(Radiology. 2000;216:11-18.)
© RSNA, 2000
Diagnosis of Colorectal Neoplasms at Double-Contrast Barium Enema Examination1
Marc S. Levine, MD,
Stephen E. Rubesin, MD,
Igor Laufer, MD and
Hans Herlinger, MD
1 From the Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St, Philadelphia, PA 19104. Received June 22, 1999; revision requested August 9; revision received August 18; accepted August 25. Address correspondence to M.S.L.
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ABSTRACT
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The double-contrast barium enema examination has been recognized as an option for colorectal cancer screening in Americans with average risk who are greater than 50 years of age. The purpose of this article is to review the principles for diagnosing colorectal neoplasms on double-contrast images and the spectrum of findings associated with these lesions. Colonic polyps can be sessile or pedunculated; their appearance depends on whether they are located on the dependent or nondependent wall of the bowel. Villous tumors may be flat, lobulated lesions, also known as "carpet" lesions, that are characterized by a finely nodular or reticular surface pattern, without a discrete mass. Colonic carcinomas may manifest as plaquelike, polypoid, semiannular ("saddle") or annular lesions. Colonic neoplasms sometimes are more difficult to detect in the region of the ileocecal valve or the distal rectum or in patients with severe diverticulosis. Careful double-contrast technique and meticulous scrutiny of the images therefore are required to optimize detection of these lesions.
Index terms: Barium enema examination, 75.1281, 75.1282 • Colon, neoplasms, 75.3111, 75.3112, 75.3113, 75.321, 75.3211 • Colon, radiography, 75.1281, 75.1282 • Rectum, neoplasms, 757.3111, 757.3112, 757.3113, 757.321, 757.3211
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INTRODUCTION
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Colorectal carcinoma is the second leading cause of cancer death in the United States (1). More than 130,000 Americans receive a diagnosis of colorectal cancer each year, and more than 50,000 die of this disease (1). It has been estimated that, without preventive action, about 6% of all Americans will develop colorectal cancer at some time in their lives (2). Most of these cancers are thought to arise from preexisting adenomatous polyps that follow a well-established adenoma–carcinoma sequence (3,4). As a result, there is a consensus that early detection and removal of colonic adenomas can substantially decrease the morbidity and mortality from colorectal cancer. The case for colon cancer screening was presented in detail in a previous article (5) in this series.
The American Cancer Society recently endorsed a new set of clinical guidelines that include double-contrast barium enema examinations at 5- or 10-year intervals for colon cancer screening in patients with average risk who are greater than 50 years of age (2,6). Also, the U.S. Health Care Finance Administration ruled that the double-contrast barium enema examination should be included in the new national Medicare coverage for colorectal cancer screening (7). As a result, the demand for barium enema examinations among older Americans could increase dramatically as we enter the next millennium.
It is important to distinguish screening barium enema examinations in patients without symptoms from diagnostic barium enema examinations in patients with rectal bleeding or with other signs or symptoms of colorectal disease. Such screening examinations require optimal double-contrast technique because of the need to detect early, curable colorectal cancers or, even more commonly, adenomatous polyps prior to the development of overt carcinoma. It is fortunate that the risk of developing colorectal cancer is related to the presence of polyps 1 cm or greater in diameter (3,4) and that the vast majority of these lesions can be detected on double-contrast images (8–10). It therefore is essential that radiologists be able to perform double-contrast barium enema examinations and interpret the images with the same skill and expertise needed for other imaging modalities, such as computed tomography (CT) and magnetic resonance imaging.
In a previous article (11) in this series, the technical aspects of performing high-quality double-contrast barium enema examinations were reviewed. The purpose of this article is to review the principles for diagnosing colorectal neoplasms, which include polyps and cancers, at barium enema examination and to review the spectrum of findings associated with these lesions.
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POLYPS
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Hyperplastic Polyps
The two major polyps found in the colon are hyperplastic and adenomatous. Hyperplastic polyps are nonneoplastic proliferations of epithelium that are located predominantly in the rectosigmoid colon (12,13). These polyps almost never undergo malignant degeneration, so there is minimal or no risk of cancer developing in these lesions. Most hyperplastic polyps are smooth, round, sessile nodules less than 5 mm in diameter (14,15). On occasion, however, hyperplastic polyps can be larger than 1 cm in diameter or can be lobulated or pedunculated (16).
Adenomatous Polyps
Unlike hyperplastic polyps, adenomatous polyps may undergo malignant transformation into invasive adenocarcinoma by following the adenoma-carcinoma sequence described previously (3,4). The rationale for colon cancer screening therefore is to find and remove adenomatous polyps before the development of overt carcinoma. At histologic examination, these lesions may be classified as tubular adenomas, tubulovillous adenomas, or villous adenomas. In general, the greater the villous component of the polyp, the greater the risk of malignant degeneration (17). In the past, the vast majority of polyps less than 5 mm in diameter were thought to be hyperplastic, but the results of a number of studies have shown that a substantial proportion of these diminutive polyps are in fact adenomatous (18,19). Nevertheless, malignant degeneration occurs rarely in these diminutive polyps, as the risk of developing adenocarcinoma is related directly to the size of the polyp; only about 1% of adenomas less than 1 cm in diameter harbor adenocarcinoma, whereas 10%–20% of adenomas 1–2 cm in diameter and 40%–50% of those greater than 2 cm in diameter harbor adenocarcinoma (3,4,14). Results of some studies indicate that double-contrast barium enema examinations have a sensitivity as high as 95% in detecting polyps greater than 1 cm in diameter (8–10). Thus, double-contrast barium enema examinations can be used to detect most polyps that are at risk for malignant degeneration.
Adenomatous polyps can be sessile, if they arise directly from the bowel wall, or can be pedunculated, if they arise on a stalk. When polyps are pedunculated, the pedicle length is important, as polyps on stalks longer than 2 cm are almost never associated with malignant invasion of the adjacent colonic wall (20). Pedunculated polyps therefore may be viewed differently from sessile polyps in terms of their danger to the patient and in terms of the need for endoscopic versus surgical removal.
Radiographic Findings
The appearance of sessile polyps on double-contrast barium enema images depends on whether they are located on the dependent or nondependent wall of the bowel. Sessile polyps on the dependent wall appear as filling defects in the barium pool, whereas sessile polyps on the nondependent wall appear as ring shadows that are etched in white as a result of barium coating the rim of the polyp (21). Regardless of their location, polyps larger than 1 cm in diameter are more likely to harbor adenocarcinoma, in particular if they have a lobulated contour or have a basal indentation (Fig 1) (22). Although polyps that are larger are detected readily on double-contrast images, polyps that are small or flat or that directly abut a haustral fold may be subtle. All of the images therefore must be evaluated carefully to optimize detection of these lesions.
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Figure 1. Double-contrast barium enema spot image obtained with the patient in a supine position shows a lobulated polyp. The lobulated contour (arrow) of this adenomatous polyp in the descending colon increases the risk that it harbors adenocarcinoma.
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Sessile polyps viewed en face at a certain degree of obliquity on double-contrast images may appear as "bowler hats," with the brim of the hat representing the base of the polyp and with the dome of the hat representing the head of the polyp (Fig 2) (23). In the past, it has been recognized that both polyps and diverticula may manifest on double-contrast images as bowler hats (Figs 2, 3) (24,25). In polyps, however, the dome of the hat points toward the lumen of the bowel (Fig 2), whereas in diverticula, the dome of the hat points away from the lumen (Fig 3) (26). When bowler hats are encountered on double-contrast images, this principle therefore provides a simple and objective means of differentiating polyps from diverticula.
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Figure 2. Left posterior oblique double-contrast barium enema spot image shows a sessile polyp with the bowler hat sign. Note that the dome of the hat (arrowhead) points (arrow notes the direction) toward the center of the lumen of the sigmoid colon.
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Figure 3. Supine double-contrast barium enema spot image shows a diverticulum with the bowler hat sign. In this case, note that the dome of the hat (arrowhead) points (arrow notes the direction) away from the center of the lumen, which indicates a diverticulum. (Reprinted from reference 26.)
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Unlike sessile polyps, pedunculated polyps can be recognized by the presence of a discrete stalk (Fig 4). On occasion, pedunculated polyps hanging down from the nondependent wall of the bowel may manifest on double-contrast images as the "Mexican hat" sign, which is characterized by a pair of concentric rings, with the outer ring representing the head of the polyp and with the inner ring representing the stalk seen through the head (21). By rotating the patient 180° or by placing the patient in an upright position, the stalk almost always can be visualized in profile, and the presence of a pedunculated polyp can be confirmed.
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Figure 4. Upright double-contrast barium enema spot image shows a pedunculated polyp. The head (straight arrow) and stalk (curved arrow) of this polyp are readily visible in the descending colon despite the presence of multiple diverticula. By using optimal technique, polypoid lesions can be detected even in patients with severe diverticulosis.
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Differential Diagnosis
Polyps sometimes can be difficult to differentiate from air bubbles, retained stool, or diverticula on double-contrast images. However, at fluoroscopy, air bubbles usually occur as a transient finding that can be dispersed easily by rotating the patient one or more times or by palpating the bowel gently with a lead glove or with a manual compression device.
It is essential to perform adequate colonic cleansing before double-contrast barium enema examination. When such cleansing is inadequate, retained stool sometimes can be differentiated from polyps by its inconstant location on fluoroscopic images or on horizontal-beam overhead (eg, left or right lateral decubitus) images. Retained fecal debris also tends to have an irregular configuration and sometimes becomes impregnated with barium, which allows differentiation from polyps. However, adherent stool can be difficult or impossible to differentiate from true polypoid lesions in the colon. In such cases, a repeat barium enema examination may be performed to rule out neoplastic lesions after more rigorous preparation of the patient.
Diverticula that are viewed en face on the nondependent wall may also be etched in white and may appear as ring shadows that are indistinguishable from those caused by polyps on the nondependent wall. When the patient is rotated 90°, however, the diverticula should be recognized in profile as outpouchings from the wall, whereas polyps should protrude into the lumen on tangential images. In rare cases, inverted diverticula may be difficult to differentiate from true polyps (27).
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VILLOUS TUMORS
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Adenomas that contain a high degree of villous change, known as villous adenomas, are particularly important, since they have an even higher risk of malignant degeneration than tubular adenomas or tubulovillous adenomas. These villous tumors may be recognized on double-contrast images as polypoid lesions that have a granular or reticular appearance due to trapping of barium between the frondlike components of the tumor (Fig 5) (28,29).
Other villous tumors may be flat, lobulated lesions, also known as "carpet" lesions, that are characterized by subtle alterations in the surface texture of the colon, with little or no protrusion into the lumen (30). Some carpet lesions may be extensive, involving a considerable surface area of the colon. In one series, the mean size of the lesions was 6 x 4 cm, and 20% encircled the lumen completely. For reasons that are unclear, carpet lesions are located predominantly in the rectum, cecum, and ascending colon (30).
Carpet lesions usually manifest en face on double-contrast images as tiny, coalescent nodules and plaques and produce a finely nodular or reticular pattern with sharply demarcated borders (Fig 6) (30). When viewed in profile, these lesions have an irregular contour in contrast with the smooth, fine contour of the adjacent normal bowel. Despite the characteristic radiographic findings, carpet lesions are so flat that they can be missed at colonoscopy (31). Some patients suspected of having carpet lesions at barium enema examination therefore may require one or more repeat endoscopic examinations for a definitive diagnosis. As with other villous tumors, carpet lesions should be resected because of the risk of malignant degeneration.
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Figure 6. Right posterior oblique double-contrast barium enema spot image shows a carpet lesion. Note the finely nodular or reticular surface pattern of the lesion (arrows) in the cecum due to barium filling the interstices of this tubulovillous adenoma.
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CARCINOMA
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Colorectal carcinomas may manifest on double-contrast images as plaquelike, polypoid, semiannular, annular, or carpet lesions. Although the double-contrast barium enema examination is valuable for diagnosing colorectal carcinomas, it is not infallible. When lesions are missed on double-contrast images, a majority of radiographic errors are perceptive or interpretive rather than technical in nature (32,33). Some lesions are overlooked because of superimposed bowel loops, whereas others are hidden by the barium pool or even by deep haustral folds. Optimal double-contrast technique and meticulous scrutiny of the images therefore are required to avoid missing these lesions.
In a recent study, 53% of all colonic carcinomas diagnosed at barium enema examination appeared as annular or semiannular lesions; 38%, as polypoid lesions; and 9%, as plaquelike or carpet lesions (34). These various lesions are considered separately in the following sections.
Plaquelike Lesions
Plaquelike carcinomas tend to be early cancers that, if adequately treated, are associated with a high probability of cure. These plaquelike tumors may represent a stage in the evolution of small, flat, infiltrating lesions that arise as de novo carcinomas rather than progress through the usual polypoid adenoma–carcinoma sequence (34). Plaquelike carcinomas are found most commonly in the rectum (34). These tumors may be recognized in profile on double-contrast images as flat, protruded lesions with a broad base and with relatively little elevation of the overlying mucosa (Fig 7). They usually have discrete borders and sometimes contain shallow central ulcers. Although the tangential features are characteristic, plaquelike lesions may manifest en face only as curvilinear or undulating lines, which represent a portion of the lesion tangential to the x-ray beam. When a plaquelike lesion is suspected, it therefore is essential to depict the bowel in multiple projections to demonstrate the lesion in profile.
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Figure 7. Upright right posterior oblique double-contrast barium enema spot image shows a plaquelike carcinoma. A subtle plaquelike lesion (arrow) is seen in the splenic flexure. This lesion could be missed easily without meticulous scrutiny of the images.
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Polypoid Lesions
Polypoid carcinomas are found most commonly in the cecum or rectum; it is presumed that this is because of the larger caliber of these segments of the colon (34). As with colonic polyps, polypoid carcinomas on the dependent wall of the bowel appear as filling defects in the barium pool, whereas polypoid lesions on the nondependent wall are etched in white (21). This principle can be used to determine the location of the lesion in the bowel. If, for example, a polypoid carcinoma appears as a filling defect on supine views and is etched in white on prone views, it must be located on the posterior wall. Conversely, if a polypoid lesion is etched in white on supine views (Fig 8a) and appears as a filling defect in the barium pool on prone views (Fig 8b), it must be located on the anterior wall. Whenever possible, lateral views should be obtained to confirm the location of the lesion in the bowel.
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Figure 8a. Double-contrast barium enema spot images show a polypoid carcinoma on the anterior wall of the bowel. (a) Supine spot image shows a polypoid mass etched with barium (arrows) near the lateral border of the ascending colon. (b) On the prone image, however, the lesion is seen as a filling defect (arrows) in the barium pool. The lesion therefore must be located on the anterior wall.
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Figure 8b. Double-contrast barium enema spot images show a polypoid carcinoma on the anterior wall of the bowel. (a) Supine spot image shows a polypoid mass etched with barium (arrows) near the lateral border of the ascending colon. (b) On the prone image, however, the lesion is seen as a filling defect (arrows) in the barium pool. The lesion therefore must be located on the anterior wall.
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The demonstration of polypoid lesions on double-contrast images requires adequate distention of the bowel, proper positioning of the patient, and careful manipulation of the barium pool. Polypoid lesions can be missed easily if the bowel is not distended adequately (Fig 9). In such cases, the borders of the lesion may be obscured by the adjoining bowel wall. It therefore is essential that each loop of colon be distended adequately at fluoroscopy. Polypoid lesions can also be missed if they are hidden by other superimposed loops of bowel. Proper positioning of the patient therefore is required at fluoroscopy to separate each loop of bowel from adjoining loops.
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Figure 9a. Double-contrast barium enema spot images show a polypoid carcinoma and the importance of distention. (a) Initial supine spot image of the distal descending colon shows no definite lesion. (b) Repeat supine spot image with better distention of the bowel shows a polypoid mass (arrows) that was not visible in a.
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Figure 9b. Double-contrast barium enema spot images show a polypoid carcinoma and the importance of distention. (a) Initial supine spot image of the distal descending colon shows no definite lesion. (b) Repeat supine spot image with better distention of the bowel shows a polypoid mass (arrows) that was not visible in a.
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Even with adequate distention of bowel and with proper positioning of the patient, lesions may be obscured by the barium pool (Fig 10). It therefore is important for radiologists to be aware of the limitations presented by the barium pool, which compromises our ability to detect protruded lesions on the nondependent wall. For example, polypoid lesions on the anterior wall may be obscured completely on supine views by the barium pool on the posterior wall. Conversely, polypoid lesions on the posterior wall may be obscured on prone views by the barium pool on the anterior wall. It therefore is essential to obtain one or more double-contrast views of all segments of the colon, since even large lesions can be hidden by the barium pool.
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Figure 10a. Double-contrast barium enema spot images show a polypoid carcinoma obscured by the barium pool. (a) Initial supine image shows no definite lesion, but too much barium is present in the proximal sigmoid colon. (b) Repeat supine image obtained after the barium was cleared from this region shows a polypoid mass (arrows) that was obscured by the barium pool.
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Figure 10b. Double-contrast barium enema spot images show a polypoid carcinoma obscured by the barium pool. (a) Initial supine image shows no definite lesion, but too much barium is present in the proximal sigmoid colon. (b) Repeat supine image obtained after the barium was cleared from this region shows a polypoid mass (arrows) that was obscured by the barium pool.
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The importance of evaluating all of the radiographic images for abnormal barium lines cannot be overstated. Some lesions may manifest as one or more barium-etched, curvilinear lines, which represent part of the contour of the polypoid tumor tangential to the x-ray beam (Fig 11). Other small polypoid tumors may cause focal enlargement, lobulation, or distortion of a haustral fold as the only radiographic abnormality (Fig 12). If the findings are equivocal, endoscopy should be performed for a more definitive diagnosis.
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Figure 11. Upright right posterior oblique double-contrast barium enema spot image shows a polypoid carcinoma. A barium-etched polypoid lesion (arrows) is seen in the splenic flexure.
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Figure 12. Left posterior oblique double-contrast barium enema spot image shows a small polypoid carcinoma. This relatively subtle polypoid lesion in the hepatic flexure causes focal enlargement of a haustral fold (arrows).
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Semiannular Lesions
Semiannular lesions are polypoid carcinomas that straddle one-third to one-half the circumference of the bowel. It is presumed that these semiannular tumors represent a transition stage in the progression from a polypoid to an annular carcinoma (34). When viewed in profile, semiannular lesions may be recognized on double-contrast images by their convex, barium-etched margins (Fig 13). Because of its shape, this tumor has also been described as a saddle lesion (34).
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Figure 13. Supine double-contrast barium enema spot image shows a semiannular "saddle" carcinoma. This lesion in the transverse colon manifests as two convex, barium-etched lines (arrows) that represent the edges of the lesion, which straddles one-half of the circumference of the bowel.
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Annular Lesions
Annular carcinomas are located most commonly in the sigmoid colon but also are found frequently in the descending, transverse, and ascending colon (34). In contrast, they are not found often in the cecum or rectum because of the greater caliber of these bowel segments. Annular lesions are characterized at barium enema examination by circumferential narrowing of the bowel, with mucosal destruction, and by shelflike, overhanging borders (Figs 14, 15). It is essential to separate each loop of bowel at fluoroscopy, as annular lesions can be missed if individual loops are not displayed in profile (Fig 15).
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Figure 14. Supine double-contrast barium enema spot image shows synchronous carcinomas. An annular carcinoma in the distal transverse colon is characterized by mucosal destruction and by shelflike, overhanging borders (straight white arrows). A second polypoid carcinoma (black arrow) is seen more proximally in the transverse colon. This patient also has an adenomatous polyp (curved white arrow) adjacent to the distal aspect of the annular lesion.
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Figure 15a. Double-contrast barium enema digital spot images show an annular carcinoma and the importance of projection. (a) Initial supine image of the hepatic flexure shows diverticulosis without other definite abnormalities in this region. However, the hepatic flexure has not been displayed adequately in profile. (b) Repeat left posterior oblique image obtained after the hepatic flexure was displayed in profile reveals an annular carcinoma (arrow) of the hepatic flexure that was not visible in a.
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Figure 15b. Double-contrast barium enema digital spot images show an annular carcinoma and the importance of projection. (a) Initial supine image of the hepatic flexure shows diverticulosis without other definite abnormalities in this region. However, the hepatic flexure has not been displayed adequately in profile. (b) Repeat left posterior oblique image obtained after the hepatic flexure was displayed in profile reveals an annular carcinoma (arrow) of the hepatic flexure that was not visible in a.
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When annular carcinomas are nonobstructive, it usually is possible to perform a double-contrast examination so that the entire colon may be evaluated carefully for other synchronous colonic neoplasms (Fig 14). When these annular lesions are associated with signs of obstruction on conventional abdominal radiographs, however, a limited single-contrast examination should be performed to confirm the presence of an obstructive lesion and to determine its location. In patients with high-grade obstruction, the vascular supply of the dilated colon proximal to the obstructing lesion may be compromised, which may cause ischemic colitis. This ischemia may manifest as thumbprinting and/or as bowel wall edema of the dilated proximal colon at barium enema examination or, even more commonly, at abdominal CT (35).
The major consideration in the differential diagnosis of an annular carcinoma, in particular a sigmoid carcinoma, is diverticulitis with circumferential narrowing of the bowel. In most patients with diverticulitis, the narrowed segment has smooth, tapered borders and has preserved but tethered mucosal folds. These findings usually allow differentiation from an annular cancer, in which the narrowed segment has more abrupt, shelflike borders and has obliterated mucosal folds. On occasion, however, the area of narrowing in diverticulitis may have more abrupt borders and may mimic the appearance of tumor. Conversely, a perforated colonic carcinoma sometimes has a large pericolic inflammatory component, so the clinical and radiographic findings may be indistinguishable from those in diverticulitis (36). If the barium enema examination reveals equivocal findings, endoscopy should be performed after treatment for diverticulitis to rule out an underlying carcinoma as the cause of these findings.
Carpet Lesions
Malignant villous tumors may also appear on double-contrast images as carpet lesions, with only minimal protrusion into the lumen (30). As in patients with benign carpet lesions, in patients with malignant villous tumors, barium often fills the interstices of the tumor. This results in radiolucent nodules surrounded by barium-filled grooves, which produces a finely nodular or reticular appearance (30). When malignant degeneration has occurred, however, obvious malignant features may be present within a portion of the lesion (30).
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PROBLEM AREAS
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Diverticulosis
Colonic neoplasms are more difficult to detect in patients with severe diverticulosis, as polypoid lesions may be obscured by overlying diverticula or by circular muscle thickening; this is most common in the rectosigmoid or distal descending colon. With careful radiographic technique, however, polypoid carcinomas and sessile or pedunculated polyps may be recognized in the sigmoid or descending colon, even in the presence of massive diverticulosis (Fig 4). On occasion, in patients with severe sigmoid diverticulosis and/or equivocal findings on the initial double-contrast images, low-density barium may be instilled into the rectosigmoid colon at the conclusion of the double-contrast examination—the so-called sigmoid flush—to depict polypoid lesions that cannot be seen on routine double-contrast images because of the superimposed diverticula (37).
Ileocecal Valve
Another area that may pose diagnostic difficulties is the ileocecal valve, which normally appears as a smooth-lipped, round, or bulbous structure on the medial wall of the cecum. While some carcinomas arising at the ileocecal valve may be obvious polypoid lesions, others may manifest as relatively subtle splaying, straightening, or distortion of the valve. This area therefore should be evaluated carefully at fluoroscopy in all patients.
Distal Rectum
The distal rectum often is not visualized optimally because the rectal tip used to perform the barium enema examination may obscure plaquelike or polypoid lesions in the distal rectum at or near the anorectal verge. It therefore is important to obtain frontal and lateral views of the rectum after the tip has been removed to avoid missing lesions in this location. If a rectal balloon is insufflated during the examination because of inadequate anal sphincter tone, proctoscopy may be performed after the barium enema examination to rule out rectal neoplasms that could be obscured by the balloon.
It also is important to differentiate lesions in the distal rectum from internal hemorrhoids, a relatively common finding on double-contrast images. Internal hemorrhoids appear either as thickened, undulating folds that extend 3 cm or less from the anorectal verge (Fig 16) or as a cluster of small submucosal nodules that has been likened to the appearance of a bunch of grapes (38). In many cases, internal hemorrhoids can be diagnosed confidently on the basis of the radiographic findings. On occasion, however, large or thrombosed hemorrhoids can mimic the appearance of tumor, whereas rectal carcinomas that infiltrate the submucosa can mimic the appearance of hemorrhoids (Fig 17) (38,39). Digital rectal examination and/or proctoscopy therefore should be performed whenever the radiographic findings are equivocal.
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Figure 16. Left lateral decubitus double-contrast barium enema overhead radiograph shows internal hemorrhoids. Thickened, undulating folds (arrows) are seen extending less than 3 cm from both sides of the anorectal verge.
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Figure 17. Supine double-contrast barium enema spot image shows rectal carcinoma, which mimics internal hemorrhoids. Thickened, lobulated folds (arrows) are seen along the left lateral wall of the distal rectum because of submucosal spread of the tumor. Although this appearance could be mistaken for internal hemorrhoids, the possibility of tumor should be considered because these lesions extend further than 3 cm from the anorectal verge and are confined to one side of the rectum. (Reprinted, with permission, from reference 39.)
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SYNCHRONOUS AND METACHRONOUS LESIONS
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Approximately 5% of patients with colorectal cancers have synchronous colonic carcinomas, and more than one-third have other adenomatous polyps in the colon (Fig 14) (40,41). The entire colon therefore should be evaluated carefully for other synchronous lesions when a colorectal cancer is found on barium enema images. Approximately 5% of patients with colorectal cancer are also found to develop metachronous carcinomas at a later point in time (40). Careful radiographic or endoscopic follow-up therefore is required to detect these metachronous lesions at the earliest possible stage.
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LIMITATIONS OF ENDOSCOPY
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Although proctoscopy, sigmoidoscopy, and colonoscopy are highly accurate for diagnosing colorectal neoplasms, it is important to recognize that these procedures are not infallible. For a variety of technical reasons, the endoscopist is unable to reach the cecum in up to 15% of patients who undergo colonoscopy (42). There also are endoscopic blind spots behind haustral folds and at sharp bends in the bowel (43,44). Because each examination has its own limitations, the double-contrast barium enema examination and colonoscopy ultimately should be viewed as complementary techniques for the diagnosis of colorectal neoplasms.
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ABSTRACT
INTRODUCTION
