Amphibian radiology (Proceedings)

As amphibians become more and more popular as pet, the owners request good medicine and pay for adequate clinical work up. One of the most useful clinical tools in the daily practice of seeing exotic pets is radiology or other imaging methods such as ultrasound.

As in many other exotic species, a vast majority of problems are somehow related to mistakes in the husbandry. Some of these problems can easily be documented with radiology. Either acute or chronic problems arising from poor husbandry, which effect the health of the amphibian patient can be identified by radiographs.

Manual restrained is often adequate for the amphibian patient when taking radiographs. Often the patient is presented in a sick state and reluctant to move, not posing a serious problem to take a dorso-ventral exposure. However, in order to avoid accidental injuries to the animal from hopping crawling off the table or the radiograph plate, the patient can be confined in a plastic container and the radiographs can be obtained through the container. Visual confirmation of the patient during the exposure is recommended to make sure positioning is optimal. In rare cases chemical restrain is needed, the anesthetic agent can be either applied in the water (MS-222, eugenol), given topically (isoflorane in gel) or injected (propofol).

For very small and delicate patients, routine films might not result in adequate detailed information. High detail film such as mammography film or dental films are recommended. The newest generation of digital radiology units (DR) can produce stunning results with incredible details on 'normal' cassettes. Setting should be elected to result in a short exposure time as many amphibians can have relatively high respiratory rates.

It has been shown that amphibian erythrocytes are more sensitive to radiation damage than in other species. This might be due to the fact, that the amphibian erythrocyte is one of the largest in the animal kingdom. Repeated imaging and large dosages should be avoided when possible.

When taking images and evaluating the images, general concepts of radiology apply to the amphibian patient such as taking orthogonal views and evaluate for symmetry. However. Due to the fact that many amphibians are dorsoventrally flattened the accurate interpretation of the lateral image might pose a significant problem. Due to the lack of a diaphragm, it is recommend to take the lateral image with a horizontal beam in order to avoid an abnormal positioning of the coelomic organs when the animal is placed in lateral recumbency when the cathode is kept in a vertical position (the concept applies to all animals without a diaphragm!).

If one is not familiar wit the species that is examined it might be possible to ask if the owner has a second individual of the same species. If this is the case, the healthy animal can be placed on the same image in order to serve as a control for the evaluation process.

In some cases the use of contrast material is indicated. Barium sulfate can be tubed orally at a rate of 10-15 ml/kg bodyweight. Images can be obtained immediately after feeding , 30 min, 60 min and so on, until the contrast material reached the cloaca. Organic iodine compounds might be toxic if given but no reliable data on this observation is currently available. Air can be injected into the coelomic cavity if negative contrast is needed to outline an organ.

All adult amphibians are strict carnivores and have therefore a very short GI tract with a rapid transit time.

Nutritional secondary hyperparathyroidism can often be detected. Acute cases often show up as a mild radiolucency in the bones and a GI bloat at the same time. In advanced cases the bone density is very low, digits can't often be noted in the radiographs and in chronic cases fractures of the long bones are often present. Foreign bodies such as gravel stones, or coins can often be seen in the anorectic patient.

If radiographs show indication of a soft tissue problem, an ultrasound exam is often very useful to differentiate between tissue and fluid accumulation in the coelom. Remember that water is an excellent medium for ultrasound waves to travel through. If the amphibian patient is partly or fully submersed in water, the images are usually very diagnostic.

With a bit of practice and skill, radiological valuation of the amphibian patient is relatively easy and can be of a significant aid in working up the amphibian patient in your clinic.