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Spiral CT of Colon Cancer: Imaging Features and Role in Management¹

¹ From the Department of Radiology, Johns Hopkins Medical Institutions, 601 N Caroline St, Baltimore, MD 21287 (K.M.H., E.K.F.); and the Department of Radiation Oncology, Johns Hopkins Hospital, Baltimore (R.A.A.). Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 3, 1999; revision requested April 21 and received May 14; accepted May 17. Address reprint requests to E.K.F. (e-mail: efishman@jhmi.edu).

	Abstract

Top Abstract Introduction Technique Staging Primary Tumors Local Spread Metastases Tumor Recurrence Therapeutic Considerations Conclusions References

 
Colorectal cancer is a common malignancy that results in significant morbidity and mortality. Abdominal computed tomography (CT) is valuable in planning surgery for colon cancer because it can demonstrate regional extension of tumor as well as adenopathy and distant metastases. At CT, colorectal cancer typically appears as a discrete soft-tissue mass that narrows the colonic lumen. Colorectal cancer can also manifest as focal colonic wall thickening and luminal narrowing. Complications of primary colonic malignancies such as obstruction, perforation, and fistula can be readily visualized with CT. At CT, local extension of tumor appears as an extracolic mass or simply as thickening and infiltration of pericolic fat. Extracolic spread is also suggested by loss of fat planes between the colon and adjacent organs. The liver is the predominant organ to be involved with metastases from colorectal cancer. At CT, hepatic metastases usually appear as hypoattenuating masses, which are best visualized during the portal venous phase of liver enhancement. Other common sites of metastases from colon cancer include the lungs, adrenal glands, and bones. Use of CT is critical for identifying recurrences, evaluating anatomic relationships, documenting "normal" postoperative anatomy, and confirming the absence of new lesions during and after therapy.

Index Terms: Colon, CT, 75.12115 • Colon, neoplasms, 75.32 • Intestinal neoplasms, CT, 75.12115, 75.32 • Intestinal neoplasms, diagnosis, 75.32 • Intestinal neoplasms, staging, 75.32

	Introduction

Top Abstract Introduction Technique Staging Primary Tumors Local Spread Metastases Tumor Recurrence Therapeutic Considerations Conclusions References

 
Colorectal cancer is the second most common cause of cancer death in developed countries. In 1998, there were 131,000 new cases of colorectal cancer and 56,000 deaths in the United States (1). The initial diagnosis is usually made with colonoscopy or air-barium enema examination; however, with the increased use of computed tomography (CT) as the initial imaging modality in patients with a variety of gastrointestinal symptoms, the radiologist may be the first to suggest the diagnosis of colon cancer on the basis of CT findings. Nevertheless, at this time, CT is not routinely performed for detection of colon cancer, although continued advancements in scanner and computer technology may allow CT to play a future role in detection of polyps and early-stage colon cancer.

The current role of CT in patients with known colon cancer is controversial. Accuracy rates for preoperative staging of colon cancer with CT have been disappointing, ranging between 48% and 77% (2–6). Limitations of CT staging include an inability to definitively identify nodes that contain tumor or to determine the exact depth of tumor invasion through the wall. Despite these limitations, CT is valuable in the management of colon cancer. Preoperative CT is useful for planning surgery or radiation therapy, particularly when local extension of tumor into adjacent organs or distant metastases are detected. In addition, preoperative CT provides baseline findings for comparison during the postoperative period and is the modality of choice for detection of local recurrence after surgical resection.

Given the prevalence of colon cancer in the United States and the role of CT in preoperative staging, treatment planning, and postoperative follow-up, the radiologist should be familiar with the CT appearance of colon cancer. This article discusses the technique of colon CT, staging of colon cancer, primary tumors, local spread, metastases, tumor recurrence, and therapeutic considerations.

	Technique

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When abdominal CT is performed to image a wide variety of colonic diseases, colonic opacification must be optimal. Oral contrast material (diatrizoate sodium meglumine [Hypaque 3%; Nycomed Amersham, Princeton, NJ] or barium sulfate [Barocat 2%; Lafayette Pharmaceuticals, Lafayette, Ind]) can be administered the night before the study as well as 30–90 minutes prior to the study to ensure that adequate contrast material reaches the colon. In urgent cases or in patients in whom limited rectosigmoid disease is suspected, positive contrast material can be gently administered via the rectum. A topogram can then be obtained to confirm filling of the entire colon before CT is performed. Neutral agents (water) (7,8) or negative agents (air) (9) can also be easily administered via a rectal tube and provide excellent contrast for colonic imaging. In a small series by Gazelle et al (5), CT performed after administration of a water enema was effective in staging colorectal cancers; this technique may improve the ability of CT to demonstrate the depth of tumor invasion of the wall and extension into the pericolic fat. Air or carbon dioxide can also be used to distend the colon and is particularly helpful for detection of polyps and small masses when used after bowel cleansing. In addition, water or air is preferred over positive agents (diatrizoate sodium meglumine or barium) when performing three-dimensional (3D) imaging of the abdomen for CT angiography because positive contrast agents interfere with data manipulation, thus necessitating extensive editing.

Recently, CT (ie, virtual colonoscopy) is being investigated as a potential method for screening patients for polyps and early-stage colon cancers. However, significant advances in data acquisition and computer image processing techniques will be needed before the technology can become a reliable, cost-effective alternative to conventional colonoscopy. If CT is performed for polyp or tumor detection, bowel cleansing is essential to help avoid confusion between adherent stool and polyps or masses. Go-Lytely solution (polyethylene glycol; Braintree Scientific, Braintree, Mass) taken the evening before the study will reliably cleanse the colon but may leave residual fluid within the colon. Imaging in both the supine and prone positions will help shift fluid, which may obscure underlying lesions, and help distend collapsed segments that were dependent on the supine images. Also, imaging in different positions may help one definitively identify fecal matter by demonstrating its mobility. Glucagon can be administered in selected patients to help relieve spasm and cramping if necessary.

Administration of intravenous contrast material is essential for complete staging of known colorectal cancer and for evaluation of recurrent or metastatic disease. At our institution, we routinely administer 100–120 mL of iohexol (Omnipaque 350; Nycomed Amersham) intravenously at a rate of 2–3 mL/sec.

When evaluating a patient with known or suspected colon cancer, the abdomen should be routinely imaged from the diaphragm to the symphysis pubis. When spiral CT is used, 5-mm collimation can be performed with a table speed of 8 mm/sec and reconstruction of the data at 5-mm intervals. Our standard spiral CT protocol is to acquire data during the portal venous phase of liver enhancement, 45–50 seconds after the start of contrast material injection, to maximize the detection of hepatic metastases. Scanning too late may result in streak artifact in the abdomen due to concentrated contrast material within the renal collecting system. The patient is usually scanned in the supine position. If necessary, repeat imaging can be performed with the patient prone or after administration of more air or contrast material to distend collapsed segments. Also, multiplanar reconstruction and 3D volume rendering techniques can be used in problem cases to better visualize colon anatomy and the location of the suspected mass or abnormality.

	Staging

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Not all patients with colon cancer will require CT evaluation prior to initial surgical management. The diagnosis is usually made with colonoscopy and biopsy or after barium enema and colonoscopy. Overt metastatic disease at initial presentation is uncommon (<10%–15% of cases) and is usually suggested by symptoms, abnormalities at physical examination (eg, hepatomegaly), or abnormal results of laboratory tests (liver function tests, measurement of carcinoembryonic antigen level) (10,11). Preoperative CT is typically performed for the following indications: (a) suspected hematogenous or distal nodal (eg, paraaortic) metastases, (b) suspected invasion into adjacent organs or abscess formation, (c) unexplained or atypical symptoms, and (d) unusual histologic results (eg, lymphoma). The major goal of CT is to determine if there is direct invasion of adjacent organs, enlargement of local nodes, or evidence of distant metastases. The TNM classification is commonly used for staging of colorectal cancer and is based on the extent of tumoral, nodal, and metastatic involvement (Tables 1, 2) (12). Many pathologists prefer to use the Dukes staging system, especially for rectal cancers (Table 2) (13).

	Primary Tumors

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The sensitivity of CT in detection of primary colon cancer is variable and depends on the size of the tumor. In a study of 158 patients with colorectal cancer, the primary tumor could be identified with CT in only 75% of cases (14). CT is limited in detection of small tumors or lesions less than 3–5 mm in diameter (15). However, because the risk of malignancy in a polyp less than 1 cm in diameter is less than 1%, this size limitation of CT detection is probably not clinically significant (16). Recent advances in spiral CT and the use of interactive multiplanar 3D CT performed after osmotic bowel preparation will likely improve the sensitivity of CT for these smaller lesions.

In patients with colorectal cancer, CT typically demonstrates a discrete soft-tissue mass that narrows the colonic lumen (Figs 1, 2). Large masses may undergo central necrosis and thus appear as a soft-tissue mass with central low attenuation or rarely air attenuation. This appearance may resemble that of an abscess. In addition, a significant percentage of colorectal cancers manifest as focal colonic wall thickening and luminal narrowing (Figs 3, 4), an appearance that emphasizes the importance of adequate colonic opacification and distention. In particular, rectal and sigmoid cancers may appear as asymmetric nodular wall thickening that narrows the lumen (Figs 4, 5). This appearance may mimic diverticulitis, especially if the tumor involvement of the wall has resulted in infiltration of the pericolic fat (Fig 6). In a study by Padidar et al (17) of 69 patients with sigmoid diverticulitis and 29 patients with sigmoid cancer, the presence of fluid in the root of the sigmoid mesentery and engorgement of adjacent sigmoid mesenteric vasculature favored the diagnosis of diverticulitis. Conversely, the presence of pericolic lymph nodes in patients with suspected diverticulitis should raise the suspicion of colon cancer (18). However, in some cases it may not be possible to distinguish diverticulitis from colon cancer with CT alone, and histologic samples will be required.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 1.   Colon cancer in a 74-year-old man. Contrast material-enhanced spiral CT scan shows luminal narrowing and marked wall thickening involving the right side of the transverse colon (arrow). There is adjacent stranding of the serosa and mesenteric fat, a finding compatible with local tumor extension.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 2.   Adenocarcinoma in a 64-year-old woman with right lower quadrant pain. Contrast-enhanced CT scan shows marked circumferential thickening of the cecum (curved arrows). The wall has a low-attenuation component (straight arrow), which is due to necrosis. There is also stranding of the pericolic fat, a finding suggestive of tumor invasion through the wall. Adenocarcinoma was confirmed at endoscopy.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 3.   Adenocarcinoma in an 89-year-old woman with severe abdominal pain. Spiral CT scan obtained with oral contrast material shows segmental circumferential thickening of the hepatic flexure (arrows) with ascites. Adenocarcinoma was confirmed at colonoscopy and biopsy.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 4.   Adenocarcinoma in a 77-year-old woman with lower abdominal pain. Spiral CT scan obtained with oral contrast material shows air distention of the rectosigmoid and focal eccentric wall thickening (arrow). Although this appearance could be due to diverticulitis or colon cancer, the lack of pericolic inflammation or fluid favors colon cancer. Colonoscopy and biopsy were recommended, and adenocarcinoma was diagnosed.

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 5.   Rectal cancer in a 65-year-old man with rectal bleeding. Spiral CT scan obtained with rectal contrast material shows an eccentric rectal cancer (black arrow) as well as adjacent nodes (white arrows).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 6.   Diverticulitis in a 42-year-old man with pain and heme-positive stools. CT scan obtained with oral contrast material shows focal, masslike thickening of the sigmoid colon (straight arrows) with adjacent stranding of the pericolic fat. On the basis of the CT appearance and clinical history, colon cancer was suspected. At endoscopy, diverticulitis was diagnosed. In retrospect, the presence of minimal adjacent mesenteric fluid (curved arrow) favored diverticulitis.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 7.   Bowel obstruction in a 66-year-old man with a family history of colon cancer. Coronal 3D image obtained with intravenous contrast material and after air distention of the colon shows a focal applecore lesion in the descending colon (arrow). L = lung, S = stomach.

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.   Intussusception due to colon cancer in a 66-year-old woman. Contrast-enhanced spiral CT scans show a large ileocolic intussusception in the transverse (a) and longitudinal (b) planes. A colon cancer was found to be the lead point at endoscopy.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.   Intussusception due to colon cancer in a 66-year-old woman. Contrast-enhanced spiral CT scans show a large ileocolic intussusception in the transverse (a) and longitudinal (b) planes. A colon cancer was found to be the lead point at endoscopy.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 9.   Colonic perforation in a 57-year-old woman with a history of stage IV cervical carcinoma who presented with pain and sepsis. On plain radiographs of the abdomen obtained earlier the same day (not shown), there was mottled air in the right side of the pelvis, a finding suggestive of abscess. Emergent nonenhanced CT scan shows extensive mottled extraluminal air in the right side of the pelvis. At surgery, a perforating cecal cancer was discovered.

	Local Spread

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View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 10.   Tumor invasion in a 71-year-old woman with a palpable abdominal mass. Contrast-enhanced CT scan shows a large, circumferential soft-tissue mass in the cecum, a finding compatible with carcinoma. The mass extends to involve the anterior abdominal wall (arrow), an appearance compatible with tumor invasion. Tumor invasion was confirmed at surgery.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 11.   Tumor invasion in a 72-year-old woman with sigmoid cancer. Contrast-enhanced CT scan shows a mass in the sigmoid colon (arrow) with infiltration of the surrounding fat and extension into the presacral space.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 12.   Tumor invasion in a 40-year-old man with gastrointestinal hemorrhage. Coronal oblique 3D image obtained with intravenous contrast material and water used as an oral contrast material shows a large mass in the left upper quadrant (solid arrows). The mass is ulcerated, and there is a direct connection (open arrow) between the mass and the stomach (S). At surgery, an adenocarcinoma with a gastrocolic fistula was found.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 13.   Enlarged lymph nodes in a 43-year-old man with metastatic colon cancer. Contrast-enhanced spiral CT scan shows multiple hepatic metastases as well as enlarged portacaval and aortocaval nodes (arrows).

	Metastases

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Using spiral CT, Kuszyk et al (27) achieved a sensitivity of more than 90% for detection of liver lesions larger than 1 cm in diameter and a sensitivity of 56% for detection of lesions smaller than 1 cm. These results represent an improvement over those achieved with traditional incremental CT. The accuracy of dynamic contrast-enhanced CT and of nonenhanced MR imaging in the detection of metastatic liver disease appears to be equal at 85% (22). In a series of 478 patients with colorectal cancer, the specificity of both CT (97%) and MR imaging (94%) for the detection of hepatic metastases was similar to that in most other reported series (22). The sensitivity of the two techniques in that study was 62% and 70%, respectively (22). Thus, MR imaging allows detection of smaller lesions; however, as at CT, small lesions often lack morphologic features and cannot be definitively characterized as benign or malignant. Serial imaging is often required when small lesions are detected with either modality.

At CT, hepatic metastases usually appear as hypoattenuating masses (Fig 13), which are best visualized during the portal venous phase of liver enhancement. Mucinous colorectal cancer can produce cystic (Fig 14) or calcified (Fig 15) hepatic metastases. The metastases can vary widely in size.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 14.   Hepatic metastases in a 53-year-old woman with colon cancer. Contrast-enhanced spiral CT scan shows multiple low-attenuation hepatic metastases.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 15.   Hepatic metastases in a 64-year-old woman with metastatic colon cancer. Contrast-enhanced spiral CT scan shows metastatic disease involving the liver, predominantly the right lobe (arrows). The metastases are partially calcified.

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   Figure 16.   Pulmonary metastases in a 47-year-old man with colon cancer. Spiral CT scan shows numerous metastases in the lungs.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 17.   Peritoneal metastases in a 59-year-old man with colon cancer. Contrast-enhanced spiral CT scan shows metastatic implants involving the liver edge with scalloping of the liver. In addition, peritoneal implants are seen in the left side of the abdomen.

	Tumor Recurrence

Top Abstract Introduction Technique Staging Primary Tumors Local Spread Metastases Tumor Recurrence Therapeutic Considerations Conclusions References

Recurrent tumor after surgery usually appears as a soft-tissue mass in or near the surgical site (Fig 18). CT is better than colonoscopy at demonstrating early, masslike tumor recurrence at the surgical anastomosis due to the often largely extrinsic component of such recurrence (Fig 19) (32). This appearance can mimic postoperative fibrosis, although fibrosis usually appears more linear without a discrete mass. Occasionally, distinction between postoperative fibrosis and recurrent tumor is not possible unless serial scans are obtained. CT findings clearly indicative of recurrent malignant disease include enlargement of a soft-tissue mass over time, enlarging regional lymphadenopathy, and invasion of contiguous structures. If indicated, CT-guided biopsy for tissue confirmation can be performed.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 18.   Tumor recurrence in a 53-year-old woman 3 months after local resection of a cancer of the transverse colon. Contrast-enhanced spiral CT scan shows a local recurrence at the surgical site (arrow). A diverting ileostomy is also present.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 19.   Tumor recurrence in a 59-year-old man 4 months after resection of colon cancer. Contrast-enhanced spiral CT scan shows a large, heterogeneous mass (arrowhead) involving the left anterior aspect of the abdomen adjacent to the ostomy site (arrow). The mass also invades the anterior abdominal wall. This appearance is compatible with recurrence at the surgical site, which was confirmed at surgery.

	Therapeutic Considerations

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Surgical resection is the treatment of choice for patients with localized disease. Adjuvant therapy is then given according to the statistical risk of recurrence, which is based on identified prognostic features (eg, overall stage, T stage). The goal is to decrease the risk of recurrence for patients who would otherwise be at risk.

Chemotherapy has an established role as adjuvant therapy for patients with stage III disease (34). Both fluorouracil with levamisole and fluorouracil with leucovorin are considered acceptable. The role of adjuvant therapy for selected patients with stage II disease is less clear (35).

Adjuvant radiation therapy has a definite role in the treatment of rectal carcinoma, but its usefulness is less well established in patients with colon cancer. Also, radiation therapy may be recommended to treat invasion into adjacent organs and is usually given with concurrent chemotherapy. If radiation therapy is used, CT information is critical for identifying treatment volumes and optimal field placement and angulation.

Overall, the expectation of cure depends on the stage of the initial tumor. Primary tumors confined to the submucosa are cured more than 90% of the time (30). Tumors that have extended through the bowel wall without lymph node involvement are cured 60%–80% of the time (30). Patients with one to three positive lymph nodes have a 5-year survival rate of 66% (36). If four or more lymph nodes are positive, the 5-year survival rate is only 37% (36).

CT is critical for identifying recurrences and helping to evaluate anatomic relationships, document "normal" postoperative anatomy, and confirm the absence of new lesions during and after therapy. Localized hepatic recurrences can be resected with curative intent. Other intraabdominal disease recurrences (eg, in the lymph nodes, peritoneum, or other organ sites) are generally managed with chemotherapy. Obstructive symptoms may require surgery (intestinal) or radiation therapy. Radiation therapy is also useful for painful lesions near the spine or other retroperitoneal sites. CT is generally essential for identifying and localizing such lesions for management with irradiation.

Disease recurrence can also occur in extraabdominal sites such as the bones, lungs, mediastinum, and brain. Lesions in mediastinal nodes that cause compression of major structures or in the brain can be identified and localized for radiation therapy with CT. CT is also critical for assessing the response to chemotherapy by means of index lesions in the lung or lymph nodes. Bone scanning combined with plain radiography is generally adequate for monitoring osseous metastases managed with radiation therapy; however, when the results of these modalities are ambiguous, CT scans obtained with bone windows are generally definitive.

	Conclusions

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Colorectal cancer is a common malignancy that results in significant morbidity and mortality. Although colonoscopy and barium enema examination are accurate in detection of colon cancer, they do not allow evaluation of extracolic disease. CT is valuable in preoperative assessment and staging of colorectal cancer as well as in postoperative surveillance for recurrence. Rapid advances in technology will likely continue to improve the accuracy and usefulness of CT.

	Footnotes

 
See also the article by Horton et al (pp 399–418 ) in this issue.

Abbreviation: 3D = three-dimensional

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				R. G. H. Beets-Tan and G. L. Beets Rectal Cancer: Review with Emphasis on MR Imaging Radiology, August 1, 2004; 232(2): 335 - 346. [Abstract] [Full Text] [PDF]

				A. Filippone, R. Ambrosini, M. Fuschi, T. Marinelli, D. Genovesi, and L. Bonomo Preoperative T and N Staging of Colorectal Cancer: Accuracy of Contrast-enhanced Multi-Detector Row CT Colonography--Initial Experience Radiology, April 1, 2004; 231(1): 83 - 90. [Abstract] [Full Text] [PDF]

				J. Wittenberg, M. G. Harisinghani, K. Jhaveri, J. Varghese, and P. R. Mueller Algorithmic Approach to CT Diagnosis of the Abnormal Bowel Wall RadioGraphics, September 1, 2002; 22(5): 1093 - 1107. [Abstract] [Full Text] [PDF]

				E. Neri, P. Giusti, L. Battolla, P. Vagli, P. Boraschi, R. Lencioni, D. Caramella, and C. Bartolozzi Colorectal Cancer: Role of CT Colonography in Preoperative Evaluation after Incomplete Colonoscopy Radiology, June 1, 2002; 223(3): 615 - 619. [Abstract] [Full Text] [PDF]

				C S Ng, T C Doyle, A K Dixon, R Miller, and M J Arends Histopathological correlates of abnormal pericolic fat on CT in the assessment of colorectal carcinoma Br. J. Radiol., January 1, 2002; 75(889): 31 - 37. [Abstract] [Full Text] [PDF]

				M. Macari and E. J. Balthazar CT of Bowel Wall Thickening: Significance and Pitfalls of Interpretation Am. J. Roentgenol., May 1, 2001; 176(5): 1105 - 1116. [Full Text] [PDF]