Introduction: Chiari I malformation (CMI) is associated with a small posterior cranial fossa (PCF). We have previously documented that CMI is also associated with reduced 4th ventricle volume resulting from a normally developed hindbrain confined in a smaller PCF. Decompression surgery aims to relieve “over-crowdedness” of the PCF. The effect of decompression surgery on the size of the 4th ventricle was assessed by MRI using an automated method for segmentation of the PCF sub-compartments.
Methods: Normative references of PCF and 4th ventricular volume were obtained from 39 healthy subjects (13M: 26F, 35±12 years). Effect of surgery was assessed in 11 CMI patients (3M: 8F, 34±10 years). All patients were operated by the same neurosurgeon. Surgery included suboccipital craniectomy, C1 laminectomy, and pericranial graft duraplasty. Post-operative MRI was obtained at approximately 3 month follow-up. 3D volumetric high resolution T1 and T2-weighted MRI scans obtained on a 3T scanner (TRIO, Siemens) were used for the analysis in conjunction with dedicated software for brain parcellation (FreeSurfer).
Results: Mean and SD of the PCF volumes in the healthy and the patients cohorts were 211±15 and 185±11 mL, respectively. This difference was statistically significant with P< 0.000001. The corresponding mean and SD of the 4th ventricular volumes were 2.2±0.67 and 1.3±0.33mL, respectively (P<0.000001). Following surgery, 4th ventricle volume increased in 9 of the 11 patients, unchanged in one patient, and slightly decreased in one patient. This patient’s symptoms were atypical for CMI. Relative ventricular volume increase ranged from 8 to 178%, with a mean of 46±49% (P < 0.04). Mean post-operative 4th ventricle volume was 1.9±0.71mL. On average, post-operative 4th ventricle volume was within normative reference.
Conclusions: The 4th ventricle volume is significantly reduced in CMI. Decompression surgery that includes suboccipital craniectomy with duraplasty and C1 laminectomy leads to restoration of the 4th ventricle to normative state.
Patient Care: Provides a sensitive measure for the diagnosis and treatment outcome in Chiari I Malformations
Learning Objectives: By conclusion of this session, participants should be able to 1) Learn about automated measurements of the PCF sub compartments by MRI. 2) Learn about the effect of decompression on the 4th ventricle volumes and its relation to surgical outcome in CMI.