Radiology and Imaging in Identification and Age Determination
Postmortem individual animal identification is not commonly performed in veterinary forensic radiology and imaging. Some skeletal features of the skull, spine, long bones, or thoracic cavity can indicate a general breed or body type, such as brachycephalic and chondrodystrophic dogs and brachycephalic cats. When previous clinical images are available for comparison, matching trabecular patterns in long bones, evaluating nasal conchae patterns or anomalous bone malformations and injuries, and comparing previous surgical or dental procedures can facilitate individual animal identification. Regression formulas have been used to estimate the shoulder height of dogs from long bone measurements and from the internal dimensions of the cranial cavity (Chroszcz et al., 2007). Although these formulas are described on skeletal specimens in dogs, the use of anthropometric measurements obtained from CT and radiographic images is well documented to estimate stature in humans (Hishmat et al., 2015).
The appearance time of centers of ossification and the time of growth plate closure are used in age determination when other indications of age are inconclusive or absent (Figure 18.6). Physeal closure does not occur uniformly and is variable in different species. Physeal closure can vary among dog breeds and by sex and reproductive status. Physeal closure determined by radiography will differ from physeal closure determined by US or histological examination; however, the charts found in most reference texts are based on radiographic closure and can be used to estimate age. Most physeal closure in dogs ranges from approximately 4 to 12 months. Most physes in the cat close slightly later, primarily from 4 to 19 months. The general health and nutritional status of the animal and the load-bearing status will affect physeal closure. Knowledge of the location of primary and secondary centers of ossification and familiarity with the location and closure times of growth plates in various species is important to prevent mistaking these normal structures for trauma.
Figure 18.6 Craniocaudal elbow radiograph of a 10-week-old pit bull-type dog. The physis of the medial and lateral humeral condyle is open and typically fuses between 8-12 weeks of age.
The radiographic determination of the pulp cavity to tooth width or tooth volume ratio is another method described for estimating the chronological age of domestic cats, foxes, coyotes, wild dogs, and in human remains (Park et al., 2014). With age, the volume of the pulp cavity decreases in size owing to the deposition of dentin. Measurement of this ratio on radiographs can be performed in the live or deceased animal or in incomplete skeletal remains which include some teeth. The canine teeth are primarily used for measurement of the pulp cavity to tooth width ratio at the cementoenamel junction. A bisecting angle technique is applied to prevent radiographic distortion, which occurs if the imaging receptor is not parallel to the long axis of the tooth.
