Abstract

Computed tomography offers a rapid, repeatable, and comprehensive advanced imaging by minimizing anatomic superimposition and operator variability.¹ Although widely used in many animal species, the use of iodinated intravenous contrast is undocumented in live koi (Cyprinus carpio). Prior research has evaluated the distribution of positive contrast administered per os in pacu (Colossoma macroponum), a similar teleost fish species.² Non-contrast-enhanced computed tomography has also been utilized in imaging the skeletal structures, swim bladder, and coelomic neoplasia in koi.^3,4,5 There is an increasing demand for thorough diagnostic imaging in our fish patients to aid in prognostication and guide surgical treatment. The goals of this study were to 1) document the distribution of injected intravenous contrast administered into the caudal vein, 2) determine the conspicuity of coelomic organs, and 3) evaluate differences in the appearance of coelomic contrast uptake with two different doses of intravenous contrast. Ten koi were imaged with two different IV iopamidol contrast doses; half were administered 480 mg iodine/kg, and the other half were administered 800 mg iodine/kg. Each fish was placed under general anesthesia with 100 mg/L of buffered tricaine methanesulfonate. A pre-IV contrast CT scan was performed, which was then followed by two post-IV contrast scans performed at 2–3 and at 5–10 min post-injection to evaluate the systemic distribution of the contrast agent. Objective parameters, including contrast uptake (Hounsfield units) into the kidneys, heart, liver, spleen, gonads, and venous circulatory system, as well as qualitative parameters such as organ recognition, ability to identify margins and attenuation compared to adjacent structures were evaluated. Results show that the caudal vein, hepatic portal vein, hepatic vein, posterior cardinal vein, and sinus venosus of the heart are consistently visualized on the earlier post-IV contrast scans. All but one fish had similar contrast enhancement distribution, where in this fish a subjectively large amount of the contrast injection went perivascular. Variation in the branching morphology of the hepatic vein was identified in this population of fish. The posterior kidney was the most strongly contrast-enhancing organ on the first of two post-IV contrast scans, and several fish demonstrated increased enhancement in the right side of the posterior kidney. The later post-contrast scans show repeatable and improved homogeneous contrast enhancement of the coelomic organs. The spleen was the only organ not able to be identified as separate from the adjacent liver parenchyma in the mid coelom. The two doses of contrast showed similar distribution patterns, and both produced excellent vascular enhancement. In conclusion, the injection of IV contrast into the caudal vein of koi is a feasible technique for the study of coelomic anatomy in vivo. The information obtained from this study may serve as a baseline reference for the use of contrast-enhanced intravenous computed tomography as a diagnostic procedure in fish. Additional research regarding diseased koi can be investigated with the information gained from this project.

Acknowledgements

The authors would like to acknowledge support of the UC Davis Center for Companion Animal Health, Dr. Josephine Bryk of the Indianapolis Zoo, and Claire Vergneau-Grosset of the Université de Montréal for their help with the creation of this project, and also thank the veterinary students of the UC Davis Aquatic Animal Health Service.

* Presenting author
+ Student presenter

Literature Cited

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2.  Carr A, Weber EP, Murphy CJ, Zwingenberger A. 2014. Computed tomographic and cross-sectional anatomy of the normal pacu (Colossoma macroponum). J Zoo Wildl Med. 45:184–189.

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