Hi rodemooney,
There is no necessary reason why a diver who undergoes successful repair of a Chiari malformation without complications could not return to scuba once all healing is complete, the treating neurosurgeon okays it, he feels up to it and is physically fit to do so.
The diver who is cleared for return to scuba will want to carefully monitor any residual signs and symptoms so that the effects of the operated condition are not confused with decompression illness (DCI) or vice-versa.
Also, there is at least the theoretical concern of increased risk of DCI due to disordered spinal blood flow secondary to a history of surgical intervention. While there is very limited evidence for concern, conservative post-treatment dive profiles would be prudent.
Regards,
DocVikingo
This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual, and should not be construed as such.