Chiari malformations: principles of diagnosis and managementBMJ 2019; 365 doi: https://doi.org/10.1136/bmj.l1159 (Published 08 April 2019) Cite this as: BMJ 2019;365:l1159
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With interest I read the article by Rory Piper et al. on Chiari malformations which provides very useful information for non-neurological and non-neurosurgical colleagues. When looking at figure 4, the generic investigation and treatment pathway for Chiari 1 malformation suggests that the mere presence of a hydrocephalus should lead to CSF diversion. However, in the absence of symptoms this could be disputed. Likewise, the pathway suggests that persistent syrinx after foramen magnum decompression should lead to a syrinx shunt. Again, in the absence of symptoms, treatment of only a radiological abnormality could be disputed.
In my experience it is always important to ensure an adequate fourth ventricle CSF outflow when performing a cranio-cervical decompression for Chiari malformation. If necessary by means of a 4th ventricular-subarachnoid or 4th ventricular-pleural shunt. Usually this leads to collaps of the syrinx. When symptoms or syrinx persist despite foramen magnum decompression, additional radiological investigations, including 3D-CISS and 4D-PC sequences, should be performed to study cranio-cervical CSF movement. Only then an informed decision can be made whether additional surgery is advisable, and if so, which procedure would be most indicated.
Nowadays, a syrinx shunt should be a last resort measure only as any surgical procedure obviating the need of a myelotomy is far preferable. Especially the example in figure 2 shows a cervical syrinx which certainly isn't an easy/safe target for a syrinx shunt!
Finally, the generic neurosurgical treatment pathway in Chiari 2 malformation in figure 5 states that foramen magnum decompression is indicated in the presence of symptoms due to CM2, but I would like to emphasize that the foramen magnum typically is unusually large in CM 2, contrary to CM1, due to its embryological genesis, and that the procedure of choice is actually a cervical laminectomy down to the level of the normal spinal cord, i.e. past the lowest limit of the descending tonsils and medullary 'kink'. At the level C1 one quite often finds a constrictive fibrous dural band which should be released. A foramen magnum decompression may actually be quite dangerous as the posterior fossa is very small, with the tentorium at a very steep angle causing the confluens sinuum/torcular to be dangerously close to the posterior rim of the foramen magnum.
Competing interests: No competing interests