Excretory urography

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Excretory urogram of a young Newfoundland dog with urinary incontinence and recurrent cystitis due to bilateral ectopic ureters with marked secondary hydroureter[1]

Excretory urography (Intravenous urography, intravenous pyelography) is a diagnostic test used to visually clarify renal function in the canine patient, allowing contrast media-enhanced visualization of the kidneys, ureters, urinary bladder and urethra.

Radiographic imaging using intravascular iodinated contrast agents was the mainstay of many advanced diagnostic procedures prior to the 1990s, prior to the advent of diagnostic ultrasonography and CT scans, which resulted in a marked decrease of abdominal and cardiac contrast procedures in many referral veterinary centers[2]. However, it is still a viable procedure in many non-referral veterinary practices.

Although lacking the accuracy of visual inspection afforded with laparotomy, it is a relatively non-invasive, low-risk procedure for detection of renal parenchymal filling defects, renal pelvic dilatation or pelvic defects, pyelonephritis, renal agenesis[3], renal dysplasia, ectopic kidney, hydroureter, hydronephrosis, ureterolithiasis, ureteral stenosis[4], ureteral atresia, ectopic ureters[5] and urinary tract ruptures[6].

This diagnostic test involves induction of general anesthesia and serial radiographic images taken following the intravenous injection of radio-opaque contrast dyes such as diatrizoate meglumine, iothalamte, iohexol or iodixanol[7]. These dyes are categorized according to their physical and chemical properties.

The most commonly used second generation iodinated compounds (iopamidol and iohexol) are low osmolar, non-ionic monomers which have improved vascular tolerability and thus have fewer side effects[8].

Third generation iodinated contrast media (iodixanol and iotrolan) are iso-osmolar, non-ionic dimers and are reported to be the safest contrast agents to date. However, their high cost limits their use in acute renal injury patients[9]. Anaphylaxis has been reported with use of gadobenate dimeglumine used as an MRI contrast medium, and antihistamines should be employed prior to use of this drug[10].

Excretory urography is normal indicated in dogs with a history of incontinence, acute renal injury and non-age-related chronic renal disease and complicated urolithiasis cases. Plain radiographs should be performed in most cases prior to this test, to assess normal kidney size (usually bean-shaped and 2.5 - 3.5 times large than the length of the second lumbar vertebra. The right kidney is usually one-half length cranial to the left kidney and have a soft-tissue or watery density throughout and are more dense than perirenal fat.

As a prior workup on cases, contrast cystography should be conducted to exclude urinary bladder position, size or shape and evidence of filling defects. Ultrasonography will also help exclude mass effects, urinary calculi and extrinsic nonskeletal abnormalities such as amyloidosis or renal tumors[11].

Prior to excretory urography, the canine patient should be fasted for 24 hours and administered a cleansing enema the evening before as well as 1 - 3 hours prior to procedure.

General anesthesia is then induced and an intravenous bolus injection given at 500 mg of iodine/kg bodyweight.

Imaging is best performed using either normal radiography or CT scans[12][13], showing greater accuracy than digital fluoroscopic excretory urography[14] but inferior to transurethral cystoscopy when detecting ectopic ureters at the ureterovesicular junction[15].

Following injection of the iodinated dye, a ventrodorsal radiographs of the abdomen is obtained immediately, then at 1, 5, 10, 20, 40 and 60 minutes after injection, including left to right lateral radiographs at 10 minutes after injection.

The addition of furosemide (at 4 mg/kg)[16], ascorbic acid[17] and low dose dopamine[18] have been shown to improve visualization of the renal pelvis and protect renal tubules from prolonged exposure to concentrated contrast medium..

Side-effects associated with iodinated contrast dyes are not uncommon, including transient vomiting, anaphylactoid reactions, hypotension, tachycardia, muscle tremors, contrast-induced renal failure, urticaria and bronchospasm[19].

References

  1. Heuter KJ (2005) Excretory urography. Clin Tech Small Anim Pract 20(1):39-45
  2. Kirberger RM et al (2012) The effects of repeated intravenous iohexol administration on renal function in healthy beagles--a preliminary report. Acta Vet Scand 54:47
  3. Diez-Prieto I et al (2001) Diagnosis of renal agenesis in a beagle. J Small Anim Pract 42(12):599-602
  4. Lam NK et al (2012) Endoscopic placement of ureteral stents for treatment of congenital bilateral ureteral stenosis in a dog. J Am Vet Med Assoc 240(8):983-990
  5. Anders KJ et al (2012) Ectopic ureters in male dogs: review of 16 clinical cases (1999-2007). J Am Anim Hosp Assoc 48(6):390-398
  6. Bischoff MG (2003) Radiographic techniques and interpretation of the acute abdomen. Clin Tech Small Anim Pract 18(1):7-19
  7. Kishimoto M et al (2007) Comparison of excretory urographic contrast effects of dimeric and monomeric non-ionic iodinated contrast media in dogs. J Vet Med Sci 69(7):713-715
  8. Widmark JM (2007) Imaging-related medications: A class overview. Pro Baylor Med Cen Pharmacol Notes 20:408-417
  9. Hsieh YC et al(2006) Iso-osmolar contrast medium better preserves short- and long term renal function after cardiovascular catheterizations in patients with severe baseline renal insufficiency. Int J Cardiol 111:182-184
  10. Girard NM & Leece EA (2010) Suspected anaphylactoid reaction following intravenous administration of a gadolinium-based contrast agent in three dogs undergoing magnetic resonance imaging. Vet Anaesth Analg 37(4):352-356
  11. Silverman S & Long CD (2000) The diagnosis of urinary incontinence and abnormal urination in dogs and cats. Vet Clin North Am Small Anim Pract 30(2):427-448
  12. Feeney DA et al (1979) Normal canine excretory urogram: effects of dose, time, and individual dog variation. Am J Vet Res 40(11):1596-1604
  13. Rozear L & Tidwell AS (2003) Evaluation of the ureter and ureterovesicular junction using helical computed tomographic excretory urography in healthy dogs. Vet Radiol Ultrasound 44(2):155-164
  14. Samii VF et al (2004) Digital fluoroscopic excretory urography, digital fluoroscopic urethrography, helical computed tomography, and cystoscopy in 24 dogs with suspected ureteral ectopia. J Vet Intern Med 18(3):271-281
  15. Cannizzo KL et al (2003) Evaluation of transurethral cystoscopy and excretory urography for diagnosis of ectopic ureters in female dogs: 25 cases (1992-2000). J Am Vet Med Assoc 223(4):475-481
  16. Secrest S et al (2013) Effects of furosemide on ureteral diameter and attenuation using computed tomographic excretory urography in normal dogs. Vet Radiol Ultrasound 54(1):17-24
  17. Romano G et al (2008) Contrast agents and renal cell apoptosis. Eur Heart J 29(20):2569-2576
  18. Choi J et al (2001) Effect of dopamine on excretory urographic image quality and the prevention of contrast-induced nephropathy in dogs. J Vet Med Sci 63(4):383-388
  19. Hita Rosino E et al (1999) The adverse effects of the water-soluble iodinated contrast media used in excretory urography in the canine species. Actas Urol Esp 23(5):385-393