Abstract

Respiratory tract infections are a major cause for morbidity in cetaceans, and traditional methods of diagnosing and managing these infections, such as monitoring physical signs, laboratory testing and examination of blowhole flora often lack sufficient specificity and sensitivity.

Computed tomography (CT-scan) has been successfully used in imaging the respiratory organs of numerous species. In recent years multislice spiral CT-scanning has become available and has gained an important role in the diagnosis and management of respiratory disease. This technique enables shorter exposure time, increases the quality of the images and makes reconstructions in several planes as well as three dimensional images possible.

A Siemens Somaton sensation 4 four slice CT-scan was used in Tursiops truncatus and Phocoena phocoena . Of both species healthy as well as diseased animals were scanned. The animals were transported by van from their habitat to the hospital facility. They were sedated with diazepam. The T. truncatus were prepared for this examination by specific training.

Of all animals highly detailed images could be obtained with high resolution. Depending on window settings of the computer the lung fields or the central airways, mediastinal structures and pulmonary vessels were visualized. In dependent lung zones of Tursiops truncatus a ground glass pattern was encountered, most probably because of the rigid peripheral airways which prevent air trapping in compressed lung tissue. This phenomenon must be considered when judging the images.

In the diseased animals, various abnormalities were seen, such as bronchopulmonary infiltrates, abscess forming, and interstitial lung disease. The character as well as the extent of these abnormalities could be accurately assessed. Furthermore, the effect of therapeutic interventions could be monitored in serial studies. In a P. phocoena with lungworm infection intravenous contrast (Omnipaque 300, 120 ml, 2ml/s) was used. In the pulmonary arteries several intraluminal filling defects could be seen, which were interpreted as nematodes within the pulmonary vessels. This finding was later confirmed by autopsy. The use of intravenous contrast was well tolerated.

We focused on the respiratory organs, but of course this technique is also very useful in examining various other organ systems.

CT-scanning unfortunately has disadvantages, also. The most important ones are the considerable cost and the limited availability. Although movable CT-scanners in trucks do exist, it is usually necessary to transport the animal to the radiography department of a nearby hospital. Furthermore, the weight and the size of the animal must be within limits to allow this technique. The maximum weight should not exceed 200kg for most scanners. In many species the dorsal fin will not fit in the scanner, which is also true for T. truncatus, but fortunately the entire respiratory system is situated rostral of the dorsal fin.

In conclusion spiral CT scanning is a highly useful technique in diagnosing respiratory disorders in small cetaceans. High quality images can be obtained and the use of contrast further increases the yield. Due to the high cost and limited availability this technique should be considered as a second line diagnostic tool.