Subcutaneous Pyelograms (SCP) as an Early Diagnostic Technique for Urolithiasis in Asian Short-Clawed Otters (Aonyx cinerea)
Subcutaneous renal contrast media with hyaluronidase was found to be highly effective yet simple means of early diagnosis of urolithiasis in Asian short-clawed otters (Aonyx cinerea). As a well-documented cause of morbidity and mortality in this species early detection may be critical to treatment.1,2,4,6 With training, it may be possible to utilize this technique for anesthetic-free radiographic studies of renal function and morphology. No adverse effects were observed from this technique.
Asian short-clawed otters (Aonyx cinerea) have been found to have a high incidence of urolithiasis.4 In one study, renal calculi alone occurred in 66.1%, while 23.2% exhibited both cystic and renal calculi.1 Renal pathology and failure caused or contributed to the morbidity and mortality of animals over 10-years of age, in the referenced reports.1,2,4,5 This report documents a subcutaneous excretory urogram radiographic imaging technique for early diagnosis of primary urolithiasis, secondary hydronephrosis, and hydroureter.
Intravenous bolus injection and renal excretion of iodinated radiopaque contrast media provides the diagnostician with two interpretive phases.7,11 The first phase, the nephrogram, provides rapid radiographic opacification of the renal cortex and parenchyma on the first pass of renal blood flow. The second phase, the pyelogram, opacifies renal calyces, renal pelvises, and ureters, where significant uroliths occur. The cystic opacification follows.7
Intravenous injections may be difficult in exotic and wild animals. Accidental extravascular injection of contrast media can cause irritation and local necrosis.5 Hyaluronidase, 150 IU/ml (Wydase®, Wyeth Laboratories, Inc., Philadelphia, PA, USA) combined with the contrast media at 150 IU per dose, up to 1 L of solution, enables subcutaneous excretory urograms, eliminating the need for an intravenous bolus. This results in a subcutaneous pyelogram and cystogram visualization only. The nephrogram or first phase is lost. However clinical urolithic renal disease occurs primarily after renal pelvic, ureter, and cystic stones occur, usually with hydronephrosis/ureter.1,2,4,6 The stones themselves are poorly visualized, however, contrast media silhouettes the stones and clearly demonstrates the secondary hydronephrosis/hydroureter.
Hyaluronidase hydrolyzes interstitial connective tissue hyaluronic acid, accelerating distribution and lymphatic absorption. The enhanced diffusion rate and the vascular absorption of the contrast media allow sufficient renal uptake to be a simple efficient diagnostic screening technique.5 In a dose of 150 IU of hyaluronidase added to an injectable IV solution has also been shown to prevent dermal necrosis caused by extravasation of irritant compounds swine.8 Through behavior modification, many animals can be trained to tolerate subcutaneous injections while awake. Then trained to stand or target on a radiographic intensifying screen for the exposure.9
Animals trained to position themselves for radiographs present many potential benefits. By eliminating the risks, cost, and the time involved with general anesthesia this provides more opportunity to routinely evaluate the urinary tract.
Methods: Dose and Diagnostic Technique
Following a 24-hour fast, two 5-year-old, female Asian short-clawed otters were examined at least annually. Each animal was manually restrained for intramuscular injections of 15 mg tiletamine and zolazepam hydrochloride (Telazol®, A&H Robins, Richmond, VA, USA) then, via mask administration, taken to the level of general anesthesia with 5% isoflurane (Aerrane®, Ohmeda PPD, Inc., Liberty Corner, NJ, USA). They were maintained on 1.5% isoflurane. Atropine sulfate (Atropine®, Vet Tek, Inc., Blue Springs, MO, USA) at a dose of 1.5 mg per otter was administered at 20 minutes post-induction to control salivation and bronchial secretions.
The weights of the specimens varied over time by 1–1.6 kg each, but were consistently within the average weight of captive Asian short-clawed otters 2.7–5.4 kg.3 Lateral and ventrodorsal survey radiographs were exposed initially. In a well hydrated animal 150 IU (1 ml) of Wydase® in 10 ml of 52% diatrizoate meglumine and 8% diatrizoate sodium (Renografin®, Bristol-Myers Squibb Company, 345 Park Avenue, New York, NY, USA) was administered subcutaneously in the cervical dorsal/suprascapular area. This location insured any residual subcutaneous contrast media would not be superimposed over the urinary tract.
Because the uptake of the contrast media is slower with the subcutaneous injection, the protocol for obtaining radiographs is altered to accommodate the extra time required for the contrast media to reach a concentration adequate for radiographic opacification. Lateral and ventrodorsal radiographs are taken sequentially at 20, 40, 60, and 80 minutes.11
Initially survey radiographs were non-diagnostic and no calculi were visible without contrast media. Later in the study, as the severity increased, some calculi were visible on survey films, but dilation of urinary tract lacked contrast to delineate without a contrast agent. Two years after initial diagnosis, survey radiographs revealed bilateral, multiple, smoothly marginated, round mineral radiopacities up to 1 cm dispersed throughout the renal pelvises and calyces. No mineral radiopacities were visible within the ureter lumen initially but they were later visualized radiographically within 2 years, as well as within the urinary bladder.
The nephrographic stage was not obtained with this technique, therefore, unsuitable for diagnostics of the renal cortex. The pyelogram was well delineated and exhibited variable hydronephrosis and/or hydroureter most clearly and bilaterally at 20- and 40-minute radiographs. The optimal visualization of the ureters was observed at 60 minutes, and the bladder at 80 minutes.
The renal calyces were mildly dilated, lobular, and disorganized. The opacification of the renal calyces, renal pelvis, and ureters was found to be sufficient for a diagnostic pyelogram. Over the next 2 years, ureters and pelvis became progressively twisted, lobulated, and disorganized. The study animals died in polyuric renal failure and were confirmed as grossly severely affected with cystic, ureter, and renal pelvic urolithiasis.
Necropsies performed on 26 otters in previous reports with radiographic evidence of mineral radiopacities confirmed the cause of opacification to be calculi.1 In this study stones surgically removed from the bladder, or from necropsy were described as a smooth nodular white surface, and a core of approximately 1:1 ratio of uric acid and calcium oxalate, devoid of bacterial components (Urinary Stone Analysis Laboratory, Davis, CA). No adverse effects were documented from the technique in this study.
Recommendations and Discussion
Diagnostic subcutaneous excretory urography can be achieved in Asian short-clawed otters using intravenous renal contrast media in combination with 150 IU hyaluronidase. Renal cortical evaluation (i.e., first phase nephrogram) is limited with this technique, but pyelography, urethrography, and cystography are good to excellent. Hydrostatic distension secondary to partial excretory blockage (hydronephrosis/hydroureter) may be evident years prior to the radiographic opacity observed from the uroliths themselves. Although resolution or reversal of the mineralization process was not evident, therapeutic agents, diet modification, urine pH modifiers may be indicated earlier in the course of the disease. Thus, early diagnosis enhances the potential for successful treatment. All urine samples should be obtained prior to the administration of any therapeutic or diagnostic agent in order to avoid inaccurate test result.
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