MRI assessment of epaxial myosteatosis in dogs with intervertebral disc extrusions and associations with patient factors and outcome.

Fat infiltration of skeletal muscle (myosteatosis) is a characteristic of reduced muscle quality. Objectives of this retrospective, observer agreement, methods comparison, cross-sectional study were to compare epaxial myosteatosis of dogs with surgically confirmed intervertebral disc extrusion (IVDE) using a visual semi-quantitative method and quantitative 2-point Dixon fat-water chemical-shift separation MRI method. Thoracolumbar MRI studies of 86 dogs were reviewed. Assessed locations were the site of extrusion and the adjacent intervertebral disc space immediately cranial. A visual fat score (VFS) was assigned to fat infiltration of the epaxial muscles. Quantitative assessment of fat infiltration was determined by calculating a muscle-fat fraction (MFF). There was moderate agreement between the two reviewers for VFS assessment (weighted Kappa 0.60, 95%CI 0.53-0.66) with moderate to strong correlation between scoring methods (P ≤ .001). Both VFS (P = .023, P = .02) and MFF (P = .041, P = .043) were significantly correlated with neurologic grade at presentation for the erector spinae muscle group at both sites. Higher VFS in the multifidus muscle increased the odds of a successful outcome when assessed at the extrusion site (odds ratio and 95%CI 4.3 (1.02-78.7), P = .0461). In summary, the visual and Dixon method of epaxial muscle-fat assessment are feasible in dogs with IVDE with moderate to strong correlation. Increased VFS of myosteatosis in the multifidus muscle at the extrusion site significantly increased the odds of a successful outcome. Further studies are indicated to assess the utility of myosteatosis as an MRI imaging biomarker in the preoperative imaging assessment of dogs with IVDE.

Effect of contrast agent viscosity and massage on success of computed tomography lymphangiography with aqueous contrast for sentinel lymph node identification in healthy dogs.

Sentinel lymph node (SLN) evaluation is important for accurate cancer staging. Computed tomography (CT) lymphangiography with aqueous contrast is a feasible technique for SLN identification in dogs. Although most studies report success rates around 90%, success rates as low as 60% have been reported. One reason for low success rates may be the difference in viscosity of the various agents used in comparison to normal lymph viscosity. The objective of this study was to evaluate contrast agents of differing viscosities for use in CT lymphangiography for SLN identification and to determine the influence of massage on contrast flow rates. The hypothesis was that lower viscosity agents would have a higher success rate and faster time to identification of the SLN than higher viscosity agents and that massage would increase contrast flow rates. Dogs were anaesthetised and CT lymphangiography was performed with four contrast agents of differing viscosities in a randomized crossover design. Injections were made on the dorsal pes bilaterally on two study days and the popliteal lymph nodes were evaluated for contrast uptake. There was no significant difference in success of SLN identification or time to SLN identification among the four agents. Massage of the injection site increased rate of contrast flow through the lymphatics. No specific recommendation for one contrast agent over another can be made with these results. Massage is recommended to improve lymphatic flow when performing CT lymphangiography with aqueous contrast in dogs.