Use of radiographic contrast media in horses

Radiographic contrast examinations in horses are used to demonstrate soft tissue abnormalities that are not apparent by means of routine radiography. Contrast media may be negative or positive. The nonionic contrast agents are ideal media for many imaging procedures because of the low toxicity and osmolality of the agents; however, their cost may be prohibitive for routine use in horses. Survey radiographs must be taken before contrast examination in order to prevent lesions or structures from being obscured by contrast agents and to ensure proper exposure factors. Positive contrast medium is more opaque than bone or metal and can prevent visualization of any structure of lesser density. Contrast studies that are routinely performed in horses include arthrography, fistulography, esophagography, and myelography. Other contrast procedures that are less often performed include tendonography, paranasal sinusography, and dacryocystorhinography. Upper and lower gastrointestinal contrast studies and cystography are procedures that can be performed in foals.