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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 91-101

Magnetic resonance urography in the evaluation of obstructive uropathy


1 Department of Surgery, Sher-I-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India
2 Department of Radiodiagnosis, Sher-I-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India
3 Department of Obstetrics and Gynecology, Sher-I-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India
4 Department of Urology, Sher-I-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India

Date of Web Publication8-May-2018

Correspondence Address:
Mohd Ilyas
Department of Radiodiagnosis, Sher-I-Kashmir Institute of Medical Sciences, Radiodiagnosis, Soura, Srinagar - 190 011, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/AIHB.AIHB_61_17

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  Abstract 

Purpose: The purpose of this study was to study the utility of magnetic resonance urography (MRU) in the evaluation of obstructive urological diseases in comparison to intravenous urography (IVU). Materials and Methods: The study was carried out over a period of 2 years. A total of 55 patients were included in this study with ages between 14 and 70 years (average age 37 years). The patients were selected on the basis of ultrasonographic findings of hydronephrosis. The patients were subjected to IVU followed by static and dynamic MRU. The results obtained were compared and the inferences drawn thereof. Results and Conclusions: MRU has high sensitivity in the diagnosis of urinary tract obstruction, detecting the level of obstruction and acts as an aid in the diagnosis of obstructive uropathy, thus showing promising results. MRU is safer than IVU due to avoidance of iodinated contrast material and could also be done without using contrast material so having less contrast related events.

Keywords: Crossed fused ectopia, intravenous urography, magnetic resonance urography, obstructive uropathy, PUJ obstruction


How to cite this article:
Ahmad I, Ilyas M, Khan I, Robbani I, Wazir BS. Magnetic resonance urography in the evaluation of obstructive uropathy. Adv Hum Biol 2018;8:91-101

How to cite this URL:
Ahmad I, Ilyas M, Khan I, Robbani I, Wazir BS. Magnetic resonance urography in the evaluation of obstructive uropathy. Adv Hum Biol [serial online] 2018 [cited 2019 Jul 22];8:91-101. Available from: http://www.aihbonline.com/text.asp?2018/8/2/91/232025


  Introduction Top


Urinary tract obstruction is a relatively common problem. The obstruction to urinary flow may be acute or chronic, partial or complete, unilateral or bilateral and may occur at any site in the urinary tract. Urinary obstruction is one of the few reversible causes of renal failure. Early diagnosis and treatment is important and can salvage the kidney. Temporary or permanent obstruction of urinary tract can result from variety of causes such as calculi, blood clots, prostate enlargement, stricture, pelvi-ureteric junction (PUJ) obstruction, vesicoureteric reflux (VUR), retroperitoneal fibrosis, compression from outside like tumours of adjacent structures, pregnancy or rare causes such as tubo-ovarian masses, endometriosis, abdominal aortic aneurysm, iliac artery aneurysm and circumcaval ureter.[1] Hydronephrosis and obstructive uropathy are not synonymous, and hence, it is important to differentiate between obstructive and non-obstructive hydronephrosis and to know the level of obstruction for proper management and to prevent its progression to obstructive nephropathy as prolonged obstruction leads to worsening of renal functions and unlike other renal diseases, obstructive nephropathy which if treated early is a potentially curable disease of the kidney. The practicing urologist should be well versed with the diagnostic imaging modalities currently available as well as their relative advantages, limitations, and appropriate modifications.[2]

Ultrasonography (USG) is the mainstay in the evaluation of suspected urinary tract obstruction. It is considered safe in paediatric and pregnant patients due to no associated ionisation risk, and there is no need of contrast injection; hence, USG can be used in patients with azotemia or contrast allergy.[2] Being inexpensive and widely available, USG is often used as a first-line investigation.[2] Although USG is an inexpensive and rapid way of detecting a ureteric obstruction, however, the level of obstruction is often difficult to determine due to overlying bowel gas shadows and is unable to provide information on functional aspects and whether the obstruction is complete or incomplete.[3],[4],[5]

Although frequently used for the detection of a ureteral obstruction, the usage of intravenous urography (IVU) is limited by the nephrotoxicity of contrast material in patients already having obstructive nephropathy with non-excretion of contrast in non-functioning kidneys rendering it useless.[1],[2],[3],[6],[7] IVU may be contraindicated in pregnant and paediatric patients because of radiation exposure and its subsequent side effects and risk of contrast nephropathy.[2],[3],[4],[5],[8] Conditions that arise outside urinary tract can also result in urinary tract obstruction and may go unnoticed with IVU. IVU has an inherited disadvantage in providing limited information on mural pathology and none on extramural pathology.[3] Therefore, it is important to determine the cause and level of obstruction by an effective protocol.

CT directly reveals calculi, classically considered radiolucent when evaluated by plain radiography, including uric acid, xanthine, dihydroxyadenine, and many drug-induced calculi except calculi composed of protease inhibitors.[2],[8] Various secondary features of obstruction on computed tomography (CT) include hydroureter, perinephric stranding, hydronephrosis, periureteral oedema and renal swelling.[1],[2],[3],[9],[10] However an non-contrast CT does not indicate function of the kidneys, cannot differentiate between acute and chronic obstruction, has difficulty in differentiating distal calculi from pelvic phleboliths,[1],[2],[10],[11] has risk of radiation exposure which precludes its application in pregnant and young patients and there is risk of contrast allergy in case of contrast-enhanced CT.[2],[3],[5],[8],[10],[12],[13]

Magnetic resonance urography (MRU) (as a technique for the assessment of urinary tract was first described by Henning et al. in 1987) is free of any radiation risk and can be done both with or without using intravenous contrast as the case may be, and is more suitable for examination of paediatric, pregnant patients and patients with compromised renal function.[1],[2],[4],[12],[13] The use of magnetic resonance imaging (MRI) facilitates simultaneous examination of the kidneys, ureters, renal vessels and inferior vena cava (IVC) which is useful for assessing renal parenchymal, perinephric and periureteric tumour extension in cases where tumour is the cause of obstruction.[9],[13] Sequential imaging of ureters with MRU can be used to overcome problems with intermittent lack of ureteral distension due to peristalsis, which can lead to misdiagnosis of stricture and obstruction.[9] The combination of static-MRU (sMRU) and excretory-MRU is useful in cases of obstructive uropathy because T2-weighted images can show the extent of dilatation of the obstructed system and excretory-MRU can provide information on functional effects of excretion.[4],[5] Sequential imaging can also be used to map the pattern of enhancement after contrast administration which can be useful for characterising the lesions and quantifying renal function.[4],[5] The incorporation of intravenous administration of gadopentetate-DTPA has allowed a dynamic, functional assessment of the collecting system that correlates well with diuretic scintigraphy yet provides far greater anatomic detail than nuclear studies.[5],[6],[14],[15] Cost, availability, time for acquisition of images and need for sedation in paediatric patients have all been cited as possible limitations of this technique, but the superior anatomical details, functional assessment, elimination of risk of contrast-induced nephropathy, and lack of ionising radiation make this technique an attractive option that is likely to continue to evolve.[2],[4],[9]

In view of fallacies and difficulties in the diagnosis of obstructive uropathy despite the availability of multiple investigations and shortcomings of above-mentioned investigations such as radiation exposure, invasiveness, non-utility in pregnant, paediatric and patients with compromised renal functions there is still scope of improvement in the diagnostic workup of obstructive uropathy. MRU being non-invasive and radiation-free procedure might have an advantage in such circumstances. This study was conducted focussing on MRU as a diagnostic modality in patients with obstructive uropathy and its advantages and limitations in comparison to IVU in terms of safety, accuracy, reliability and adverse effect.

Aim and objectives

  • To study patients with obstructive uropathy using MRU as a diagnostic technique
  • To analyse the statistical data obtained and draw inferences thereto
  • To assess the sensitivity, accuracy and safety of MRU in comparison to that of IVU.



  Material and Methods Top


This study was conducted at our Institution over a period of 2 years, on patients having symptoms such as abdominal/flank pain, haematuria and dysuria. A total of 55 patients were included in this study with ages between 14 and 70 years (average age 37 years). Thorough clinical examination of patients was done followed by few baseline investigations including urea, creatinine and routine urinary examination were done in all patients.

These patients first underwent screening USG using Aloka Prosound ultrasound machine and patients showing dilated pelvi-calyceal system on screening USG, and normal serum creatinine (<1.5 mg/dL) levels were subjected to IVU.

Informed consent was taken from patients before each investigative procedure. After adequate bowel preparation, IVUs were done using non-iodinated contrast media, omnipaque 300 at a dose of 1–1.5 ml/kg body weight (approximately 50 ml in adults). Patients were carefully observed for any adverse contrast reaction in the meantime, and emergency drugs were kept standby. Plain films followed by films at 5, 10, 15, 30 and 60 min, full bladder and post-voiding films, and 24 h films (if required) were taken. Patients in whom there was no contrast excretion at 24 h, poor contrast excretion, persistent nephrogram and/or diagnosis was not clear on IVU and those with contrast reactions on IVU were subjected to MRU.

MRU was done using 1.5-Tesla Magnetom Vision (Avanto Siemens Germany) using the standard circularly polarised body coil with use contrast material in the case of dynamic MRU. The contrast material used was 0.1 mmol of Gadopentetate dimeglumine (Magnevist, Schering, Berlin, Germany) per kg body weight or Gadodiamide (Omniscan). Before starting the first breath-hold MR sequence, the patients lying inside the magnet were trained once or twice to suspend their breath for 25–30 s to get familiar with this special requirement of the examination. MRU sequences were routinely repeated 5 and 15 min after the administration of contrast material and delayed films were taken when necessary. Subsequently, detailed MRUs and finally, the source images were performed until completion of the examination after usually 25–30 min of contrast material injection. The total imaging time for complete MR urography was approximately 35 min in the majority of patients. Maximum intensity projection (MIP) images were post-processed from the original source images of each three-dimensional sequence dataset. Images were reviewed by senior radiologists both the original and MIP. Subsequently, the results were discussed and consensus reached.

Diuretic-enhanced excretory MRU was performed using a breath-hold sequence in the coronal plane with an anteriorly located pre-saturation slab. MRUs were obtained with a repetition time ms/echo of 7/2.8, a 30° flip angle, a 1.8–2.2 mm section thickness and an overlap of 1 mm, two signals acquired, a 128 × 210 matrix. Field of view was adjusted individually to accommodate different patient sizes. Each MIP image could be easily reconstructed without extra time while the subsequent MR sequence was performed. Before contrast material injection, a heavily T-2 weighted survey MR urogram was obtained using a half-Fourier acquisition single-shot turbo spin echo (HASTE) sequence in coronal plane followed by conventional axial T2-weighted tubro spin echo sequence of the kidney or the pelvis. The HASTE sequence was applied in the axial, sagittal and coronal planes. The data were compiled and computed for various results. The final diagnosis was confirmed intraoperatively on open or endoscopic surgery and was considered the reference standard.


  Results and Observations Top


This study was a prospective study conducted in the Departments of Urology and Radiodiagnosis at our Institution over a period of 2 years on patients of age group 14–70 years with an average age of 37 years. Out of 55 patients 19 (34.5%) were female and 36 (65.5%) were male. Majority of patients had unilateral symptoms, left side slightly more common (41.8%) than the right side (40%). The pain was most common symptom present in 92.7% of our patients followed by burning micturition in 27.2%, dysuria in 20% and increased frequency/urgency in 14.5%. One patient presented with the only complaint of dyspepsia had no urological symptoms and was found to have Grade-IV hydronephrosis of right kidney as an incidental finding on USG abdomen. The average duration of symptoms in our study patients was 4 months (range between 2 weeks and 15 months).

A total number of kidney units was 110. Five patients had a bilateral obstruction, and 49 patients had a unilateral obstruction, and one patient had no obstruction at final workup. Hence, the total number of obstructed renal units was 59 and number of non-obstructed renal units was 51. Out of 55 patients, 28 patients (31 renal units) had no excretion of contrast on IVU, diagnosis was not clear on IVU in 2 patients (1 renal unit) despite contrast excretion, 12 patients (14 renal units) had persistent nephrogram, 9 had poor excretion of contrast material and 4 had contrast allergy [Table 1] and [Table 2]. [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7] describe the statistical data evaluated from the results.
Table 1: Reasons for inability of intravenous urography to diagnose ureteral obstruction

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Table 2: List of final diagnoses in our study patients (including few important non-obstructive conditions diagnosed in our study patients)

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Figure 1: (a) Pie chart showing the percentage of multiplicity of symptoms in our patients. About 74.5% of patients had multiple symptoms. (b) Diagram showing laterality of symptoms among two sexes in our study patients (n = 55). Majority of patients had unilateral symptoms, left side slightly more common (41.8%) than the right side (40%).

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Figure 2: (a) Bar diagram showing age distribution among study patients: Average age in our study patients was 37 years (range 14–70 years). (b) Pie chart showing frequency of different symptoms in our study patients. Majority of patients had more than one symptoms and pain was the most common symptom present in 92.7% of patients.

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Figure 3: (a) Bar diagram showing levels of obstruction on magnetic resonance urography. Majority (83%) of patients in our study had pelvi-ureteric junction obstruction (total number of renal units n = 59). (b) Bar diagram showing comparison between fallacies of intravenous urography with level of obstruction on magnetic resonance urography (n = number of obstructed units = 59). (c) Pie chart showing relative percentages of different grades of hydronephrosis on magnetic resonance urography. Nunmber of obstructed units n = 59. It is noticed from the above chart that 67.6% of patients had Grade-III or IV hydronephrosis which could be the reason that majority (52.5%) of our patients had no excretion of contrast on intravenous urography imaging.

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Figure 4: (a) Bar diagram showing time period for excretion of contrast material in magnetic resonance urography in our study patients. The majority (78.1%) of patients had contrast excretion within 10 min of contrast injection and all patients had contrast excretion within 30 min. (b) Bar diagram showing the comparison between fallacies on intravenous urography with the time period for excretion of contrast material on dynamic magnetic resonance urography (n = 32).

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Figure 5: (a) Bar diagram showing comparison between fallacies on intravenous urography (obstructed units only) with intra-operative grades of hydronephrosis (n = 59). (b) Bar diagram showing comparison between grades of hydronephrosis on magnetic resonance urography with those of Intra-operative grades. It shows that grades of hydronephrosis on magnetic resonance urography are almost similar to those intra-operativly and the difference is statistically significant (P ≤ 0.00001).

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Figure 6: (a) Bar diagram showing the comparison between fallacies on intravenous urography (obstructed units only) with grades of hydronephrosis on magnetic resonance urography (n = 59). (b) Bar diagram showing percentages of intra-operative grades of hydronephrosis among study patients. In patients labeled as 'not applicable', grade of hydronephrosis could not be assessed because of the endoscopic approach of surgery.

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Figure 7: (a) Intravenous urography image of patient at 10 min showing no excretion of contrast material from left kidney. There was no excretion of contrast till 24 h on repeated films. (b) Coronal thick slab T2-weighted magnetic resonance urography image of the same patient showing grossly hydronephrotic left kidney with visualization of normal caliber left ureter s/o pelvi-ureteric junction obstruction. (c) Coronal post-contrast three-dimensional FLASH subtraction image of the same patient showing uptake of contrast in right kidney and residual renal parenchyma of the left kidney.

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Majority of our study patients (78.1%) had contrast excretion within 10 min of contrast media injection on d-MRU, and all patients had contrast excretion by 30 min. Urinary obstruction was caused by PUJ narrowing in 49 renal units, ureteral strictures in 6 (one stricture each in upper and mid-ureter, 4 strictures at vesico-ureteric junction [VUJ]), circumcaval ureter in 1 unit, carcinoma cervix with bladder outlet obstruction in 1 unit, ureterocele in 1 and compression of lower ureter by crossing of iliac vessels in one patient. The cause of ureteral strictures was urinary tuberculosis (1 renal unit) of mid-ureter, prior abdominal surgery/urological procedures in 2 renal units (upper ureter and VUJ), history of the passage of documented VUJ stone in the past (1), primary VUJ obstruction (2).

Level of obstruction was identified in 58 of 59 (98.3%) renal units by sMRU and in 32 of 32 (100%) by dynamic MRU. The sensitivity of MRU in detecting hydronephrosis was 100%. Intraoperatively, the majority of patients (74.57%) had mild or moderate hydronephrosis which was same as the sum of Grade-I, II and III on MRU. Intraoperatively, mild hydronephrosis was consistent with Grade-I and II hydronephrosis on MRU, moderate hydronephrosis consistent with Grade-III and severe hydronephrosis with Grade-IV. MRU well delineated the pelvicalyceal anatomy in all patients.

Image quality was good in all patients and fluid-filled bowel was not a problem. There was no motion-related artifacts. MRU showed better anatomic details. Ectopic kidneys were correctly identified on MRU in all patients. Average creatinine was 0.82 mg/dL (range 0.4–1.4 mg/dL). No gross change in serum creatinine was observed after d-MRU examination, and none of the patients developed any type of contrast-related event with MRU contrast injection. MRU clearly visualised upper and mid ureter in all renal units, and lower ureter was visualised in 108 of 110 renal units (98.1%).

Out of 25 patients with excretion of contrast on MRU within 10 min period, only 9 (36%) patients had no excretion of contrast material on IVU, whereas out of 7 patients with excretion between 10 min and 30 min, 5 (71.4%) patients had no excretion of contrast material on IVU. It signifies that patients showing no contrast excretion on IVU had more chances of delayed contrast excretion on MRU but the difference is not statistically significant (P = 0.3).

Majority of patients had PUJ obstruction. Out of 31 renal units showing no excretion of contrast on IVU, 27 (87.1%) had PUJ obstruction. Similarly, 11 of 14 renal units having persistent nephrogram on IVU had PUJ obstruction, and 8 of 9 renal units with poor excretion on IVU had PUJ obstruction. It is concluded from the above figures that there was no significant relationship between fallacies on IVU with the level of obstruction on MRU and the difference is statistically insignificant (P = 0.95).

In the present study, all the 11 renal units with Grade-IV hydronephrosis on MRU had no excretion of contrast on IVU, whereas the majority of patients with Grade II-III hydronephrosis showed persistent nephrogram or poor contrast excretion on IVU. So as the grade of hydronephrosis increases the chances of getting no excretion on IVU increase or patients showing no excretion of contrast material on IVU have a more severe degree of hydronephrosis, and the difference is statistically significant (P = 0.004).

All the 11 renal units showing no excretion of contrast material on IVU were found to have severe hydronephrosis intraoperatively whereas the majority of renal units with persistent nephrogram or poor excretion on IVU had mild-to-moderate hydronephrosis. This again signifies that patients showing no contrast excretion on IVU had a higher degree of hydronephrosis as confirmed intra-operatively and the difference is statistically significant (P = 0.001).

[Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15] describe the imaging correlation between IVU and MRU, of various obstructive uropathic conditions encountered in our study.
Figure 8: (a) A 20 min intravenous urography image of 18-year-old female showing right sided double moiety with normal contrast excretion bilaterally. (b) A 2-h intravenous urography image of the same patient showing doubtful dilatation in relation to the lower end of the left ureter. ? ureterocele/bladder diverticulum/gut loop. (c) Coronal post-contrast three-dimensional FLASH magnetic resonance urography image showing bilateral double moiety with HUN (Hydroureteronephrosis) of the left upper moiety. (d) Coronal HASTE magnetic resonance imaging sequence of same patient showing left ureterocele.

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Figure 9: (a) coronal T2-weighted thick slab magnetic resonance urography image of the same patient as in figure 8 showing left ureterocele with dilated left lower ureter. (b) Coronal T2-weighted thick slab magnetic resonance urography image of the same patient showing HUN of left upper moiety with secondary to left ureterocele.

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Figure 10: (a) Fifteen minutes prone intravenous urography image showing normal contrast excretion from right kidney with no contrast uptake or excretion from left kidney. (b) Coronal T2-weighted magnetic resonance urography (thick slab) of same patient showing Grade-IV HUN. Subsequent micturating cysto-urethrogram showed Grade-IV vesicoureteric reflux.

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Figure 11: (a) A 2 h intravenous urography film showing no excretion of contrast bilaterally with radio-opaque shadow in left renal area s/o calculus. (b) Coronal T2-weighted static magnetic resonance urography thick slab image of same patient showing bilateral Grade-IV hydroureteronephrosis. MCU of the patient showed bilateral Grade-IV vesicoureteric reflux. (c) Axial HASTE image of same patient showing bilateral hydronephrosis with 2 filling defects (calculi) in left renal pelvis.

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Figure 12: (a) A 10 min intravenous urography film showing contrast excretion in right renal area with possible double collecting system. No contrast uptake/excretion was seen on left side. (b) Axial T2-weighted static magnetic resonance urography image of the same patient showing separate renal pelvis and ureter on right side with non-visualisation of kidney on left side. (c) Coronal T2W static magnetic resonance urography image (thick slab) showing crossed fused renal ectopia.

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Figure 13: (a) A 25 min intravenous urography image showing nephrogram but no excretion of contrast from left kidney with normal contrast excretion from right kidney. (b) Coronal post-contrast three-dimensional FLASH magnetic resonance urography image showing external compression of left ureter by crossing of left common iliac vessels causing left HUN. Note the normal calibre ureter below the level of obstruction. (c) Coronal post-contrast three-dimensional FLASH image of same patient showing extrinsic ureteric compression caused by left common iliac vessels.

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Figure 14: (a) A 6 h intravenous urography image showing no uptake or excretion of contrast material from both kidneys. (b) Axial HASTE magnetic resonance imaging image showing bilateral hydronephrosis with hypoplastic left kidney. (c) Coronal TW Fat Sat image showing a lesion indenting the bladder neck.

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Figure 15: (a) A 5-min intravenous urography image showing non-excretion of contrast from right kidney with non-visualisation of right ureter. (b) Coronal T2-weighted thick slab magnetic resonance urography image of the same patient showing right hydroureteronephrosis with possible right vesico-ureteric junction stricture.

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  Discussion Top


IVU has been used as the primary imaging technique for diagnostic evaluation of urinary tract for years, especially in determining the degree and level of ureteric obstruction,[2] and it acts as an aid to identify the possible diagnosis. Unfortunately, IVU has its own drawbacks such as contrast reactions, radiation exposure [2] and non-excretion of contrast material in moderate-to-severe hydronephrosis (falsely labelling kidney as non-functional), precluding its use in a significant number of cases such as patients of renal impairment, pregnant and paediatric patients.[2] Although CT urography is promising in evaluating hydronephrosis, it is also not without the above-mentioned hazards. In these cases, MRU offers the possibility of evaluating the urinary system and showing high-quality images of the urinary tract without exposing the patient to the main disadvantages of IVU or CT urography. MR urography is a promising technique which affords equivalent functional and additional anatomical information to isotope renography.[13]

In obstructive uropathy, the main reason for the failure of IVU to diagnose upper tract pathology is the absence of contrast medium excretion.[14] Here, MRU scores over IVU. This is of important significance in our study in which majority of patients had no or very poor excretion of contrast material on IVU. 50.9% of our patients had no excretion of contrast on IVU. Shokeir et al.[16] also observed “no excretion of contrast” as the most common reason (26%) for the failure of IVU to diagnose obstruction, though it was not as common as in our study. It could be because of the reason that 69.1% of our patients had Grade III–IV hydronephrosis.

A total of 55 patients were included in this study with the age range of 14–70 years with an average age of 37 years. Majority of patients had unilateral symptoms, left side slightly more common (41.8%) than the right side (40%) (reason not known). The pain was most common symptom present in 92.7% of our patients followed by burning micturition in 27.2%, dysuria in 20% and increased frequency/urgency in 14.5%. Khanna et al.[14] observed a similar trend in the symptomatology of patients in their study though pain and dysuria were slightly more common in our patients and burning micturition, as well as haematuria, were less common as compared to their study. One patient presented with the only complaint of dyspepsia and had no urological symptom, the patient visited a private clinician and was found to have Grade-IV hydronephrosis of the right kidney on USG and was referred to our institute for further management. The average duration of symptoms in our study patients was 4 months (range between 2 weeks and 15 months).

One significant advantage of MR urography over IVU is that during MR urography the level of obstruction is readily apparent without the need for delayed films.[17] In our study, level of obstruction was identified in 98.3% of renal units by sMRU and in 100% by dynamic MRU. Comparable results were obtained in a study conducted by Regan et al.[4] in which HASTE imaging showed the level of obstruction within 13 s coronal scan in all the obstructed kidneys (100% sensitivity). Another study conducted by Sen et al.[3] showed that exact level of obstruction was identified in 25 of 25 (100%) patients.

MRU correctly identified the grade of obstruction in all patients. MRU showed Grade-II hydronephrosis in 18 renal units and Grade-I in a single unit (total 19). Out of these, 17 units had mild hydronephrosis intraoperatively (consistent with Grade-I and II HDN), and in two units hydronephrosis could not be assessed intra-operatively because of endoscopic approach. Similarly, MRU showed Grade-III HDN in 29 units, of which 27 were confirmed as moderate HDN intraoperatively and 2 could not be assessed because of an endoscopic procedure. MRU showed Grade-IV HDN in 11 units, all of which were confirmed intraoperatively. Grades of hydronephrosis on MRU are almost similar to those intraoperatively and the difference is statistically significant (P ≤ 0.00001).

MRU showed dilatation of urinary tract in 55 of 55 patients in our study (sensitivity of 100% for detection of obstruction). It was consistent with many studies done in the past. A study conducted by Zielonko et al.[15] in 2002 showed a sensitivity as well as specificity of 100% to detect urinary tract dilatation by sMRU. In a study by Karabacakoglu et al.[6] in 2003, the sensitivity of MRU to correctly identify dilated urinary tracts was 100%. Sudah et al.[10] also showed that sensitivity, specificity and accuracy of MRU to diagnose obstruction was 100%. Muthusami et al.[13] also found similar results in their study in which they showed that the overall sensitivity and specificity of MRU to detect hydronephrosis was 95% and 100%, respectively. O'Malley et al.[18] concluded in a study that MR urography was highly accurate, with a sensitivity of 100% and a specificity of 96% in the detection of renal pelvicalyceal and ureteric dilatation. Patients showing no excretion of contrast material on IVU had a more severe degree of hydronephrosis, and the difference is statistically significant (P = 0.004).

The total imaging time for complete MR urography was approximately 35 min in our study. Similar results were obtained in a study conducted by Sudah et al.[10] in which total imaging time for all MR sequences, if excretion was not delayed, was approximately 25 min. Farres et al.[12] also showed similar results in their study in which total examination time for dynamic, Gd enhanced MRU was usually 30 min. Riccabona et al.[5] also obtained mean study time of 38 min for MRU in their study.

MR urography was successful in making a diagnosis in 98.3% in our study patients. Similarly, results were obtained in a study conducted by Farres et al.[12] in which dynamic MR urography was adequate in making diagnosis in 95% of patients. In another study, conducted by Aerts et al.[19] demonstrated that MRU depicted all pathological conditions in all patients (100%) including renal hypoplasia. One more study (conducted by Zielonko et al.)[15] showed similar results; in which the diagnosis of calculi group by MRU correlated with other modalities in 85% of cases, whereas in group of PUJ strictures, results of sMRU correlated with verification methods in 100%. In another study, conducted by Szopinski et al.,[20] the diagnostic values of MRU were considered satisfactory in 98.9% of FLASH 2D studies. Extrinsic causes of obstruction were better diagnosed by MRU because coronal and axial sections could depict abdominal and pelvic pathologies causing ureteric compression as we observed a case of circumcaval ureter and also crossing of iliac vessels causing compression of the lower ureter.[19],[21],[22],[23],[24]

The final diagnosis in our patients included PUJ obstruction in 49 renal units, VUJ strictures in 4, ureteric strictures in two patients. Khanna et al.[14] obtained PUJ obstruction in 22.5% of study patients. A study by Riccabona et al.[5] found PUJ obstruction in 48% of pathological diagnosis followed by VUR. Sen et al.[3] found PUJ obstruction in 12% of patients followed by ureteric strictures in 8% and carcinoma cervix in 4%. All these studies obtained calculi as the most common cause of obstructive uropathy, but in our study calculi were not seen as the most common cause because calculi are almost always detected on IVU and hence are excluded from the study and it might be considered a limitation of our study.

In our study, prior abdominal surgery/urological procedures were done in 2 out of 6 ureteric strictures (33.3%). Results comparable to our study were observed in a study conducted by Zielonko et al.[15] in which they revealed prior urological procedure as the cause of stricture in 4 and prior surgery in 3 cases (total of 7 of 23 ureteric strictures) which comes out to be 30.4%. The above-mentioned figures in our study might be falsely higher due to the very small number of patients with ureteric strictures (small sample size) in our study.

MRU revealed overall better anatomy in the majority of urinary systems, particularly concerning the renal parenchyma, ureter and dilated collecting system, using T2-weighted sequences. Gadolinium-enhanced dynamic MRU allowed accurate anatomical assessment of the complete collecting system and enabled a reliable estimate of pelvi-ureteral drainage. Diuretic-enhanced excretory MRU seems to provide the best possible non-invasive performance in the pre-operative and post-operative assessment of ureteral compression and partial or complete displacement by extrinsic tumour diseases.[25] In suspected strictures, particularly if malignant, one of the major advantages of MR imaging is the capability to obtain additional information as the extension of a pathologic process and the presence of lymphadenopathy or distant metastases.[26]

T2-weighted MRU is safe during pregnancy; therefore, it can differentiate physiologic dilatation in pregnancy from pathologic dilatation.[27] Another important advantage of dynamic MRU is that it can give details regarding functional (including split functions of two kidneys) as well as anatomical aspects of urinary tract, so avoiding need for multiple investigations like IVU followed by CT and/or renal scan for functional and anatomical aspects separately when a single investigation is not diagnostic. It becomes more time-consuming, adding patient discomfort and also less cost-effective than dynamic MRU alone. MRU could reveale the pathology even in non-functioning.[3]

A complete MRU protocol can be used for imaging all components of the kidneys and the urinary collecting system in a single imaging session.[28] MRU has better contrast resolution than CT urography without exposure to ionising radiation and can be done without contrast administration, making it more suitable for examination of paediatric and pregnant patients and patients with renal impairment.[29] MRI may have a role in screening patients with inherited conditions affecting the kidneys, such as Von Hippel Lindau disease, which is characterised by haemangioblastomas of the CNS with a high prevalence of renal cysts, angiomas, and renal cell carcinoma. MRU is as effective as excretory urography, ultrasound and nuclear medicine techniques for the investigation of most paediatric uropathologic conditions and for the investigation of congenital anomalies. MRU is better than IV urography for the depiction of renal scarring in patients with spinal dysraphism.[8],[7],[17],[26],[30],[31],[32]

The option of performing either static-fluid or excretory MRU is useful in the context of renal obstruction, such as that associated with an obstructed upper pole moiety in a duplicated collecting system. In a duplex collecting system, the ureter draining the upper pole principle moiety inserts ectopically inferior and medial to the ureter draining the lower pole moiety below the level of trigone and is prone to obstruction. The lower pole and interpolar regions of the kidney are drained by a separate ureter that has an orthotopic insertion but is prone to VUR.[28] This principle is known as the  Weigert-Meyer rule More Details. The obstructed moiety is likely to excrete IV contrast material slower than is the lower moiety, if at all. Static-fluid MRU can be used in such circumstances to visualise differential dilatation of the upper pole moiety relative to that of the lower pole.[9]

The combination of static-fluid and excretory MRU can be useful in the evaluation of obstructive uropathy because T2-weighted images can show the extent of dilatation of the obstructed system and excretory MRU can provide information on the functional effects on excretion.[9] The use of MRI facilitates simultaneous evaluation of the kidneys, ureters, renal arteries, renal veins, and IVC, which is useful for assessing renal parenchymal, perinephric, and periureteral tumour extension. Sequential imaging of the ureters with MRU can be used to overcome problems with intermittent lack of ureteral distension due to peristalsis, which can lead to misdiagnosis of stricture and obstruction at CT urography.[29] Sequential imaging also can be used to map the pattern of renal and lesional enhancement after contrast administration, which can be useful for characterising lesions and quantifying renal function.[9] In cases of compromised renal function such as chronic renal failure, dynamic MRU is shown to be effective because it is highly sensitive to even small amounts of gadolinium in the collecting system.[12] Besides, Gd-DTPA complex is safe in such patients due to its hydrophilicity.

Although MRU has great potential for detection, localisation and characterisation of renal and urothelial pathologic conditions, it also has few limitations. Intravenous contrast material (gadolinium) is routinely required for complete evaluation. Contrast material has to be used judiciously, especially in cases of patients with renal impairment due to the risk of nephrogenic systemic fibrosis.[33] The optimal dose of IV gadolinium for MRU has yet to be established. The standard 0.1-mmol/kg dose of gadolinium is reported to cause T2 effects, and doses of 0.05 mmol/kg may impair contrast resolution.


  Conclusions Top


On MRU, it is the static fluid in a urinary system which allows to us study the urinary tract without the use of contrast material and provides images similar to those obtained on IVU. An MRU study using a low-dose contrast agent coupled with a T2-weighted study is an attractive alternative to the conventional imaging of the kidneys and urinary tract, especially in cases of renal tumours. MRU contributes critical information regarding both morphological and functional aspects of urinary tract avoiding exposure to radiation as well as iodinated contrast and could be done without using contrast material and is suitable for pregnant, paediatric patients and patients of renal failure. HASTE-MRU is a rapid, non-invasive technique for visualisation of urinary tract abnormalities. MRU has high sensitivity in the diagnosis of urinary tract obstruction, detecting the level of obstruction and as an aid in the diagnosis of obstructive uropathy, thus showing promising results. MRU is safer than IVU due to avoidance of iodinated contrast material and could also be done without using contrast material so having less contrast related events.

.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15]
 
 
    Tables

  [Table 1], [Table 2]



 

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