CT Abdomen

Aka: CT Abdomen, Abdominal CT, CT Abdomen and Pelvis, Abdominopelvic CT, Intravenous Contrast for Abdominopelvic CT, Oral Contrast for Abdominopelvic CT

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II. Background

  1. Modern CT Scanners capture isotropic voxels (3 dimensional pixels)
    1. Voxels allows for software recompositing of imaging into any slice plane (e.g. coronal slices)
    2. Does not require specific instructions beyond overall imaging technique (e.g. IV contrast)
    3. Jaffe (2007) Radiology 242:175-81 [PubMed]

III. Indications: Acute Abdominal Pain (Oral water and IV Contrast unless otherwise noted)

  1. Appendicitis
  2. Diverticulitis
  3. Bowel Obstruction
  4. Acute Pancreatitis
  5. Ureterolithiasis or Nephrolithiasis (no contrast)
  6. Abdominal Aortic Aneurysm (IV contrast only)
  7. Mesenteric Ischemia
  8. Crohn's Disease (CT enterography)
  9. Abdominal Trauma (IV contrast only)
  10. Intraabdominal abscess (with Oral Contrast in addition to IV contrast)

IV. Technique: Oral Contrast

  1. Most Abdominal CT protocols require oral water only (no Oral Contrast)
    1. Patients with increased abdominal fat require less contrast
    2. Evaluation for Appendicitis or Diverticulitis does NOT require Oral Contrast
  2. Low Attenuation Contrast (air, water) is usually preferable to high attenuation Oral Contrast (e.g. barium, diatrizoate)
    1. High attenuation contrast may obscure malignancy and intestinal Hemorrhage
    2. Air alone is an excellent contrast due to low attenuation (-1000 Hounsfield Units)
      1. Allows for pneumoperitoneum (perforation) detection
    3. Oral water (400-600 ml) immediately prior to CT helps identify gastric lesions
      1. Water distends Stomach and differentiates gastric masses from Stomach wall
    4. References
      1. Broder (2018) Crit Dec Emerg Med 32(6): 12-3
  3. High Attentuation Oral Contrast (Gastrografin/Gastroview, Omnipaque, Readi-Cat/Barium) Indications
    1. Patient indications for Oral Contrast
      1. Lean patient (e.g. BMI <19-20 kg/m2)
      2. Age <18 years old
    2. Condition indications for Oral Contrast
      1. Bowel Fistula
      2. Bowel perforation or Peptic Ulcer perforation
      3. Intraabdominal Abscess
  4. References
    1. Anderson (2005) Am J Surg 190(3): 474-8 [PubMed]
    2. Garcia (2013) Acad Emerg Med 20(8): 795-800 [PubMed]
    3. Harrison (2013) West J Emerg Med 14(6): 595-7 [PubMed]

V. Technique: Intravenous Contrast

  1. Types
    1. Non-Contrast CT
    2. Single Phase CT
      1. Imaging at a single time period after contrast injection
    3. Multi-Phase CT
      1. Imaging at more than one time period after contrast injection
      2. Generally avoided if possible due to greater radiation exposure
      3. Used in Blunt Abdominal Trauma to highlight vascular, parenchymal and urinary tract injuries
  2. Non-Contrast CT (or precontrast CT)
    1. Clearly delineates intraabdominal anatomy and identifies abnormal lesions
    2. Preferred imaging when Ureteral Stone is suspected
      1. Ureteral Stones are also seen well on IV contrast imaging (but avoid Oral Contrast)
    3. Non-Contrast CT also has high sensitivity for other conditions in which contrast is often used
      1. Pneumoperitoneum
      2. Abdominal Aortic Aneurysm
      3. Appendicitis
      4. Diverticulitis
      5. Small Bowel Obstruction
    4. Low sensitivity for lesions requiring CT contrast (high False Negative Rate)
      1. Vascular abnormalities (e.g. dissection, vessel obstruction, active Hemorrhage with extravasation)
      2. Solid organ infarction
      3. Biliary obstruction (surrounding liver parenchyma enhances with IV contrast)
      4. Solid organ mass (IV contrast highlights mass borders and invasion)
        1. With IV contrast, masses may be bright if hypervascular or enhance less if hypovascular
  3. Early Arterial Phase (15 to 25 sec after contrast injection)
    1. Evaluates for arterial pathology (e.g. Aortic Dissection, Mesenteric Ischemia, vascular injury)
  4. Late Arterial Phase (30 to 40 sec after contrast injection)
    1. Evaluates for vascular injury or dissection
    2. Also evaluates for hypervascular solid organ lesions (e.g. Hepatocellular Carcinoma)
  5. Pancreatic Phase (40 to 50 sec after contrast injection)
    1. Evaluates pancreatic lesions
  6. Portal Venous Phase (60 to 90 sec after contrast injection, Standard CT Timing)
    1. Standard CT imaging timing is the default protocol that identifies most pathology
    2. Primary imaging phase used in undifferentiated Abdominal Pain and solid organ Trauma
  7. Nephrogenic Phase or delayed phase (85 to 120 sec after contrast injection, e.g. CT Urogram)
    1. Additional images obtained as Kidney is clearing IV contrast
    2. Evaluates for renal and ureteral pathology, ideal for evaluation of persistent Hematuria source
    3. Also identifies urinary tract fistulas, masses
  8. Excretory Phase (5 to 10 minutes after contrast injection)
    1. Evaluates for urinary tract injury or leak

VI. Adverse Effects: Children

  1. Sold-tumor risk from CT radiation exposure in children
    1. See CT-associated Radiation Exposure
    2. Girls: 1 new cancer per 300-390 CT Abdomen and Pelvis
    3. Boys: 1 new cancer per 670-760 CT Abdomen and Pelvis
    4. Miglioretti (2013) JAMA Pediatr 167(8): 700-7 [PubMed]

VII. References

  1. Ashoo, Orman and Hollander in Herbert (2015) EM:Rap 15(6): 17
  2. Broder (2022) Crit Dec Emerg Med 36(5): 20-1
  3. Broder (2024) Crit Dec Emerg Med 38(8): 22-3

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