Accuracy, intermethod agreement, and inter-reviewer agreement for use of magnetic resonance imaging and myelography in small-breed dogs with naturally occurring first-time intervertebral disk extrusion

Objective—To determine accuracy, intermethod agreement, and inter-reviewer agreement for multisequence magnetic resonance imaging (MRI) and 2-view orthogonal myelography in small-breed dogs with first-time intervertebral disk (IVD) extrusion. Design—Prospective evaluation study. Animals—24 dogs with thoracolumbar IVD extrusion. Procedures—Each dog underwent MRI and myelography. Images obtained with each modality were independently evaluated and assigned standardized scores in a blinded manner by 3 reviewers. Results were compared with surgical findings. Inter-reviewer and intermethod agreements were assessed via ? statistics. Accuracy was assessed as the percentage of dogs for which = 2 of 3 reviewers recorded findings identical to those determined surgically. Results—Inter-reviewer agreement was substantial for site (? = 0.70) and side of IVD extrusion (? = 0.62) in T2-weighted magnetic resonance images and was substantial for site (? = 0.72) and fair for side of extrusion (? = 0.37) in myelographic images. Agreement for site between each modality and surgical findings was near perfect (? = 0.94 and 0.88 for MRI and myelography, respectively). Intermethod agreement was substantial for site (? = 0.71) and moderate for side of extrusion (? = 0.40). Accuracy of MRI for site and side was 100% when results for T1-weighted, T2-weighted, and contrast-enhanced T1-weighted sequences were combined. Accuracy of myelography was 90.9% and 54.5% for site and side, respectively. Conclusions and Clinical Relevance—Agreement between imaging results and surgical findings for identification of IVD extrusion sites in small-breed dogs was similar for MRI and myelography. However, MRI appeared to be more accurate than myelography and allowed evaluation of extradural compressive mass composition.