CT Urography Recognition Pattern

Systematic approach to interpreting CT urography studies with key anatomical landmarks and pathological patterns

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1. Basic Principles

A. Standard Protocol

• Unenhanced phase:
  - Baseline for calcifications
  - Slice thickness 2-3mm
• Nephrographic phase:
  - 100-120 sec post-contrast
  - Parenchymal evaluation
• Excretory phase:
  - 8-15 min post-contrast
  - Urothelial evaluation
  - Optional prone imaging

B. Reconstruction Parameters

• Axial images:
  - 2-3mm for parenchyma
  - 0.5-1mm for vasculature
• Coronal/Sagittal MPR:
  - Essential for ureteric tracking
  - 2-3mm slice thickness
• 3D Reconstructions:
  - MIP for vascular anatomy
  - Volume rendering for urothelial mapping

2. ABCDE Systematic Approach

Step	Assessment	Key Elements
A	Adrenal glands	Masses, hyperplasia
B	Bowel/Background	Incidental findings, artifacts
C	Collecting system	Urothelial thickening, filling defects
D	Delayed excretion	Obstruction, renal function
E	Enhancement	Masses, perfusion abnormalities

3. Renal Parenchyma Evaluation

A. Normal Measurements

Parameter	Normal Value
Kidney length	9-13 cm
Cortical thickness	7-10 mm
HU unenhanced	30-50 HU
Corticomedullary diff	100-200 HU

B. Mass Characterization

• Bosniak Classification:
  I: Simple cyst
  II: Minimally complex
  IIF: Follow-up needed
  III: Indeterminate
  IV: Clearly malignant
• RCC Features:
  - Heterogeneous enhancement
  - ± Necrosis, calcification
  - Cortical origin
• AML Features:
  - Fat-containing (-10 to -100 HU)
  - May have minimal fat

4. Collecting System Pathology

A. Urothelial Carcinoma

• Findings:
  - Focal wall thickening >3mm
  - Irregular luminal narrowing
  - Enhancing soft tissue mass

B. Stone Disease

Stone Type	HU Range	Features
Calcium oxalate	800-1200	Most common, dense
Uric acid	200-500	Radiolucent on XR
Struvite	400-800	Staghorn configuration

C. Obstruction Patterns

• Acute obstruction:
  - Perinephric stranding
  - Nephromegaly
  - Delayed nephrogram
• Chronic obstruction:
  - Cortical thinning
  - Hydronephrosis
  - Compensatory hypertrophy

5. Vascular Evaluation

A. Renal Artery

• Stenosis:
  - Focal narrowing
  - Post-stenotic dilatation
  - Delayed cortical enhancement
• Fibromuscular dysplasia:
  - "String of beads" appearance
  - Mid-distal artery

B. Renal Vein

• Thrombosis:
  - Filling defects
  - Tumor thrombus (RCC extension)
  - Bland thrombus (enlarged vein)

6. Congenital Variants

Variant	Features	Significance
Duplex collecting system	Two ureters	Increased UTI risk
Horseshoe kidney	Fused lower poles	Increased stone risk
UPJ obstruction	Abrupt ureteral cutoff	May need pyeloplasty
Ectopic ureter	Insertion below trigone	Incontinence in females

7. CT Urography Reporting Template

1. Technique:
   - Phases acquired
   - Contrast dose/rate
   - Reconstruction methods
2. Kidneys:
   - Size/symmetry
   - Cortical thickness
   - Masses (Bosniak if cystic)
3. Collecting system:
   - Urothelial thickening
   - Filling defects
   - Obstruction level
4. Ureters:
   - Course/dilation
   - Strictures
   - Periureteric findings
5. Bladder:
   - Wall thickening
   - Masses
   - Diverticula
6. Incidental findings:
   - Adrenal, liver, etc.

Always correlate with clinical history (hematuria, stone risk factors). Review all phases systematically - unenhanced for stones, nephrographic for masses, excretory for urothelium. Use MPR to track ureters completely. For hematuria evaluation, ensure adequate distension of collecting system. Note any variants that may impact surgical planning. Consider radiation dose reduction strategies in younger patients.

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