Effects of Image Plane, Patient Positioning, and Foraminal Zone on Magnetic Resonance Imaging Measurements of Canine Lumbosacral Intervertebral Foramina

Abstract

Degenerative lumbosacral stenosis has been suspected to have a dynamic component, especially regarding encroachment of the L7 nerve roots exiting the lumbosacral foramina. Angled cross-sectional imaging of the neuroforamina has been found improve the accuracy of the diagnosis of stenosis in humans. In this anatomic study, foraminal apertures were evaluated by MRI at the entry, middle, and exit zones of the nerve roots in 30 dogs that were clinically affected by lumbosacral disease. Standard vs. oblique planar orientation and neutral vs. hyperextended positioning of the lumbosacral area were compared by measuring the median values for entry, middle, and exit zones. The neuroforaminal area acquired using oblique plane acquisition was significantly smaller than standard parasagittal measurements. Furthermore, standard parasagittal neuroforaminal dimensions in the hyperextended position were significantly smaller than standard parasagittal measurements in the neutral position. This statistical difference was even more pronounced for neuroforaminal dimension evaluated in the oblique plane and hyperextended position. Positioning of the dog during imaging has a significant effect on neuroforaminal dimension, corroborating the notion that spinal position may influence neural claudication in clinically affected patients. Reductions in neuroforaminal dimension are more evident on oblique planar image acquisition, suggesting that this approach may be more useful than parasagittal imaging as a tool for identifying subtle changes in L7 neuroforaminal dimensions in cases of canine lumbosacral stenosis.

CT measures of lumbosacral paraspinal muscle size are not correlated with CT measures of lumbosacral stability in military working Labrador Retrievers

“…Similar findings have been reported for radiographic measures of lumbosacral range of motion in dogs . In the present study, mean lumbosacral angles were greater in flexion than extension for both measurement techniques, a phenomenon previously documented with CT and MRI …”

“…In the present study, significant differences in intervertebral foraminal area were found between parasagittal and parasagittal oblique planar measurement methods. Previous studies also found differences between parasagittal and parasagittal oblique methods for quantifying intervertebral foraminal areas at L7‐S1 using CT and MRI . In both of these studies, the parasagittal planar method for measuring intervertebral foraminal area yielded values that were significantly larger than the parasagittal oblique measurement techniques.…”

“…Since initiation of our study, other studies have reported the use of neutral hip positioning to measure dynamic CT changes in the canine lumbosacral vertebral column . Our study made measurements only from flexed and extended hip positions because of limitations imposed by using dogs and CT scans from a previous study.…”

Dynamic MRI is reliable for evaluation of the lumbosacral spine in healthy dogs

“…Dynamic imaging techniques, in which the patient is imaged with the spine in a flexed and extended position, have been shown to detect changes that may be underestimated or missed on neutral imaging in the canine cervical spine 6 . Recent veterinary studies have shown that dynamic positioning leads to a change in LS foramina, which may be clinically significant 5,7‐9 …”

“…Studies have shown low rates of interobserver agreement on some measurements performed in the LS spine 10,11 . Many studies that have evaluated measurements of the LS spine to differentiate between affected and unaffected dogs have had only one observer performing the measurements 5,7‐9 . The anatomy of the LS spine is complex especially around the foramina, making it especially important to confirm interobserver agreement when attempting to create a clinically useful reference range.…”