Ultrasonography of the kidneys, bladder and prostate is well established. Unfortunately, it is often used indiscriminately. An ultrasound scan cannot provide the detailed visualization of the calyces and pelvis required to demonstrate pelvicalyceal abnormalities such as reflux nephropathy or papillary necrosis. It does not visualize the greater part of the ureter and gives no functional information on the upper tract. It requires considerable operator skill in performance. For the general investigation of suspected renal disease, IVU remains the imaging technique of first choice.
The particular value of ultrasound is in defining:
RENAL MASSES OR CYSTIC DISEASE
PRESENCE OR ABSENCE OF OBSTRUCTION in patients with renal failure when urography is unlikely to provide calyceal detail and the administration of contrast medium may be less safe
RENAL SIZE in a patient with renal failure BLADDER EMPTYING combined with urodynamic studies
THE PROSTATE by means of a rectal transducer Computed tomography (cr) CT has a valuable role in the diagnosis of renal tumours when this is not possible by ultrasound or excretion urography, and in the diagnosis of retroperitoneal masses. It is also valuable in defining the presence and spread of bladder or prostatic tumours and in visualizing uric acid stones which are radiolucent on conventional X-ray.
Antegrade urography involves percutaneous puncture of a renal calyx, with the insertion of a fine catheter and the injection of contrast medium in an antegrade fashion. It is the procedure of choice in patients with upper urinary tract obstruction demonstrated by ultrasound. Not only does it allow definition of the site of obstruction but also the catheter may be left in situ to allow urine drainage in oliguric patients.
Following cystoscopy, preferably under screening control,a catheter is either impacted in the ureteral orifice or passed a short distance up the ureter, and contrast medium is injected; this is followed by X-ray filming. This investigation is less often used as it is invasive, commonly requires a general anaesthetic and may result in the introduction of infection. It is mainly used to investigate lesions of the ureter and to define the lower level of ureteral obstruction shown on excretion urography or ultrasound plus antegrade studies.
Micturating cystourography (MCU) This involves catheterization and the instillation of contrast medium into the bladder. The patient is then screened and filmed during voiding to demonstrate or exclude vesicoureteric reflux and to study bladder emptying. It is primarily used in children with recurrent infection and in adults with disturbed bladder function, when it may be combined with urodynamic studies of bladder pressure and urethral flow. MCU is not an appropriate part of the investigation of the adult female with recurrent bacterial cystitis in whom IVU, including an after-micturition bladder film, is normal. The presence or absence of vesicoureteric reflux may also be investigated by scintigraphy.
Aortography or renal arteriography
Conventional or digital subtraction angiography (DSA) are used. The latter allows the use of smaller doses of contrast medium which can be injected via a central venous catheter (venous DSA) or via a fine transfemoral arterial catheter (arterial DSA). Angiography is mainly used for extrarenal or intra renal arterial disease and the presence and extent of renal tumours.
Renal scintigraphy using a gamma camera is divided into:
1 Dynamic studies in which the function of the kidney is examined serially over a period of time, most often using a radiopharmaceutical excreted by glomerular filtration
2 Static studies involving imaging of tracer that is taken up and retained by the renal tubule
The radiopharmaceutical most often used is [99mTcjDTPA. It is excreted by glomerular filtration. 123I_ labelled ortho-iodohippuric acid (Hippuran) is both filtered and secreted by the tubules and is also used but is more expensive and not generally available. Following venous injection of a bolus of tracer, emissions from the kidney can be recorded and stored on computer for analysis of time-activity curves. Analogue images can also be generated at intervals as the study proceeds. This information allows examination of blood perfusion of the kidney, uptake of tracer as a result of glomerular filtration, transit of tracer through the kidney and the outflow of tracer-containing urine from the collecting system.
Dynamic studies are used for:
RENAL BLOOD FLOW. To investigate patients in whom renal artery stenosis is suspected as a cause for hypertension and in patients with severe oliguria (posttraumatic, post-aortic surgery, or after a kidney transplant) to establish whether and to what extent there is renal perfusion. In patients with unilateral renal artery stenosis there is, typically, a slowed and reduced uptake of tracer with delay in reaching a peak. Studies carried out before and after administration of an ACE inhibitor may demonstrate a fall in uptake that is suggestive of functional arterial stenosis. The usefulness and reliability of this test has recently been questioned. In patients with total renal artery occlusion, no kidney uptake of tracers is observed.
INVESTIGATION OF OBSTRUCTION. Renography can demonstrate the severity of obstruction. The results obtained from overall uptake and outflow curves must be treated with caution because of the large ‘dead space’ commonly contributed by dilated calyces and pelves. Dynamic scintigraphy combined with the injection of frusemide can commonly distinguish functional obstruction from a dilated non-obstructed system. BLADDER EMPTYING. At the end of dynamic studies, bladder emptying may be investigated and any postmicturition residual measured. Vesicoureteric reflux may be observed, although the sensitivity for detection of this is low. Increased sensitivity can be obtained by direct isotope cystography when a dilute isotope solution is instilled into the bladder by catheter.
GLOMERULAR FILTRATION RATE .
Static renal scintigraphy
This is usually performed using [99mTcjDMSA (dimercaptosuccinic acid), which is taken up by tubular cells. Uptake is proportional to renal function. Static studies are used for:
RELATIVE RENAL FUNCTION. Function is normally evenly divided between the kidneys with a range of 45- 55%. Static studies are particularly useful in unilateral renal disease, where the relative uptake of the two kidneys can be calculated.
KIDNEY VISUALIZATION. Normal kidneys show a uniform uptake with a smooth renal outline. Scars can be identified as photon-deficient ‘bites’. Static scintigraphy is of considerable value in identifying ectopic kidneys or ‘pseudotumours’ of the kidneys, i.e. normally functioning renal tissue abnormally placed within the kidney.
LOCALIZATION OF INFECTION. The use of citrate labelled with gallium-67 or isotopically labelled leucocytes that are taken up by inflammatory tissue may be of value in defining localized infection, such as renal abscesses or infection within a renal cyst.
Indications and contraindications for renal biopsy. The biopsies are carried out under ultrasound control using a spring loaded biopsy needle. Tissue must be examined by conventional histochemical staining, by electron microscopy and by immunofluorescence. The complications of transcutaneous renal biopsy are shown.