Anatomical characteristics of posterior cranial fossa and surgical outcomes in patients with Chiari I malformation

Abstract

Objective To discuss the anatomical characteristics of posterior cranial fossa and surgical outcomes in patients with Chiari Ⅰ malformation. Methods Thirty-eight patients diagnosed with Chiari I malformation were admitted to Department of Neurosurgery, General Hospital of Tianjin Medical University from January 2015 to December 2017 and retrospectively enrolled into the patient group of this study, whose clinical data were compared with those of 30 radiologically healthy persons (as controls) admitted to physical examination center of the same hospital during the same period. Two groups of people underwent cervical MRI scan and 3D reconstruction. Clivus length, Mcrae line, Twing line, length of squamousal part of occipital bone, basal angle, Boogard angle, cerebellar volume (CV), posterior cranial fossa volume (PV) and ratio of CV/PV were measured and their anatomical differences were compared between 2 groups according to volume analysis software. Thirty-seven patients were treated with posterior cranial fossa decompression and C1 laminectomy in patient group, and the remaining 1 patient did not undergo relevant treatment. All patients underwent follow-up in outpatient department, an imaging review of cranial-cervical junction MRI and assessment based on cervical Japanese Orthopaedic Association (JOA) scale to assess the improvement of syringomyelia-related symptoms. The outcomes were classified into excellent, good, stable and poor. Results There was no significant difference in age or gender (P>0.05). Compared with healthy control group, PV was decreased (170.7±10.7 mm3vs. 186.8±9.8 mm3), ratio of CV/PV was increased 0.755±0.042 vs. 0.682±0.036, clivus length was shortened (3.9±0.3 mm vs. 4.4±0.3 mm), and Boogard angle was increased (124.2±8.2° vs. 116.6±3.6°) in the patient group (all P 0.05). All 37 patients underwent successful operation. There were no cases of new neurological deficits or death after operation. At 12 weeks post surgery, the JOA score was improved compared with preoperative conditions (15.20±2.36 points vs.11.71±2.92 points. P<0.05). The follow-up duration of 37 patients was 15.2 ± 6.8 months and ranged from 6 to 30 months. At the last follow-up, the improvement rate of syringomyelia-related symptoms was 69.9±29.0%. The outcomes were determined as excellent in 20 (54.1%) patients, good in 11 (29.7%) and stable in 6 (16.2%). Conclusions The decrease of posterior fossa volume and increase of ratio of cerebellar volume and posterior cranial fossa volume could be important factors in Chiari Ⅰ malformation contributing to cerebellar tonsillar herniation. The surgery of posterior fossa decompression could effectively improve clinical symptoms. Key words: Arnold-Chiari malformation; Cranial fossa, posterior; Anatomy; Neurosurgical procedures; Treatment outcome