Small Mammal Radiology

Heidi L. Hoefer, DVM, ABVP
Long Island Veterinary Specialists, Plainview, New York
West Hills Animal Hospital, Huntington, New York

Restraint

Proper restraint and positioning are necessary for diagnostic films. Most small mammal patients tolerate radiographic procedures well but stressed and debilitated patients may require treatment before films are taken. Stabilize dyspneic animals and consider using sedation and an oxygen face mask during the procedure.

For screening films in a quiet small mammal in good condition, manual restraint can often be used. Ferrets can be difficult to maintain under manual restraint and often need to be sedated for radiographs. The choice of anesthetic agent varies with the individual practitioner and the area of radiographic interest. Isoflurane delivered through a face mask is quick and safe in most cases. Injectable agents can be used for radiographs of the head and neck area. Endotracheal intubation might be necessary for skull films but can be difficult in the smaller species. This author prefers midazalam (Versed @ .5 -1 mg/kg IM) for tranquilization, IV ketamine/valium for short sedation, and isoflurane face mask for full immobilization.

Equipment

For maximum detail, fine or detail intensifying screens/cassettes can be used (Curix Fine, Agfa, Orangeburg, NY or Qanta Detail, E.I. Dupont, Wilmington, DE or Lanex Fine, Eastman Kodak, Rochester, NY) in combination with detail XRAY film (Curix Detail RPIL, Agfa or Cronex 10, Dupont or TMG film, Eastman Kodak). Mammography film provides exceptional detail in very small animals. At the author's practice, a Min R single intensifying screen cassette with Min R single emulsion film is used with excellent results. This system uses higher mAs settings (10 mAS) and kVp in the 60-70 range. Used cassettes are available from most distributors and are cost effective. Dental film can be useful for very small animals or body parts (e.g., limbs and digits).

With any film/screen combination, most exotics can be positioned directly on the cassette and whole body radiographs are usually done. This allows for quick examination of the entire body.

Contrast

Contrast procedures can be performed using standard contrast agents. Undiluted barium can be syringe fed or tube-fed for gastrointestinal studies (10-15 ml/kg) body weight. Injectable iodinated contrast media (iothalamate meglumine 60%) can be used for renal (IVP) or angiographic studies. Follow doses used for dogs and cats.

Interpretation

Proper positioning and technique and a knowledge of normals is essential for radiographic interpretation. Certain radiographic differences exist between species and are important to be familiar with. For example, hind-gut fermenting herbivores (rabbit, guinea pig, chinchilla) will normally have varying amounts of gastrointestinal gas. This amount of GI gas in a ferret would be abnormal. The cranial lung lobes are difficult to visualize in small rabbits and rodents making the heart appear large and the cranial mediastinum "full". This is in sharp contrast to the ferret thorax which is relatively much larger than in other small mammals and easier to visualize. Review normal radiographs for the common exotic pet species and become familiar with the anatomical variations. Taking radiographs on healthy volunteers is helpful in perfecting technique and evaluating "normals".

References And Recommended Reading

1.  Silverman S: Diagnostic imaging of exotic pets. In Vet Clinics of North America, Small Animal Practice, 23(6): 1287-1299, 1993.

2.  Rubel GA, Isenbugel E, Wolvekamp P: Atlas of Diagnostic Radiology of Exotic Pets. Philadelphia, WB Saunders, 1991.

3.  Stefanacci JD, Hoefer HL: Small mammal radiology. In Hillyer EV, and Quesenberry KE (Eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1997