Investigation of the urinary tract

With the exception of renal and scrotal masses or tenderness, a palpable bladder or an abnormal prostate on digital rectal examination, urological conditions are most likely to be diagnosed from the history or by investigations.

Urine

Dipsticks impregnated with chemicals which change colour in the presence of blood, protein or nitrites (Multistix; Labstix) are a convenient way to screen urine for the presence of abnormalities. When the urine is macroscopically clear and negative on dipstick testing the chances of finding an abnormality on microscopy and culture of a midstream clean-catch specimen are small. Indeed, some bacteriological laboratories decline further examination of the urine in these circumstances on the grounds that it is not cost-effective. The presence of protein and nitrites (which are a product of the activity of organisms in the urine) indicates the likelihood of infection. The significance of microscopic haematunia is discussed above. Some dipsticks also give an indication of the pH and specific gravity of the urine.

Microscopy is essential to confirm the presence of white and red blood cells in the urine, and bacteria may also be visible under light microscopy. The presence of protein casts suggests disease affecting the renal parenchyma, as does red cell dysmorphia seen on phase contrast microscopy. Schistosoma ova have a typical appearance (Fig. 63.2), and vegetable or meat fibres may be present if there is a fistula connecting the bowel with the urinary tract.

Cytological examination of the urinary sediment is sensitive and specific for poorly differentiated transitional cell tumours anywhere in the urinary tract. However, false negatives are common in the 50 per cent of these cancers that are well differentiated. A new chemical rest (BTA-Bard©) detects a bladder tumour antigen in the urine, and its findings can complement cytological examination of the urine.

Bacteriological culture of a clean catch midstream specimen of the urine is the standard means of identifying urinary pathogens. The presence of organisms at a level of 105/ml is deemed to indicate the presence of infection rather than contamination of the urine by bacteria. If there are pus cells in the urine but there is no growth on the routine culture media (sterile pyuria) it is worth testing for more fastidious organisms. The centrifuged sediment of multiple early morning urine specimens must be cultured on Lowenstein—Jensen medium to detect urinary tract tuberculosis. Chlamydia is another common urinary pathogen that will not be detected on routine culture.

Biochemical examination for electrolytes, glucose, bilirubin, haemoglobin and myoglobin is essential to detect abnormal amounts of these substances in urine. Analysis of a 24-hour specimen of urine will quantify the rate of loss, and is especially useful in the investigation of calculus disease due to abnormal excretion of calcium, oxalate, uric acid and other products of metabolism.

Tests of renal function

More than 70 per cent of the kidney function must be lost before renal failure becomes evident: there is a large functional reserve. It follows that renal damage must be extensive before changes occur in blood constituents whose level is controlled by renal excretion. Such damage is of three main types: reduction of renal plasma flow, destruction of glomeruli or impairment of tubular function. In severe hypertension or renal artery stenosis, the plasma flow is impaired. In glomerulonephritis or acute cortical necrosis, there is a loss of glomeruli, while in pyelonephritis tubular function is most severely affected. In obstructive nephropathy, back-pressure on the renal parenchyma causes all three types of damage.

Levels of blood urea and serum creatinine can be affected by various factors but in practice, when taken together, they serve as a useful clinical guide to overall renal function. A creatinine clearance will give an approximate value for glomerular filtration rate but is prone to error. A more accurate assessment of glomerular function can be obtained from an estimate of the clearance of chromium-51-labelled ethylenediaminetetra acetic acid. Surgeons will usually call on their nephrological colleagues for more detailed investigation of tubular function and renal blood flow

The specific gravity of the urine is fixed at a low level when the kidney loses the power to concentrate because of renal tubular dysfunction. Estimation of urinary loss of sodium, B2-microglobulin or the tubular enzyme N-acetyl-B-D-glucosamine (NAG) will further define the nature of functional impairment.

Radiology—contrast studies

A plain abdominal X-ray showing the kidneys, ureters and bladder (the KUB) can disclose a wealth of useful information. With the film properly orientated (with the liver on the right and gastric air-bubble on the left unless there is situs invertus!) a glance at the spine and bony structures may reveal the presence of scoliosis, spina bifida, degenerative disease of the spine, metastases, fractures and arthritis. All of these may have a relevance to the urological diagnosis. The soft-tissue shadows of the kidneys, outlined to a greater or lesser extent by their more radiolucent fatty coverings, overlie the upper attachments of the psoas muscles. A full bladder often presents a hazy outline arising from the pelvis.

Most urinary calculi absorb X-rays and should be sought in the region of the renal shadows and along the course of each ureter. This normally follows the tips of the transverse processes of the vertebrae, crosses the sacroiliac joints and heads for the ischial spine before hooking medially towards the bladder base. Stones with a low calcium content and those overlying bony structure may be difficult to see on the plain film. Pelvic phleboliths are very common and can look like lower ureteric calculi. Uric acid stones are the most common radiolucent calculi.

Intravenous urogram (urography; IVU) (Fig. 63.3)

Excretion renography has been a mainstay of urological investigation since the introduction of intravenous contrast media in the 1930s. These are organic chemicals to which iodine atoms are attached to absorb X-rays. When injected, usually into a vein in the antecubital fossa, the substance is filtered from the blood by the glomeruli and does not undergo tubular absorption. As a result, it rapidly passes through the renal parenchyma into the urine which it renders radio­opaque.

Although the IVU gives excellent images of the urinary tract, its use should be restricted because in a few patients the iodine in the contrast medium may provoke a potentially life-threatening anaphylactic reaction. Patients with a history of allergy, atopy and eczema are particularly vulnerable, but severe reactions may occur without warning. Less invasive and dangerous imaging techniques are clearly to be preferred where they give comparable diagnostic information.

Preparation

It is usual to give a laxative to clear faeces that might otherwise obscure details of urinary tract anatomy. Modest fluid restriction is permissible but dehydration is dangerous because it may precipitate acute renal failure.

Technique

The patient is observed carefully while the first few drops of contrast medium (Urografin or Niopam 370) are injected. The earliest films, taken within minutes of the injection, show the renal parenchyma opacified by contrast medium the nephrogram phase. A delayed nephrogram on one side indicates unilateral functional impairment. Distortion of the renal outline or failure of part of the kidney to function suggests a space occupying lesion.

After a few minutes, the contrast is excreted into the collecting system opacifying the calyces and the renal pelvis. Later films show the ureters and, at the end of the study, the patient is asked to pass urine and a final film is taken to show detail of the bladder area. It is important to bear in mind that the static images of the IVU provide only snapshots of dynamic events in the urinary tract. The appearance of a normal ureter changes as peristaltic waves of contraction pass along it.

An IVU is particularly valuable to demonstrate tumours and calculi within the urinary tract which are sometimes difficult to see on ultrasonography. It may also be useful to show details of abnormal anatomy which are difficult to interpret on an ultrasonogram.

As ultrasonography and other forms of scanning have become more sophisticated, the indications for the urogram are fewer. Obstruction to the upper urinary tract interferes with transport of contrast medium into the urine which will show up as a nonfunctioning kidney on the standard urogram films. In these circumstances, a further radiograph taken many hours after injection of the contrast medium may show hazy opacification of a dilated system. Distortion of the calyces or the renal outline can equally be caused by a tumour or by harmless simple cysts. In each of these cases, more information can be obtained from ultrasonography or computerised tomography (CT).

Retrograde ureteropyelography (syn. retrograde ureterogram)

A fine ureteric catheter can be passed into the ureteric orifice through a cystoscope (Fig. 63.4). Contrast medium injected through the catheter will demonstrate the anatomy of the upper urinary tract. The procedure is particularly useful if there is doubt about an intraluminal lesion (Fig. 63.5) or if renal function is deficient (before surgery for pelviureteric junction obstruction, for instance). When a transitional tumour is found it can be sampled by aspiration of urine from the upper tract or by brush biopsy. Retrograde uretero-pyelography is possible under topical urethral anaesthesia using the flexible cystoscope.

Antegrade pyelography

Percutaneous puncture of a dilated renal collecting system is a reasonably simple procedure for the experienced interven­tional radiologist. The most common indication is the placement of a nephrostomy tube to drain an obstructed infected kidney or to provide access for percutaneous nephrolithotomy. Antegrade pyelography where contrast medium is introduced through the nephrostomy can be helpful when retrograde studies are prevented by obstruction at the extreme lower end of the ureter.

Digital subtraction arteriography (DSA)

Refinements in radiological imaging have now almost eliminated the need for translumbar aortography. Satisfactory imaging of the renal vessels can even be achieved by digital subtraction angiography after intravenous injection of contrast medium. More precise information can be obtained by intra-arterial injection through a fine catheter inserted into the femoral artery using the Seldinger technique. Arterography is now rarely used to demonstrate tumour vasculature in a hypernephroma (Fig. 63.6), but a flush venogram is useful when CT suggests tumour invasion of the renal vein and vena cava.

Cystography

Cystography is now most commonly a component of video-urodynamic assessment (see Chapter 65). Its role in assessing ureteric reflux in children has been largely superseded by radioisotope scanning and dynamic ultrasonography.

Urethrography

Ascending urethrography is valuable to demonstrate the extent of a urethral stricture (Fig. 63.7) and the presence of false passages and diverticula associated with it. A urethrogram can be used to assess the extent of urethral trauma, but there is a serious danger that contrast medium may pass into the circulation. Lipiodol carries the danger of fat embolus and should never be used, and death has followed the use of barium emulsion. Umbradil viscous V is a radio-opaque water-soluble gel that contains the local anaesthetic lignocaine. It can be injected gently and safely using Knutsson’s apparatus even if the urothelium is breached.

Venography

Because extension of a renal carcinoma from the renal vein into the vena cava can usually be demonstrated by ultrasound or, venography is now infrequently used for this purpose.

Ultrasonography

High-resolution ultrasonography is perhaps the imaging technique most widely used in urology. The size of the kidney, the thickness of its cortex, and the presence and degree of hydro­nephrosis can be measured with great accuracy. Intra renal masses can be diagnosed as smooth walled and fluid filled (simple cysts) or solid and complex (possible tumours). The volume of urine in the bladder before and after micturition can be calculated, and even tiny filling defects within it detected. Scrotal contents can be displayed in great detail. Only the lower ureter resists effective investigation by transabdominal ultrasonography because of its small calibre and its proximity to the large bones of the pelvis and spine.

Transrectal ultrasonography

This has become a routine component of the investigation of suspected carcinoma of the prostate. Most commonly, suspicion has arisen because the patient has a raised prostate specific antigen or there is an abnormality of the texture or outline of the prostate on digital rectal examination. The features of carcinoma or benign enlargement of the prostate, while not absolutely specific, are sufficiently well recognised to allow an experienced ultrasonographer to identify promising sites for transrectal fine-needle biopsy.

Computerised tomography

CT is particularly useful to assess structures in the retroperitoneum (Fig. 63.8). In renal carcinoma it will show:

  the size and site of the tumour and. the degree of invasion of adjacent tissue;

   the presence of enlarged lymph nodes at the renal hilum;

   invasion of the renal vein and vena cava.

CT is of crucial importance in the initial staging and follow-up of men with testicular cancer in whom the presence of retroperitoneal lymph node masses is a feature of advanced disease. It has also been used to stage bladder and prostate cancer, but its value is less clear cut in these diseases.

Magnetic resonance imaging

In the investigation of renal, bladder and prostatic disease, magnetic resonance imaging is not clearly superior to good-quality CT. Positron emission tomography may prove to be more valuable in staging urological maligancies.

Radioisotope scanning

Radioisotope scanning is used in particular to obtain information about function in individual renal units. Diethyltriaminepentacetic acid (DTPA) behaves in the kidney like inulin: it is filtered by the glomeruli and not absorbed by the tubules. Using a gamma camera, DTPA labelled with technetium-99m can be followed during its transit through individual kidneys to give dynamic representation of renal function. A 99”Tc-DTPA scan is particularly useful to prove that collecting system dilatation is due to obstruction. In obstruction, radioactivity will remain in the kidney even if urine flow is stimulated by administration of a diuretic. Other substances (DMSA, MAG-3 and Hippuran) labelled with suitable radioactive isotopes have similarly been used to investigate renal function (Fig. 63.9).

Isotope bone scanning is fundamental to staging kidney and prostate cancers which typically metastasise to the skeleton.

Endoscopy

Effective visual inspection of the lower urinary tract has been possible since 1877 when Nitze invented his cystoscope. A second leap forward in urological endoscopy came with the introduction by Hopkins of the rodlens telescope and fibre-optic illumination. This permitted the development of a family of endoscopes which allow the urologist to visualise the upper and lower urinary tract for diagnosis and therapy. Finally, in the early 1980s, the small calibre flexible fibrescopic cystoscope was introduced. This allows simple diagnostic cystourethroscopy, bladder biopsy and retrograde ureterography to be performed under topical urethral anaesthesia with minimal discomfort to the patient.