The genitourinary system

Modalities

 

KUB (Kidney-ureter-bladder survey)

A plain film of the kidneys and bladder is useful for the diagnosis of calculi, soft-tissue calcifications and gas. It is an integral part of all conventional X-ray examinations of the urinary tract (Fig. 1); it should always be performed prior to contrast medium injection.

Intravenous urography (IVU or IVP)

After the KUB has be en taken, contrast medium (e.g. 1 ml per kg body weight of a 300 mg I/ml solution independent of the kidney function) is injected into a vein. Within the first 60 seconds up to three exposures over the kidney are done in order to visualize the renal parenchyma during the nephrographic phase of the contrast passage (Fig. 2 a). Many radiologists make these exposures with tomographic technique (Fig. 2 b). Another film over the kidney region is taken 5 min. post contrast. If there are no contraindications (e.g. hydronephrosis, aortic aneurysm, recent surgery, big abdominal tumor), abdominal compression is applied in order to retain the opacified urine in the pelvis and ureter (Fig. 3). Five min. thereafter additional exposures of the kidneys including oblique views are taken. The compression is then removed and a full abdominal exposure is obtained. When the bladder is well filled a coned exposure of it is taken (Fig. 4). Linear tomograms of the kidneys, late radiographs, erect or prone views, bladder view after voiding are taken as needed.

	Figure 1. KUB covering the majority of the abdomen and the pelvic cavity. This is an indispensable adjunct to intravenous urography, and one should not attempt to interpret a urogram without it. The most common defiency is failure to demonstrate the upper and lower reaches of the urinary tract.
a	Figure 2. Nephrographic phase. a) Nephrogram taken 30s after start an intravenous bolus injection of contrast medium. At this time there is an obvious demarcation between medulla and cortex in normal kidneys. b) Nephrotomogram taken 45s after administration of contrast.
b
a	Figure 3. Urogram of the normal upper urinary tract taken before (a) and after (b) application of abdominal compression. The calyces are much better visualized after the abdominal compression has been applied.
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	Figure 4. Coned exposure of the bladder filled with contrast medium during intravenous urography.
	Figure 5. Multiple calyces/papillae demonstrated at intravenous urography. An uncommon normal variant.

Urography includes standard exposures, but should principally be individualized. The strengths of urography are 1) rapid overview of the entire urinary tract, 2) detailed anatomy of the collecting system, 3) demonstration of calcifications, 4) it is sensitive for obstruction, and 5) low cost, whereas the weaknesses are that: l) it depends on kidney function, 2) it provides little assessment of parenchymal structure (e.g. cystic vs. solid), 3) it does not show the whole renal contour and may miss masses arising from the anterior or posterior part of kidney, 4) the perinephric space is not demonstrated, 5) it necessitates the use of radiation and contrast medium, and 6) it provides no assessment of glomerular filtration rate. However, the latter can be determined by drawing a blood sample 3 to 4 hours after the contrast medium injection and measuring the iodine content in the sample; from this measurement the glomerular filtration rate can be calculated.

The ability of urography to show detailed calyceal anatomy and the overlying parenchyma makes it useful for the diagnosis of papillary necrosis, urothelial neoplasms, sponge kidney, adult polycystic kidney disease and urogenital tuberculosis. It is able to demonstrate the majority of calcifications within the urinary tract, but it is not as sensitive as CT. Its role in obstruction is debated; a combination of KUB, ultrasonography and diuresis renography is an alternative, but with acute obstruction (Le. colic) the urogram is usually diagnostic. Small mucosal abnormalities in the pyelocalyceal system and the ureter is best diagnosed at intravenous urography and it is therefore important for the diagnosis of early transitional cell carcinoma in the upper urinary tract. Congenital anomalies such as fusions, rotation anomalies, calyceal variants (Fig. 5) and duplications are well demonstrated by intravenous urography. In trauma, when the renal injury is thought to be minor, urography provides a quick and effective screen.

Direct Pyelography

Direct pyelography means direct injection of contrast medium (75-100 mg I/ml) into the upper urinary tract. It may be performed either through a catheter placed in the ureter during cystoscopy (retrograde) or through a needle or a nephrostomy tube (antegrade). A meticulous technique (e.g. sterile conditions, low injection pressure, diluted contrast medium solution with a low viscosity, fluoroscopic surveillance) should always be employed (Fig. 6). At this examination the visualization of the calyces, pelvis and ureter is independent of the kidney function in contrast to intravenous urography. Backflow (extravasation) into the renal parenchyma and surroundings (pyelosinous backflow, intrarenal backflow, pyelovenous backflow and pyelolymphatic backflow) should be avoided through a low injection pressure since backflow not only may cause complications (e.g. pain, infection) but also obscure the disease.

The examination is excellent for demonstration of 1) small mucosal abnormalities, 2) diverticula and cavities, 3) urinary leakage, and 4) obstructing process in the upper urinary tract, when intravenous urography has not been conclusive. The indications include: 1) non-visualization of the upper urinary tract on intravenous urography (unless there is an obvious cause such as a large tumor, in which case CT would be preferred), 2) an inconclusive or suspicious-appearing segment of the upper urinary tract which may be better visualized with direct pyelography, 3) unexplained hematuria in which intravenous urography did not completely delineate the entire ureter and/or renal pelvic cavity, 4) to differentiate intrinsic from extrensic ureteral processes, 5) severe contrast material reaction during intravenous urography (the examination may be performed with gas), 6) as an aid in the diagnosis of renal failure, e.g. renal papillary necrosis and 7) possibility of upper urinary tract obstruction (stricture,

Figure 6. Normal antegrade pyelogram demonstrating the pelvis and the upper part of the ureter. It is of utmost importance not to overdistend the pelvis and to use no greater than a 10-20 % contrast solution in order to avoid obscuring at both retrograde and antegrade pyelography.

calculus, papilla), 8) as an aid to brush biopsy, 9) with endourological procedures (e.g. percutaneous nephrolithotomy (PCNL)).

Cystography

Cystography means specific examination of the bladder with contrast medium. It can be performed following intravenous injection of contrast media (in conjunction with intravenous urography) or following direct installation of contrast medium either through a urethral or a suprapubic catheter. The bladder is examined in several views and exposures are often also taken during voiding (Fig. 7 a). A post-void film is essential. If vesicoureteric reflux is suspected the field of view should include both ureters and kidneys and fluoroscopic surveillance should be performed both during the filling (low pressure) and voiding (high pressure) phase keeping fluoroscopy time to a minimum. In case of examination for female incontinence the vagina is marked with barium sulphate, so-called colpocystourethrography. Cystography is mainly performed for the diagnosis of posttraumatic or post-operative urinary extravasation, to evaluate certain diverticula and to look for vesico-ureteral reflux.

Urethrography

Urethrography may be performed antegrade (micturition, voiding) or retrograde. Urethrography is an example of an examination which modern imaging techniques have not yet displaced. In males an obturating canula system or a small balloon catheter is placed with the tip in the fossa

a	b
Figure 7. Cystourethrogram in females. a) Normal cystogram obtained during voiding. b) Double balloon catheters can be used for visualization of a diverticulum (arrow) in the female urethra. Contrast medium enters the urethra via a catheter opening between the balloons which occlude the bladder neck and external urethral meatus.

navicularis and water-soluble contrast medium is injected retrogradely through the urethra and up into the bladder. In females the short urethra is difficult to examine but special catheters with two balloons (one for the internal orifice and one for the external orifice) have been developed (Fig. 7 b). Examination during voiding is best for the posterior urethra, but nearly always results in inferior visualization of the anterior urethra. Retrograde studies are excellent for the anterior urethra, but inferior for the posterior urethra.

Urethrography is used for the diagnosis of urethral strictures, diverticula, tumors and in trauma. It may also be helpful in certain postoperative conditions.

Hysterosalpingography

Today hysterosalpingography is primarily used in the work -up of female infertility; previously it was also used for diagnosis of uterine body and cervical disease. As with urethrography either a cone-tipped obturator is placed in the external cervical orifice or a tiny balloon catheter inserted in the uterine cavity. A water-soluble contrast medium is injected slowly in order to demonstrate that the salpinges are open and that contrast spreads freely in the peritoneal space (Fig. 8). Exposures are taken after the patient has been lying on all sides for a few minutes in order to secure

Figure 8. Normal hysterosalpingogram (HSG). There is free flow through the salpinges and out into the peritoneal space.

free distribution of the contrast medium in the pelvic cavity of the peritoneal space.

Angiography

Angiography of the genitourinary system does not differ from the same examination of other organ systems. A catheter is introduced into the venous or arterial system using Seldinger technique. The tip of the catheter is placed during fluoroscopic guidance in a vessel leading to or coming from the region of interest. Injection of vasoconstrictive drugs may be useful when the veins are examined through retrograde injection but with the modem digital equipment visualization of the venous tree is often possible following intraarterial injection of contrast material.

Renal arteriography to diagnose and differentiate renal masses is rarely performed now due to the advent of ultrasonograhy and especially CT. Angiography may be performed in the planning of surgery on an anomaly (e.g. horseshoe kidney) or partial nephrectomy. Other residual indications for renal arteriography includes suspected renal artery stenosis, vasculitis (e.g. polyarteritis nodosa), aneurysms and arterio-venous fistulae. Arteriography is necessary during vascular interventions such as embolization, stenting and balloon dilatation of the venal vessels.

Ultrasonography

Ultrasonography has gained a central position in genito-urinary imaging. It has a diagnostic potential in almost every part of the genito-urinary tract and is furthermore easy, cheap and non-invasive. The major disadvantage is that it is very operator dependent.

Figure 9. Ultrasonography of a normal kidney. The normal parenchyma is echo poor, whereas the renal sinus is echo rich. The non-dilated renal pelvis is obscured by the sinus echoes.

Several special probes have been developed for ultrasonographic examination of the genito-urinary tract. First of all there are the traditional abdominal transducers, which are useful for examination of the kidneys (Fig. 9) and the adrenals and overview examination of the pelvic organs. If the examination with this probe is inadequate one can supplement by using a transrectal (proximal urethra, prostate), transvaginal (female genitals, posterior part of the bladder) or transurethral probe (bladder wall).
Traditional ultrasonography gives information about morphology (e.g. solid vs. cystic), but not about function. Perfusional data require Doppler or color Doppler. By flow characteristics and frequency shifts color Doppler can detect arterial stenosis and demonstrate the vascular nature of various lesions.
Ultrasonography is superb for guidance in relation to interventional procedures like nephrostomy, biopsy, and drainage.

Computed tomography (CT)

CT has assumed an important role in the visualization of the urinary system. Within a few minutes the entire urinary tract may be visualized including the surrounding tissue. When doing renal CT one must remember that the iodine concentration in the urine may be high enough to obscure small changes e.g. small tumors. Therefore only 10 to 20 ml of a 300 mg l/ml solution should be used when the collecting system is the main area of interest. For visualization of the renal parenchyma and the bladder 100 ml of a 300 mg I/ml solution are appropriate. Modem CT scanners are fast and sometimes too fast for human physiology. The

a	Figure 10. CT of normal kidneys before (a) and after (b) intravenous administration of contrast medium.
b

entire urinary tract may be examined before the excreted contrast material has reached the renal pelvis (approx. 1 1/2 min. after the contrast medium has reached the renal artery) (Fig. 10). Therefore the timing of the scans should be tailored to the specific purpose of the examination. Dynamic CT with rapid scans through the same slice or spiral CT after bolus contrast administration is sometimes used to study vascularity more precisely.

CT is excellent in detecting and differentiating renal masses and in staging renal malignancies. It is very sensitive in identifying calcifications, even non opaque stones. It surpasses the efficiency of ultrasonography in identifying perinephric, peri-ureteral and pelvic processes secondarily affecting the urinary tract. CT is the method of choice for evaluating renal injuries thought to be clinically severe (or if the initial

a	Figure 11. MRl of normal kidney. a) Coronal T1-weighted image showing good demarcation between cortex and medulla. b) Axial T1-weighted image. c) Coronal T2-weighted image showing that the kidney parenchyma is signal intense.
b
c

urogram is abnormal). It is the best modality to demonstrate the normal adrenal glands in detail and it has become the mainstay in diagnosing and differentiating adrenal pathology.

Magnetic Resonance Imaging (MRI)

The role of MR in the imaging of the urinary tract is not completely established whereas it has assumed a very important role in the imaging of the genital organs. Principally the examination is performed in the same way as it is performed of other regions of interest (Fig. 11). Special coils (endovaginal and endorectal) are available for pelvic uroradiologic imaging. When paramagnetic contrast media containing gadolinium are used one should remember that high concentration results in overshooting (T2-effeet) producing low rather than high signal on T1-weighted images. As with CT the dose of contrast medium should be adjusted according to the purpose of the examination. High (1.5 T), mid (0.5 T) and low (0.1 T) field units are suitable for genitourinary imaging. A role for MR spectroscopy of the urogenital organs has not been shown, whereas MR angiography within the next years may replace X-ray angiography. Pelvic imaging (bladder, prostate, uterus and genital organs) are for the time being the major area for MRI within the genitourinary system. It seems very useful for local staging of various types of cancers; preliminary indications are that it may surpass the sensitivity of CT in detecting enhancement of small lesions. At present its use in the kidney is usually reserved for eases which cannot be solved whit CT and US, when iodinated contrast media is contraindicated, and for vascular lesions.

Nuclear Medicine

Nuclear medical examinations give functional information about the genitourinary system, especially about the kidneys and the adrenals (Fig.12). Their role in imaging of the lower urinary tract and genital organs is limited. In contrast to conventional X-ray the ionizing radiation is internal and generated by radionuclides, which emit radiation that is detected by a gamma camera or Single Photon Emission Computer Tomography (SPECT). Many radiopharmaceuticals are available for examination of the genitourinary tract. The most frequently used are: ^99mTc MAG3, ^99mTc DTPA, ¹³¹I-Hippuran ¹²³I-Hippuran, ⁹⁹mTc DMSA, ⁹⁹mTc Glucoheptonate, ⁵⁷Cr-EDTA. The latter is used for in-vitro determination of the glomerular filtration rate. The rate at which ⁹⁹mTc DTPA and

a	Figure 12.Renography (a: Histogram b: Scintigram) of normal kidneys performed with 99mTc MAG3. Normal histogram values: Time to peak < 3,5 min.; Split function within the normal range 43-57 %; and Residual ,. activity at 20 min. < 22 %.
b

X-ray and MR contrast media are cleared from the plasma, can also be used. DTP A is nearly exclusively filtered by the glomeruli, whereas hippuran and MAG3 are both filtered by the glomeruli and excreted by the tubular cells. DMSA and glucoheptonate accumulate in the functioning

Figure 13. Coronal section of the kidney showing the relationship of the cortex, the medulla, and the renal collecting system.

tubular cells and are excellent for renal scintigraphy. MAG₃, DTPA and hippuran are used for renography and interventional renography. With all 6 radiopharrnaceuticals the function of each individual kidney can be determined. Nuclear medical imaging is an indispensable complement to all the more morphologic imaging modalities since it provides information about renal function/perfusion and particularly about renal outflow obstruction (diuresis renography), renal artery stenosis (captopril renography), split functions, scar detection, and renal transplant monitoring. Scintigraphy is useful for diagnosis of urinary leakage, and isotope cystography is an alternative to conventional cystography for the diagnosis of vesico-ureteral reflux. Special radiopharrnaceuticals are available for both cortical (¹³¹I cholesterol) and medullary (¹³¹I or ¹²³I MIBG) adrenal imaging.

 

Henrik S. Thomsen and Howard M. Pollack