What is the best method for imaging the bladder lumen?

Best Methods for Imaging the Bladder Lumen

Cystoscopy is the gold standard for imaging the bladder lumen, with CT urography (CTU) or MR urography (MRU) being the most appropriate supplementary imaging modalities when additional evaluation is needed. 1

Primary Diagnostic Approach

• Cystoscopy remains the cornerstone for direct visualization of the bladder lumen, allowing for thorough examination of the entire urethra and bladder with documentation of tumor size, location, configuration, number, and mucosal abnormalities 1
• During cystoscopy, clinicians should describe all macroscopic features of any tumors and mucosal abnormalities using a bladder diagram for documentation 1
• Cystoscopy enables direct tissue sampling through biopsy or transurethral resection of bladder tumor (TURBT) for definitive diagnosis 1

Cross-Sectional Imaging Options

CT Urography

• CTU is the preferred cross-sectional imaging modality for comprehensive evaluation of the bladder lumen and upper urinary tract in patients who can receive intravenous contrast 1
• A complete CTU protocol includes:
  • Unenhanced images
  • IV contrast-enhanced images with nephrographic phase
  • Excretory phase (at least 5 minutes after contrast injection)
  • Thin-slice acquisition with maximum-intensity projection or 3D volume rendering 1
• CTU should be used unless contraindicated due to contrast administration concerns or radiation exposure 1

MR Urography

• MRU is the appropriate alternative when CT is contraindicated due to contrast or radiation concerns 1
• MRU protocol should include:
  • Heavily T2-weighted imaging of the intrinsic high signal intensity from urine
  • IV contrast-enhanced series with corticomedullary, nephrographic, and excretory phases
  • Thin-slice acquisition and multiplanar imaging 1
• MRU provides more functional information than CT but has lower sensitivity for detecting urinary tract calculi (69% vs 100% for CT) 1

Advanced Imaging Techniques

Virtual Cystoscopy

• Virtual cystoscopy using CT or MRI can provide supplementary information but does not replace conventional cystoscopy 1, 2
• MR-based virtual cystoscopy offers advantages including:
  • Minimal invasiveness
  • Evaluation of the urethral orifice from a cranial perspective
  • Opportunity to observe diverticula formations and inner urethral space 2
• Despite these advantages, virtual cystoscopy is not commonly performed in routine practice and does not eliminate the need for conventional cystoscopy 1

Special Imaging Considerations

For Suspected Bladder Trauma

• Retrograde cystography (conventional radiography or CT) is the diagnostic procedure of choice for suspected bladder injuries 1
• The technique requires:
  • Retrograde, gravity filling of the bladder with contrast
  • Minimum volume of 300 mL or until patient tolerance
  • At least two views: one at maximal fill and one after bladder drainage 1
• Simply clamping a Foley catheter to allow excreted IV contrast to accumulate is inadequate and results in missed bladder injuries 1

For Bladder Cancer Staging

• MRI can distinguish muscle-invasive from non-muscle-invasive tumors with accurate local staging 3
• The Vesical Imaging-Reporting and Data System (VI-RADS) score helps predict tumor aggressiveness and therapeutic response 1, 3
• PET/CT is superior for nodal staging and is highly recommended for restaging and determining therapeutic effect 3

Pitfalls and Limitations

• CT and MRI both have limitations in detailing the depth of muscle invasion in bladder cancer 4
• Conventional cystoscopy cannot always depict carcinoma in situ (CIS) or differentiate benign from malignant tumors prior to biopsy 3
• Virtual cystoscopy techniques have not gained widespread clinical adoption despite theoretical advantages 1
• Passive anterograde distension of the bladder with IV contrast by clamping a urinary catheter has a high false negative rate due to low intravesical pressure 1

Emerging Technologies

• Photodynamic diagnosis (blue light cystoscopy) improves detection rates of bladder cancer and should be considered when available, especially in cases with normal cystoscopy and positive cytology 1, 5
• Narrow-band imaging is another enhanced cystoscopic technique that has demonstrated improved detection rates of bladder cancer 5
• Optical coherence tomography aims at real-time noninvasive pathological diagnosis and can accurately discriminate bladder cancer from normal bladder mucosa 5
• AI-assisted cystoscopic imaging shows promise in improving bladder tumor detection with sensitivity and specificity comparable to expert urologists 6