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
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,
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.
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
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