CT Abdomen

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

1. See Also
   1. Abdominal Pain Evaluation
   2. CT Abdomen in Appendicitis
   3. CT Urogram
2. 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]
3. 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)
4. 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]
5. Technique: Intravenous Contrast
   1. Non-Contrast 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)
   2. Early Image Acquisition (Arterial Phase)
      1. Evaluates for arterial pathology (e.g. Aortic Dissection, Mesenteric Ischemia)
   3. Portal Venous Phase Imaging (Standard Timing)
      1. Standard CT imaging timing is the default protocol that identifies most pathology
   4. Delayed Image Acquisition (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
   5. References
      1. Broder (2022) Crit Dec Emerg Med 36(5): 20-1
6. 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]
7. References
   1. Ashoo, Orman and Hollander in Herbert (2015) EM:Rap 15(6): 17