Intraoperative Phase Contrast MRI Analysis of Cerebrospinal Fluid Velocities During Posterior Fossa Decompression for Chiari I Malformation.

BACKGROUND: Cerebrospinal fluid (CSF) velocity at the craniovertebral junction (CVJ) is known to be altered in patients with Chiari I malformation (CMI), and normalization of CSF velocities is associated with symptom resolution. However, preoperative and intraoperative prediction methods have thus far failed to identify patients in whom CSF velocities can be normalized with posterior fossa decompression (PFD) without duraplasty. Phase contrast MRI (PC-MRI) may assist not only in diagnosis of CMI but also in guiding the intraoperative decision to perform duraplasty during PFD.

PURPOSE: To use intraoperative MRI data to quantify changes in CSF hydrodynamics at the CVJ during each step of PFD with duraplasty (PFDD) in 12 consecutive patients.

STUDY TYPE: Retrospective case series with all patients imaged before, during and after decompression, and all data analyzed postprocedure.

POPULATION/SUBJECTS: Pediatric patients, mean age 14 years (range 4-18), undergoing PFD for CMI.

FIELD STRENGTH/SEQUENCE: Intraoperative studies involved a dedicated 1.5T Siemens MRI imager. PC-MRI scans were in the axial plane at the CVJ.

ASSESSMENT: Two observers assessed measurements.

STATISTICAL TEST: The equality of matched pairs of observations was tested using the Wilcoxon matched-pairs signed-ranks test.

RESULTS: Data analyses of the PC-MRI demonstrated a marked and immediate increase in CSF velocity at the posterior CVJ during PFDD. Mean cranially-directed velocities increased by a mean of 1.049cm/s (P = 0.028) from preincision to postoperative measurement. There was a mean 0.45 cm/s (P = 0.022) increase in mean cranial velocity from preincision to bone decompression scans, and a mean 0.48 cm/s (P = 0.018) increase in mean velocity from preincision to duraplasty.

DATA CONCLUSION: In all subjects, significant increases in the mean and peak velocities of cranially- and caudally-directed velocities were observed from preincision to post-PFDD scans at the posterior CVJ.

LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 4.