous malformation, Chiari I malformation may resolve. Other situations occur rarely and include cerebellar venous congestion following status epilepticus.

Not all children with Chiari I malformation require operative intervention. Where surgical intervention is recommended, the Division of Neurosurgery has a developed a consistent surgical approach to this problem based on experience over many years and the options that are reported in the literature. It is our goal to re-establish CSF flow from the fourth ventricle and reconstitute the cisterna magna based on the clinical and experimental evidence that either CSF outflow is impaired, as evidenced by an associated syrinx or that the posterior fossa is too small for the volume of the posterior fossa content. Intraoperative imaging is used to guide the extent of operation. The procedure begins with small posterior fossa bony decompression. Intraoperative ultrasound is used to assess the size of the cisterna magna and the compression on the hindbrain hernia. If, as the assessment is done, there is no dural relaxation and decompression of the neural structures, the dura is opened and plans made for dural patching with the patients own tissues. At this time, the arachnoid surrounding the brainstem and herniated cerebellar tonsils is inspected and the outlet of the fourth ventricle is assessed. If there is syringomyelia and if the outlet of the fourth ventricle is closed with arachnoid adhesions, the foramen is opened and one or more of the tonsils may be resected to achieve decompression of the neural structures, reconstitution of the cisterna magna and free CSF flow form the fourth ventricle.

Post operatively, children are placed in a collar when up, largely for comfort. Post operative evaluations are performed at 2-3 months, with repeat MR imaging . Re-operation is considered if the syrinx decompression is not demonstrated by 12 months.

Re-operation may be entail repeat posterior fossa exploration with or without fourth ventricle shunting or syringo-subarachnoid shunting. Syringo-pleural or syringo-peritoneal shunting has not been found to be necessary.

Over the past two decades, 50 patients with Chiari I malformation have been treated at BCCH. Resolution of clinical symptoms has been achieved in all patients. Only three patients have required repeat operation.