Abdomen and PelvisLive data

CT Colonography

CT colonography (CTC, virtual colonoscopy) is a minimally invasive examination of the entire colon and rectum using thin-section CT of the cleansed, gas-distended colon. Combined 2D and 3D interpretation allows detection of polyps and masses with performance comparable to optical colonoscopy for clinically significant lesions.

Indications

Colorectal cancer screening in average-risk adults
Incomplete optical colonoscopy (e.g. redundant or obstructed colon)
Patients unable or unwilling to undergo optical colonoscopy or with high sedation risk
Evaluation of colon proximal to an obstructing carcinoma
Follow-up surveillance where endoscopy is contraindicated

Contraindications & Cautions

Acute diverticulitis, toxic megacolon or suspected colonic perforation
Symptomatic acute colitis
Recent colonic biopsy with deep resection or recent surgery (risk of perforation)
Inability to tolerate bowel preparation or colonic insufflation

Patient Preparation

Cathartic bowel preparation (e.g. polyethylene glycol or sodium phosphate regimen)
Oral faecal tagging with barium and/or iodinated contrast to label residual stool and fluid
Low-residue diet in the day(s) preceding the examination
Clear explanation of insufflation to improve tolerance and distension

Technique & Parameters

Rectal catheter with automated CO2 insufflation to achieve optimal colonic distension
Supine and prone (or decubitus) acquisitions to redistribute residual fluid and stool
Low-dose thin-section acquisition (≤1.25 mm collimation) reconstructed at 1 mm intervals
Intravenous contrast reserved for symptomatic/staging studies, not routine screening
Consider hyoscine/glucagon spasmolytic to improve distension where permitted

Systematic Review

Confirm adequate distension of all colonic segments on both positions
Perform primary 2D review with 3D endoluminal fly-through problem solving (or vice versa)
Differentiate polyps from tagged stool using mobility between positions and internal attenuation
Measure lesions in the 2D window on the long axis of the polyp head
Review extracolonic organs for incidental significant findings

Key Findings & Significance

Sessile or pedunculated soft-tissue polyps arising from the colonic wall
Annular or polypoid masses causing luminal narrowing (apple-core morphology)
Tagged mobile residual stool that changes position and often contains gas or high-density tag
Diverticulosis and haustral fold thickening
Extracolonic findings such as aortic aneurysm, renal or hepatic lesions

Differential Considerations

Residual tagged stool versus true polyp (mobility and attenuation are discriminators)
Prominent ileocaecal valve or lipoma versus neoplastic polyp
Diverticular stricture versus annular carcinoma
Inverted diverticulum mimicking a polyp
Extrinsic compression versus intrinsic mural mass

Pearls & Pitfalls

Report clinically significant polyps using CT Colonography Reporting and Data System (C-RADS)
Polyps ≥6 mm are generally reported; ≥10 mm warrant referral for polypectomy
Dual positioning is critical to distinguish mobile stool from fixed polyps and to complete distension
Suboptimal preparation or distension markedly reduces sensitivity and should be stated explicitly

Structured Report

Use C-RADS to categorise colonic (C0-C4) and extracolonic (E0-E4) findings
Report size, morphology and segmental location of each significant polyp or mass
Comment on adequacy of preparation, tagging and distension
Provide management recommendation (surveillance versus colonoscopy referral)
Document clinically important extracolonic findings and follow-up needs

References

ACR-SAR-SCBT-MR Practice Parameter for the Performance of CT Colonography in Adults
C-RADS: CT Colonography Reporting and Data System, American College of Radiology
Radiographics: Pickhardt PJ. CT Colonography: Pitfalls in Interpretation
ACR Appropriateness Criteria: Colorectal Cancer Screening

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

CT Colonography

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References