Hi and welcome to the Chiari forum.
Surgery does not remove Chiari...just helps lessen symptoms and slows progression, so it is possible to require a second surgery.
May I ask, outside of syringomyelia and Chiari do you have any other related conditions?
Related conditions would be, Syringomyelia (syrinx), Ehlers-Danlos Syndrome, POTS, ICP, CCI,tethered cord, bulging disks, scoliosis,retroflexed odontoid,Basilar ingvagnation, sleep apnea,.....as well as the non related conditions lymes, lupus and MS should be ruled out.