Karen L. Rosenthal, DVM, MS, Diplomate ABVP-Avian
It is not difficult to become proficient in interpreting small mammal radiographs. The same principles used to interpret dog and cat radiographs apply to small mammals such as ferrets and rabbits. It is only a matter of understanding some of the particular unique features commonly found in each species. A new set of techniques, both handling and mechanical, may have to be developed to work with these different species. A new technique chart will have to be designed for the small mammals just as it is done in dogs and cats. One also has to decide on the type of film that is used. For the smaller mammals, dental film may be an excellent choice for the detail it provides.
Mammography film also offers greater detail than conventional film but one must invest not only in new film but also in new cassettes for this film. Usually, small mammals are safely radiographed on the table top which gives overall better detail than if a grid is used. Finally, one has to decide how these animals are to be restrained. In some localities, regulations are such that no one is allowed to restrain the animal while radiographs are being taken. For small mammals, this means that some sort of tranquilization or anesthesia must be used for proper positioning. If personnel are allowed into the room while the films are taken, one must again decide how to hold these animals as the thick, leaded gloves are usually too clumsy to hold a ferret or rabbit.
The appearance of the normal ferret radiograph is not unlike that of other carnivores. The ferret's thoracic area is relatively large. Occasionally, the heart on the lateral radiograph appears "elevated" above the sternum not unlike what is seen when a pneumothorax is present. This is a normal finding in a ferret radiograph. An enlarged heart shadow is evidence of either increased heart size due to cardiomyopathy, a mass or pericardial effusion. All conditions occur in ferrets, although cardiomyopathy is the most common. To determine which is present, further investigation by echocardiography is necessary. Radiographic signs of heart disease include a large heart shadow, an elevated trachea, pleural effusion, contact between the heart shadow and the diaphragm, and lung congestion. Thoracic radiographs can be used to monitor heart disease as it progresses. The size of the heart and the other thoracic changes become more pronounced as the disease continues. Thoracic masses are also common in ferrets. They usually appear in the anterior mediastinal area. The most common type of thoracic neoplasia is lymphosarcoma but other cancers have been identified in ferrets. Megaesophagus is infrequently noted in ferrets. On radiographs, it can be seen as a gas filled esophagus in the thorax. At times it is necessary to perform a barium swallow to identify a megaesophagus.
In the normal ferret abdominal radiograph the following organs are usually identifiable: stomach, intestinal loops, kidneys, urinary bladder, spleen, and liver. It is not unusual to observe an enlarged spleen. Splenomegaly can be so great that the spleen is seen on both the left and right sides of the abdomen. Normally, there is very little gas in the ferret gastrointestinal tract, therefore, abdominal radiographs are useful to identify gastrointestinal obstructions. Objects causing pyloric obstruction (i.e., foreign bodies, trichobezoars, neoplasia) usually enlarge the stomach and gastric gas is typically present. Obstructions in the intestines are usually accompanied by a pronounced intestinal gas pattern. In fact, significant gas in the ferret gastrointestinal tract is a good indication that an obstruction is present. Non-obstructive ileus in the past was uncommon. The disease, epizootic catarrhal enteritis (ECE), can cause a severe ileus in ferrets. The radiographic appearance of ferrets with ECE can mimic that of one with an obstruction. It may not be possible to determine radiographically if an obstruction or ileus is present, even with contrast radiographs.
Although not common, urinary tract calculi can be seen; most are radio-opaque. Bladder sand can also occur. An enlarged bladder with no signs of urinary tract calculi can be caused by prostatic disease. Prostatic disease is an infrequently seen disease in male ferrets. Typically, the enlarged prostate is caused by the hormones produced by adrenal gland disease. The enlarged prostate impinges on the urethra leading to urinary blockage and a large bladder. Occasionally, in this disease, the large prostate is radiographically visible. Male ferrets have an os penis that is easily seen on radiographs. A rare disease in ferrets, gallstones, is apparent radiographically as slightly radio-opaque masses in the anterior part of the abdomen.
Orthopedic disease is not common in ferrets. Luxations and fractures are easily identified. A common orthopedic injury is an elbow luxation. Ferrets rarely get osteomyelitis and, as such, it is very uncommon to see this on radiographs. Bony neoplasias are also not common in ferrets but can be seen radiographically when present.
It is important when ferret radiographs are discussed to mention diseases that are not identified on radiographs. Pancreatic beta cell tumors (insulinoma) cannot be seen on radiographs. If the insulinoma is chronic and has metastasized to the liver, then hepatomegaly may be appreciated. It is extremely rare to view enlarged adrenal glands on radiographs. Mineralization does not typically occur and the adrenal glands do not enlarge enough to be observed on radiographs. Another common disease of ferrets, lymphosarcoma, is usually not apparent radiographically. Occasionally, enlarged abdominal lymph nodes are seen radiographically. And if lymphosarcoma has invaded bone, typical signs of bony neoplasia are observed.
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