Colonography

Colonography, also known as CT colonography or virtual colonoscopy, is a radiologic method to image the large intestine. It uses computed tomography (CT) or magnetic resonance imaging (MRI) to create two- and three-dimensional reconstructions of the colon after bowel insufflation with gas (usually carbon dioxide) and bowel preparation. The technique aims to detect polyps, colorectal cancer, and other colonic pathology. There is also traditional radiographic colonography with barium enema, now largely obsolete.

Procedure involves bowel preparation, followed by insufflation of the colon with gas to distend it. CT colonography uses low-dose CT scans; MR colonography uses MRI without ionizing radiation. The collected data are reconstructed into 2D and 3D images for interpretation. The exam is less invasive than conventional colonoscopy, typically without sedation, and has a shorter recovery. However, it cannot perform therapeutic procedures such as polypectomy or biopsy; if polyps or occult pathology are found, a follow-up standard colonoscopy is required.

Indications include screening for colorectal cancer in adults who cannot or prefer not to undergo colonoscopy, evaluation of symptoms such as unexplained abdominal pain or bleeding, and surveillance in high-risk patients. Limitations include variable sensitivity for small polyps, visualization challenges from retained stool or diverticular disease, and, for CT colonography, exposure to ionizing radiation. MR colonography avoids radiation but is less widely available and longer. Safety profiles are favorable, but perforation is a rare risk.