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ORIGINAL ARTICLE
Year : 2015  |  Volume : 28  |  Issue : 2  |  Page : 554-558

The role of multidetector computed tomography urography in the evaluation of obstructive uropathy


Department of Radiology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission12-Jun-2014
Date of Acceptance15-Aug-2014
Date of Web Publication31-Aug-2015

Correspondence Address:
Mahmoud M Ahmed Moawad
Ashlim, Quisna, Menoufia 32958
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.163917

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  Abstract 

Objective
The aim of this work was to assess the value of multislice computed tomography (CT) urography in patients presenting with obstructive uropathy.
Background
Obstructive uropathy is a structural impedance to the flow of urine anywhere along the urinary tract. Multidetector computed tomography urography (MDCTU) has the advantage of being able to detect not only the level of obstruction but also its cause, including urinary stones, pelviureteric junction stenosis, ureteric strictures, ureteric injury, retroperitoneal fibrosis, and pelvic masses.
Patients and methods
This study included 30 patients of variable ages, complaining of urinary tract obstruction manifestations referred from urology and urosurgery clinics. MDCTU was performed for all patients.
Results
Causes of obstructive uropathy as detected by MDCTU were as follow: 14 (46.6%) cases caused by urinary tract stones, four (13.3%) with urinary bladder masses involving ureteric orifices, three (10%) with pelviureteric junction obstruction (PUJ) obstruction, three (10%) with compression of ureters, three (10%) with ureteric injuries, two (6.6%) with bladder neck obstruction, and one (3.3%) case with ureteric stricture.
Conclusion
MDCTU enabled an accurate diagnosis of the level of obstruction and its etiology, including nephroureterolithiasis, pelviureteric junction stenosis, ureteric strictures, ureteric injury, retroperitoneal fibrosis, and pelvic masses.

Keywords: multidetector computed tomography urography, obstructive uropathy, urinary stone disease


How to cite this article:
Ahmed Moawad MM, El-Zawawy MS. The role of multidetector computed tomography urography in the evaluation of obstructive uropathy. Menoufia Med J 2015;28:554-8

How to cite this URL:
Ahmed Moawad MM, El-Zawawy MS. The role of multidetector computed tomography urography in the evaluation of obstructive uropathy. Menoufia Med J [serial online] 2015 [cited 2020 Apr 6];28:554-8. Available from: http://www.mmj.eg.net/text.asp?2015/28/2/554/163917


  Introduction Top


Obstructive uropathy is a structural impedance to the flow of urine anywhere along the urinary tract [1] .

Obstruction of the urinary tract can occur in any part of the system, including the urethra, the bladder, ureters, or the renal pelvis, and depending on the duration and the specific nature of the blockage, urine may move as far up the urinary tract as the renal pelvis. The urine accumulation increases the pressure and dilates the affected regions of the renal pelvis, calyces, and ureters [2] .

Many imaging modalities are used to evaluate the obstructive uropathy including plain radiography of the urinary tract, ultrasonography, intravenous urography, computed tomography (CT), MRI, and radionuclide renography. Ultrasonography is 98% sensitive for detecting hydronephrosis secondary to obstruction, but the specificity is 78% [3] .

With the introduction of multidetector technology, CT is the test of choice for many urologic problems, including urolithiasis, renal masses, urinary tract infection, trauma, and obstructive uropathy. CT urography provides a detailed anatomic depiction of each of the major portions of the urinary tract [4] .

Multidetector computed tomography urography (MDCTU) offers several advantages for the imaging of the urinary tract: single breath-hold coverage of the entire urinary tract and rapid imaging with optimum contrast medium opacification. In addition, acquisition of multiple thin overlapping slices provides excellent two-dimensional and three-dimensional (3D) reformations and facilitates virtual cystoscopy [5] .


  Patients and methods Top


The study included 30 patients complaining of urinary tract obstruction manifestations referred from urology clinics. Approval of the ethical committee and informed consents of the participants were obtained. The study was conducted in Menoufia University Hospital during the period between January 2013 and March 2014.

Full history was obtained from every patient including patient laboratory data, with particular interest in the results of the renal function tests; if any previous imaging study showed hydronephrotic changes with no apparent cause for the obstruction or in case of an inability to detect the level of obstruction, then MDCTU was performed.

The MDCTU examination includes unenhanced, nephrographic, and excretory-phase images through the abdomen and the pelvis, transverse images and 3D reformations were taken and reviewed. All multidetector row CT urographic examinations were performed with a 16-channel multidetector row CT scanner (Toshiba Aquilion).

All patients were taught how to hold their breath during examination, positioned supine on the CT table in the 'head-first' position, and an 18-20-G catheter was placed into a superficial vein within the antecubital fossa and tested by manual saline infusion before the contrast material was administered by the injector.

One scout was acquired in the anteroposterior view. The examination was planned on these scouts from the level of the diaphragmatic cupola to the perineum caudally, and then the unenhanced (precontrast) sequence was performed. A single bolus injection of contrast was administered (100 ml of iohexol 300 with a power injector at a rate of 3-4 ml/s) before images of the nephrographic and the excretory phases were obtained. Nephrographic-phase images were obtained 120 s after the initiation of the injection of the contrast material. Excretory-phase images were then obtained beginning 8-10 min after the initiation of the injection.

3D reconstructions of the excretory-phase scan were created at an independent workstation for processing and interpreting the studies. 3D reconstructions in the coronal and the coronal oblique projections were created with maximum intensity projection (MIP), curved multiplanar reformation and volume-rendering algorithms. MIP selects and displays the maximum voxel value along a line of the viewer's projection through a given volume.


  Results Top


This study included 30 patients (19 male and 11 female), who presented with urinary tract obstruction to determine the cause and the level of the obstruction. The age of the patients ranged from 2 days to 70 years, with an average age of presentation of about 40.3 years.

Causes of obstructive uropathy as detected by MDCTU were as follows: 14 (46.6%) cases were caused by urinary tract stones, four (13.3%) had urinary bladder masses involving ureteric orifices, three (10%) had PUJ obstruction, three (10%) had compression of ureters, three (10%) had ureteric injuries, two (6.6%) had bladder neck obstruction, and one (3.3%) case had ureteric stricture. [Table 1].
Table 1 Causes of obstructive uropathy as diagnosed by multidetector computed tomography urography (N = 30)

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The most common cause of obstructive uropathy was urinary tract stones; they were further analyzed and characterized by multidetector computed tomography (MDCT) according to their sites, densities and sizes [Table 2].
Table 2 Characterization of the urinary tract stones by multidetector computed tomography urography (N = 14)

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The second most common cause of obstructive uropathy in this study was urinary bladder masses, with ureteric orifice involvement representing 13.3% of the cases. It was classified by MDCTU according to the laterality and the ureteric orifice involved [Table 3].
Table 3 Ureteric orifi ce involvement by bladder masses as detected by multidetector computed tomography urography (N = 8)

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  Discussion Top


Obstructive uropathy is defined as a narrowing of the urinary tract necessitating elevation of the proximal pressure to enable urine flow [6] . Intravenous urogram (IVU) was the corner stone in the diagnosis of obstructive uropathy, but IVU could not detect well the level and the cause of obstruction, especially with nonexcretory function of the obstructed kidney. The most characteristic abnormalities on IVU are an asymmetrical nephrographic density and excretion of contrast material. With advances in MDCT, the cause and the level of obstruction can be easily identified even without contrast injection [7] .

The MDCTU examination used in this study was composed of three phases: the first phase was the precontrast imaging of the abdomen obtained to locate the kidneys, and for the determination of calcifications and evaluation of urolithiasis. The second phase was the nephographic phase obtained 100 s after starting the intravenous contrast medium. This phase is optimal for the detection of focal masses arising in the cortex or the medulla and for the evaluation of the renal parenchyma. The third phase was the delayed or the excretory phase obtained 10 min after contrast media administration and is used to evaluate the renal collecting system and ureters. In this phase, while the intensity of the nephrogram decreases, excretion of the contrast medium permits opacification of the calyces, renal pelvises, and ureters. This technique is based on the standard CT urography protocol postulated by Kocakoc et al. [8] .

In this study, the axial-source images and the postprocessing images were obtained to examine entire kidneys and the collecting system. Multiple techniques were used: multiplanar reformat, curved planar reformat, MIP, and the 3D reconstruction volume-rendering technique.

In this study, multiple levels of obstruction were diagnosed by MDCTU, beginning from the PUJ, ureters (upper, mid, and lower ureters), Ureterovesical junction (UVJ), and bladder neck obstruction, which agreed with Yarger [2] , who stated that obstructive uropathy can occur in any part of the urinary tract including the urethra, the bladder, ureters, or the renal pelvis.

In our study, the most common cause of obstructive uropathy was urinary tract stones, which represented about 46% of all cases (14 from the total number of 60) [Figure 1]. This was in agreement with Chevalier and Klahr [9] , who reported that upper urinary tract obstructions usually involve renal stones that create a ureteral obstruction, and also agreed with Cronin et al. [10] , who stated that the unenhanced portion of their CT examination provides optimal evaluation of all urinary calculi as well as the evaluation of the level of obstruction and demonstrates reliable secondary signs of obstructing calculi.
Figure 1: (a) The axial image of the noncontrast phase shows a large branching stone in the right renal pelvis measuring about 2.7 × 2.1 × 3.8 cm in dimensions. (b) The coronal image shows the stone with a maximum density of 916 HU and an average attenuation of 637 HU and subsequent mild hydronephrosis. (c, d) Maximum intensity projection and volume-rendering images demonstrate the stone; marked spondylotic changes are also noted, affecting the whole spine.

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In our study, the sensitivity and the specificity of different MDCT techniques for calculi diagnosis were very high, reaching up to 100%, which was in agreement with Boulay et al. [11] , who stated that unenhanced CT has been found to have a high degree of sensitivity (95-98%) and specificity (96-100%) in the diagnosis of urolithiasis.

In contrast to excretory urography, ultrasonography, and nephrotomography, MDCT enabled the accurate assessment of these crucial disease characteristics and the differentiation between urinary calculi and other pathologic processes, such as blood clots or tumors [12] .

The main determinants in the clinical care of patients with urolithiasis are the location, the size, and the chemical composition of calculi, and the presence of anatomic and functional anomalies in the upper urinary tract [13] .

In our study, we were able to predict the chemical composition of the urinary tract stones by measuring their densities in Hounsfield unit (HU). Sixty-four percent of the obstructing stones in this study were radiolucent (their densities ranged from 250 to 450 HU) and 36% of the stones were radio-opaque (their densities were more than 450 HU). Most of the cases with urinary tract stones were referred by the presence of hydronephrosis detected by US examination or nonconclusive PUT and IVU, which was in agreement with Sandhu et al. [14] , who concluded that stones are composed of a combination of crystals and proteins. Calcium-based stones account for 70-80% of upper urinary tract stones, and their densities ranged from 1700 to 2800 HU (radio-opaque). Struvite stones account for 5-l5% of the stones, and their densities ranged from 600 to 900 HU (radio-opaque). Uric acid stones account for 5-10% of stones, and their densities 200-450 HU (radiolucent). Other stones, including cystine, xanthine, and protein matrix stones, as well as drug-induced calculi (e.g. triamterene, indinavir), account for less than 5% of stones, brushite 2-4% (densities l700-2800 HU, radio-opaque), and cystine 1-2.5%, with densities of 600-1100 HU (mildly radio-opaque).

The second most common cause of obstructive uropathy in this study was bladder masses involving the ureteric orifices [Figure 2], which represented 13.3%. There was a high incidence of bladder cancer in this study, which was in agreement with Wang et al. [15] , who stated that the prevalence of urinary bladder squamous cell carcinoma varies considerably depending on the geographic location. Squamous cell carcinomas account for only 3-7% of bladder cancers in the USA and 1% in England, but up to 75% in Egypt. The high incidence of bladder cancer in this study was due to the high incidence of bilharziasis in Egypt, which is in agreement with Wang et al. [15] , who also reported that in Egypt, about 80% of squamous cell carcinomas are associated with chronic Schistosoma haematobium infection.
Figure 2: (a) The venous-phase axial image of urinary bladder (UB) shows circumferential wall thickening measuring 21 mm in its maximum thickness. (b) The venous-phase axial image of both kidneys shows bilateral moderate hydronephrosis with delayed excretion affecting the left side more. (c) The sagittal image of the urinary bladder demonstrates the UB wall thickness and bladder wall calcifi cations. (d) The curved multiplanar reformation of the ureters shows the bilateral moderate hydroureteronephrosis denoting the invasion of both orifices.

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In our study, there were four cases with bladder masses causing obstructive uropathy, representing l3.3% of the total number (30) of cases. About 75% were unilateral (involving one ureteric orifice only), and 25% were bilaterally (involving both ureteric orifices). The sensitivity and the specificity of multiplanar reformation and curved planar reformat in the detection of the cause and the level of obstruction associated with bladder masses were 100%. These results agreed with Kim et al. [16] , who reported that CT urography was used successfully to detect 97% of bladder cancers; however, these results were found in a population of 67 patients with known bladder cancer already detected by cystoscopy. MDCTU is an accurate, noninvasive test for detecting bladder cancer. CT urography can be used to evaluate the upper tracts.

In this study, three (10%) cases were diagnosed by MDCTU as ureteric compression and two (66.6%) cases showed bilateral compression upon ureters by large pelvic masses (one was due to a large fibroid and the other was due to hydrocolpos in a case of imperforate hymen compressing both lower ureters). Only one (33.3%) case was of retroperitoneal fibrosis compressing the left ureter, exerting mild back pressure on the left side. The only case in this study that was diagnosed as retroperitoneal fibrosis was that of a 52-year-old female patient. This disagreed with Miller et al. [17] , who stated that idiopathic retroperitoneal fibrosis is seen more commonly in men, with a 2: 1 to 3: 1 ratio compared with women. This disagreement may be due to the sample size, which was 100 in the comparative study.

In this study, three (10%) cases were diagnosed by MDCTU as ureteric injury: two (66.6%) cases were caused by iatrogenic injury during hysterectomy and one (33.3%) after a road traffic accident; the three cases show unilateral ureteric injury. These results agreed with Kim et al. [16] , who stated that ureteral injuries after external violence are rare, occurring in less than 4% of cases of penetrating trauma and less than 1% cases of blunt trauma. However, iatrogenic ureteral Injury is much more common; the majority (75%) of the ureteral injuries occur during gynecologic surgery.

Regarding the cases of bladder neck obstruction with strained urinary bladder and ureteric reflux, there were two cases, representing 6.6% of the total number of cases (60) diagnosed by MDCTU. The two cases were diagnosed as prostatic problems, and ureteric reflux was presented in both.

Our study also had one patient with a history of bilharziasis associated with mild unilateral hydronephrosis, showing ureteric calcification using the unenhanced phase of MDCT. Our results agreed with Jorulf and Lindstedt [18] , who stated that fine ureteral calcification may be observed at an early stage of schistosomiasis, initially with areas of sparing, but eventually coalescing until the entire length of the ureter is calcified, from the bladder to the kidney. The fine ureteral calcification is visible as a linear or a parallel linear pattern on radiographs and as a circular pattern on axial CT images. These radiologic imaging findings are considered to be pathognomonic.


  Conclusion Top


MDCTU enabled an accurate diagnosis of the level of obstruction, as well as its etiology, including nephroureterolithiasis, pelviureteric junction stenosis, ureteric strictures, ureteric injury, retroperitoneal fibrosis, and pelvic masses.


  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Sandhu C, Anson KM, Patel U. Urinary tract stones. Role of radiological imaging in diagnosis and treatment planning. Clin Radiol 2003; 58 :415-421.  Back to cited text no. 14
    
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Wang LJ, Wong YC, Huang CC. Multidetector computerized tomography urography is more accurate than excretory urography for diagnosing transitional cell carcinoma of the upper urinary tract in adults with hematuria. J Urol 2010; 183 :48-55.  Back to cited text no. 15
    
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Kim JK, Park SY, Kim HS, Cho KS. Comparison of virtual cystoscopy, multiplanar reformation, and source CT images with contrast material-filled bladder for detecting lesions. Am J Roentgenol 2005; 185 :689-696.  Back to cited text no. 16
    
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    Tables

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