DOI: 10.1148/rg.255045184
RadioGraphics 2005;25:1321-1334
© RSNA, 2005
CT Colonography with Intravenous Contrast Material: Varied Appearances of Colorectal Carcinoma1
Alvin C. Silva, MD,
Amy K. Hara, MD,
Jonathan A. Leighton, MD and
Jacques P. Heppell, MD
1 From the Department of Diagnostic Radiology (A.C.S., A.K.H.), Division of Gastroenterology and Hepatology (J.A.L.), and Division of Colon and Rectal Surgery (J.P.H.), Mayo Clinic, 13400 E Shea Blvd, Scottsdale, AZ 85259. Recipient of a Cum Laude award for an education exhibit at the 2003 RSNA Annual Meeting. Received September 30, 2004; revision requested November 8 and received May 11, 2005; accepted May 12. A.K.H. receives royalties from GE Medical Systems, Waukesha, Wis, for a CT colonoscopy software license; all other authors have no financial relationships to disclose.
Address correspondence to A.C.S. (e-mail: silva.alvin{at}mayo.edu).
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Abstract
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Computed tomographic (CT) colonography is a noninvasive, rapidly evolving technique that has been shown in some studies to be comparable with conventional colonoscopy for the screening of colorectal cancer. Because colorectal cancer has a widely varying appearance at both endoscopy and CT colonography, familiarity with the gamut of morphologic appearances can help improve interpretation of the results. The addition of intravenous contrast material to CT colonography can aid differentiation of true colonic masses from pseudolesions such as residual stool and improves the depiction of enhancing masses that might otherwise be obscured by residual colonic fluid. In contrast to staging of most other tumors, staging of colorectal carcinoma depends more on the depth of tumor invasion than on the size of the primary mass. The diverse appearances of colorectal cancers at two- and three-dimensional CT colonography include sessile, annular, ulcerated, necrotic, mucinous, invasive, and noninvasive lesions. Imaging pitfalls that can simulate or obscure neoplasms are retained fecal material or fluid, incomplete distention, and advanced diverticulosis.
© RSNA, 2005
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Describe the technique of CT colonography performed with intravenous contrast material.
- Identify the varied appearances of colorectal carcinoma at CT colonography.
- Discuss how to avoid imaging pitfalls that can simulate or obscure neoplasms.
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Introduction
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Colorectal carcinoma (Fig 1) is the second leading cause of cancer-related deaths and the fourth most common cancer overall in the United States, with an estimated 56,730 deaths and 146,940 new cases expected to have occurred during 2004 (1). Because of the natural history of the progression from colorectal polyp to carcinoma, effective screening and early diagnosis can have a significant effect on patient mortality. When detected at an early stage, this type of cancer has great potential for cure, with a 5-year survival rate of 90% when the cancer is localized versus a survival rate of less than 10% when it has metastasized. Unfortunately, while incidence rates have stabilized since the mid-1990s, only 38% of colorectal carcinomas are localized at initial diagnosis, whereas almost 20% of newly diagnosed cases have distant metastases (1).
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Figure 1. Drawing illustrates the morphologic variations of colon carcinoma reviewed in this article. (Courtesy of the Mayo Foundation for Medical Education and Research, Rochester, Minn.)
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Computed tomographic (CT) colonography for colon screening is typically performed at a lower radiation dose than standard CT, and it does not use intravenous contrast media (2–5). However, in the absence of barium stool and fluid tagging, the addition of an intravenous contrast medium can help differentiate true colon masses from pseudolesions such as residual stool, and it improves the depiction of submerged enhancing masses that might otherwise be obscured by residual colonic fluid (6,7). Administration of an intravenous contrast medium is routinely used for staging colorectal cancer and for postoperative surveillance to exclude recurrence and metastasis. CT colonography is also useful in evaluating the proximal colon when there are obstructing neoplasms, and it is more accurate than conventional colonoscopy in localizing a mass before surgical resection (8).
In this article, we review our protocol for CT colonography with intravenous contrast media, illustrate the role of this technique in cancer staging, present the range of expression of colon cancer at CT colonography, and suggest ways to avoid potential pitfalls.
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Technique of CT Colonography
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Optimal colon preparation and distention are required for accurate interpretation of CT colonographic images because the most common diagnostic pitfalls are retained fecal material or fluid and collapsed segments of bowel. Bowel preparation is generally the same as that required for colonoscopy. The two types of regimens are (a) saline cathartics, including sodium phosphate and sodium biphosphate (Phospho-Soda; Fleet, Lynchburg, Va) and magnesium citrate (LoSo Prep; E-Z-Em, Westbury, NY), and (b) a lavage solution consisting of polyethylene glycol–electrolyte solution (PEG-ES). In general, we prefer saline cathartics, which are easier for patients to ingest than the high-volume PEG-ES and also tend to result in a drier colon at CT colonography (9). We commonly perform CT colonography after a PEG-ES preparation, however, as many gastroenterologists prefer this preparation prior to colonoscopy.
Colonic distention was achieved at our institution by means of a dedicated electronic CO2 insufflator. This device maintains a preset intracolonic pressure with the regulated administration of CO2 gas through a rectal tube. The end point is generally 2 L of gas or maximum patient tolerance. Patients were scanned with a Sensation 4 or Sensation 16 multi–detector row CT scanner(Siemens Medical Systems, Iselin, NJ). Nonenhanced prone images and contrast-enhanced supine images were obtained by using the parameters listed in Table 1, and postcontrast images were interpreted in the standard supine perspective.
The optimal interpretation strategy remains in debate, including proponents for two-dimensional (2D) axial review only (10), primary 2D review with selective three-dimensional (3D) review for problem solving (11), primary 3D review with selective 2D review for problem solving (12), and virtual colon dissection (13). However, the current general consensus is that 2D and 3D images are complementary (14), with preferences influenced by vendor-specific workstations and proprietary software (15).
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Staging and Appearances of Colorectal Carcinoma
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In 1932, Dr Cuthbert E. Dukes, a London pathologist, described a classification system for staging rectal carcinoma. This classification was divided into stage A (limited to the rectal wall), stage B (extrarectal extension without regional lymph node involvement), and stage C (regional lymph node metastasis) (16). Although Dukes never formally named a stage D, he did describe a fourth stage that included spread of the disease to distant organs (17). Adjacent organ invasion and mesenteric or peritoneal metastasis are typically considered stage D as well. Although the original article did not include colon carcinomas, Dukes has asserted that all gastrointestinal carcinomas could also be staged in this manner (16).
Colorectal carcinomas are clinically staged by using the modified Astler-Coller-Dukes staging system (Table 2) or the TNM staging system established by the American Joint Committee on Cancer (Table 3). Accurate staging is necessary to determining patient prognosis and therapeutic management. In contrast to most other tumors, the staging for colorectal tumors depends more on the depth of invasion than on the size of the primary mass. However, conventional CT has not been accurate in determining the depth of invasion (18,19) or in evaluating tumor foci in nonenlarged lymph nodes. Therefore, routine preoperative assessment for local disease is generally not performed. In patients suspected to have distant metastases or adjacent organ invasion, conventional CT has been shown to be accurate in determining the appropriate surgical procedure and neoadjuvant therapy (18,20–22).
The role of CT colonography in staging has yet to be defined. A recent study reported that multi-detector CT colonography with contrast media has an 83% accuracy for identifying tumor wall invasion by colorectal carcinoma and an 80% accuracy for identifying regional lymph node involvement with a combined transverse and multiplanar reformation image evaluation (23). In addition, a preoperative CT colonography examination is increasingly being performed after incomplete colonoscopy to assess for synchronous lesions and metastases (24). With the increasing acceptance of laparoscopically assisted colectomy (25), it is also being used for more accurate localization of the site of the mass prior to resection. Finally, contrast-enhanced CT colonography may have a promising role in the postoperative surveillance of colorectal carcinomas (22,26).
The CT colonographic finding correlates to the modified Astler-Coller-Dukes classification are as follows:
- In stage A and B1, CT colonography shows a well-defined peripheral wall with clear adjacent fat (Fig 2); however, CT colonography does not allow reliable differentiation of a tumor confined to the colon wall.
- In stage B2, CT colonography shows a poorly defined peripheral wall with a rounded or nodular margin and pericolonic fat infiltration or a pericolonic mass (Fig 3).
- In stage C, CT colonography shows enlarged or clustered small pericolonic lymph nodes (Fig 4).
- In stage D, CT colonography shows distant metastasis (Fig 5) or direct local invasion (Fig 6 ).
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Figure 2. Stage B1 carcinoma (modified Astler-Coller-Dukes classification). Axial CT image shows a carcinoma of the sigmoid colon (long arrow). Note the well-defined periphery and clear adjacent fat (short arrows). At pathologic inspection, the tumor was found to be infiltrating the muscularis. CT colonography does not allow reliable differentiation of a carcinoma confined to the mucosa or submucosa (stage A) from one invading the muscularis (stage B1).
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Figure 3. Stage B2 carcinoma (modified Astler-Coller-Dukes classification). Axial CT image shows a polypoid carcinoma with a poorly defined, nodular peripheral margin that bulges into the pericolonic fat (arrows). At pathologic inspection, the tumor was found to extend into the mesenteric fat, but regional lymph nodes were negative.
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Figure 4a. Stage C carcinoma (modified Astler-Coller-Dukes classification). (a, b) Axial 2D images show a circumferential mass of the transverse colon (arrows) with an enlarged, necrotic pericolonic lymph node (arrowheads in b). (c, d) Intraluminal 3D image (c) and volume-rendered image (d) show only a small residual lumen (arrow). (The 3D image demonstrates the perspective indicated on the volume-rendered image [arrow in d].) Note the classic "apple core" appearance of the carcinoma on the volume-rendered image. Because annular masses may be indistinguishable from incompletely distended segments of the colon on 3D images, correlation with the axial 2D images is often required for differentiation.
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Figure 4b. Stage C carcinoma (modified Astler-Coller-Dukes classification). (a, b) Axial 2D images show a circumferential mass of the transverse colon (arrows) with an enlarged, necrotic pericolonic lymph node (arrowheads in b). (c, d) Intraluminal 3D image (c) and volume-rendered image (d) show only a small residual lumen (arrow). (The 3D image demonstrates the perspective indicated on the volume-rendered image [arrow in d].) Note the classic "apple core" appearance of the carcinoma on the volume-rendered image. Because annular masses may be indistinguishable from incompletely distended segments of the colon on 3D images, correlation with the axial 2D images is often required for differentiation.
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Figure 4c. Stage C carcinoma (modified Astler-Coller-Dukes classification). (a, b) Axial 2D images show a circumferential mass of the transverse colon (arrows) with an enlarged, necrotic pericolonic lymph node (arrowheads in b). (c, d) Intraluminal 3D image (c) and volume-rendered image (d) show only a small residual lumen (arrow). (The 3D image demonstrates the perspective indicated on the volume-rendered image [arrow in d].) Note the classic "apple core" appearance of the carcinoma on the volume-rendered image. Because annular masses may be indistinguishable from incompletely distended segments of the colon on 3D images, correlation with the axial 2D images is often required for differentiation.
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Figure 4d. Stage C carcinoma (modified Astler-Coller-Dukes classification). (a, b) Axial 2D images show a circumferential mass of the transverse colon (arrows) with an enlarged, necrotic pericolonic lymph node (arrowheads in b). (c, d) Intraluminal 3D image (c) and volume-rendered image (d) show only a small residual lumen (arrow). (The 3D image demonstrates the perspective indicated on the volume-rendered image [arrow in d].) Note the classic "apple core" appearance of the carcinoma on the volume-rendered image. Because annular masses may be indistinguishable from incompletely distended segments of the colon on 3D images, correlation with the axial 2D images is often required for differentiation.
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Figure 5a. Stage D carcinoma (modified Astler-Coller-Dukes classification). (a) Coronal contrast-enhanced 2D image shows a mass of the sigmoid colon (white arrows) and an associated liver metastasis (black arrow). (b–d) Intraluminal 3D image (b), colonoscopic image (c), and volume-rendered image (d) show a high-grade intraluminal obstruction with elevated, irregular margins (arrowheads in b and c) and a small residual lumen (arrow). (The 3D and colonoscopic images demonstrate the perspective indicated on the volume-rendered image [arrow in d].)
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Figure 5b. Stage D carcinoma (modified Astler-Coller-Dukes classification). (a) Coronal contrast-enhanced 2D image shows a mass of the sigmoid colon (white arrows) and an associated liver metastasis (black arrow). (b–d) Intraluminal 3D image (b), colonoscopic image (c), and volume-rendered image (d) show a high-grade intraluminal obstruction with elevated, irregular margins (arrowheads in b and c) and a small residual lumen (arrow). (The 3D and colonoscopic images demonstrate the perspective indicated on the volume-rendered image [arrow in d].)
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Figure 5c. Stage D carcinoma (modified Astler-Coller-Dukes classification). (a) Coronal contrast-enhanced 2D image shows a mass of the sigmoid colon (white arrows) and an associated liver metastasis (black arrow). (b–d) Intraluminal 3D image (b), colonoscopic image (c), and volume-rendered image (d) show a high-grade intraluminal obstruction with elevated, irregular margins (arrowheads in b and c) and a small residual lumen (arrow). (The 3D and colonoscopic images demonstrate the perspective indicated on the volume-rendered image [arrow in d].)
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Figure 5d. Stage D carcinoma (modified Astler-Coller-Dukes classification). (a) Coronal contrast-enhanced 2D image shows a mass of the sigmoid colon (white arrows) and an associated liver metastasis (black arrow). (b–d) Intraluminal 3D image (b), colonoscopic image (c), and volume-rendered image (d) show a high-grade intraluminal obstruction with elevated, irregular margins (arrowheads in b and c) and a small residual lumen (arrow). (The 3D and colonoscopic images demonstrate the perspective indicated on the volume-rendered image [arrow in d].)
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Figure 6a. Stage D invasive carcinoma (modified Astler-Coller-Dukes classification). (a) Axial 2D supine image shows loss of the normal fat planes (arrows) between a mass of the splenic flexure (M) and the stomach (S). Direct invasion was found at surgical resection. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass (arrows) nearly occludes the colonic lumen.
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Figure 6b. Stage D invasive carcinoma (modified Astler-Coller-Dukes classification). (a) Axial 2D supine image shows loss of the normal fat planes (arrows) between a mass of the splenic flexure (M) and the stomach (S). Direct invasion was found at surgical resection. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass (arrows) nearly occludes the colonic lumen.
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Figure 6c. Stage D invasive carcinoma (modified Astler-Coller-Dukes classification). (a) Axial 2D supine image shows loss of the normal fat planes (arrows) between a mass of the splenic flexure (M) and the stomach (S). Direct invasion was found at surgical resection. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass (arrows) nearly occludes the colonic lumen.
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Between 1975 and 1994, 39% of all colorectal carcinomas in the United States involved the proximal colon, which includes the area from the cecum to the splenic flexure; the rest were divided almost evenly between the distal colon, descending or sigmoid (30%), and the rectum (29%) (27). This left-to-right shift in cancer distribution during the latter half of the 20th century is most likely the result of colon screening, with more frequent use of sigmoidoscopy and polypectomy, which has decreased the incidence of distal lesions (28–30). Our study of 120 CT colonographic examinations with intravenous contrast media also demonstrated a greater number of right-sided cancers, with 20 proximal lesions, six distal lesions, and four rectal lesions. Of these 30 cancers, 28 were primary colon cancers and two were metastases.
Histologically, most colon carcinomas arise from the mucosal lining and are adenocarcinomas. Morphologically, colorectal carcinomas initially arise in situ, then slowly progress into a sessile mass (Fig 7). Their subsequent appearance and clinical behavior depend on where they originate. Left-sided lesions form annular masses (Fig 5), which tend to be diagnosed earlier because they cause obstruction, and are susceptible to ulceration (Fig 8) due to vascular encroachment. Right-sided lesions are generally diagnosed later because of the relatively larger caliber of the right colon, and they tend to grow into polypoid fun-gating masses with a propensity for necrosis (Fig 9).
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Figure 7a. Sessile adenocarcinoma. (a) Axial supine 2D image shows a sessile mass of the right colon (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 7b. Sessile adenocarcinoma. (a) Axial supine 2D image shows a sessile mass of the right colon (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 7c. Sessile adenocarcinoma. (a) Axial supine 2D image shows a sessile mass of the right colon (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 8a. Ulcerated adenocarcinoma. (a) Axial supine 2D image shows a polypoid rectal mass (arrow). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass has a central ulceration (arrow).
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Figure 8b. Ulcerated adenocarcinoma. (a) Axial supine 2D image shows a polypoid rectal mass (arrow). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass has a central ulceration (arrow).
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Figure 8c. Ulcerated adenocarcinoma. (a) Axial supine 2D image shows a polypoid rectal mass (arrow). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass has a central ulceration (arrow).
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Figure 9a. Necrotic adenocarcinoma. (a) Axial contrast-enhanced 2D image shows a polypoid adenocarcinoma with avascular regions (arrows) in the right colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the adenocarcinoma. At pathologic inspection, the avascular regions corresponded to areas of necrosis.
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Figure 9b. Necrotic adenocarcinoma. (a) Axial contrast-enhanced 2D image shows a polypoid adenocarcinoma with avascular regions (arrows) in the right colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the adenocarcinoma. At pathologic inspection, the avascular regions corresponded to areas of necrosis.
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Figure 9c. Necrotic adenocarcinoma. (a) Axial contrast-enhanced 2D image shows a polypoid adenocarcinoma with avascular regions (arrows) in the right colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the adenocarcinoma. At pathologic inspection, the avascular regions corresponded to areas of necrosis.
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The mucinous adenocarcinoma subtype (Fig 10) occurs in about 10% of patients. It is found more frequently in men and is generally more aggressive. Thus, these patients will more often present with an advanced stage of cancer (31,32).
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Figure 10a. Mucinous carcinoma. (a) Intraluminal 3D image shows an oval filling defect involving the distal transverse colon (arrowheads). (b) Oblique axial 2D image shows that the mass (arrowheads) has heterogeneous hypovascularity (arrow), which corresponded to mucinous material at pathologic inspection.
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Figure 10b. Mucinous carcinoma. (a) Intraluminal 3D image shows an oval filling defect involving the distal transverse colon (arrowheads). (b) Oblique axial 2D image shows that the mass (arrowheads) has heterogeneous hypovascularity (arrow), which corresponded to mucinous material at pathologic inspection.
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Flat lesions, defined as masses with a height no more than one-half their width, are potentially problematic because their morphologic characteristics can result in a false-negative diagnosis at CT colonography (33,34). However, one study suggested no significant difference in detection rates for flat versus polypoid masses when an initial 3D endoluminal survey with verification on axial 2D images was performed (35). In addition, there is disagreement as to the actual prevalence and histologic aggressiveness of this type of lesion. The prevalence has been reported from as low as 8% to as high as 40% of adenomas (36–39), with the variability potentially attributed to inherent genetic or environmental differences between East Asian and Western populations (35,40–43). In general, their appearance at CT colonography varies with their location: between haustral folds (Fig 11), exophytic off a fold (Fig 12), or involving the fold itself (Fig 13).
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Figure 11a. Flat adenocarcinoma. (a) Axial supine 2D image shows a tumor that is wider than it is tall (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass conforms to the nondependent colonic wall (arrows).
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Figure 11b. Flat adenocarcinoma. (a) Axial supine 2D image shows a tumor that is wider than it is tall (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass conforms to the nondependent colonic wall (arrows).
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Figure 11c. Flat adenocarcinoma. (a) Axial supine 2D image shows a tumor that is wider than it is tall (arrows). (b, c) Intraluminal 3D (b) and colonoscopic (c) images show that the mass conforms to the nondependent colonic wall (arrows).
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Figure 12a. Ulcerated flat adenocarcinoma growing off a haustral fold. (a) Axial 2D image shows an ulcerated mass (arrow) emanating from a haustral fold in the distal ascending colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 12b. Ulcerated flat adenocarcinoma growing off a haustral fold. (a) Axial 2D image shows an ulcerated mass (arrow) emanating from a haustral fold in the distal ascending colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 12c. Ulcerated flat adenocarcinoma growing off a haustral fold. (a) Axial 2D image shows an ulcerated mass (arrow) emanating from a haustral fold in the distal ascending colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images also show the mass (arrows).
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Figure 13a. Flat adenocarcinoma mimicking a thickened fold. (a) Axial 2D image shows an adenocarcinoma (arrowheads) confined to a haustral fold in the transverse colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show only partial involvement (arrows) of the haustral fold (arrowhead in b).
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Figure 13b. Flat adenocarcinoma mimicking a thickened fold. (a) Axial 2D image shows an adenocarcinoma (arrowheads) confined to a haustral fold in the transverse colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show only partial involvement (arrows) of the haustral fold (arrowhead in b).
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Figure 13c. Flat adenocarcinoma mimicking a thickened fold. (a) Axial 2D image shows an adenocarcinoma (arrowheads) confined to a haustral fold in the transverse colon. (b, c) Intraluminal 3D (b) and colonoscopic (c) images show only partial involvement (arrows) of the haustral fold (arrowhead in b).
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Although relatively uncommon, metastatic disease to the colon can occur by hematogenous spread, direct invasion (Fig 14), or serosal implantation (Fig 15).
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Figure 14a. Direct invasion by an endometrial carcinoma. (a) Axial 2D image shows a large mass (M) that markedly displaces and attenuates the rectosigmoid colon with polypoid invasion through the bowel wall (arrows). (b) Intraluminal 3D image also shows the polypoid invasion through the bowel wall (arrows).
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Figure 14b. Direct invasion by an endometrial carcinoma. (a) Axial 2D image shows a large mass (M) that markedly displaces and attenuates the rectosigmoid colon with polypoid invasion through the bowel wall (arrows). (b) Intraluminal 3D image also shows the polypoid invasion through the bowel wall (arrows).
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Figure 15a. Metastatic lymph node with secondary colonic extension. (a) Axial 2D image shows a large mass involving the sigmoid colon (arrows). The epicenter of the mass is extraluminal. (b) Intraluminal 3D image shows the irregular mucosal surface of the mass (arrows), which is pressing on the lumen. CT colonography performed 10 months earlier showed an adenocarcinoma of the right colon (not shown). (c) Axial 2D image obtained 10 months earlier shows a small peri–sigmoid colon lymph node (arrow). In retrospect, the location of this lymph node corresponded to the location of the subsequent mass.
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Figure 15b. Metastatic lymph node with secondary colonic extension. (a) Axial 2D image shows a large mass involving the sigmoid colon (arrows). The epicenter of the mass is extraluminal. (b) Intraluminal 3D image shows the irregular mucosal surface of the mass (arrows), which is pressing on the lumen. CT colonography performed 10 months earlier showed an adenocarcinoma of the right colon (not shown). (c) Axial 2D image obtained 10 months earlier shows a small peri–sigmoid colon lymph node (arrow). In retrospect, the location of this lymph node corresponded to the location of the subsequent mass.
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Figure 15c. Metastatic lymph node with secondary colonic extension. (a) Axial 2D image shows a large mass involving the sigmoid colon (arrows). The epicenter of the mass is extraluminal. (b) Intraluminal 3D image shows the irregular mucosal surface of the mass (arrows), which is pressing on the lumen. CT colonography performed 10 months earlier showed an adenocarcinoma of the right colon (not shown). (c) Axial 2D image obtained 10 months earlier shows a small peri–sigmoid colon lymph node (arrow). In retrospect, the location of this lymph node corresponded to the location of the subsequent mass.
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Imaging Pitfalls
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Familiarity with the potential pitfalls of CT colonography will help reduce interpretive errors (44–46). Incomplete distention (Fig 16) and residual fecal matter (Fig 17) are two of the most common causes of inaccuracy. Interpretive errors related to residual fecal material can be reduced with barium stool tagging (47–49). The day before the examination, the patient should drink 12 mL of a 40% barium solution with every meal. This type of bowel preparation allows differentiation of hyperattenuating residual stool, due to the intermixture with barium (Fig 17), from intermediate-attenuation polyps or cancers. Residual fluid may also obscure lesions; this pitfall can sometimes be resolved by using prone and supine imaging, oral administration of water-soluble contrast material, or use of intravenous contrast material (Fig 18 ).
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Figure 16a. Incomplete distention. (a) Supine axial 2D image obtained with intravenous contrast material shows an eccentric carcinoma of the sigmoid colon (arrows). (b) On a prone axial 2D image, the carcinoma is obscured by underdistention.
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Figure 16b. Incomplete distention. (a) Supine axial 2D image obtained with intravenous contrast material shows an eccentric carcinoma of the sigmoid colon (arrows). (b) On a prone axial 2D image, the carcinoma is obscured by underdistention.
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Figure 17a. Adherent stool. (a) Intraluminal 3D image shows a polypoid mass (arrows). (b, c) Prone (b) and supine (c) axial 2D images show that the mass (arrow) is adherent to the posterolateral colonic wall. The heterogeneous high attenuation of the lesion is due to barium tagging and thus indicates stool rather than a polyp or malignancy.
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Figure 17b. Adherent stool. (a) Intraluminal 3D image shows a polypoid mass (arrows). (b, c) Prone (b) and supine (c) axial 2D images show that the mass (arrow) is adherent to the posterolateral colonic wall. The heterogeneous high attenuation of the lesion is due to barium tagging and thus indicates stool rather than a polyp or malignancy.
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Figure 17c. Adherent stool. (a) Intraluminal 3D image shows a polypoid mass (arrows). (b, c) Prone (b) and supine (c) axial 2D images show that the mass (arrow) is adherent to the posterolateral colonic wall. The heterogeneous high attenuation of the lesion is due to barium tagging and thus indicates stool rather than a polyp or malignancy.
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Figure 18a. Residual fluid. (a, b) Prone axial 2D (a) and intraluminal 3D (b) images show a polypoid cecal adenocarcinoma (arrow). Note the layering, dependent mixture of residual fluid and stool (FS in a). (c, d) On supine axial 2D (c) and intraluminal 3D (d) images, the adenocarcinoma is obscured by the fluid. However, the addition of intravenous contrast material increases the conspicuity of the submerged, enhancing lesion (arrow in c) relative to that of the nonenhancing fluid and stool.
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Figure 18b. Residual fluid. (a, b) Prone axial 2D (a) and intraluminal 3D (b) images show a polypoid cecal adenocarcinoma (arrow). Note the layering, dependent mixture of residual fluid and stool (FS in a). (c, d) On supine axial 2D (c) and intraluminal 3D (d) images, the adenocarcinoma is obscured by the fluid. However, the addition of intravenous contrast material increases the conspicuity of the submerged, enhancing lesion (arrow in c) relative to that of the nonenhancing fluid and stool.
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Figure 18c. Residual fluid. (a, b) Prone axial 2D (a) and intraluminal 3D (b) images show a polypoid cecal adenocarcinoma (arrow). Note the layering, dependent mixture of residual fluid and stool (FS in a). (c, d) On supine axial 2D (c) and intraluminal 3D (d) images, the adenocarcinoma is obscured by the fluid. However, the addition of intravenous contrast material increases the conspicuity of the submerged, enhancing lesion (arrow in c) relative to that of the nonenhancing fluid and stool.
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Figure 18d. Residual fluid. (a, b) Prone axial 2D (a) and intraluminal 3D (b) images show a polypoid cecal adenocarcinoma (arrow). Note the layering, dependent mixture of residual fluid and stool (FS in a). (c, d) On supine axial 2D (c) and intraluminal 3D (d) images, the adenocarcinoma is obscured by the fluid. However, the addition of intravenous contrast material increases the conspicuity of the submerged, enhancing lesion (arrow in c) relative to that of the nonenhancing fluid and stool.
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Long-standing diverticular disease can be particularly problematic because chronic strictures are difficult to differentiate from obstructing malignancies (Fig 19). Positron emission tomography may be useful in differentiating between chronic diverticular disease and colon cancer (50). For confirmation, however, these patients may require repeat biopsies and follow-up studies.
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Figure 19a. Chronic stricture caused by diverticular disease. (a) Prone axial 2D image shows a masslike lesion of the sigmoid colon (arrows). (b) Supine axial 2D image obtained with intravenous contrast material shows the elongated, enhancing lesion (arrows) as well as diverticula (arrowheads). Repeat biopsies revealed chronic inflammatory cells but no malignancy.
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Figure 19b. Chronic stricture caused by diverticular disease. (a) Prone axial 2D image shows a masslike lesion of the sigmoid colon (arrows). (b) Supine axial 2D image obtained with intravenous contrast material shows the elongated, enhancing lesion (arrows) as well as diverticula (arrowheads). Repeat biopsies revealed chronic inflammatory cells but no malignancy.
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Conclusions
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CT colonography is developing into an effective screening technique for colorectal carcinoma. Knowledge of the varied presentations of disease at CT colonography can improve performance and minimize interpretive errors. The addition of an intravenous contrast medium can help avoid the more common pitfalls in interpretation and is essential for accurate staging of tumors and for postoperative surveillance.
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Acknowledgments
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The authors thank Bonnie Schimek and M. Alice McKinney for technical graphics support.
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Footnotes
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Abbreviations: 3D = three-dimensional, 2D = two-dimensional
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References
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Abstract
LEARNING OBJECTIVES
