Introduction

Diagnostic imaging is routinely used in reptile medicine and surgery for the morphologic and functional assessment of internal organs as well as the diagnosis of a variety of diseases. Application and interpretation of imaging modalities in reptiles is often challenging due to their unique anatomy, physiology and pathophysiology of diseases. It is essential to have a detailed knowledge of normal anatomy and the pathophysiology of diseases in order to accurately select and interpret diagnostic imaging modalities. Radiography is most commonly used to provide a general overview of anatomy and gross morphologic changes. Radiographic anatomy of lizards, snakes and chelonians has been described.¹ Ultrasonography will provide more detailed information on organ architecture, however detailed descriptions of reptile ultrasonographic anatomy are scant. Computed tomography (CT) is a cross-sectional diagnostic imaging modality which is used to detect skeletal abnormalities and soft tissue enlargements. Further studies are needed to describe normal CT anatomy in reptiles in order to detect various diseases in reptiles. As is the case in domestic animal imaging, no imaging modality will provide all the necessary information needed to diagnose and treat the reptilian patient. In many cases, a combination of several imaging modalities is necessary to make a diagnosis. The use of ultrasonography and CT in reptiles follows the same principles and standards established for domestic animals. Detailed descriptions of the use of ultrasonography and computed tomography in reptiles have been published.^2,3,4,5,6

Ultrasonography

Ultrasound examination of reptiles is an important diagnostic tool for the detection of soft tissue abnormalities e.g., neoplasia as well as detection of intracoelomic fluid. In reptiles, ultrasound is routinely used for the evaluation of the gastro-intestinal tract, reproductive tract and various visceral organs such as kidneys and liver. Ultrasonography will also aid in the collection of diagnostic samples such as biopsies and aspirates of visceral organs, masses and fluids.

While most reptile species can be imaged with manual restraint alone, larger and/or dangerous species will require sedation or general anesthesia to facilitate handling. Small species will require high-resolution equipment and 7.5-10.0 MHz transducers with small footprints. Chelonians are the most challenging reptiles to perform an ultrasound examination on due to the presence of the shell. With the legs extended, the inguinal and axillary region present windows for imaging internal organs. Snakes should be placed in dorsal recumbency and are imaged from ventral to avoid the ribs. Lizards can be imaged from both lateral and ventral depending on the organ system to be evaluated.

Reproductive ultrasonography is routinely used in reptiles in order to determine the reproductive status of female reptiles. This includes determination of ovarian activity and pregnancy. The liver of snakes and lizards is relatively easy to image and should be evaluated for any changes within the parenchyma. Pathologic changes such as neoplasia, abscesses can be identified and ultrasound guided biopsies should be collected for histopathological evaluation. In chelonians the liver is difficult to visualize due to the lack of a suitable imaging window. The spleen and pancreas are very difficult to identify via ultrasonography unless they are enlarged. The kidneys should be evaluated for any gross changes such as enlargement and changes in shape. If pathological changes are present, ultrasound guided kidney biopsies should be collected for histopathological and microbiological evaluation.

Echocardiography has been performed in reptiles, however due to the lack of reference data it is often of limited value. Snakes are the easiest reptile species to evaluate while chelonians are very difficult to image unless an esophageal probe is being used. In lizards it is often difficult to visualize both atria and the ventricle due to the cranial location of the heart in between the front limbs and the pectoral girdle. In larger reptiles M-mode and Doppler studies can be performed.

Computed Tomography

CT studies are increasingly used in reptile medicine however more studies are needed describing normal CT appearance of various organs. Recent advances in technology have not only improved image quality but have also shortened the time required to perform a CT study. CT scans are performed in transverse direction and programs are capable to create a three-dimensional (3-D) reconstruction of the slices. This is of special diagnostic value in the evaluation of neoplasia and skeletal abnormalities such as the skull. Contrast studies are routinely performed to evaluate the vascular characteristics of a mass or an organ. One of the major disadvantages of CT when compared to MRI is the relatively low differentiation of soft tissues.

Abnormalities of the skeletal system such as fractures or neoplasia can be readily detected and identified by CT. Fractures of the shell in chelonians, mandibular and/or maxillary abscesses in lizards and osteomyelitis of the spine in snakes are commonly diagnosed and evaluated by CT. CT scans of the lungs are of particular usefulness in chelonians for the detection of pneumonia as well as neoplasia and masses. In snakes and lizards, CT is commonly used for the evaluation of the upper and lower respiratory tract. In reptiles, the reproductive tract is most commonly evaluated via ultrasonography, however CT is more accurate in the detection of the total number of follicles in chelonians. The digestive tract of snakes, lizards and chelonians can be visualized by CT. In order to diagnose pathological changes, administration of contrast media is often necessary. Visceral organs such as liver, spleen and kidneys can be identified by CT and abnormalities can be evaluated. Renal disease is a common clinical finding in reptiles. Changes in renal morphology such as enlargement, cysts, neoplasia or masses can be diagnosed via CT.

References

1.  Mader. Mader's Reptile Medicine and Surgery 2006; 2nd ed:1097.

2.  Schumacher, et al. Sem Avian Exotic Pet Med 2001;10 (4):162.

3.  Silverman. Mader's Reptile Medicine and Surgery 2006; 2nd ed: 471.

4.  Holland. JAVMA 2008;233(4):590.

5.  Gumpenberger, et al. Sem Avian Exotic Pet Med 2001;10(4):174.

6.  Spaulding. Fowler's Zoo & Wild Animal Medicine 1999. Current Therapy 4:83.