CT colonography prepares to enter clinical mainstream

If you were to ask a random group of general radiologists to nominate the body part that currently causes their patients the greatest anguish and arouses the most controversy, serious contenders would probably include the breast, brain, heart, and liver. But the colon would no doubt be a popular choice.

At its seminar in London on 21 October, the British Institute of Radiology is devoting a whole day to clinical imaging of the colon. The 10 invited lecturers will focus on bowel preparation in CT, a radiographer-led service, imaging for colorectal cancer (CRC) screening, colonic stenting, patients' views and perceptions, the role of MR imaging, and other hot topics. The BIR organizes training sessions like this about once a month, and they are well regarded and of great educational value. The institute's decision to focus on the colon is therefore significant.

CRC is associated with an increased risk of developing primary cancers at other sites, especially in the small intestine and female reproductive organs. It also has the second highest cancer-related mortality in the developed world. Early detection is vital, which is why imaging has an important role.

CT and MR can recognize intramural, serosal, and mesenteric changes in various benign conditions. CT is useful for visualizing the ascending and descending portions of the colon because they are partially surrounded by the fat of the anterior pararenal space. In malignant cases, CT's ability to detect adenopathy and distant metastases has made it a routine staging modality.

CT colonography (CTC), made possible by the development of spiral scanners, represents a major breakthrough, as outlined in the cover story of this issue. It is safe, generally well tolerated, and enables rapid acquisition of thin-section CT slices of the entire bowel. These slices can be manipulated to resemble the endoluminal views familiar to endoscopists.

Several aspects of CTC are still under discussion, however. Most practitioners employ bowel preparation prior to the procedure, but some are investigating the merits of a "prepless" examination accompanied by stool labeling with oral contrast agents and electronic subtraction of labeled fecal material. Meanwhile, a formal accreditation process in CTC has yet to be agreed upon, and the procedure's role in screening average-risk asymptomatic patients over 50 years old remains uncertain.

Even the name of the procedure itself is contested. While the term "CTC" is used widely in academic centers and published articles, because the primary method of interpretation of these studies has remained the 2D axial image, others favor "virtual colonoscopy." They argue that the use of 3D data sets is becoming more widespread and patient acceptance will be higher if the term "virtual" is included.

Imaging of the colon appears certain to attract attention for some time to come.