INTRAARTERIAL CONTRAST-ENHANCED COMPUTED TOMOGRAPHY OF THE EQUINE DISTAL EXTREMITY

A technique for regional delivery of contrast medium to the foot of the horse to increase the diagnostic utility of computed tomography (CT) for the characterization of soft tissue structures within the hoof capsule was developed. An intraarterial catheter was placed under ultrasound guidance into the medial palmar artery at the level of the carpus to facilitate a steady-state infusion of iodinated contrast medium. Two 5 mm collimated contiguous acquisition CT scans were performed in 10 horses without lameness or radiographic evidence of distal sesamoid bone degeneration. CT examination was performed before and during regional arterial infusion of iodinated contrast medium administered at a rate of 2 ml/s. Cross-sectional area and mean pre- and post-contrast attenuation of the deep digital flexor tendon and the collateral ligaments of the distal interphalangeal joint were quantified from CT images. Soft tissue anatomy of the foot was also qualitatively characterized from pre- and postcontrast images. Catheterization was successful and without complication in all horses. The evaluated tendons and ligaments were clearly visible and had a small (8-20 Hounsfield Unit) but significant (P < 0.05, paired t-test) increase in attenuation during the steady-state infusion of contrast medium. This study should enhance the diagnostic potential of CT by providing baseline quantitative data for comparison with horses affected with soft tissue injuries in the distal extremity causing lameness that is alleviated with a palmar digital nerve block.