What are the key findings to evaluate on a computed tomography (CT) scan of the kidney to determine living donor candidacy?

Key Findings on CT Scan for Living Kidney Donor Candidacy Evaluation

Computed tomography (CT) angiography is the preferred single radiological diagnostic modality for comprehensive anatomical and functional assessment of potential living kidney donors, providing critical information about renal vasculature, parenchyma, and collecting system.

Vascular Anatomy Evaluation

• Renal Arteries:

  • Number of renal arteries (detection of supernumerary arteries)
  • Early branching patterns of renal arteries (branching within 2 cm of origin)
  • Presence of atherosclerotic disease or fibromuscular dysplasia
  • Arterial caliber and length

• Renal Veins:

  • Number and configuration of renal veins
  • Venous anomalies (circumaortic or retroaortic left renal vein)
  • Venous length, especially for right kidney (shorter right renal vein)

Parenchymal Assessment

• Kidney Size and Volume:

  • Comparative size of both kidneys
  • Volumetric assessment to ensure adequate remaining function for donor
  • Detection of asymmetry in kidney size (>10% difference may be significant)

• Parenchymal Quality:

  • Presence of cysts or masses
  • Evidence of scarring or atrophy
  • Nephrolithiasis or nephrocalcinosis
  • Congenital abnormalities

Collecting System Evaluation

• Urinary Tract Anatomy:
  • Presence of duplicated collecting systems
  • Ureteropelvic junction obstruction
  • Abnormal rotation or position of kidneys

Technical Considerations for CT Imaging

• Multi-detector CT with contrast enhancement is recommended 1
• Arterial and venous phase acquisitions are necessary 2
• Sliding thin-slab reconstruction techniques provide superior accuracy compared to thick-slab methods 3
• 3D reconstruction improves visualization of complex vascular anatomy 4

Functional Assessment

• CT can provide information on split renal function (differential GFR) 5
• Perfect correlation has been demonstrated between CT GFR and isotope clearance studies 5

Clinical Decision-Making Implications

• Left kidney is generally preferred for laparoscopic donation due to longer vascular pedicle 6
• Presence of multiple renal arteries (>3) requires experienced surgical team 6
• Atherosclerotic renal artery disease or fibromuscular dysplasia involving both renal artery orifices is a contraindication to donation 6
• CT findings may necessitate right kidney selection in cases of left kidney anatomical complexity 6

Pitfalls to Avoid

1. Failing to obtain both arterial and venous phase images, which can miss vascular anomalies
2. Overlooking small accessory renal arteries, which decreases in accuracy as the number of arteries increases 4
3. Relying solely on CT volume estimates without considering the coefficient of variation (approximately 17.8%) 4
4. Neglecting to evaluate for early arterial branching, which impacts surgical planning
5. Missing parenchymal abnormalities that could affect long-term donor outcomes

CT angiography with 3D reconstruction provides comprehensive anatomical and functional assessment with high accuracy (>90% for arterial anatomy, >98% for vessel detection) in a single radiological session, making it the preferred imaging modality for living kidney donor evaluation 5, 2, 7.