European Journal of Cardiovascular Medicine

Urinary tract obstruction is defined as any blockage or hindrance to the normal flow of excreted urine, caused by either structural or functional abnormalities within the urinary tract. It can occur at any point along the urinary tract, from the kidneys to the urethra. Three main categories of causes can lead to urinary tract obstruction which include extraluminal, luminal, and intraluminal, each with distinct characteristics¹.Urinary tract obstruction is a significant contributor to renal failure, accounting for 10% of acute cases and 4% of chronic end-stage cases, as reported in epidemiological studies².  Renal failure can occur within a few weeks or a few years depending on degree and type of obstruction³. Several diagnostic modalities are available to investigate urinary tract obstruction in patients with symptoms include abdomen radiography, intravenous urography, ultrasonography, non-contrast or contrast enhanced CT (NCCT or CECT), non-contrast or contrast enhanced magnetic resonance imaging (NCMRI or CEMRI)¹.

Conventional radiography unfortunately has sensitivity of about 60% for detection of urolithiasis, because the bowel contents overlying soft tissues, bowel gaseous shadows and osseus structures may obscure small radio-opaque calculi. Intravenous urography (IVU) can assess anatomy and to some extent the function of the kidney. Obstruction can be diagnosed by presence of hydronephrosis or hydroureter. Visualization of filling defects helps to determine the level and the cause of the obstruction. But IVU has limitations of longer time required for the procedure and significant amount of radiation exposure that may not be ideal for young children or pregnant women⁵.

Fowler et al reported an overall sensitivity of only 24% and specificity of 90% for the detection of renal calculi by USG and hence NCCT is indicated for accurate determination of the size, number and position of the renal calculi as well as the cause and level of obstruction⁶. Advantages of ultrasonography are economical, readily available, and to an extent can identify the cause of obstructive uropathy without radiation⁷. The limitations of this imaging modality include low signal-to-noise ratio, lack of tissue specificity, restricted field of view, operator-dependent results and patient body habitus⁸.

With the introduction of multidetector technology, computed tomography is the preferred diagnostic tool for a range of urological conditions, including urolithiasis, urinary tract infections, renal injuries, tumors and obstructive uropathy⁹. Most of the patients with urinary tract obstruction will have impaired renal functions and therefore contrast urography cannot be done. In such conditions non-contrast CT is the investigation modality of choice. An added advantage of NCCT is contrast related complications can be avoided and is of particular value in the patients with renal failure where intravenous contrast can be avoided without compromising effectiveness in identifying the cause and level of obstruction¹⁰.

MR urography though an evolving technique in providing the most comprehensive and specific imaging method for many urinary tract abnormalities without the use of ionizing radiation¹¹, has certain limitations which include longer examination time, decreased spatial resolution and an inability to reliably depict calcifications and calculi¹².

Non-contrast CT is a rapid and safe imaging technique that accurately diagnoses urinary tract obstruction, detecting urolithiasis with a sensitivity of 92-95%¹³. Additionally, CT abdomen is useful in ruling out calculi and can provide a definitive diagnosis in up to 40% of cases with non-calculus related obstruction¹⁰. The key factors that guide the clinical management of patients with urolithiasis are the   location of calculus, size, and chemical composition, as well as any underlying urinary tract anomalies, which can be effectively evaluated using NCCT¹⁴. Site of obstruction can be diagnosed by NCCT which plays a key role in the management and helps to decide on the surgical approach. For example, depending on the severity of the obstruction, lower tract obstructions may be treated with medical management, bladder catheterization, or minimally invasive procedures, whereas upper tract obstructions may require more invasive interventions, such as ureteric stenting or nephrostomy tube placement, to effectively decompress the blocked collecting system and restore urinary tract patency¹⁵.

In this study we aim at evaluating the role of NCCT study of abdomen in patients presenting with urinary tract obstruction and also to determine the cause and level of obstruction.

A descriptive cross-sectional study of 80 subjects referred from various clinical departments to the Department of Radiodiagnosis, which is done at a tertiary care hospital for a period of 1 year from April 2019 to October 2019 presenting with suspected urinary tract obstruction. The sample size is calculated based on the study conducted by Kamal Sharma et al¹ by considering the proportion of urinary tract calculi, p = 66%. Using the formula n= 4pq/d², p= 66 (prevalence), q=34 (100 –p), d=11 (margin of error), the sample size of 74 is required for the study. After the informed consent was obtained and brief history was taken, the NCCT abdomen scan was performed using Wipro GE Revolution ACTS (16-slice). Images were reconstructed at a slice thickness of 1.25 mm. Urinary tract was assessed using multiplanar images for the site and cause of obstruction including the associated findings.

RESULTS AND DISCUSSION:

Demographic features of the study group:

Table-1: Age distribution:

Table 2: Gender distribution

Presenting complaints and duration:

Table-3: Presenting complaints

Table 4: Duration of symptoms

Flank pain was the commonest accounting for 66 (82.5%) cases, followed by hematuria in 6 (7.5%) cases. Other symptoms (14 cases; 17.5%) include anuria, difficulty in micturition, pain during micturition, urgency, lower back pain. 57 (71.25%) cases had symptoms for less than 1 week, followed by 3 (3.75%) cases had symptoms for 1-2 weeks and 20 (25.0%) cases had symptoms for more than 1 week (tables 3 & 4).

Causes of urinary obstruction and laterality:

Figure 1: NCCT image in soft tissue window axial section showing a large left pelvi ureteric junction calculus (straight arrow) causing gross hydronephrosis (curved arrow).                       

Figure 2: NCCT image in soft tissue window axial section showing right vesicoureteric junction calculus (arrow) causing moderate hydroureteronephrosis.

Table 5: Causes of urinary obstruction

Table 6: Laterality of calculus

Amongst the total 80 cases, findings were noted in 71 cases and calculus was the commonest cause of obstruction, accounting for 55 (68.75%) cases, followed by pelvi-ureteric junction (PUJ) obstruction (Figure 3) and prostatomegaly (Figure 4) as in the table-5. 

Figure 3: NCCT image in soft tissue window coronal section showing left pelvi-ureteric junction obstruction-abrupt narrowing (arrow) at L3-L4 vertebral level causing mild left hydronephrosis.

Figure 4: NCCT image in soft tissue window axial section showing prostatomegaly (arrow) 64 cc in volume causing bladder outlet obstruction.

Amongst the 55 patients in whom calculi were found, 4 patients had calculi at multiple sites and one had bilateral calculi. Ureter was the commonest site of calculi, accounting for 48 cases followed by renal calculi in 10 cases and 1 case had vesical calculus (table-6).

It was noted that all the obstructive renal calculi were located at the pelvi-ureteric junction. The majority of ureteric calculus were at the proximal and distal segments of ureter and at vesico- ureteric junctions. Among the renal calculi, the smallest measured ~2.3 mm, and the largest was ~23 mm. Similarly, the smallest ureteric calculus measured ~2 mm, and the largest measured ~17 mm (tables 7 & 8).

Sites and sizes of calculi:

Table 7: Various sites of calculus

Table 8: Size range of calculus

Density of calculi:

Among the renal stones, the lowest Hounsfield unit (HU) measured was around 200 and the highest            HU measured was around 1500. Similarly, the lowest HU in ureteric stone was around 200, and the highest HU was around 1300 (table-9).

Table 9: Hounsfield unit range of calculus among the study population

Secondary signs of obstruction and other findings (Figures 5A & B):

All patients with stones at PUJ showed a dilated pelvicalyceal system, with 4 of them being mild and moderate in severity and 2 showed severe dilatation. However, stones in the ureter were associated majorly with mild hydroureteronephrosis (HUN) (33), followed by moderate (12) and severe (2) hydroureteronephrosis. Fat stranding was also observed in 14 cases (table-10 and Figure 6 B).

Overall, 30 patients (37.5%) had urinary tract stones only with no other associated pathologies detected by non-contrast CT and 25 patients (31.25%) had incidental findings besides urinary tract stones, 7 patients (8.75%) had an incidental finding with non-calculus obstruction, and 9 patients (11.25%) had non-calculus obstruction without incidental findings like ureteral strictures (Figure 7), iatrogenic ureteral perforations and urothelial malignancies (Figure 8) and 9 cases  (11.2%) had neither stones nor incidental findings seen in non-contrast CT study (table-11).

Table 10: Secondary signs of obstruction

Table 11: Various combinations of findings

Figure 5 (A and B): Unenhanced CT images soft tissue window sagittal and axial section showing uterus displaced inferiorly with respect to pubococcygeal line (arrow in A) with mild to moderate hydroureteronephrosis (arrows in B) secondary to uterovaginal prolapse also indicating secondary signs of obstruction.

Figure 6: (A and B): Unenhanced CT images in soft tissue window axial section showing bilateral moderate hydroureteronephrosis (arrows in A) with cortical thinning (arrows in B) secondary to vesico-ureteric reflux. Also showing perirenal subtle stranding indicating secondary signs of obstruction.

Figure 7: Unenhanced CT images in soft tissue window axial section showing bilateral adnexal lesions (arrows) causing obstruction of          bilateral distal ureters resulting in hydroureteronephrosis.

Figure 8: Unenhanced CT images in soft tissue window axial section shows well distended urinary bladder is well distended with heterogeneously enhancing intraluminal polypoidal lesion (arrow) suggestive of neoplastic etiology.

Incidental findings:

Incidental findings related to the urinary system was found in 12 cases (29.27%), Among the urinary tract group, renal cysts were the common association, followed by chronic cystitis and least common being prostatic abscess. Incidental findings unrelated to the urinary system was found in 29 cases (36.25%), Most common being vertebral defects like lumbar spondylosis, anterolisthesis followed by fatty liver, hepatomegaly, cholelithiasis and umbilical hernia. Inguinal hernia and enlarged lymph node (tables 12 & 13).

Table 12: Incidental findings related to urinary tract

Table 13: Incidental findings unrelated to urinary tract

Non-contrast CT abdomen is the most widely used investigation modality in patients presenting with symptoms of urinary tract obstruction. It can be performed rapidly even in patients with deranged renal function test, due to the advanced multirow detector technology. The detection of urinary calculi using unenhanced CT has become the gold standard due to its high sensitivity and specificity. Additionally, NCCT scans can detect other pathological conditions that may mimic renal colic, beyond stone disease¹⁶.

In present study, we examined 80 patients with symptoms of urinary tract obstruction, comprising 59 males (73.75%) and 21 females (26.25%). Similar gender distribution is noted in the study conducted by Meenakumari A et al¹⁷. The average age of the patients in present study was 36.4 years for males and 40.9 years for females which is comparable to that of study conducted by Sharma et al, which reported a mean age of 33.5 years ¹. The clinical presentation in the present study is similar to study conducted by Jivnani DA where pain was presenting complaint in 58%, followed by hematuria in 8%, lump in 5% & micturition disturbances in 6%¹⁸.

Unenhanced MDCT is the preferred imaging modality for suspected urolithiasis, offering high sensitivity (95-98%) and specificity (96-100%). MDCT provides precise information on urinary tract stone size, location, and presence of urinary obstruction, making it a reliable diagnostic tool¹⁹. In present study, urolithiasis was the leading cause of urinary tract obstruction, accounting for 66.2% of cases, which is consistent with the results of a study by F.U. Chowdhurya et al, which reported a positive rate of 44% (221 out of 500 patients) for urolithiasis, highlighting its significance as a common cause of urinary tract obstruction²⁰. A study by Sharma et al, found that the most common cause of urinary tract obstruction was urinary tract calculi, which accounted for 66% of cases, also aligning with our findings¹.

The location and site of impaction of a stone are crucial factors in determining the best course of treatment, with stones in the lower third of the ureter having a higher success rate of treatment. CT provide accurate detection and localization of ureteral calculi, enabling targeted and effective management²¹. The locations of the ureteric calculi in the present study were similar to study conducted by Hanno Hoppe, in which, among 1035 patients with urinary tract calculi, 377 (36%) had ureterolithiasis, 309 (30%) had nephrolithiasis, and 349 (34%) had nephrolithiasis and ureterolithiasis²². In present study pelvicalyceal system dilatation was found in all 10 cases of PUJ calculus and hydroureteronephrosis in all 47 cases of ureteral stone, with different degrees of hydroureteronephrosis. Fat stranding was found in 14 cases. Earlier studies   support these findings. One study by Ege G and Akman H et al found that most patients (82.7%) had a hydroureter, 80% had hydronephrosis, 59% had periureteric edema and 57.2% had unilateral renal enlargement²³. These signs are important indicators of ureteral obstruction. Another study by Chen and Zagoria et al found similar results, with 82% of patients with ureteral stones showing signs of hydroureter and periureteral oedema²⁴.

Precise pre-treatment determination of urinary stone composition is essential and considerably impacts appropriate management. Knowledge of the stone composition is also useful for the prevention of recurrent disease²⁵. The HU measurements of the various urinary stones at 120 kV usually fall under the following range: Uric acid, 200–450 HU; struvite, 600–900 HU; cysteine, 600–1100 HU; calcium phosphate, 1200–1600 HU; and calcium oxalate monohydrate and brushite, 1700–2800 HU²⁶. Despite the substantial accuracy of CT in determining stone composition in vitro studies, HU measurement for predicting stone composition in vivo is less reliable and challenging. To assess stone composition using CT attenuation values (HU), it's crucial to accurately place the ROI over the stone, ensure the appropriate size of the ROI and use the correct slice thickness. This precise technique is necessary to avoid partial volume averaging effects, which can lead to inaccurate readings²⁷. In present study the HU measurements for renal stones ranged from 200-1500 and for ureteric stones from 200-1300. However, it's important to note that stones are often composed of mixed attenuation, making precise identification challenging. Additionally, the overlap in attenuation measurements of various stone types limits the effectiveness of ROI-based methods in distinguishing between them²⁸.

PUJ obstruction is a recognized cause of urinary tract obstruction, as reported by study conducted by Shokeir AA et al (1 case) and corroborated with present study (6.25%, 5 cases)²⁹. The hallmark of PUJ obstruction is pyelocaliectasis with abrupt narrowing, consistently observed in all affected cases³⁰. While multidetector CT angiography is essential for confirmation and treatment planning, it offers a detailed assessment of PUJ obstruction, crossing vessels (its presence and location) and renal anatomy. This comprehensive evaluation enables the selection of most appropriate surgical approach and treatment strategy³¹.

A study conducted by Halle, showed 62 patients out of 229 (27%) had benign prostatic hyperplasia³². Our study identified 4 cases of benign prostatic hyperplasia that caused obstructive uropathy. Ureteric stricture is a relatively rare condition, reported in 6% of cases (3/50) by study conducted by Sharma et al¹. Consistent with this, present study found ureteral stricture in 2 cases. However, accurate characterization of stricture length and location is critical for effective treatment planning. Therefore, CT urography is essential to determine the cause, length, and location of the stricture, guiding appropriate management⁴ Although bladder masses are uncommon, with a reported incidence of 0.4% (6 out of 1500 patients) in study conducted by Hoppe H and Studer R, present study detected 2 such cases²². When subtle indicators of urinary tract neoplasm appear, such as focal bladder wall thickening or soft tissue masses, administering intravenous contrast material is crucial for further evaluation and definitive diagnosis¹⁶.

Moawad MM and El-Zawawy MS et al, reported that 2 cases had bilateral compression of the ureters due to large pelvic masses³³. Similarly, our study found 2 cases of external compression leading to obstructive uropathy, resulting in bilateral hydroureteronephrosis. One case was caused by bilateral adnexal lesions, and the other                   was due to uterovaginal prolapse, causing mild to moderate hydroureteronephrosis. CT urography is essential for further evaluation, providing information on the level and degree of obstruction, as well as characterization of the primary lesion.

CT with multiformat reconstructions is a superior imaging modality for evaluating vesico- ureteric reflux, able to illustrate the renal tract and any secondary changes resulting from chronic VUR. In fact, CT outperforms both ultrasound and IVP in detecting focal parenchymal abnormalities, defining the extent of disease, and identifying perinephric fluid collections and abscesses³⁴. In our study, we identified one case of VUR, highlighting the importance of CT in diagnosis. However, CECT is essential for further evaluation.

A study by Sharma K et al. demonstrated the utility of MDCT urography in diagnosing additional significant findings, including enlarged lymph nodes, urinoma formation, recto- vesical fistula, and ureterocele¹. Similarly, our study revealed incidental findings in 41 cases, with 12 related to the urinary system and 29 unrelated. The urinary system findings included renal cysts (most common), chronic cystitis extrarenal pelvis, mal-rotated ectopic kidney and prostatic abscess (least common). Meanwhile, the non-urinary system findings comprised vertebral defects (lumbar spondylosis, anterolisthesis), fatty liver, hepatomegaly, cholelithiasis, umbilical hernia, inguinal hernia and enlarged lymph nodes.

Flank pain is one of the most common presenting symptoms related to urinary tract obstruction. Non-contrast CT abdomen is the most widely used investigation modality in patients presenting with symptoms of urinary tract obstruction. Due to its widespread availability, ease of use, and high sensitivity, NCCT abdomen is the preferred diagnostic tool. CT has become the standard of reference in the detection of urinary calculi due to its high sensitivity (95%–98%), high specificity (98%–99%), and ability to help delineate alternative causes of flank pain. In selected cases, intravenous contrast material may be administered to further evaluate and characterize non-calculus causes of urinary tract obstruction offering further diagnostic precision.

In present study, NCCT abdomen enabled an accurate diagnosis of the level of obstruction, as well as its aetiology, including urolithiasis, pelvi-ureteric junction obstruction. Addition to this NCCT abdomen also provided information regarding a wide spectrum of alternate diagnosis.

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