Imaging factors affecting early prognosis of syrinx after posterior fossa decompression surgery for Chiari malformation type Ⅰ combined with syringomyelia

English Keywords:Chiari malformation type Ⅰ  Syringomyelia  Posterior fossa decompression  Prognosis  Imaging parameters

English Abstract:

  【Abstract】 Objectives: To investigate the imaging factors influencing the early prognosis of syrinx in patients with Chiari malformation type Ⅰ(CMⅠ) and syringomyelia (SM) who underwent posterior fossa decompression (PFD). Methods: Clinical data of 60 patients with CMⅠ and SM treated in the Department of Neurosurgery of Peking University Third Hospital from March 2013 to November 2022 were analyzed retrospectively. There were 18 males and 42 females with an average age of 48.8±9.1(range, 27-65) years old. All the patients underwent PFD. Imaging assessments were performed preoperatively by cervical spine MRI and X-ray, and parameters were collected, including maximum anterior-posterior and transverse diameters of syrinx, spinal cord anterior-posterior diameter, longitudinal distances of bulbo-pontine sulcus, fourth ventricle and cerebellar tonsil, length of McRae line, length of clivus, clivus-canal angle, C0-C2 and C2-C7 Cobb angles as well as cervical sagittal vertical axis. The maximum syrinx/cord ratio and maximum syrinx area were calculated. Within 1 month postoperatively, the maximum anterior-posterior diameter of syrinx was measured again by cervical spine MRI and its change rate was calculated to evaluate the early prognosis of syrinx. The patients were divided into improved(the change rate≥20%) and unimproved(the change rate<20%) groups. The imaging findings were compared between the two groups, and a multi-variate logistic regression analysis was employed to identify significant predictors. Results: All the patients were followed up for 12.2±7.1d(range, 5-31d). After PFD surgery, 24 cases were improved in syrinx(the improved group), while 36 cases were not improved(the unimproved group). Age and gender were not significantly different between the two groups(P>0.05). Postoperatively, there were 2 cases with fever, 2 cases with transient occipital pain, 4 cases with CSF leakage, 1 case with poor incision healing, and there was no significant difference of overall complication ratio between the two groups(P>0.05). The clivus-canal angle and cervical sagittal vertical axis of CMⅠ patients in improved group(153.47°±9.99°, 22.10±11.10mm) were significantly greater than those of unimproved patients(147.98°±9.55°, 15.83±9.00mm)(P<0.05). The maximum transverse diameter of syrinx in improved group(8.34±3.20mm) was significantly smaller than that of unimproved group(10.36±3.71mm, P<0.05). No significant differences were found in other preoperative imaging parameters(P>0.05). The multi-variate logisitic analysis revealed that the maximum transverse diameter of syrinx before operation was a risk factor of syrinx size reduction(OR=1.281, 95%CI 1.042-1.576, P<0.05), while the offset distance of cervical sagittal vertical axis acted as a protective factor of syrinx size reduction(OR=0.916, 95%CI 0.853-0.984, P<0.05). Conclusions: In patients with CMⅠ and SM, preoperative maximum transverse diameter of syrinx and offset distance of cervical sagittal vertical axis are independent influencing factors for early postoperative prognosis of syrinx.