Urinary tract
Methods of imaging the urinary tract
(a) CT for urological diagnosis and urological cancer staging
(b) CT for characterization of renal lesion
5. Magnetic resonance imaging (MRI):
6. Micturating cystography and cystourethrography
8. Retrograde pyeloureterography
9. Percutaneous renal procedures:
Intravenous excretion urography (IVU)
The technique is less frequently used than in the past and is now largely replaced by CT, MRI or US.
Contraindications
See Chapter 2 – general contraindications to intravenous (i.v.) water-soluble contrast media and ionizing radiation. In patients with contrast medium allergies alternative modalities such as ultrasound or MR can be considered. Patients with impaired renal function, particularly those with diabetes should be prepared with oral or intravenous hydration, or an alternative imaging modality considered. See Chapter 2.
Preliminary images
If necessary, the location of overlying opacities may be further determined by:
• supine AP film of the renal areas, in expiration. The X-ray beam is centred in the mid-line at the level of the lower costal margin or
• 35° posterior oblique views (side of interest towards the film) or
The examination should not proceed further until these images have been reviewed by the radiologist or radiographer and deemed satisfactory.
Images
1. Immediate film. AP of the renal areas. This film is exposed 10–14 s after the injection (approximate ‘arm-to-kidney’ time). It aims to show the nephrogram at its most dense, i.e. the renal parenchyma opacified by contrast medium in the renal tubules. Tomography may assist in evaluation of the renal outline or possible masses (or ultrasound if subsequently available).
2. 5-min film. AP of the renal areas. This film gives an initial assessment of pathology – specifically the presence or absence of obstruction before administering compression.
(a) after recent abdominal surgery
(c) if there is a large abdominal mass or aortic aneurysm
(d) when the 5-min film shows already distended calyces indicative of obstruction.
3. 10-min film. AP of the renal areas. There is usually adequate distension of the pelvicalyceal systems with opaque urine by this time. Compression is released when satisfactory demonstration of the pelvicalyceal system has been achieved. If the compression film is inadequate the compression should be checked and repositioned if necessary and a further 50 ml of contrast medium administered and the film after 5 minutes.
4. Release film. Supine AP abdomen taken immediately after release of compression. This film is taken to show the ureters. If this film is satisfactory, the patient is asked to empty their bladder.
5. After micturition film. Full-length supine AP abdomen. The aims of this film are to assess bladder emptying, to demonstrate drainage of the upper tracts, to aid the diagnosis of bladder tumours, to confirm ureterovesical junction calculi and, uncommonly, to demonstrate a urethral diverticulum in females.
Additional images
1. 35° posterior obliques of the kidneys, ureters or bladder – for equivocal collecting system lesions or localization of calculi.
2. Tomography – if renal outlines are not well seen.
3. Prone abdomen following the release film – may improve visualization of distal ureters by making them more dependent.
4. Delayed films at increasing (doubling of time intervals) up to 24 h after injection in renal obstruction.
Ultrasound of the urinary tract
Indications
Technique
1. Patient supine, right (RAO) and left anterior oblique (LAO) positions or lateral for kidneys. The kidneys are scanned longitudinally in an oblique coronal plane supplemented by transverse sections perpendicular to the axis. The right kidney may be scanned through the liver and posteriorly in the right loin. The left kidney is harder to visualize anteriorly, but can be visualized from a lateral approach. In difficult cases the patient should lie on their side with a pillow under the left loin to widen the space between the rib cage and pelvis.
2. The length of the kidney measured by US is 1–2 cm smaller than that measured at excretion urography because there is no geometric magnification. With US measurement, care must be taken to ensure that the true longitudinal lengthwise measurement is obtained. The range of lengths of the normal kidneys is 9–12 cm, and the difference between each kidney should be less than 1–2 cm.
3. The bladder is scanned suprapubically in transverse and longitudinal planes. Measurements taken of the three orthogonal diameters before and after micturition enable an approximate volume to be calculated by multiplying the three diameters and applying a conversion factor. (A conversion factor is usually pre-programmed into modern ultrasound machines.)
4. Renal transplants are usually located in the right or left iliac fossa. These usually lie fairly superficially and are easy to evaluate using oblique planes and gentle pressure to displace overlying bowel loops.
5. The native or transplant kidneys can be evaluated for vascular pathology using Doppler techniques.
• Renal artery stenosis is diagnosed by direct Doppler interrogation of the main renal arteries from a transabdominal approach. Elevated peak systolic velocities greater than 200 cm s–1 are suggestive of a >50% stenosis. Alternatively, as the main renal arteries in the native kidneys are often hard to visualize, the intrarenal arteries can be evaluated from a flank approach for downstream changes in waveform – the tardusparvus pattern;1 a slow rise (tardus) to a reduced peak (parvus) producing a prolonged acceleration time (a value >70 ms is indicative of a severe stenosis).
• Renal vein thrombosis is diagnosed by absent colour Doppler venous flow, direct visualization of thrombus within the distended vein, and a raised resistive index with reversal of arterial diastolic flow within the intrarenal arteries.
Computed tomography of the urinary tract
Indications
1. Renal colic/renal stone disease
5. Staging and follow-up of renal, collecting system or prostatic cancer (local staging of prostatic cancer is performed using thin-section MRI)
6. Investigation of renal tract obstruction
7. CT angiography may be used to assess renal vessels for suspected renal artery stenosis or arterio-venous fistula or malformation.
Techniques
Standard diagnostic CT
3. Scanogram of chest, abdomen and pelvis as appropriate
5. Scans obtained approximately 70 s (portal venous phase) after i.v. contrast (arterial phase scans of the liver (20–25 s after i.v. contrast) may be appropriate in those patients with suspected metastatic renal cancer who may have hypervascular liver metastases.)
Adrenal lesion characterization CT
Indication: adrenal mass is suspected or needs characterization.
Technique: Unenhanced CT of the abdomen to enable measurement of attenuation of any adrenal mass.
(Alternatively chemical shift MRI may be used for characterization.)
CT KUB
1. No intravenous or oral contrast is given.
2. Patient supine. (Some authorities advise prone scanning to differentiate if stones are impacted at the vesicoureteric junction or have passed into the bladder.)
3. A low-radiation-dose technique is used to scan from the top of the kidneys to include the bladder base with a slice thickness of 5 mm or less, as determined by CT scanner. (Due to the low-dose nature of the scan and the absence of i.v. and oral contrast, the scan has a very limited role in identifying pathology other than renal tract calculus disease and should not be used indiscriminately for investigation of non-specific abdominal pain.)
CT urogram (CTU)
1. An oral water load of 500–1000 ml 30–60 minutes before injection is recommended to ensure a diuresis and collecting system dilatation. No positive oral contrast
3. Initial low-dose unenhanced scans of urinary tract (CT KUB) to determine if renal tract calculus disease is present
4. Low osmolar contrast material (LOCM) 300 mg I ml–1 100 ml is given as bolus intravenously
5. Thin-section (usually 1 mm) scans are obtained from diaphragm to lower poles of kidneys during nephrographic/parenchymal enhancement phase (100 s following start of bolus injection). Alternatively, scan may instead be acquired during the portal venous phase (70 s) but normal corticomedullary differentiation may make small tumours difficult to appreciate
6. Delayed thin-section (1 mm) scans are acquired from upper pole of kidneys to bladder base 20 min after contrast injection, to examine collecting systems and ureters
7. Source images are reviewed along with multiplanar reconstructions. Post-processing with maximum-intensity projections and surface-shaded displays may be helpful, especially for demonstration.
CT angiography
Technique
1. No oral iodinated contrast used
2. Scan from the upper pole of the kidneys to the aortic bifurcation. Modern scanners are fast enough to produce high-quality studies of the whole abdomen
4. 100–150 ml i.v. contrast medium (LOCM 300) injected at 3–4 ml s–1
5. Use of bolus tracking/triggering devices or timing test injections is recommended to ensure appropriate timing. Otherwise scans are initiated after a preset empiric delay of 20–25 s from start of contrast material injection
6. Source axial scans are supplemented by multiplanar reconstructions and maximum intensity projection and volume-rendered surface-shaded display postprocessing.
Adrenal Lesion Characterization CT
Johnson, PT, Horton, KM, Fishman, EK. Adrenal imaging with multidetector CT: evidence-based protocol optimization and interpretive practice. RadioGraphics. 2009; 29:1319–1331.
Low, G, Dhliwayo, H, Lomas, DJ. Adrenal neoplasms. Clin Radiol. 2012; 67(10):988–1000.
O’Regan, KN, O’Connor, OJ, McLoughlin, P, et al. The role of imaging in the investigation of painless hematuria in adults. Semin Ultrasound, CT and MRI. 2009; 30(4):258–270.
Van Der Molen, AJ, Cowan, NC, Mueller-Lisse, UG, et al. CT urography working group of the European Society of Urogenital Radiology (ESUR). CT urography: definition, indications and techniques. A guideline for clinical practice. Eur Radiol. 2008; 18(1):4–17.
Magnetic resonance imaging of the urinary tract
Indications
1. Local staging of prostatic cancer
2. Local staging of bladder cancer
3. Staging of pelvic lymph nodes
5. Screening of patients with von Hippel–Lindau disease or their relatives, or other genetic conditions
6. MR urography where intravenous or CT urography contraindicated
7. MR angiography: potential living related donors, suspected renal artery stenosis.
