Abstract
Like in reptiles, diagnostic imaging methods are of great value in clinical evaluation of amphibians. In amphibian medicine the use of diagnostic imagining methods is described in only a very few articles. The use of radiologic methods in amphibians has been described5 and the use of endoscopic techniques has been explained in detail.4,6 In contrast to endoscopic techniques, ultrasound examination is non-invasive and, therefore, does not require anesthesia.7,8 Like in other imaging methods, the large number of species is problematic and demand special knowledge of the anatomic situations. Amphibians do not possess horny scales, the skin is leather-like or mucous.1 Ultrasonography has been described as a tool for determination of gender in giant salamanders3 and a general tool in amphibian medicine.9,10
For endoscopic examination amphibians have to be anesthetized. Endoscopic equipment and technique are described in detail.4,6 Endoscopic examination produces three-dimensional pictures of inner organs in normal size, shape, color, and surrounding. Endoscopic examination of the coelomic cavity in amphibians permits to visualization of heart, lung, liver, spleen, intestines, gonads, kidneys, bladder, and fatbody from on singly point of entry.
For ultrasonographic examination of amphibians we used a fully digitized real-time ultrasound unit, Logique 200 Pro (General Electric, Glattbrugg, Switzerland), equipped with two scanners, a 5.5–6.5 MHz microconvex-scanner and a 6–9 MHz linear-transducer, both shiftable frequencies. Even though resorption through the skin is well known in amphibians, no negative side effects occurred using coupling gel. In none of the examinations amphibians where sedated or anesthetized. Careful handling and slow movements of the examiner caused calm patients. The patient was placed in a cryo-plastic container filled with water. The scanner was either placed directly on the frogs surface (no coupling gel) or on the bottom of the container. Stand-offs were not used. The whole coelomic cavity was scanned in transverse and longitudinal sections from cranial to caudal.
Real-time ultrasonography produces a two-dimensional sectorial picture in graduated black and white depending on the different reflexibility of the inner organs. It has no self-proofing method. To furnish proof of the diagnoses, postmortem examinations with measurements, cryo-cuttings, and waterbath examinations of fresh organs were performed. For waterbath examination, inner organs (heart, liver, kidney, gonad, intestine, and fatbody) of recently deceased animals were divided into a plastic container filled with distilled water (to prevent air bubbles which jeopardize ultrasonographic examination). While dissecting the animals, photographs were taken and removed organs were measured. In addition, cryocuttings of frozen carcasses were performed.
The coelomic cavity of amphibians does not developed a diaphragm. The only separated compartment is the pericardial sac with the heart.2 This undivided pleuro-peritoneal cavity displays the heart far in the rostral part, between the two shoulder joints. The lobulated liver covers the mid-third of the ventral part of the body cavity. In anurans the cranial parts of the left and right lobes are placed left and right to the ventricle of the heart. The stomach is situated dorsally in the left part of the coelom. The intestines fill the contralateral right part of the pleuro-peritoneal cavity. In pregnant female amphibians the follicles and/or ova could occupy large parts of the coelom and, therefore, distend the abdomen. Gonads and kidneys are placed dorsal and caudal, left and right to the aorta abdominalis.
The amphibian skin is a hyperechoic thin line and permits easy penetration of the ultrasound beam. The lack of horny or calcified scales like in reptiles prevents from the well-known problems of coupling the scanner to the skin. Even though the skin is moist in most species (not in some toads) the use of coupling gel is preferred for homogenous transmission. The underlying layers of body muscle appear as hypoechoic structures as in mammals and reptiles. Often there is a anechoic fluid visible in the pleuro-peritoneal cavity of amphibians. Like in some reptile species, this is of physiologic nature and could be used for easier visualization of organs, such as a fluid-filled abdomen in mammals.
Endoscopy allows to examine the pericardium and the surface of the heart and to assess the quality of the heart action. The ultrasonographic examination reveals diagnosis concerning the inner structure of the heart while it is working (real time).
During endoscopic examination, liver and gallbladder can be identified immediately adjacent and caudal to the liver. The lobes of the liver encircle the heart caudally, left and right. Endoscopic examination permits the visualization of the liver and gallbladder. In addition, biopsy under endoscopic control could easily be performed.
The liver parenchyma is hyperechoic and displays only very few, small vessels. The gallbladder is situated on the caudodorsal aspect of the liver. It is characterized by anechoic contents and thin hyperechoic wall. The liver of Anura is more hyperechoic than described for reptiles. Like explained for Cryptobranchidae the liver of anurans display less larger vessels than in reptiles or birds.
The stomach is placed caudally to the liver and can be demonstrated endoscopically. Size and shapes vary within a wide range depending on the species (size) and the food-intake. In ultrasonographic examination the stomach displays a wall with three layers: hypoechoic, anechoic, hypoechoic. Small and large intestines are difficult to differentiated.
The gonads of amphibians are placed far dorsally, adjacent to the kidneys. The ovaries could easily be demonstrated endoscopically, independent from size, sexual status, and age of the animal. The ovaries filled with developing follicles display ultrasonographically as large nonhomogeneous structures caudal to the liver. The single ovum is separated into hypoechoic (anechoic, yolk) and hyperechoic (embryo) structures. The very large amount of ova leads to a nonhomogeneous connected mass. Growing follicles of sexual active giant salamanders are described as anechoic bubbles within the ovary, whereas the ones in sexual inactive animals are hyperechoic. Ultrasonographically, testis could only be described for giant salamanders as lobulated hypoechoic ovoid structures.3 The endoscopic visualization of testes can easily be performed.4,6
The fat bodies of Anura can easily be demonstrated endoscopically. They display as yellow, fingerlike organs. Ultrasonographically they display as hyperechoic structures. They emerge from the basis of the mesovarium and mesotestis and protrude into the pleuro-peritoneal cavity, between the other organs.
The kidneys of amphibians are cigar-shaped cylinders located caudal to and adjacent left and right to the spine. Endoscopically they display as dark red, cigar-shaped structures. The sonographic appearance is homogenous and hypoechoic. In Cryptobranchidae, testes and kidneys are separated from each other (testes cranial to the kidneys) and could, therefore, easily been differentiated. In Anura the testes are placed adjacent to the kidneys and are difficult to differentiate.
The bladder is situated far caudal in the coelom, ventral to the large intestine. Endoscopically it displays as a translucent gray to blue-colored bowl. Ultrasonographically the wall of the bladder can be demonstrated as a hypoechoic surrounding of the unechoic contents. The size and shaped can vary in a wide range, depending on the contents.
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