Colorectal Adenocarcinoma

Radiologic-Pathologic Correlation

Abstract Introduction Etiologic and Growth Characteristics

Tumor Spread and Staging Role of Radiology Treatment and Follow-Up Prognosis

Conclusion Source Information References

Role of Radiology

The role of the radiologist in the management of colorectal cancer is fivefold and includes screening, detection, staging, the evaluation of complications, and the evaluation of recurrent disease. The barium enema examination is the mainstay of radiologic screening and detection of colorectal adenomas and carcinoma. CT, ultrasound (US), or magnetic resonance (MR) imaging may be used for staging and the evaluation of complications and recurrent disease. Complications include perforation, abscess formation, intussusception, fistula formation, and obstruction.

The barium enema examination is an accurate, cost-effective, and safe method for the screening and detection of adenomas and adenocarcinomas. Its overall sensitivity is greater than 90% for the detection of adenomas larger than 1 cm. The radiology literature indicates that there is little or no difference between single- and double-contrast barium examinations for the detection of cancer and adenomas 1 cm or larger (32,33). The double-contrast examination has greater sensitivity for the detection of lesions smaller than 1 cm.

The alternative to the barium enema examination is colonoscopy, which has the added advantage of allowing a biopsy of suspicious lesions and removal of polypoid adenomas during the procedure. In studies that compare the results of barium enema studies to those of the "gold standard" of colonoscopy, the barium enema examination is automatically shown to be inferior. Colonoscopy, however, is far from perfect. Up to 10%-20% of colorectal lesions are missed at colonoscopy, usually because of an incomplete evaluation of the right side of the colon (34,35). Furthermore, colonoscopy is approximately three times more expensive than a barium enema examination and has a higher complication rate. In a recent review of 100,773 diagnostic colonoscopies reported in the literature, hemorrhage and perforation occurred in one in 3,600 and one in 600 examinations, respectively, and the mortality rate was one in 5,000 procedures (36). The barium enema examination has a perforation rate of one in 10,000 and a mortality rate of one in 50,000 (37). These facts would seem to preclude the use of colonoscopy as a primary screening method in asymptomatic patients and make it more appropriate for use in high-risk patients (36,37). However, the matter of the best screening examination for adenomas and adenocarcinomas remains controversial. At the very least, the advent of colonoscopy has improved the barium enema examination, since radiologists have been more accountable in their interpretations of the latter studies. Indeed, properly performed barium enema examinations should reveal an adenoma in 9%-12% of adults undergoing the study (38).

Although most patients with invasive adenocarcinoma of the colon undergo surgery, there is a rationale for accurate preoperative staging. First, there are reports that use of preoperative radiation therapy and chemotherapy improves the outcome for advanced rectal carcinoma, compared with the use of postoperative radiation therapy alone (39). Second, accurate staging is helpful to the surgeon in determining the extent of the colectomy, whether reanastomosis is attempted, and whether segmental liver resection may be indicated in certain patient populations (40,41).

Initially, CT was supposed to be an excellent preoperative staging method for colorectal carcinoma. A CT staging system was developed that attempted to parallel the extension of disease recorded in the various pathologic staging systems (42,43,44). Initial reports demonstrated that CT had over 85%-90% accuracy in depicting the extent of disease. However, further studies have demonstrated that CT has a lower accuracy rate, especially in depicting the early stages of disease, and have suggested that CT should not be used routinely to stage colorectal carcinoma (45,46,47,48). It may, however, be useful in patients suspected of having liver metastases at the time of diagnosis.

One of the causes of the inaccuracy of CT for staging colorectal carcinoma is its inability to demonstrate microscopic tumor extension through the bowel wall. This is not surprising, since CT does not resolve the different layers of the bowel. CT also does not allow distinguishing normal-sized lymph nodes without tumor from those with tumor. This is not surprising either, since the average size of lymph nodes affected with metastatic disease is less than 5 mm in pathologic specimens (Figure 6) (49). Understandably, no criteria can be developed that will be both sensitive and specific. The best CT criteria proposed for the detection of lymph node involvement are (a) any node that is 1 cm or larger, (b) a cluster of three or more nodes less than 1 cm, and (c) the demonstration of a lymph node of any size within the mesentery (48,50).

The accuracy of CT in staging colorectal carcinoma improves with the increasing stage of the disease (Figure 8). The invasion of pelvic side walls or surrounding organs and the detection of metastatic disease to the liver are two areas in which CT has a much higher accuracy (Figure 9) (43).

Liver metastases are most accurately detected with CT portography or MR imaging. In CT portography, an intraarterial catheter is placed in the superior mesenteric artery or the splenic artery; approximately 150 mL of contrast material is injected at a rate of 2-3 mL/sec and CT scanning through the liver begins after a 8-20-second delay, during peak portal venous enhancement. CT portography and MR imaging have approximately equal accuracies, and the use of one or the other usually depends on tailoring the examination to the particular clinical situation and the imaging modality most readily available (51,52,53,54,55).

CT is also accurate in the detection of metastatic disease to other intraabdominal organs, including the adrenal gland, ovary (Figure 10), mesentery, and omentum (Figure 11). Perforation, abscess formation (Figure 12), intussusception (Figure 13), and fistula formation (Figure 14) may all be appreciated on CT scans.

Transrectal and endoscopic US presently appear to be superior to CT and MR imaging in determining local tumor invasion, as well as in detecting adjacent nodal disease (56). Endoscopic US may allow accurate staging of both rectal and colonic neoplasms. It may also enable differentiation of metastatic nodes, which are predominantly hypoechoic and have clearly defined borders, from those that contain no metastatic foci, which are usually hyperechoic with indistinct boundaries (Figure 15) (56). In one study, the overall accuracy of staging with endoscopic US was 81% for rectal tumors and 93% for colonic tumors (56). Another study, however, was much less promising and suggested that only about half of the malignant nodes in patients with colorectal carcinoma were visualized with endosonography (57).

MR imaging, performed with high-resolution equipment and transrectal coils, is also useful in the local staging of rectal tumors (58). However, detection of metastases in normal-sized lymph nodes remains a problem.

Abstract Introduction Etiologic and Growth Characteristics

Tumor Spread and Staging Role of Radiology Treatment and Follow-Up Prognosis

Conclusion Source Information References