Benefits

CTC is the only colorectal cancer–screening tool that can directly image both the colon and extracolonic structures and organs. The findings outside of the colon may be completely incidental or they may be the actual cause of the patient’s presenting symptom, such as abdominal pain. This unique ability can be viewed as a benefit by patients who are becoming more interested in being advocates for their own health care and by patients who would like to be able to pursue preventive care. Some of the more commonly identified extracolonic findings on CTC include benign lesions or lesions that do not affect the management of the asymptomatic patient, such as simple renal and hepatic cysts, gallstones, and renal stones. Other findings such as abdominal aortic aneurysm (AAA) and extracolonic malignancies can benefit patients in early detection and treatment.

CTC has the ability to simultaneously screen for AAA and colorectal carcinoma. The diagnosis and sizing of AAA by CT scan does not require the administration of intravenous contrast, and thus unenhanced-screening CTC is well suited for evaluation of AAA. Patients with AAA benefit from early diagnosis because the natural history of these aneurysms is to continually enlarge over a period of years, which can potentially lead to rupture. The strongest risk factor for rupture of an AAA is its large size, particularly when it is 5.5 cm or larger in diameter. Each year there are about 15,000 deaths caused by AAA in the United States. An AAA is defined as having an infrarenal aortic diameter larger than 3.0 cm. Small AAAs measure between 3.0 and 3.9 cm, intermediate-sized AAAs measure from 4.0 to 5.4 cm, and those that are 5.5 cm or larger in diameter are considered large. The major risk factors for the development of AAAs include male gender, smoking history, and an age of 65 years or older. Thus AAA and colorectal carcinoma tend to occur with increasing frequency in similar-aged patient cohorts. In 2005, the US Preventive Services Task Force recommended the performance of one-time screening for AAA by ultrasonography in men between 65 and 75 years who have ever smoked. In 2007, the Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) act became law, enabling Medicare to cover the costs of AAA screening by ultrasonography. The prevalence of asymptomatic AAAs in screening programs using ultrasonography has been found to be about 5% in men aged 65 years and older.

AAAs do not typically cause symptoms, and they are often identified as incidental findings on imaging studies such as CTC. In a study of 243 patients undergoing elective repair of AAA, 62% of cases were identified incidentally on radiologic examinations. The diagnosis of AAA was often missed on physical examination alone. In this study, 43% of patients with AAAs detected by imaging had palpable aneurysms that should have been detected on physical examination but were missed.

The early detection of AAA allows appropriate follow-up for its increasing size, and those that are 5.5 cm or larger require surgical or endovascular repair. The mortality rate associated with elective AAA repair is 5% or less, whereas the mortality rate for surgery after aneurysm rupture is significantly higher ranging between 80% and 95%. It has been found that open surgical repair of AAAs measuring at least 5.5 cm in diameter leads to about 43% decrease in mortality in older men undergoing screening. Screening for asymptomatic AAAs can reduce the incidence rate of ruptured AAAs by 49%.

Malignant tumors outside of the colon may also be identified by CTC. These typically appear as complex cystic or solid masses of the abdominal or pelvic organs. In unenhanced low-dose CTC, extracolonic malignancies are more easily visualized when they protrude from or deform the contour of an organ. Adenopathy located in the retroperitoneum or mesenteric fat may also be identified. Intravenous contrast may be administered for diagnostic CTC when the patient has symptoms or prior studies suspicious for colorectal cancer. Contrast-enhanced diagnostic CTC allows improved visualization of extracolonic carcinomas, although higher dose CT technique using increased tube current is necessary.

It is recognized that patients with renal cell carcinoma often have no symptoms and that most of these tumors are diagnosed as an incidental finding. Renal cell carcinomas that are identified incidentally on CTC may be found at an earlier stage when they are more likely to be curable. Tsui and colleagues retrospectively evaluated 633 consecutive patients with renal cell carcinoma who underwent radical or partial nephrectomy. The investigators found that 15% of patients had incidentally detected renal cell carcinoma and that these patients had significantly lower stage and lower grade tumors compared with patients who had symptoms leading to their diagnosis. Stage 1 lesions were found in 62% of patients with incidental renal cell carcinoma when compared with 23% of the patients with symptomatic renal cell carcinoma. The 5-year survival rate was significantly higher at 85% for incidentally discovered renal cell carcinoma compared with 63% for symptomatic tumors. Similarly, the local and distal recurrence rates were higher for symptomatic lesions. Other studies have also found that there is improved prognosis and patient outcome for incidentally discovered renal cell carcinomas that are more often found at an earlier pathologic stage than symptomatic tumors.

In recognition of the increasing number of incidental renal masses identified by imaging, management recommendations for cystic and solid masses have been developed. Management of cystic renal masses is typically based on the Bosniak classification scheme. Most incidentally identified renal cystic lesions are small and if simple appearing these are to be considered benign. Bosniak suggests that cystic lesions smaller than 1 cm that measure between 0 and 20 Hounsfield units and without evidence of calcifications, septations, nodularity, or enhancement can be presumed to be benign and do not need any additional workup. Surgery is suggested for solid renal masses larger than 1 cm. Very small solid masses less than 1 cm may be observed by follow-up imaging because these have a reasonable chance of being benign and they are often not well characterized and difficult to biopsy because of their small size. Specific recommendations for the management of incidental renal lesions identified on low-dose CTC need to be defined. A standardized framework for defining, managing, and reporting incidental findings is being developed by the Incidental Findings Committee under the Commission on Body Imaging of the American College of Radiology.

The identification of disease at an earlier stage allows for more timely intervention, which can avoid the high costs of health care required for more extensive diagnostic tests, treatments such as chemotherapy, extended hospitalizations, and surgery from later presentation of disease. Although some extracolonic carcinomas that are discovered may be too advanced for surgical management, they may be found when the patient is relatively symptom free offering a wider window of time for the patient and family to plan for the future, before the onset of significant symptoms. Similarly, if metastases are identified at the time of diagnosis of colon carcinoma on CTC, this can help direct patient management without additional diagnostic evaluation or intervention.