Objective: To compare the sensitivity of computed tomography (CT) and myelography to a reference standard of CT myelography for determining localization of Type I intervertebral disc extrusions in dogs.

Study design: Prospective blinded comparative study.

Animals: Dogs with acute onset myelopathy because of suspected disc extrusions (n = 30).

Methods: Dogs had CT, myelography, and CT myelography to diagnose disc extrusions. Sensitivity of CT and myelography was compared to CT myelography for lateral, longitudinal, and combined localization. Confidence in the assessment of each imaging study was scored by 3 reviewers.

Results: Sensitivity of CT for lateral, longitudinal, and combined localization was 94%, 91%, and 81%, respectively, and was 64%, 74%, and 53%, respectively for myelography. Sensitivity of all 3 categories of localization was significantly different between modalities (P < .0001, P = .0031, P < .0001). Significant differences in the sensitivity of lateral and combined localization were found between confidence scores for myelography (P < .0001, P < .0001). Significant differences in the sensitivity of lateral, longitudinal, and combined localization were found between confidence scores for CT (P = .011, P = .013, P = .027). Poor sensitivity was obtained for both modalities except when imaging studies were assigned the highest confidence score.

Conclusions: CT is a more sensitive imaging technique than myelography for localizing disc extrusions when compared to a reference standard of CT myelography. Both modalities yielded high sensitivity with the highest confidence score and poor sensitivity for all other confidence scores.