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CT
Abdomen/PelvisDemonstration data

CT Abdomen/Pelvis with Contrast

Contrast-enhanced CT of the abdomen and pelvis is the workhorse study for acute and chronic abdominal complaints, providing comprehensive evaluation of solid organs, bowel, mesentery, vasculature, and the peritoneal cavity. Portal venous phase imaging optimizes enhancement of the liver, spleen, and bowel wall, making it sensitive for infection, inflammation, ischemia, obstruction, and malignancy. Protocol tailoring (phases, oral contrast) depends on the specific clinical question.

Indications

  • Acute abdominal or pelvic pain of uncertain cause
  • Suspected appendicitis, diverticulitis, or other intra-abdominal infection/abscess
  • Bowel obstruction, ischemia, or perforation evaluation
  • Staging, surveillance, and complication assessment of known or suspected malignancy
  • Blunt or penetrating abdominal trauma (typically portal venous, with arterial phase for active bleeding)
  • Unexplained sepsis, fever of unknown origin, or leukocytosis to seek an occult source
  • Postoperative complication assessment (collection, leak, ischemia)

Contraindications & Cautions

  • Iodinated contrast allergy: use premedication or an alternative modality; document prior reactions
  • Renal impairment: assess eGFR, weigh risk of contrast-associated nephropathy, and hydrate; avoid or reduce contrast when appropriate
  • Pregnancy: justify; use IV contrast only when essential and counsel on iodine and fetal considerations
  • Metformin: no need to stop before contrast in normal renal function; follow local policy in renal impairment
  • Severe uncorrected hypovolemia or unstable patient without resuscitation and monitoring
  • ALARA dose considerations, particularly in young patients requiring repeat imaging

Patient Preparation

  • Fasting typically 4-6 hours before IV contrast to reduce aspiration risk with reactions
  • Establish reliable IV access (18-20 G antecubital preferred) for power injection
  • Administer oral contrast (positive or neutral) over 45-90 minutes when bowel evaluation is required; omit for renal colic/trauma per protocol
  • Screen renal function, contrast allergy, and pregnancy status; obtain consent per local policy
  • Position supine, arms raised above the head to reduce streak artifact
  • Rehearse a single breath-hold to minimize respiratory motion

Technique & Parameters

  • Helical acquisition from the diaphragmatic domes to the pubic symphysis (include lung bases and ischial tuberosities)
  • IV contrast 90-120 mL of iodinated agent at 2.5-4 mL/s; portal venous phase at ~65-75 s delay
  • Add arterial (~30-35 s or bolus-tracked) and delayed phases for trauma, hypervascular tumors, or hematuria as indicated
  • 120 kVp (lower kVp for slim patients / vascular studies) with automated tube-current modulation
  • Reconstruct 3-5 mm axial images with 1-2 mm thin sections for multiplanar and vascular reformats
  • Review on soft-tissue, lung (bases), and bone windows; coronal and sagittal reformats routinely

Systematic Review

  • Solid organs: liver, spleen, pancreas, adrenals, and kidneys for lesions, laceration, or enhancement abnormality
  • Hollow viscera: stomach and bowel for wall thickening, dilatation, transition point, and enhancement
  • Mesentery and peritoneum: fat stranding, free fluid, free air, nodules, and collections
  • Vasculature: aorta, mesenteric vessels, and portal/hepatic veins for aneurysm, thrombus, or active extravasation
  • Lymph nodes: mesenteric, retroperitoneal, and pelvic node size and morphology
  • Urinary tract and pelvic organs (bladder, uterus/ovaries or prostate), and hernial orifices
  • Skeleton and lung bases for metastases, fractures, and incidental thoracic findings

Key Findings & Significance

  • Dilated fluid-filled appendix >6 mm with periappendiceal fat stranding: acute appendicitis
  • Colonic wall thickening with pericolic stranding and diverticula: acute diverticulitis (assess for abscess/perforation)
  • Small-bowel dilatation with a transition point and collapsed distal loops: mechanical obstruction
  • Pneumoperitoneum or focal defect: perforation; extraluminal contrast indicates a leak
  • Reduced or absent bowel-wall enhancement, pneumatosis, and portal venous gas: bowel ischemia
  • Organ laceration, perisplenic/perihepatic blood, or a contrast blush: traumatic injury with active bleeding
  • Solid-organ or nodal masses, ascites, and peritoneal implants: malignancy or metastatic disease

Differential Considerations

  • Right lower quadrant pain: appendicitis vs mesenteric adenitis vs terminal ileitis vs ovarian pathology
  • Left lower quadrant pain: diverticulitis vs epiploic appendagitis vs colitis vs ureteric colic
  • Diffuse bowel-wall thickening: infectious/inflammatory colitis vs ischemia vs edema (low-albumin/heart failure)
  • Hypodense liver lesion: cyst vs metastasis vs hemangioma vs abscess (correlate phases)
  • Free fluid: physiologic/benign ascites vs hemoperitoneum vs infected/malignant fluid
  • Pancreatic changes: acute pancreatitis vs neoplasm; assess for necrosis and vascular complications

Pearls & Pitfalls

  • Always scrutinize the lung bases and hernial orifices, which are common sites of missed pathology
  • A closed-loop obstruction (U- or C-shaped loop, converging mesenteric vessels) mandates urgent flagging for strangulation
  • Portal venous timing can miss active arterial bleeding; add an arterial phase in trauma or GI hemorrhage
  • Under-opacified bowel can mimic wall thickening or a mass; use multiplanar review and water-density oral contrast when needed
  • Small-volume pneumoperitoneum is best seen on lung windows in the non-dependent abdomen
  • Do not overlook incidental but significant findings (adrenal, renal, and pancreatic lesions) requiring follow-up

Structured Report

  • State protocol, phase(s), oral/IV contrast, and comparison studies
  • Report the primary finding relevant to the clinical question first, with location and severity
  • Systematically document solid organs, bowel, vasculature, nodes, urinary/pelvic organs, and peritoneum
  • Quantify obstruction transition points, collection sizes, and free fluid/air
  • Note incidental findings and recommend appropriate follow-up (e.g., per ACR incidental findings guidance)
  • Impression: concise prioritized diagnosis, complications, and actionable recommendations

References

  • ACR Appropriateness Criteria: Acute Nonlocalized Abdominal Pain; Right Lower Quadrant Pain; Left Lower Quadrant Pain
  • ACR Manual on Contrast Media
  • ACR White Papers on Managing Incidental Findings
  • Federle et al., Diagnostic Imaging: Abdomen

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.