|Year : 2019 | Volume
| Issue : 3 | Page : 170-174
Diffusion weighted MR imaging in the diagnosis of acute pyelonephritis and its complications: A prospective observational study
Bhaskara Rao Sanga Reddi1, Vijayalakshmi Devi Bodagala1, AY Lakshmi1, N Anil Kumar2, V Siva Kumar3
1 Department of Radiodiagnosis, SVIMS, Tirupati, Andhra Pradesh, India
2 Department of Urology, SVIMS, Tirupati, Andhra Pradesh, India
3 Department of Nephrology, SVIMS, Tirupati, Andhra Pradesh, India
|Date of Submission||25-Dec-2018|
|Date of Acceptance||13-Aug-2019|
|Date of Web Publication||17-Oct-2019|
Dr. Vijayalakshmi Devi Bodagala
Department of Radiodiagnosis, SVIMS, Tirupati, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Introduction: In diagnosing complicated pyelonephritis, imaging is essential for which traditionally computed tomography (CT) has been in use but in renal failure patients contrast enhanced CT can't be performed due to elevated serum creatine levels. This can be overcome with the help of Diffusion weighted (DW) magnetic resonance imaging (MRI).
Purpose: To assess the morphological changes and signal abnormalities, in kidneys in patients with acute pyelonephritis (APN) on conventional MRI and DWI and to measure the ADC values in areas of abnormal signal intensity in DWI so as to differentiate between abscess and nephritis.
Materials and Methods: In our study, 32 patients with clinical and laboratory diagnosis of pyelonephritis underwent conventional and Diffusion weighted MRI. Diffusion images were obtained by using a non-breath-hold, single-shot echo-planar sequence with b values of 50/400/800 s/mm2. Circular regions of interest were drawn in the areas of normal renal parenchyma, nephritis and abscesses. The ADC values of three tissue types were compared by using the paired t-test and ANOVA.P value < 0.001 was considered to be statistically significant.
Results: In our study, areas of normal renal parenchyma showed ADC values of (1.83 ± 0.06) × 10-3 mm2/s while areas of nephritis had ADC values of (1.20 ± 0.08) × 10-3 mm2/s which was significantly lower (P < 0.001). Also, significantly lower ADC values of (0.77 ± 0.05) × 10-3 mm2/s were found in abscesses, when compared to nephritis and normal renal parenchyma.
Conclusion: Diffusion weighted MR imaging is useful to diagnose abscess formation in patients with pyelonephritis without using IV contrast medium.
Keywords: Abscess, acute pyelonephritis, diffusion weighted MR Imagin
|How to cite this article:|
Sanga Reddi BR, Bodagala VD, Lakshmi A Y, Kumar N A, Kumar V S. Diffusion weighted MR imaging in the diagnosis of acute pyelonephritis and its complications: A prospective observational study. J NTR Univ Health Sci 2019;8:170-4
|How to cite this URL:|
Sanga Reddi BR, Bodagala VD, Lakshmi A Y, Kumar N A, Kumar V S. Diffusion weighted MR imaging in the diagnosis of acute pyelonephritis and its complications: A prospective observational study. J NTR Univ Health Sci [serial online] 2019 [cited 2020 Aug 14];8:170-4. Available from: http://www.jdrntruhs.org/text.asp?2019/8/3/170/269482
| Introduction|| |
Acute Pyelonephritis is an infection of the renal pelvis and kidney that usually results from bacterial ascent up the ureters from the bladder to the kidneys, most commonly by Escherichia More Details coli. Fortunately, most of these infections are uncomplicated and involve only the urinary bladder. Both, the infection of renal pelvis and parenchyma may result either from ascent of microorganism from urinary or seeds haematogenously and is known as Pyelonephritis.,
Diagnosis of Urinary tract infection (UTI), is typically done by abnormal clinical and laboratory values. Imaging is indicated in patients who doesn't respond with antibiotic therapy. Renal imaging is also indicated if definite diagnosis of acute renal infection is not established or in patients with recurrent episodes of infection.,
Now-a-days, DW MRI is increasingly used in abdominal imaging to diagnose various conditions. Being MRI, a technique which doesn't use ionizing radiation, it can be safely used in pregnant patients. DWI is used to confirm the clinical suspicion of acute pyelonephritis. It has the potential to detect renal abscess formation in patients already diagnosed with pyelonephritis. DWI MRI capable of diagnosing renal abscesses without the need to administer iodinated contrast agents or gadolinium and is thus useful in patients with renal failure and in patients with iodine sensitivity.
Aim: To study the morphological changes and signal abnormalities in kidneys in conventional MRI sequences and to assess the value of DWI-MRI for the detection and assessment of Acute pyelonephritis and it's complications. To measure the ADC values in areas of abnormal signal intensity in DWI to differentiate between abscess and nephritis.
| Materials and Methods|| |
The study was conducted after obtaining approval from the Institutional research and Ethics Committee. Thirty-two patients presenting with clinical diagnosis of acute pyelonephritis, positive urine microscopic examination, and positive blood culture participated in the study. Patients were scheduled for MRI study on the same day after obtaining a written informed consent.
Prior to taking in the gantry absolute contradictions were ruled out. Patients were positioned head first supine position in the MRI gantry. Scout images were obtained in all three planes for further planning. T1 Weighted and T2 weighted images in axial and coronal plane were planned on scout images and obtained either during breath hold or respiratory gating by using navigator sequences. The images were obtained with field of view (FOV) adjusted so as to include both the kidneys and perinephric space, usually extending from the dome of diaphragm to lower pole of kidney with section thickness of 5 mm and inter slice gap 5 mm. T2w imaging was performed with a two-dimensional axial and coronal half-Fourier acquired single shot turbo spin echo sequence (HASTE) (TR/TE—1300/97). T1W imaging was performed with an axial three-dimensional volume interpolated breath hold exam (VIBE)-fat suppression sequence (TR/TE—4.11/2, slice thickness 5 mm, matrix 211/320.
Echo planar imaging technique was used for acquiring the DW images during free respiration. Images were obtained with routinely used ‘b’ values of 50/400/800 s/mm2. Automated apparent diffusion coefficient (ADC) parameter maps were generated by the MR system.
The images acquired were processed and analyzed on Siemens MR workstation using syngo software. T1 and T2 Images were analyzed for renal size, long axis distance from superior to inferior pole was measured for each kidney. Renal parenchymal signal intensity pattern was visually assessed. Corticomedullary diffrention on T2W was noted as visualized or not visualized either in focal area or entire kidney. The change in parenchymal intensity was visually characterized as hyperintense, hypointense, or isointense with relation to signal intensity of abdominal wall muscles. Signal intensity changes noted either focal or diffuse. The signal intensity changes in perinephric fat similarly assessed. ADC values in particular hand drawn region of interest were obtained from the renal parenchyma on the MR system generated ADC maps.
Demographic data of patient such as age and gender were noted and biochemical values like blood urea, serum creatine, CRP levels were obtained. Data regarding urine culture and pus culture were obtained where ever possible; the above obtained data was systematically tabulated and analyzed.
Data were recorded on predesigned proforma and managed using Microsoft Excel 2007 (Microsoft crop, Redmond, USA). To ensure consistency in measurement and interpretation, the information collected was meticulously cross-checked and physically verified. Analysis of the data done by using SPSS software, windows 17.0 version. P value of <0.001 will be considered as significant. ANOVA and Student's t-test was conducted for calculating the differences in the mean ADC values between normal renal parenchyma, nephritis, and abscess.
| Results|| |
In the present study 32 patients had participated; out of 32 patients 18 members were females 14 were males, age ranged from 25 to 70, mean age is 49 years [Table 1]. Majority of them presented with chief complaint of fever, chills, rigors, and abdominal pain. Out of 32 patients, 25 were positive for E. coli, one for Enterococcus on blood culture.
On MRI the lesions were hypointense on T1WI in 20 patients (62.5%) [Table 2] and hyperintense on T2WI in 22 patients (68.75%) [Table 3]. DW MRI demonstrated areas of restricted diffusion in 27 patients, thus providing a high sensitivity 84.37% [Table 4]. [Figure 1] and [Figure 2] demonstrate the advantage of diffusion weighted imaging over conventional imaging in the detection of pyelonephritis.
|Figure 1: T1axial (a), T2 axial (b), DWI with b value 800 (c) and ADC map (d) in a 69 years pt with APN showing T1 isointense,T2 hyperintense focus in lower pole of right kidney with restricted Diffusion|
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|Figure 2: T2 axial (a), T1 axial (b), DWI with b value 800 (c) and ADC map (d) in a pt of APN with micro abscess in upper pole of left kidney showing no abnormal signal on T1 and T2 and restricted diffusion on DWI|
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The normal renal cortical parenchyma showed ADC values of (1.83 ± 0.06) × 10-3 mm2/s. As against this, the areas of nephritis had ADC values of (1.20 ± 0.08) × 10-3 mm2/s. Eight patients were identified to have developed renal abscesses on DWI which showed a more hyperintense signal as compared to rest of the renal parenchyma involved by nephritis, whose ADC values were (0.77 ± 0.05) × 10-3 mm2/s (as depicted in [Figure 3]). Out of these 8 patients, US-guided aspiration of pus from the abscess cavity was done from 4 patient. In rest of the 4 patients the abscess was small in size.
|Figure 3: DWI with b value 800 (a) and ADC maps (b, c, d) in a patient with APN and abscess inter polar region of left kidney showing hyperintense signal on DWI and reduced ADC value on ADC maps|
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On statistical analysis using the paired t-test, the areas of nephritis and abscess showed significantly low ADC values compared to that of the uninvolved renal cortical parenchyma (P value < 0.001). On statistical analysis using the ANOVA test renal abscesses showed significantly low ADC values as compared to areas of nephritis (P value < 0.001).
| Discussion|| |
The diffusion sequence is an important part of MRI of the brain. It has gained importance recently in the evaluation of extra-cranial organsC. Thoeny et al. studied DW MRI in healthy volunteers and obtained reproducible measurements of the kidneys and also observed significant difference of ADC values in the renal cortex and medulla. Due to the choice of different b values, different ADC values were observed in various studies.
In our study, DW MRI provided a high sensitivity of 84.37% in contrast to T1w and T2w whose sensitivities are 62.5% and 68.76%, respectively, in the detection of pyelonephritis. In our study the areas of nephritis demonstrated restricted diffusion with lower ADC values we also observed significant difference in ADC values between nephritis and renal parenchyma. The ADC values of normal renal cortical parenchyma were (1.83 ± 0.06) × 10-3 mm2/s.) and those of nephritic areas were (1.20 ± 0.08) × 10-3 mm2/s). Retrospective study by Faletti et al. showed ADC values of (2.16 ± 0.24) × 10-3 mm2/s in healthy renal parenchyma and (1.46 ± 0.27) × 10-3 mm2/s in pyelonephritis foci. Verswijvel et al. studied retrospectively utility of DW MRI in three patients with pyelonephritis and observed significant difference in ADC values 1.63 and 1.9 × 10-3 mm2/s in the normal contralateral kidney and (1.1 ± 0.3) × 10-3 mm2/s in areas of restricted diffusion in the affected kidneys.
In our study significant difference was observed in between nephritis and abscesses, areas of nephritis had ADC value of (1.20 ± 0.08) × 10-3 mm2/s and renal abscesses had ADC value of (0.77 ± 0.05) × 10-3 mm2/s similar ADC values of nephritic foci (1.46 ± 0.27) × 10-3 mm2/s and abscesses (1.13 ± 0.4) × 10-3 mm2/s) observed in retrospective study by Faletti et al. A substantial low ADC value of 0.83 × 10-3 mm2/s was also reported in a renal abscess by Verswijvel et al. ([Table 5] is showing comparison of our study with different studies). In our study using DW MRI, abscess could be diagnosed in patients which further helped in the management of the patients.
We would like to point out few limitations of our study.
- Small sample size
For small renal abscesses, treatment with antibacterial agents without drainage may be effective and aspiration of the abscess may be necessary in patients with large abscess. As renal biopsy is a relative contraindication for pyelonephritis, histopathology is not a major limitation for our study.
| Conclusion|| |
In conclusion, DW MRI has a higher sensitivity for detection of acute pyelonephritis as compared to conventional MRI. The ADC values of renal abscesses are significantly lower than that of areas of pyelonephritis. Hence, DW MRI could be potentially used to detect abscess formation in patients with pyelonephritis, especially if contrast administration is to be avoided due to renal dysfunction. Further prospective studies in larger number of patients would be useful to consolidate these observations.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]