Supplemental Digital Content: MRI and Calculations
MRI was performed with a 1.5T magnet (GE Milwaukee, WI). MRI studies included sagittal T1-weighted
images (fast spin echo, repetition time (TR) 467-2626 msec/echo, echo time (TE1/TE2) 10.1 msec, echo
train length (ETL) 1-6 and number of excitation 1-2. Sagittal T2 weighted images (fast echo; TR 3200-6887
msec/echo, TE1/TE 2110-119 msec, ETL 24-33 and number of excitation 1-2. Slice thickness 3-3.5 and
Matrix 512-224.; All MRI scans were analysed independently by two neurosurgeons using image analysis
software (Image J, free software National Institutes of Health). The Surgeons (BA and DM) were blinded to
patients name, demographics, clinical and functional status. Sagittal T1 and T2 were analysed for the
presence of signal change. Type of T2 signal change was categorised as follows: No signal change (0),
diffuse signal change (1), focal signal change (2), and multiple focal T2 signal change (Figure 1). Signal
intensity within the cord was compared to a consistent CSF signal location outside the cord (immediately
posterior to the dense on mid sagittal T2 image. The signal was termed diffuse if the intensity was less than
75% CSF signal and focal if it was greater than 75%). Using these strict criteria, excellent consensus was
obtained among observers. In only two cases (out of total 57) there was a disagreement in the presence of
low T1 signal change. This was settled by consensus. Other T2 signal parameters measured were the
number of sagittal cuts in which the signal change was present (N), the maximum height of signal change
(H) and maximum area of signal change (A). The degree of cord compression and canal compromise (MCC
and MSCC) were measured on mid sagittal MRI views 27,28 . Briefly, the mid sagittal distance in the most
compressed region for both the canal diameter (Di) and the cord diameter (di) was measured. This was
fractionalised as a percentage of an average of the non-compressed areas above and below the compression
region (Da and Db and da db for the spinal canal and the spinal cord respectively) using the following
equations.
MCC = 1- [(Di/ (Da+Db)/2] x 100
MSCC = 1- [(di/ (da+db)/2] x 100