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Diagnostic Radiology · Diagnostic Radiology of the Abdominal Organs

Diagnostic imaging of urinary tract obstruction

Urinary tract obstruction requires rapid and accurate identification of the cause, most often lumen-blocking calculi. The choice of radiological method depends on the clinical picture: unenhanced computed tomography is the gold standard, whereas ultrasound and magnetic resonance urography take precedence in pregnant patients.

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Hidden ThreatIn acute renal colic, ultrasound may fail to detect obstruction in 30% of patients during the first few hours.
Normal in Pregnancy80% of pregnant women exhibit physiological hydronephrosis without calculi.
Gold StandardUnenhanced CT outperforms all other methods in detecting calculi.
Risk FactorMacroscopic haematuria is a strict predictor of serious urological pathology.
4 min readFor medical studentsUpdated Sep 25, 2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Ultrasound and plain radiography

Ultrasound (ultrasound) aims to detect direct signs of obstruction: dilation of the renal pelvis — hydronephrosis (hydronephrosis) — and the ureter — hydroureter (hydroureter). It is important to remember that with recent stone impaction, dilation of the pelvicalyceal system does not develop immediately. It takes several hours for hydronephrosis to form, so in the early stages, ultrasound may not show acute pathology in a third of patients.

Plain radiography (plain radiography) has low sensitivity for detecting calculi—about 58–62% (according to a study by Levine et al., its sensitivity is only 59% compared to CT). Today, the isolated use of radiography is limited. The combination of X-ray and ultrasound is often used for acute loin pain, but this diagnostic approach is still significantly inferior to computed tomography.

Computed tomography (CT)

Unenhanced computed tomography (unenhanced CT) is recognized as the absolute leader in the diagnosis of calculi due to its superior sensitivity and specificity. Patients over 40 years of age presenting with macroscopic haematuria (macroscopic haematuria) must undergo mandatory triage for CT, as this symptom often indicates serious urological pathology.

Depending on the clinical objective, specialized protocols are used:

  • Renal mass protocol (renal mass protocol CT): includes unenhanced scanning, corticomedullary, and nephrographic phases.
  • CT urography (CT urography): must include the pyelographic (excretory) phase and serves as the first-line imaging method when upper urinary tract urothelial cancer is suspected.
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Diagnostic features in pregnancy and the role of MRI

Diagnosing obstruction in pregnant women is complicated by the fact that 80% of them develop physiological hydronephrosis occurring without calculus formation. It arises due to uterine pressure and hormonal changes, with the right side being more frequently affected.

Magnetic resonance urography (MR urography) is prescribed to pregnant women following ultrasound to confirm true obstructive hydronephrosis and locate the level of blockage. However, for patients with acute flank pain, the method has several limitations:

  1. Low sensitivity to calcifications: MRI visualizes stones in the kidneys and ureters poorly.
  2. Differential diagnosis challenges: on MRI, a stone appears as an intraluminal filling defect, which is extremely difficult to distinguish from a blood clot or a tumour.
  3. Long scanning time and limited equipment availability in emergency situations.

Low-dose CT (low-dose CT) is emerging as a promising alternative for pregnant women, demonstrating good results, but its routine use remains controversial.

Complex clinical cases

Radiological methods are critical for assessing complications and concomitant pathologies.

  • Von Hippel-Lindau Syndrome (Von Hippel-Lindau Syndrome): coronal T2-weighted MRI scans in such patients reveal multiple renal and pancreatic cysts. There is often a history of renal cell carcinoma requiring partial nephrectomy.
  • Vascular complications: patients with haematuria following percutaneous nephrostomy may develop a renal pseudoaneurysm. During digital subtraction angiography, the nephrostomy catheter can create a tamponade effect (tamponade effect). To adequately visualize the pseudoaneurysm, the catheter is sometimes pulled back over a guidewire. If profuse bleeding occurs, it is immediately returned to its position before embolization.

Class and exam questions

Why might ultrasound show normal findings during acute renal colic?

Hydronephrosis and hydroureter take several hours to develop after a stone blocks the ureter. Therefore, in the early stages, the examination will not show dilatation of the pelvicalyceal system.

Can plain radiography alone be used to search for stones?

No, its sensitivity is about 58–62%. A plain radiograph is inferior to unenhanced CT and is used predominantly in combination with ultrasound, although this approach is also less effective.

What is the main problem with MRI in the diagnosis of urolithiasis?

MRI has significantly reduced sensitivity to calcifications. A stone appears as a filling defect that is difficult to distinguish on scans from a blood clot or an intraluminal tumour.

What CT strategy should be chosen when urothelial cancer is suspected?

The first-line method is CT urography, which invariably includes the pyelographic (excretory) phase.

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What else to study on this topic

  • MRI findings in Von Hippel-Lindau syndrome (cystic lesions of the kidneys and pancreas)
  • Digital subtraction angiography in renal pseudoaneurysm and the tamponade effect
  • Technique for performing the renal mass CT protocol (contrast phases)
  • Low-dose computed tomography (Low-dose CT) in the diagnosis of urolithiasis in pregnant women

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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

HematuriaLow-dose renal CTRenal massesRenal impairmentContrast-induced nephropathyAcute pyelonephritisRenal abscessEmphysematous renal infectionsXanthogranulomatous pyelonephritisChronic pyelonephritisRenal tuberculosisChronic cystitisProstate CT
Entire section "Diagnostic Radiology of the Abdominal Organs"

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