Barium enema

The role of the single-contrast barium enema or the DCBE in diagnosing and staging known or suspected CRC is threefold: (1) it can be used to diagnose colon cancer in those patients undergoing screening or work-up of symptoms; (2) it can be used to complete the total colon examination in cases of incomplete colonoscopy, a role traditionally reserved for barium enema, but now largely replaced by CTC; and (3) it can simply confirm a suspected diagnosis of CRC from other imaging or clinical tests when colonoscopy is not available, not affordable, or not preferred by the patient. Although it is inferior to colonoscopy in the detection of small polyps, large polyps, and cancers, it has many advantages including lower cost, lack of necessity for sedation, greater safety, and wider availability. Furthermore, because colonoscopy can occasionally miss lesions, these two examinations may be viewed as complementary, the development of CTC notwithstanding. It is unfortunate that the explosive technologic imaging revolution has resulted in a diminishing cadre of highly skilled radiologists who perform and teach these worthwhile examinations. Nonetheless, with scrupulous attention to good colonic cleansing and with rigorous fluoroscopic-radiographic technique, described in detail elsewhere [50], most polyps and cancers can be detected with DCBE.

The detection of adenomatous polyps, which may undergo malignant transformation through the adenoma-carcinoma sequence, and the detection of neoplasms is the primary goal. Most polyps never become CRC [51], and the risk is related to polyp size. Only about 1% of polyps less than 10 mm harbor CRC, whereas 10% to 20% of adenomas 10 to 20 mm in diameter and 40% to 50% of those greater than 20 mm in diameter harbor adenocarcinoma.

Small, classic, hyperplastic polyps, often effaced by distention, are not important to detect, because they are not believed to undergo this transformation (a recently described hyperplastic polyposis syndrome of "serrated" adenomas is one exception, but these are larger lesions) [52].

Adenomas are classified as tubular, tubulovil-lous, or villous at histologic examination. The greater the amount of the villous component, the greater is the risk of malignant degeneration. Polyps may be flat, sessile, or pedunculated (Fig. 1). A pedunculated polyp with a stalk longer than 2 cm is rarely associated with invasive carcinoma. On DCBE, sessile polyps on the dependent surface appear as filling defects in a pool of barium. Those on the nondependent surface are etched in white and appear as ring shadows (Fig. 2). These can at times be confused with diverticula, but the "bowler-hat" appearance with the dome of the hat pointed inward toward the colon lumen distinguishes these from diverticula [53]. The most common entity confused with polyps is stool. Even in a well-prepared colon, one or two fragments of fecal residue may persist, requiring rotation and repositioning or gentle palpation of the patient (Fig. 3). Villous adenomas have a higher risk of malignant degeneration. They are recognized by their granular or reticular appearance because of the filling of the interstices on the polyp surface (Fig. 4). Carpet-lesions, a particularly worrisome diffuse type of villous tumor, may be hard to recognize and may be confused for stool. These may protrude very little into the colon lumen [53]. Flat-lesions are a diagnosis de rigueur of late, because of the recognition that these may easily be missed at colonoscopy and CTC. These are important and controversial lesions. It is estimated that 36% of adenomas in European populations and 22.7% of adenomas in the United States population maybe flat [54,55]. Controversy surrounds reports that these are more likely to have advanced dysplasia compared with protuberant polyps. One problem, learned from the CTC literature, is the inconsistent distinction of these from, for example, sessile lesions. A small study of flat adenomas found that their detection was limited at DCBE compared with colonoscopy [56].

Table 2: Literature survey of CT colonoscopy

N patients

Per polyp sensitivity %

Overall

Detection of polyps <6 mm

Detection of polyps 6-9 mm

Detection of polyps >9 mm

Rockey et al, 2005

614

60

64

Chung et al, 2005

51

90

84

94

100

Cotton et al, 2004

600

12.7

7.6

22.7

51.9

Macari et al, 2004

186

27.7

14.7

46.2

90.9

Van Gelder et al, 2004

249

51.8

40.6

76.7

77.8

Macari et al, 2004

68

21.4

11.5

52.9

100

Hoppe et al, 2004

92

42.6

25.4

57.9

70.6

Pickhardt et al, 2003

1233

83.6

92.2

lannaccone et al, 2003

158

70.3

51.4

83.3

100

Johnson et al, 2003

703

47.1

46.3

Pineau et al, 2003

205

46.8

29.4

75

77.8

Taylor et al, 2003

54

48.4

37.5

75

100

Ginnerup Pedersen

144

73.7

92.3

et al, 2003

Yee et al, 2003

182

69.9

60.3

79.8

92.7

Munikrishnan et al, 2003

61

75.8

53.3

83.3

100

Laghi et al, 2002

165

78.4

50

82.4

91.7

Gluecker et al, 2005

50

22.4

2.4

33.3

81.8

Lefere et al, 2002

100

77.5

56.5

90.3

100

Macari et al, 2002

105

32.6

12.1

70.4

92.9

McFarland et al, 2002

70

36.1

68.1

Yee et al, 2001

300

77.5

66.9

81.8

94.1

Hara et al, 2001

237

Spinzi et al, 2001

96

57.8

61.5

Fletcher et al, 2000

180

60.1

47.2

75.2

Morrin et al, 2000

81

32.9

64.5

90.9

Mendelson et al, 2000

53

27.5

17.5

22.2

72.7

Macari et al, 2000

42

37.5

20

60

100

Morrin et al, 2000

34

Fenlon et al, 1999

100

71.3

66.7

89.7

90.9

Rex et al, 1999

46

22

11.1

42.9

50

Dachman et al, 1998

44

46.7

7.7

33.3

83.3

Royster et al, 1997

20

91.4

66.7

90

100

Hara et al, 1997

70

37.4

25.9

57.1

70

From Mulhall BP, Veerpan GR, Jackson JL. Meta-analysis: computed tomographic colonography. Ann Intern Med 2005;142:635-650; with permission.

From Mulhall BP, Veerpan GR, Jackson JL. Meta-analysis: computed tomographic colonography. Ann Intern Med 2005;142:635-650; with permission.

Most CRC are detected on DCBE, and are either semiannular or annular (Fig. 5). Fewer than 10% appear as polypoid or carpet lesions [53]. False-negative examinations do occur when lesions are overlooked because of perceptive error from overlapping bowel loops (Fig. 6). Overlooked carcinomas in the rectum may occur if the rectal tube or balloon obscures the mucosa. Attention to technique avoids these errors (Fig. 7).

Rarely, other abnormalities may mimic annular CRC, such as amoeboma or histoplasmoma [57]. In the authors' oncologic population, slow-growing secondary malignancies, such as ovarian cancer, have occasionally been seen to mimic the annular appearance of primary CRC (Fig. 8). Because 5% of patients with CRC have a synchronous lesion, every attempt should be made to examine the entire colon at DCBE when one nonobstruc-tive lesion is found. Single-contrast barium enema has been shown to be inferior to DCBE. Although a large annular lesion may be very well appreciated, smaller malignancies can be missed in the barium pool even with systematic compression [58]. The use of single-contrast barium enema (or water soluble-based contrast enema) is best reserved for the elderly and infirm and those cases in which there is a question of obstruction, perforation, or anastomotic leak. Barium enema plays a minimal role in the diagnosis of recurrent CRC. Most cases arise extraluminally next to or distant from the regions of resection of the primary tumor, rather than at the anastomosis. For

Table 2: (continued)

Per patient sensitivity %

Detection of polyps 6-9 mm

Detection of polyps of >9 mm

Patients Overall

Overall with cancer specificity %

Sensitivity % Specificity %

Sensitivity % Specificity %

this reason, CT or PET is of greater use than lumi-nal investigations, such as barium enema or colonoscopy.

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