Syrinx of the Spinal Cord or Brain Stem By Michael Rubin, MDCM, New York Presbyterian Hospital-Cornell Medical Center Reviewed / Revised Feb 2023 View Patient Education Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Cervicothoracic Syringohydromyeli... A syrinx is a fluid-filled cavity within the spinal cord (syringomyelia) or brain stem (syringobulbia).