Diagnostic Radiology: Genitourinary Imaging Niranjan Khandelwal, Veena Chowdhury, Arun Kumar Gupta, Anupam Lal
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TECHNIQUES AND CONTRAST

Current Status of Conventional Techniques in Urogenital ImagingChapter 1

Naveen Kalra,
Manavjit Sandhu
The history of uroradiology dates back to July 11, 1896 when MacIntyre, Glasgow first reported the X-ray demonstration of a renal calculus in a patient.1 Subsequently, urologists developed cystography, retrograde pyelography and retrograde urethrography within a span of next 15 years. In 1929, Moses Swick2 introduced a successful intravenous urographic contrast agent called uroselectan (5-iodo-2-pyridone N acetic acid) which ushered in IVU (intravenous urography) that became an integral part of the urological work-up of patients. Plain X-ray of kidney, ureter and bladder (KUB) and intravenous urography (IVU) continued to be used as the primary imaging techniques for the diagnostic evaluation of urinary tract for several years (Figs 1.1A to C). However, recently with the development of ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI), there are now several techniques in the diagnostic armamentarium of the uroradiologist. While a multimodality approach is often required to come to a final conclusion, the strengths and weaknesses of each technique must be known so that both conventional and newer techniques can be used to the maximum benefit of patients.
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Figs 1.1 A to C: (A) Plain radiograph of the abdomen shows extensive calcification in the left kidney and along the course of left ureter as a result of tuberculosis infection.(B) IVU shows no contrast excretion into the calyceal system on the left side. The right kidney and ureter are normal. (C) Non-enhanced axial CT section shows extensive parenchymal calcification in the left kidney
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Availability, cost-effectiveness and radiation dose are some of the other important factors determining the choice of the imaging modality while investigating various clinical problems. This chapter will discuss the current status of conventional radiological procedures vis-à-vis the newer techniques in common clinical situations.
Patients suspected to have urolithiasis may present with acute flank pain, hematuria or recurrent urinary tract infections. A plain film of the abdomen (X-ray KUB) is usually the first radiological investigation performed in these patients. However, the diagnostic accuracy of plain film for the detection of urinary tract calculus depends on the chemical composition of the stone, its size, location, overlying bowel gas shadows and technical quality of the film. Levine et al3 in their study of 178 patients found that plain radiographs had a sensitivity of only 45 percent for detecting ureteral calculi which marginally increased to 59 percent when the plain films were retrospectively reviewed with CT as the standard of reference. However, plain films are still good as baseline study and for follow-up of stone disease post-treatment.
Recently, ultrasound on account of its simplicity, freedom from radiation and ready availability has been proposed as an alternative technique when used in combination with KUB for diagnostic evaluation of patients presenting with acute flank pain. In a prospective study conducted by Lewis-Jones et al,4 X-ray KUB and ultrasound provided similar information as that obtained by IVU in 81.4 percent of patients. Considering the cost effectiveness, the authors concluded that KUB and US could replace IVU in patients of renal colic. In a series of 180 patients, Dalla Palma et al showed a 95 percent negative predictive value of the KUB/US combination indicating that IVU was unlikely to be helpful, if the KUB/US tests were negative.5 While US is highly sensitive for detection of dilated collecting system, it has several limitations. Calculi smaller than 5 mm can be easily missed and ureteral stones that are seen in association with undilated collecting system cannot be detected.
In the last decade unenhanced CT has rapidly gained popularity for investigating a patient of renal colic and there are several studies which have reported high sensitivity and specificity (95–97%) for detection of renal and ureteral calculi.6,7 CT detects virtually all stones regardless of their composition. In a study of 20 patients by Smith et al,8 5 patients had shown calculi on both IVU and CT, 6 had a stone that was detected only on CT and one patient had a stone that was not detected either on CT or IVU. With the availability of fast spiral CT scanner, the technique is specially useful in the emergency setting. There are many centers where plain films and IVU have been replaced by helical CT in patients presenting with flank pain and hematuria. In addition the extent of perinephric edema seen on CT has been used to predict the degree of ureteral obstruction and chances of spontaneous passage of ureteral stone with an accuracy of 94 percent.9 Thus in centers where there is free access to spiral CT, unenhanced CT has actually replaced plain films and IVU for diagnosis of stones in the urinary tract. KUB and ultrasound may be used as the initial screening modality which is followed by spiral CT if the KUB and US are negative (Figs 1.2A and B). However, IVU is still the best investigation if CT is not available. The KUB/US combination has also been compared to spiral CT. In a prospective study of 66 patients, the KUB/US combination had a sensitivity of 79 percent for detecting ureteric stones.3
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Figs 1.2 A and B: Non-enhanced axial helical CT sections of a patient with renal colic and normal X-ray KUB and US. (A) The left kidney is enlarged with mild perinephric stranding (arrow). (B) A small calculus is seen in the left lower ureter
However, all the missed cases had spontaneous passage of stone and it was concluded that CT would not add useful information after a negative KUB/US study.10
Radiation dose is one of the major factors which influences the choice of appropriate imaging modality. The radiation dose of unenhaced CT is greater than that of IVU even though patients with obstruction may require more number of radiographs than those without obstruction. The low dose CT protocol for stone detection proposed by Liu et al 7 still results in approximately double the effective dose equivalent in comparison with IVU (2.8 mSv for CT, 1.33 mSv for conventional IVU).
Painless hematuria is another major urological problem which needs evaluation of both renal parenchyma and urothelium to rule out urinary tract malignancy. Traditionally IVU has been used as the baseline investigation in these patients. IVU is a time tested technique which is most acceptable to the urologist as it gives a global view of the renal parenchyma and the collecting system. However, with advent of helical CT and CT/MR urography the exact place of IVU in this clinical setting is again under question and there is no universal agreement about the first imaging modality to be used in patients with hematuria. The American Urological Association Best Practice Policy Guidelines include either IVU or CT urography as the initial imaging test for asymptomatic microscopic hematuria.11 In addition, the American College of Radiology has rated IVU and CT urography equal as to their appropriateness for evaluation of patients with hematuria.12 In patients with hematuria due to renal parenchymal disease, US is the best imaging modality for evaluating renal volume and morphology.
It is generally agreed that imaging with US/CT/MRI is superior to IVU for detection and characterization of renal masses. In addition a urogram or retrograde pyelogram may be required to visualize the urothelium of the renal collecting system and the ureters in patients when there is suspicion of urothelial neoplasm. CT urography is an evolving technique wherein three-dimensional (3D) coronal reconstruction of contrast enhanced CT images is achieved using the maximum intensity projections (Fig. 1.3).4
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Fig. 1.3: CT urography in the pyelogram phase showing good opacification of the calyceal system and ureter on the right side. There is presence of left hydroureteronephrosis with renal and ureteric calculi (arrows)
McNicholas et al 13 found no significant differences in the ability of CT urography and IV urography in opacifying the calcyces, pelvis and ureter and opined that CT urography has the potential for evaluating the urothelium. Chow et al 14 concluded that CT urography in conjunction with the axial images is a single examination which alone may be required for the work-up of patients with hematuria as it is capable of imaging both the parenchyma and the collecting system. On the other hand, Hattery and King15 have reported their experience of CT urography and found 10 percent of urinary tract abnormality were either better or only detected by IVU compared to 5 mm axial sections and CT urography. The authors listed several examples such as pyeloureteritis cystica, papillary necrosis and transitional cell carcinoma where CT urography may not provide the high quality images needed for diagnosis. The authors supported the notion that CT with digital reformatted images does not provide sufficient detail for evaluation of subtle urothelial neoplasms. Cowan et al16 compared CT urography with retrograde pyelography for the detection of urothelial carcinoma in 106 patients. The only false negative CT urogram was a small urothelial tumor that was not detected in an unopacified segment. From the aforesaid, it is clear that as refinement of CT urography continues, IVU will be replaced by CT urography subject to availability and affordability.
IVU is the only modality to detect early changes in renal calyces in tuberculosis, papillary necrosis, etc. US, CT and MRI may be totally normal in these early cases. Hence, in a suspected case of urinary tract TB, IVU is the first imaging modality for diagnosis and subsequent follow-up.17 However, it is always advisable to intergrate IVU with cross-sectional imaging in patients with suspected tuberculosis.
Children presenting with repeated attacks of UTI have been traditionally investigated with IVU and cystourethrography. The aim of imaging is to diagnose any underlying congenital renal anomaly that may predispose to recurrent urinary tract infections and detect the presence of renal scarring and vesicoureteric reflux. Recent studies have shown that diagnostic yield of IVU in this clinical setting is unacceptably low (8.3%)18 and the abnormalities detected rarely change the management. Risks of IVU in terms of radiation and possibility of adverse reaction to contrast media outweigh its benefits and there is thus a strong case for withdrawal of routine IVU as a screening test in patients with recurrent UTI. Renal scintigraphy using 99mTcDMSA is superior to IVU for detection of renal scarring. Despite many proponents of radionuclide cystography (RNC), conventional contrast voiding cystourethrography (VCUG) continues to be the gold standard 5for detecting and grading of the vesicoureteric reflux (VUR) on account of false-negative studies and poor grading accuracy of radionuclide cystography.19 RNC has a much lower radiation dose than VCUG, but the low spatial resolution cannot identify the anatomic abnormalities of the urethra, bladder and ureters. RNC is recommended for follow-up of VUR and for screening the asymptomatic siblings of patients with VUR. Initial evaluation of VUR in girls may be done with RNC but in boys RNC is inadequate as anatomic imaging of urethra and bladder can only be done with VCUG.
In children and pregnant patients being investigated for obstructive uropathy, MR urography also has the potential to replace IVU due to the absence of radiation exposure (Figs 1.4A and B). Using T2-weighted (static-fluid urography) and contrast enhanced dynamic T1-weighted sequences (excretory urography), images of sufficient diagnostic quality can be obtained in infants with oral sedation.20 Blandino et al in 200121 in their study of 115 patients found that the specificity of MR urography in detecting hydronephrosis was 98 percent and the accuracy in revealing the level of obstruction was 100 percent. The sensitivity of detecting stones, strictures and congenital ureteropelvic junction obstructions was 68.9 percent, 98.5 percent and 100 percent respectively. The sensitivity of detecting ureteral calculi is technique dependent, with higher sensitivity being reported for excretory urography than for static-fluid urography.22
In patients of renal trauma, IVU and renal arteriography were the main diagnostic tools in the past. With introduction of US and CT, IVU is no longer used in these patients and CT is considered the technique of choice for detection and characterization of renal injuries and for assessment of vascular status.
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Figs 1.4A and B: MR urography in a patient with retroperitoneal fibrosis. (A) Axial T2-weighted image shows hydronephrosis on both sides. (B) Static-fluid MRU image shows hydroureteronephrosis on both sides with medially deviated ureters
Angiography is reserved for patients who require interventional treatment such as embolisation of traumatic pseudoaneurysm or AV fistula. Contrast cystography, micturating cystourethrography and retrograde urethrography continue to be the techniques of choice for diagnosing bladder and urethral injuries and urethral strictures (Figs 1.5A and B).
Pretransplant work-up of renal donor used to include IVU and conventional angiography. Precise information of number of ureters, site of joining in case of duplication of ureter and vascular anatomy is mandatory before donor selection.6
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Figs 1.5A and B: (A) Retrograde urethrography (RGU) in a patient following pelvic trauma shows contrast extravasation from the bulbar urethra. (B) Follow-up RGU in the same patient shows stricture at the level of bulbar urethra
The reported sensitivity and specificity of MDCT angiography for the detection of accessory renal arteries, prehilar branching and venous anomalies are 88 percent and 98 percent, 100 percent and 97 percent and 100 percent and 97 percent respectively. In one of the studies, CT findings agreed with surgical findings for accessory renal arteries, prehilar branching and venous anomalies in 94 percent, 93 percent and 98 percent of patients respectively.23
At times before pelvic surgery for bladder, uterus, ovaries, etc. the surgeon needs exact relationships of the lower ureters in the surgical field or involvement of ureters by the pelvic pathology to reduce the chances of ureteral injury. However, IVU should not be used routinely before hysterectomy but should be performed in patients with large pelvic masses or known pelvic cancer.24
 
CONCLUSION
To conclude it appears that conventional uroradiology continues to play an important but limited role in urogenital imaging. Nonenhanced helical CT has nearly replaced conventional uroradiology for evaluation of urinary tract calculi. However, in countries such as ours, a blanket substitution may not be feasible due to cost factor and availability. CT and MR urography at present cannot fully substitute contrast urography although CT urography is the current heir apparent to IVU. Technical improvements in CT urography like reduction in radiation exposure and MR urography like faster imaging time and consistent image quality are required to further enhance the utility of CT and MR urography in the future.
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