Rabbit skull radiology
Corby Holson and David Martinez-Jimenez
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Introduction to rabbit radiology
Radiology in the domestic rabbit (Oryctolagus cuniculus) can be challenging due to their size, and easily stressed nature. Small mammal radiology requires a basic knowledge of anatomy and physiologic characteristics. Therefore, three important factors require further attention when taking radiographs in rabbits:
1. Rabbits are prey species and therefore, they become extremely agitated when exposed to unfamiliar situations. Manual restraint can be difficult, and dangerous, for any length of time. Sedation or anesthesia is usually required.
2. The relatively small size of rabbits has the advantage of allowing whole-body radiographs and quick examination of the entire patient. However, it may result in a loss of detail due to the differences in size between different body areas.
3. Motion of the object during the imaging sequence generally results in a blurring. Because motion artifact is a common problem in rabbits, the minimum requirement for x-ray equipment is the capacity to produce 300 mA in 1/120 (0.008) second.
Settings and equipment
The x-ray machine should be capable of working with 5.0 to 7.5 mAs exposures, and have a range of 40 to 100 KVp, which is adjusted in 1 to 2 KVp increments. Often when radiographing rabbits, mammography films and cassettes are utilized (Mamoray® cassette, Mamoray HDS, AGFA Corporation, Greenville, SC). This system provides ultra fine detail in smaller species.
Radiography in rabbits, and other small mammals, can be challenging as they are highly stressful, resistant to restraint and have a small body size in relation to their short extremities. Visual anatomic landmarks are preferred over palpated anatomic landmarks because their thick subcutaneous adipose layers and dense hair coats make it difficult to palpate accurately. Correct symmetry and stabilization of the patient can be accomplished by using radiolucent materials such as foam and tape for support.
Rabbit bones are delicate in comparison to that of other domestic companion animals. For example, the skeleton of a rabbit represents only 7-8% of body weight but is 12-13% of body weight in a cat. Paradoxically, the muscles of rabbits are extremely strong and powerful which can lead to fractures or luxations if held improperly.
Skull radiography can provide useful information about the nares, sinuses, middle ears, teeth and surrounding bone. Radiographic views should include lateral and dorsoventral views, as well as obliques when necessary (e.g. dental disease evaluation). Oblique radiographs projections require rotations at 30 degrees angles (described by the point of entrance of the x-ray beam to the point of exit).
Magnification radiography is commonly used in exotic patients when higher definition, detailed images are necessitated. It requires the use of an ultra-small focal spot x-ray tube and an increased object-film distance as compared to standard radiographs.
Pathological radiography associated to the rabbit skull
Skull radiography is an extremely valuable tool in rabbit medicine, not only because it helps localize and diagnosis specific anatomical disease, but it also serves as an important prognostic determinant. For instance, an increased density in tympanic bullae, nares, or sinuses may indicate infection. On the other hand, decreased density may occur in advanced cases of infection or neoplasia.
Degree of dental disease and prognosis can be also determined by radiographic evaluation. Facial abscesses and osteomyelitis of the maxilla or mandible in lagomorphs are often related to dental disease and bacterial infection. The precise etiology of dental disease in the pet rabbit is still unknown and is likely to be multifactorial including primary (inherit) and secondary causes (diet, metabolic, traumatic and infectious components).
Radiography is an essential diagnostic tool that can help localize both bone and soft tissue lesions before attempting surgical correction. Radiographs can also accurately grade dental disease from 1 (normal) to 5 (severe dental disease, including oral abscesses).
Radiology is an essential tool for any practitioner working with rabbits. Due to their stressful temperament and keen ability to hide disease, thorough and careful examination including radiographs is warranted. Rabbits are particularly predisposed to dental disease, and skull radiographs can detect lesions unlikely to be observed during physical examination. Radiographs also serve as an important tool for grading dental disease and are valuable in providing accurate prognosis to clients.
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The authors would like to thank Dr. Hernandez-Divers and Dr. Wilson for their help and support, as well as for some of the pictures provided.