What imaging tests can be ordered in urology?

Imaging Tests in Urology: A Comprehensive Guide

The most common imaging tests used in urology include ultrasound, CT scan with various protocols (including CT urography), MRI, nuclear imaging studies, X-ray studies, and specialized urologic imaging procedures like cystoscopy and retrograde studies. These imaging modalities are essential for diagnosing and managing a wide range of urological conditions.

Ultrasound Imaging

• Renal and Bladder Ultrasound: First-line imaging for evaluation of hematuria, hydronephrosis, and suspected renal masses 1, 2

  • Advantages: No radiation, readily available, can visualize intraluminal masses and hydronephrosis
  • Limitations: Cannot rule out all causes of hematuria or accurately stage disease 1

• Contrast-enhanced Ultrasound: Used for pediatric patients and pregnant women as an alternative to CT 1

  • Can be combined with eco-Doppler for improved vascular assessment

CT Imaging

• CT Urography: Gold standard for comprehensive evaluation of the urinary tract 1

  • Includes multiple phases (non-contrast, arterial, venous, and delayed excretory phases)
  • Recommended for confirmed muscle-invasive bladder cancer staging 1
  • Superior to IVU for detecting urinary tract abnormalities 3

• Low-dose CT: Recommended for urolithiasis evaluation with high diagnostic accuracy (93.1% sensitivity, 96.6% specificity) 1

  • Reduces radiation exposure while maintaining diagnostic quality

• CT with Delayed Phase: Essential for detection of ureteral injuries and ureteropelvic junction disruptions 1

  • A 10-minute delayed phase is recommended for optimal visualization

• CT Cystogram: More accurate than plain X-ray cystography for bladder injury evaluation 1

MRI Studies

• MR Urography: Alternative when CT is contraindicated due to contrast concerns or radiation dose 1, 3

  • Provides detailed anatomical and potentially functional information
  • Less established than CT urography but avoids ionizing radiation

• Multiparametric MRI: Used for bladder cancer staging with VI-RADS (Vesical Imaging-Reporting and Data System) score 1

  • Helps differentiate T1 from T2 tumors

• MRI Pelvis: Reserved for complex cases or pre-surgical planning 2

Nuclear Medicine Studies

• DMSA (Dimercaptosuccinic acid) Scan: Best nuclear agent for visualizing renal cortical tissue and differential function 1

  • Used to detect renal scarring and assess split renal function

• PET/CT: Increasingly used for staging of advanced urological malignancies 1

  • 18F-FDG PET/CT helps evaluate lymph node involvement and distant metastases
  • Useful in optimizing patient selection for neoadjuvant therapy in bladder cancer

• PET/MRI: Emerging modality combining benefits of MRI with functional imaging 1

  • Useful for patients who cannot receive iodine contrast

X-ray Based Studies

• KUB (Kidney-Ureter-Bladder) Radiography: Used for stone follow-up and differentiating between radiopaque and radiolucent stones 1

  • 44-77% sensitivity for stone detection 1

• Retrograde Cystography: Diagnostic procedure of choice for bladder injuries 1

  • Can be performed using conventional radiography or CT

• Retrograde Urethrography: Standard for investigating traumatic urethral injuries 1

  • Preferred over urethroscopy for penile lesions

• Intravenous Urography (IVU): Largely replaced by CT urography but still useful in unstable patients during surgery or in low-resource settings 1

  • Has high false negative rates (37-75%) 1

Specialized Urologic Procedures

• Cystoscopy: Standard diagnostic tool for direct visualization of the bladder and urethra 2

  • White light cystoscopy is the standard for evaluating microscopic hematuria

• Video-urodynamic Studies: Important for patients with suspected secondary vesicoureteral reflux or neurogenic bladder dysfunction 1

• Sentinel Node Mapping: Emerging technique using lymphoscintigraphy and single-photon emission CT/CT for bladder cancer 1

  • Uses hybrid tracer ICG-99m Tc-nanocolloid

Imaging Selection Based on Clinical Scenario

1. For Urolithiasis:

   • Initial: Low-dose non-contrast CT
   • Follow-up: KUB radiography or ultrasound

2. For Hematuria Evaluation:

   • Low-risk: Renal and bladder ultrasound
   • High-risk: CT urography with multiphasic imaging 1, 2

3. For Trauma Assessment:

   • Blunt trauma: Contrast-enhanced CT with delayed urographic phase 1
   • Penetrating trauma: Contrast-enhanced CT with delayed phase for all stable patients 1
   • Bladder injury: Retrograde cystography 1
   • Urethral injury: Retrograde urethrography 1

4. For Pediatric Patients:

   • First-line: Ultrasound
   • Second-line: MRI or low-dose CT when necessary 1

5. For Pregnant Women:

   • First-line: Ultrasound
   • Second-line: MRI
   • Last resort: Low-dose CT 1

Common Pitfalls in Urologic Imaging

• Relying solely on ultrasound for comprehensive urinary tract evaluation in high-risk patients
• Failing to include a delayed excretory phase in CT when evaluating for urothelial lesions or ureteral injuries
• Not specifying detailed measurements when ordering pelvic ultrasound (e.g., detrusor wall thickness, post-void residual) 2
• Using IVU instead of CT urography for comprehensive evaluation (IVU has high false negative rates) 1
• Performing repeat CT scans unnecessarily in follow-up when ultrasound or KUB would suffice 1

By selecting the appropriate imaging modality based on the clinical scenario, urologists can maximize diagnostic accuracy while minimizing risks associated with radiation exposure and invasive procedures.