Sharon Redrobe, BSc, BVetMed, MRCVS
BCG Newsletter No.119, Sep/Oct 1997
Ultrasound is a safe, non-invasive way of looking at the internal organs. It does not harm the animal or developing eggs or embryos. It is the same technique that is used to scan human babies in the womb. The animal does not need an anaesthetic whilst being scanned. Ultrasound waves are sent out and received by a small hand-held probe. The waves bounce off or pass through tissues inside the animal and the different patterns create the picture. The probe is placed against the skin and gel is applied to exclude the air. As a moving image is produced, the animal does not have to be kept perfectly still for imaging and thus an anaesthetic is not required.
Vets rely on a number of tools to diagnose disease in chelonia. These include blood sampling, radiography (X-rays), endoscopy, bacterial culture and faecal sampling. The diagnostic potential of radiography in chelonia is limited by the bony plastron and carapace: the skeleton and pulmonary fields are readily imaged, as are calcified shells and uroliths, but soft tissue structures are not apparent unless gas-filled or abnormally calcified. The investigation of gastro-intestinal tract abnormalities by radiography requires the use of contrast media. Laparoscopy was perhaps the only other alternative, but this method is invasive and requires full anaesthesia.
The advent of ultrasonography has made possible the non-invasive safe assessment of soft tissues in many species of reptile. The ultrasound scanning can be used to image the heart and its valves, the contractility of the heart muscle and the speed of the blood flow. It is useful in detecting heart disease such as infection (endocarditis) which is common in reptiles. Other heart problems are now being detected, especially in elderly tortoises.
Radiographs do not allow visualisation of the liver. Blood results only show current liver damage or advanced liver failure. Liver enzyme levels in the blood can be normal in an animal with hepatic lipidosis (fatty liver) or liver abscess or tumour if these lesions are well contained and slow growing. Liver lesions can be visualised directly using ultrasound. When a tortoise hasn’t eaten enough food for a while it is prone to hepatic lipidosis. This can lead to liver failure in advanced stages, or a reduced appetite and lethargy in early stages. It is obviously better to diagnose this and begin treatment as early as possible. Liver abscesses can be formed after a severe infection. These are easily detected using ultrasound.
Ultrasonography is the major tool for obstetrical work in reptiles, being useful in infertility assessment, determining the number of follicles and relating the timing of ovulation to oviposition. Ultrasound scanning is also useful in sexing animals, by imaging testes or ovaries. It can also be used to follow the ovarian cycle, timing when ovulation takes place and showing when is the best time to introduce a mate. It can be used in the diagnosis of egg retention, as the age of the eggs can be estimated. It can also aid with the diagnosis of pre-ovulatory egg retention or egg peritonitis.
There are many other useful applications. Many things are still unknown in reptiles, compared with mammals, e.g. the best way to scan the heart in tortoises and terrapins. The ‘healthy’ appearance of these species when scanning the heart, ovaries and testes has not been published for the vast majority of common species. The heart scan requires a knowledge of the normal contractility of heart muscle, the normal blood flow velocities etc. before it can be used to diagnose more subtle heart problems in tortoises. The Royal (Dick) School of Veterinary Studies in Edinburgh has been conducting a project to discover the ‘normal’ as well as ‘abnormal’ findings on reptile scans.