ABSTRACT: The purpose of this article is to give the reader background information on urinary tract radiographic studies and a step-by-step guide to their use in practice.

The urinary tract consists of the kidneys, ureters, bladder and urethra. When conducting radiographic contrast studies of the area, valuable information is also obtained about the prostate and vagina, which may be pertinent to the presenting condition. Contrast media are especially useful when the area in question has a lack of inherent contrast in comparison to the surrounding areas.

Contrast media

Both positive and negative contrast media are used, independently or in combination. The most common negative contrast medium used is room air, although CO2, N2O and O2 are safer because they are plasma soluble and therefore the risk of an air embolus is reduced.

The positive contrast agents used are water-soluble contrast media (WSCM). They are iodine-based compounds which are clear, viscous solutions and may be ionic or non-ionic. They can be injected directly into the vascular system and then excreted by the kidneys, or used by retrograde administration in the urinary bladder, urethra and, vagina.

Preparation

When undertaking a urinary tract study preparation and a systematic approach are the keys for a successful diagnostic study.

Ensure the area and indications for the study are understood and that patient preparation has been undertaken – e.g. enemas, clean hair coat etc. It is important that all the required equipment is ready. Create a practice urinary tract study box, which is replenished after each study (Table 1). Make sure the order of the technique to be used has been planned, that the animal’s clinical history and any contraindications/complications have been taken into account, and that survey radiographs in two planes (lateral and VD) are taken. These are essential as they may be diagnostic in themselves – ensures exposure and settings and processing are satisfactory, and confirms good patient preparation.

Note that urine samples should be collected before any contrast studies are conducted because contrast media are bacteriostatic; and nurses should always ensure the bladder is empty of air and/or contrast media at the end of the study.

1. Intravenous urography (IVU)

This low volume/rapid injection technique opacifies the kidneys, ureters and urinary bladder, and the sequential radiographs produced show the four phases of the study.

Indications

Urinary incontinence, dysuria, haematuria and pyuria

Patency and qualitative assessment of renal function Trauma to urinary tract Post-operative assessment of the urinary tract

Effect of retroperitoneal/intraabdominal masses.

Contraindications

Anuria or severe uraemia Severe dehydration Previous contrast reaction.

Patient preparation

Starve for 12 -24 hrs Give an enema the evening prior to, and the morning of, the study – this may need to be repeated after survey radiographs if faeces are still present Place a wide bore over-the-needle intravenous (i/v) catheter in the cephalic/saphenous vein, attach a T-connector.

Restraint

Anaesthesia.

Potential complications/Nursing considerations

Hypotension Acute renal failure

Anaphylactic reaction to contrast media i/v fluid therapy

Warm contrast to ease administration by reducing viscosity Monitoring – pulse oximeter, non- invasive blood pressure, oesophageal stethoscope, temperature, electrocardiograph, and capnography where available.

Order of study

1.   Anaesthetise the patient.

2.   Take survey lateral and VD abdominal radiographs.

3.   Perform an enema if required and repeat lateral radiograph to make sure colon/rectum empty.

4.   Catheterise the urinary bladder and empty urine (collect samples if required).

5.   Moderately fill with air (see pneumocystogram), this increases back pressure in the ureters, improving filling.

6.   Take lateral abdominal radiograph.

7.   With the animal positioned in dorsal recumbency, and the cassette, collimation and settings ready for a ventrodorsal (VD) abdominal radiograph, a total dose of WSCM between 800 -1200 mg I/kg (as low as 600 mg I/kg still gives good results e.g. 2 ml/kg of Omnipaque 300*) should be given by rapid i/v injection.

Radiographs (Figures 1 & 2) 

Figure 1: IVU series showing the different phases in a normal adult dog. A: vascular phase, contrast within the vessels can be seen. B: nephrogram showing contrast in the renal parenchyma and already in the renal pelvis and ureters. C: pyelogram showing better filling of contrast within the renal pelvis and ureters. D: 10 minutes post injection radiograph. Note. Owing to the ureteric peristalsis we can only assess the whole ureters, length by analysing radiographs taken at different times

Figure 2: A: IVU study showing bilateral hydronephrosis and hydroureter in a puppy bitch with bilateral ectopic ureter. B: One of the abnormal ureters can be seen running dorsal to the bladder neck into the urethra (*). Note the incidental metallic foreign body within the small intestine. Va: vagina, Ur: urethra, U: ureter.

Immediately after administration, VD – vascular phase

1 minute after, VD – nephrogram phase 5 minutes after, VD +/- lateral – pyelogram phase

10 minutes VD, lateral and right/left oblique views – ureteric excretion and visualisation of vesicoureteral junction

Generally all animals should be on i/v fluids; a rate of twice maintenance would be suitable in most cases, this may reduce the opacification of structures to be seen.

Note. Timings may alter and additional radiographs may be taken depending on the results of radiographs already obtained.

2. Cystography

This contrast technique evaluates the urinary bladder using negative, positive and double contrast techniques.

Indications

Urinary incontinence, dysuria, haematuria and urinary infection Suspected damage to the urinary bladder Abnormal appearance or position of urinary bladder on survey radiographs.

Patient preparation

Warming of contrast media is not required 

As heading, 1. Intravenous
urography (IVU) on page 29.

Restraint

Anaesthesia.

Pneumocystogram

This technique is useful to examine the size, shape and position of the urinary bladder, but is most useful when used in conjunction with positive contrast.

Potential complications/Nursing considerations

Bladder rupture – if severely compromised bladder wall is suspected Intramural air – caused by previous bladder damage or traumatic catheterisation

Fatal air embolus – is uncommon but bladder wall damage, e.g. severe cystitis can increase the risk. To avoid the risk use a plasma soluble gas (not pressurised), or if not available position the animal in left lateral recumbency (air will then dissipate in the right cardiac outflow) Iatrogenic bladder rupture.

Order of study

1.   Anaesthetise the patient.

2.   Take survey lateral and VD abdominal radiographs.

3.   Perform enema if required and repeat lateral radiograph.

4.   Catheterise the urinary bladder using a catheter as close to the size of the

5.   Gently fill the bladder with air. It is important to palpate the bladder whilst filling and to stop when the bladder feels turgid but not tight. A good indication of the amount of air to infuse is the volume of urine removed if the survey radiographs show a normal size bladder. The amount of air to be infused is generally reported to be somewhere between 6 – 12 ml/kg but patients undertaking studies of this type may have bladder abnormalities.

6.   Over- or under- distension should be avoided. Over-distension will obscure mucosal and mural changes whilst under distension may cause artefactual lesions.

7.   Lateral abdominal radiographs (Figures 3, 4 & 5).

Figure 3: Normal appearance of the bladder in an adult male dog after pneumocystography. Note the presence of large amounts of faeces in the colon. This is inadequate patient preparation

Figure 4: Pneumocystogram in an adult cat with marked bladder wall thickening compatible with severe cystitis. Note the amputation and crocodile clip

Figure 5: Pneumocystogram in an adult male dog showing a verrucose mass extending into the trigone (blue *) and bladder neck (white *)

In females, deflate the Foley and remove the catheter, or push the catheter into the urinary bladder to avoid bladder neck distortion. Take an exposure.

In males, remove the catheter or position the catheter at the tip of the penis and infuse air; this will show a nice negative study of the urethra (pneumourethrography). Take an exposure (Figure 6).

Figure 6: Retrograde pneumourethrography in a male dog with a small and thickened urinary bladder and wide bladder neck (blue *). Note the normal urethral lumen outlined by the negative contrast (white*). Note the tongue forceps on the prepuce

Positive contrast cystogram

The main reason to perform a positive contrast cystogram is low urinary tract rupture (bladder, urethra). The procedure is carried out in the same way as a pneumocystogram using iodine-based WSCM. A suitable concentration would be 150 mg I/ml; this can be easily achieved by diluting Omnipaque 300 (300 mg I/ml) with an equal amount of water for injection (WFI) and keeps stock items to a minimum.

If urethral rupture is suspected, inject contrast from the tip of the penis in males or the vestibule in females, occlude the prepuce/vulval lips as described in retrograde urethrography (Figure 7).

Figure 7: Positive contrast cystogram in a male dog with urinary bladder rupture. Note the leakage of contrast media into the abdominal cavity (black *) and the irregular and disrupted urinary bladder wall (white *)

Double contrast cystogram (DCC)

This technique combining negative and positive contrast is preferred to diagnose most luminal and mural lesions (Figure 8).

Figure 8: Double contrast cystogram where marked bladder wall thickening (white *) and inflammation of the urothelium is demonstrated by the contrast adherence to the bladder wall (blue *). Note the presence of gas bubbles

Potential complications/nursing considerations

As per pneumocystogram Haematuria resulting from use of nondiluted WSCM. This will resolve.

Order of study

1.   Pneumocystogram.

2.   Empty the bladder of air.

3.   Between 1 – 5 ml of WSCM (Omnipaque 300) depending on the size of the animal should be administered via a catheter.

4.   Rock /massage the bladder to ensure the mucosal wall is coated.

5.   The contrast may be left in the bladder or partially removed (personal preference).

6.   Perform a pneumocystogram, a ventrodorsal projection may also prove useful.

3. Urethrography

This technique using a dynamic retrograde infusion of WSCM is used to examine the integrity and morphology of the urethra/ bladder neck/prostatic urethra and vagina.

Indications

Urinary incontinence, haematuria, dysuria

Urinary tract obstruction Prostatic disease Urethritis and urethral neoplasia Vaginal disease.

Patient preparation

As per cystography.

Restraint

Anaesthesia.

Potential complications/Nursing considerations

Urethral rupture

Vaginal rupture – Rough collies and Shetland sheepdogs appear prone to rupture (Davies personal communication) Bladder rupture.

Retrograde urethrography – males

Perform a pneumocystogram Fill a suitably sized catheter, tom cat catheter in cats with WSCM (150 mg I/ml) to avoid bubbles Aseptically place catheter tip into the urethra at the level of the base of the os penis

Remove some air from the bladder if over-distended

Occlude the prepuce using a pair of tongue/soft tissue forceps – not in cats.

Lateral abdominal radiographs

Between 2-25 ml (depending on the size of the animal) of the WSCM should be administered (by a suitably qualified and radiation protected person) whilst the machine is prepped, the exposure is taken at a clear verbal command as the last few millilitres of contrast are injected or when the pressure to inject has increased. The use of a wide bore extension tube to administer the WSCM will increase radiation safety (Figure 9).

Figure 9: Retrograde urethrogram in a dog showing numerous calculi (angulated filling defects) within the penile urethra

Retrograde vaginourethrography – females

Perform a pneumocystogram Carefully withdraw the catheter to minimize air leakage Place a new pre-filled Foley catheter the tip of which has been cut off just distal to the balloon in the vestibule just inside the vulval lips, a very small Foley catheter should be used for cats (the tip is removed to ensure the urethral orifice is not occluded preventing filling and the WSCM will come out centrally)

Occlude the vulval lips, inflate the balloon with air just enough to give a good seal and drawn caudally against the vulval lips while injecting the WSCM (Figure 10)

Figure 10: Close-up photograph of vulval lips clamped around Foley catheter using tongue forceps

Approximately 0.5 ml/kg of 150 mg I/ml should be infused as described for male urethrography. Care must be taken on infusion to avoid possible vaginal rupture (Figure 11).

Figure 11: Close-up view of a normal retrograde vaginourethrogram in an adult dog. UB: urinary bladder,

Ur: urethra, V: vestibule,

Va: vagina, US: uterine stump,

white *: air filled Foley catheter balloon,

black *: tongue forceps

Suspended retrograde maximum distension urethrography

If the facility is available, tilting the table approximately 20-30° tail down after the pneumocystogram and prior to administering contrast will facilitate better filling of the bladder neck and distension of the urethra and therefore produce superior images to those of standard retrograde studies (Davies personal communication).

Additional reading

OWENS, J. M., BIERY, D. N., Radiographic interpretation for the Small Animal Clinician.

BSAVA Manual of Small Animal Diagnostic Imaging. Second Edition, Ed R. Lee.

BSAVA Manual of Canine and Feline Abdominal Imaging, Eds Robert O'Brien and Frances Barr.

EASTON, S., Practical Radiography for Veterinary Nurses.

Author

Frankie Blundell BA(Hons) Business Studies RVN

Frankie qualified as a veterinary nurse in 1999 and worked in general practice for a number of years before joining Davies Veterinary Specialists, a multidiscipline small animal referral centre, four years ago. Frankie now works as a specialist radiology nurse within the radiology team, carrying out both radiography and CT studies and assisting with other imaging modalities.

• VOL 25 • No5 • May 2010 • Veterinary Nursing Journal