Abdomen CT Recognition Pattern

Systematic approach to interpreting abdominal CT scans with contrast phases and key anatomical landmarks

1. CT Contrast Phases

A. Standard Protocols

• • Non-contrast:
  - Baseline for calcifications/hemorrhage
  - Renal stones, unenhanced liver lesions
• • Arterial (25-35 sec):
  - Hypervascular tumors (liver/pancreas)
  - Vascular anatomy (CTA)
• • Portal venous (60-70 sec):
  - Standard abdominal evaluation
  - Hypovascular metastases, inflammation
• • Delayed (3-5 min):
  - Cholangiography (biliary tree)
  - Fibrotic tumors (cholangiocarcinoma)

B. Organ-specific Enhancement

• • Liver:
  - Arterial: HCC, FNH
  - Portal: Metastases, hemangioma fill-in
• • Pancreas:
  - Best enhancement in late arterial
  - "Dual-phase" for tumors
• • Kidneys:
  - Corticomedullary (25-40 sec)
  - Nephrographic (100 sec)

2. ABCDEF Systematic Approach

Step

Assessment

Key Elements

A

Airway/Abdominal wall

Hernias, surgical emphysema

B

Bowel

Wall thickening, obstruction

C

Circulation

Vessels, aneurysms, thrombosis

D

Densities

Calcifications, free air, fat

E

Enhancement

Organ perfusion, masses

F

Fluid/Fat

Ascites, stranding, collections

3. Organ-specific Patterns

A. Liver Lesions

Lesion

Arterial Phase

Portal Phase

HCC

Hyperenhancing

Washout

Hemangioma

Peripheral nodular

Centripetal fill-in

Metastasis

Variable

Hypoenhancing rim

FNH

Homogeneous

Isoenhancing

B. Pancreatic Pathology

• • Pancreatitis:
  - Stranding, fluid collections
  - Necrosis (non-enhancing areas)
• • Adenocarcinoma:
  - Hypodense mass
  - "Double duct" sign
  - Vascular encasement

4. Critical Findings

A. Vascular Emergencies

• • AAA rupture:
  - Retroperitoneal hematoma
  - "High-attenuating crescent" sign
• • Mesenteric ischemia:
  - SMA/SMV thrombosis
  - Bowel wall hypoenhancement
  - Pneumatosis intestinalis

B. Bowel Pathology

• • Obstruction:
  - Transition point
  - Dilated proximal loops
• • Perforation:
  - Free air (best seen on lung windows)
  - Extraluminal contrast

5. Key Lymph Node Groups

Station

Location

Drainage

Porta hepatis

Liver hilum

Liver, gallbladder

Peripancreatic

Pancreas borders

Pancreatic tumors

Para-aortic

Retroperitoneum

Testicular, ovarian

Abnormal criteria:
- Short axis ≥1cm (except gastrohepatic ligament ≥8mm)
- Cluster of ≥3 nodes
- Necrotic center

6. CT Abdomen Reporting Template

1. 1. Technique: Phase(s), contrast dose
2. 2. Liver/Biliary:
   - Lesions (size, enhancement)
   - Bile duct dilation
3. 3. Pancreas:
   - Parenchyma, ducts
   - Peripancreatic fat
4. 4. Kidneys/Adrenals:
   - Masses, hydronephrosis
   - Stones
5. 5. Bowel/Mesentery:
   - Wall thickening
   - Inflammation
6. 6. Vascular:
   - Aorta, branches
   - Thrombosis

Always correlate with clinical history and prior imaging. For trauma, review in multiple windows to detect subtle injuries. In oncology patients, measure lesions consistently (RECIST criteria). For inflammatory conditions, assess fat stranding and fascial thickening. Document incidental findings with appropriate follow-up recommendations.