Reptile radiology (Proceedings)
Diagnosing disease in reptiles can be a challenge for even the most experienced veterinarian. The clinical signs exhibited by these ectotherms are often subtle and physical findings are seldom pathognomonic. Diagnostic imaging should be part of the clinical evaluation of any sick reptile. Radiology is a common diagnostic tool used in reptile practice and can be instrumental in the identification of disease.
There are several anatomical differences that make it difficult to obtain quality radiographs of good contrast and detail. The relatively small size of most pet reptiles, coupled with the lack of diffuse body fat often produces images of poor contrast. The presence of thick, highly keratinized scales, osteoderms or shells can severely hinder the xray beam, necessitating greater power and a subsequent loss of fine soft tissue detail.
Radiographic EquipmentDespite the aforementioned difficulties, most high-capacity radiographic units can be set to produce quality radiographs of reptilian patients. High-detailed screen-film combinations (e.g. mammography film) are essential to obtain sufficient detail and contrast, especially in smaller animals.
Various agents can be used to improve contrast. Barium sulphate (30%) can be used for gastrointestinal studies, although the authors prefer water soluble iodine compounds such as iohexol for gastrointestinal, urogenital and intravenous techniques. It should not be forgotten that the simple injection of air into the coelom of a lizard can greatly improve the appreciation of pre-ovulatory follicles.
Restraint & Positioning. Snakes can be difficult to position and restrain for radiographic examinations unless anesthetized. If the purpose of the examination is simply to rule out radiodense foreign bodies, the snake may be allowed to coil in its natural position while the radiograph is taken. If detailed examination of the skeletal, respiratory and digestive system is desired, the snake must be extended. A plastic restraint tube can be utilized for this purpose; however, this may produce some radiographic artifact. In larger snakes, several films will be needed to radiograph the entire length of the body. It is important to properly label each exposure in order to keep track of all the different views. Lateral views are best taken using horizontal beams to avoid displacement artifact of the viscera. However, standard laterals with the snake taped in lateral recumbency can be useful especially where horizontal beams are not possible or safe to undertake. The interpretation of dorsoventral views are hindered by the spine and ribs, but can still be useful when dealing with obvious lesions including eggs and mineralized masses.
Musculoskeletal System. Traumatic fractures, metabolic bone diseases, spondylitis/spondylosis, osteomyelitis, and congenital abnormalities are common indications for examining the skeletal system of snakes. Fractured ribs with periosteal bone formation are a common finding in snakes. Another common finding is exuberant vertebral periosteal bone formation. On radiographs, this appears as several "fused" vertebrae.
Digestive System. Common indications for radiographically evaluating the digestive system include hypertrophic gastritis, foreign body ingestion/impaction, constipation, hepatomegaly and hepatic masses. Contrast studies are useful in diagnosing intestinal obstruction and constipation. In addition, contrast material in the gastrointestinal tract can often outline and help determine the origin of a non-specific intracoelomic masses; intraluminal or extraluminal.
Cardiopulmonary System. Cardiomyopathy has been reported in snakes, which can be indicated by cardiomegaly on radiographs. Metastatic mineralization of large blood vessels is often apparent around the heart due to the negative contrast afforded by the adjacent lung(s).
The superimposition of other organs such as liver and stomach over the lung fields can make the radiographic interpretation of respiratory disease challenging. Common indications for evaluating the respiratory system are rhinitis, suspected neoplastic and infectious disorders of the trachea and lung, as well as abscesses or granulomas.
Urogenital System. The kidneys are not always radiographically evident, unless enlarged or mineralized. Disease processes that can cause renomegaly include renal gout and neoplasia.
Eggs of oviparous species are leathery and poorly calcified, but can often be appreciated on plain radiographs. In viviparous species fetal skeletons become visible as they mineralize late in gestation. The hemipenes of some species may appear mineralized and can be detected radiographically. Common indications for evaluating the reproductive system include dystocia, apparent infertility and reduced fecundity.
Miscellaneous. The presence of any swelling is an indication for radiography. Abscesses, which can either be extracoelomic or intracoelomic and associated with a specific organ or the coelomic wall are common findings in snakes.