HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Baker, S. R. Search for Related Content PubMed PubMed Citation Articles by Baker, S. R. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?

Abdominal CT Screening: Inflated Promises, Serious Concerns

¹ Department of Radiology, UMDNJ—New Jersey Medical School, 150 Bergen St., UH C320, Newark, NJ.

Received June 12, 2002; accepted after revision June 26, 2002.

 
Address correspondence to S. R. Baker.

Introduction

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
Whole-body CT screening is now spreading across the country like a wildfire on a hot, windy day. In big and medium-sized cities in the United States, it is difficult to avoid the advertisements promoting CT screening in the print media, on radio and TV, and even over the Internet. Testimonials abound by celebrities who proclaim the life-saving value of unenhanced CT. Typically, they proffer the notion that individuals who seem to be entirely well and avail themselves of this examination wisely take advantage of the opportunity to find that they are either free of disease or are lucky to have discovered that they have something they can take care of before it is "too late."

The emerging industry of total-body screening may become a global phenomenon, at least in affluent countries, because CT centers similar to those in the United States are now opening in Europe (Pinto F, personal communication). In many locales, the proponents of the technique can sound persuasive as they present arguments that are enticing to prospective patients. Yet, like any novel technology that has advantages and applications that appear obvious, CT screening also possesses attendant uncertainties and risks that need to be emphasized. Moreover, it engenders perhaps unanticipated but nonetheless real and difficult issues for the specialty of radiology that tend to be overlooked in the hoopla.

CT screening can be divided into four categories: calcium scoring of coronary arteries; cross-sectional imaging of the chest for the prime purpose of observing small carcinomas; colonography for the detection of largebowel polyps; and abdominal scanning for the recognition of any abnormality, be it degenerative, metabolic, vascular, or neoplastic. Chest and abdominal CT screening are often performed together as one examination, but I will confine my comments to CT studies performed on asymptomatic patients for the evaluation of disorders in organs and tissues below the diaphragm.

Limitations

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
The range of abnormalities in the viscera and vessels of the abdomen that can be observed by CT in symptom-free individuals is vast. But that virtue by itself is not enough to justify the widespread use of a diagnostic test, no matter how sensitive or specific. Equally significant are the prevalence of a detectable lesion in the population to be studied, its rate of growth, and the capabilities of treatments designed to cure it at any stage of its development. Of comparable importance, too, is the availability of well-accepted competitive tests of equal or greater sensitivity. That fact alone should be particularly cogent with respect to the use of unenhanced abdominal CT because, for many conditions, less expensive examinations, such as sonography, may be readily accessible. Furthermore, no procedure that uses ionizing radiation ought to be promoted to stimulate patient demand until its efficacy has been amply demonstrated. And, as for any other screening study, an appropriate interval between initial and subsequent examinations should be decided on by a consensus of medical experts before the screening becomes a routine exercise for the population at large.

On all these counts, the benefits of abdominal CT screening must be questioned. For most CT studies, the administration of IV contrast material before scanning is essential to enhance the conspicuity of small lesions in solid organs and to discern the nature of protrusions beyond expected visceral contours. Consequently, the sensitivity of unenhanced CT will be constrained by a lack of opacification of parenchyma and adjacent vascular conduits. Thus, in the abdomen, the diagnostic value of unenhanced CT is inherently limited.

Detection of Cancer

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
In both men and women, the most common potentially lethal malignancy of the abdomen is carcinoma of the colon and rectum. It is generally accepted that if small adenomatous polyps that protrude into the lumen of the large intestine are allowed to grow, these polyps will eventually become malignancies that can expand locally and metastasize widely. Yet potentially curable lesions of the large bowel are not shown readily on unenhanced CT. That is why CT colonography is performed at screening centers as a supplement to unenhanced abdominal screening. The introduction of air or CO₂ to distend the bowel lumen allows CT colonography to reveal the resectable polyps that unenhanced CT will never show.

In men, prostatic carcinoma has a mortality rate similar to that of colonic carcinoma, but the detection of prostatic carcinoma occurs not with CT but by rectal palpation, prostate-specific antigen serum levels, and sonographically guided biopsy. In women, early-stage carcinomas of the cervix and corpus uterus are conventionally discovered through Pap smear analysis and physical diagnosis. These are time-tested procedures that will not be supplanted by CT of the abdomen. Carcinoma of the ovary has a much better prognosis when the tumor remains localized before it grows by extension or metastasizes into the peritoneal cavity. Unenhanced CT has not played a major role in the observation of this malignancy when it is confined within the ovarian capsule. Carcinoma of the stomach is continuing to decline in incidence in the United States. In any event, CT rarely reveals early lesions without the assistance of gastric dilatation to distend the lumen and contrast injection to opacify the gastric wall. In the nearly 30-year history of whole-body CT, the observation of an incidental, resectable, and then curable adenocarcinoma of the pancreas, if one has occurred at all, must be an exceedingly rare event. Screening CT for the detection of pancreatic carcinoma cannot be justified, even though this malignancy ranks third among fatal abdominal cancers [1].

In the United States, hepatoma occurs predominantly in selected populations who are in jeopardy for it; hepatoma is rare in individuals with no known risk factors. Of the many CT techniques that have been reported to reveal hepatoma, all use contrast material. The best results have been reported when images are obtained in both the arterial and venous phases after contrast administration. Even then, 25-30% of lesions will be missed [2]. Similarly, cancer of the gallbladder is difficult to detect at an early stage and is not typically present in asymptomatic individuals, except perhaps among Indians and persons of mixed European and American Indian ancestry in the southwestern United States, who together constitute a group in which this neoplasm has a much greater incidence than elsewhere in the United States.

Ninety percent of all cases of fatal lymphoma can be assigned to one of the histologic varieties in the non-Hodgkin's group [1]. For many patients, remarkable advances in treatment have dramatically lowered the death rate. However, non-Hodgkin's lymphomas rarely present initially with abdominal node enlargement unless coincident adenopathy exists elsewhere. Furthermore, prognosis depends more on the cell type than on the volume of tumor first seen. Also, large tumors are most likely discovered by the patient and do not appear as a surprise at screening CT. Carcinoma of the bladder usually is suggested by hematuria, which is a more effective indicator of tumor in an otherwise asymptomatic individual than is cross-sectional CT. Unenhanced CT will definitively reveal a malignancy of the bladder only when the malignancy is fairly large. Likewise, adrenal carcinoma characteristically grows quietly, seldom manifesting signs or symptoms until it has become large. By consensus, adrenal tumors smaller than 3 cm are usually left untreated. Moreover, in the United States, fewer than 500 individuals die from this malignancy annually, which is hardly enough to support a generalized search for it among apparently healthy adults [1].

Renal Carcinoma

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
We then are left with only renal cell carcinoma as a neoplasm that can be revealed on unenhanced CT when the carcinoma is clinically silent and that can also be cured by surgical removal. Yet only 70% of hypernephromas are seen serendipitously on imaging of patients who also lack one or more of the three common presentations: hematuria, palpable flank mass, or fever [3]. Moreover, unless a carcinoma is large enough to protrude well beyond the renal contours (which makes it also more likely to have already metastasized), the carcinoma is apt to be missed if no contrast material is used to define a lump or discern a "hole" in the kidney. Consequently, even if widely used, screening CT will probably result in the detection of only approximately 50% of all renal carcinomas. But without contrast administration, CT is insensitive for the detection of small tumors.

Although hypernephroma is responsible for 12,000 deaths a year (50% of the number of fatal cancers of the bladder), the likelihood of its occurrence in persons 40-60 years old is approximately one in 550 in men and one in 750 in women, increasing to one in 100 men and one in 130 women in the years between 60 and 80 years old. Because the tumor increases in frequency with increasing age, the chance of its appearance in any one year in the fifth or sixth decade of life is no more than one twentieth of 550 (or one in 11,000) in men in their 40s and no more than one twentieth of 750 (or one in 15,000) in women of the same age. Inasmuch as only half these cancers will be seen on unenhanced CT, the likelihood is reduced to one in 22,000 in men 40-60 years old and, correspondingly, to one in 30,000 in women of the same age [1]. One will have to interpret many CT scans to find a celebrity who has benefited from this technique and then will be willing to trumpet the finding as a genuine case of a life saved.

Moreover, an iron law of screening is that when the prevalence is very low, the number of true-positive tests will be very low, even when the test is highly sensitive. As a corollary, even if the specificity is very high when the prevalence is very low, most positive results will be false-positive. The incidental observation on unenhanced CT screening of a suspicious finding in the kidney in a patient with no hematuria or symptoms of a mass would most likely result in further testing and possibly a laparotomy, even though the chance of the patient's actually having a malignant tumor is approximately 0.005% in individuals 40-60 years old [1]. One would not expect endorsements from those who underwent surgery after unenhanced CT showed a renal abnormality that turned out to be something other than cancer. Yet the number of individuals in this false-positive group would most likely far exceed the fortunate but very rare person for whom abdominal screening showed an asymptomatic, resectable, and curable neoplasm.

Nonmalignant Conditions

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
Nonetheless, the proponents of abdominal CT screening promise much more than just cancer detection. This powerful technique can detect stones in various abdominal locations. For example, cholelithiasis is common among adults in the United States, existing in approximately 15% of all adult individuals [4]. Yet does its incidental recognition really promote health? Or does such detection make the asymptomatic possessor of a gallstone even more worried now that he or she knows that the calculi are there, even if quiescent? Furthermore, a more efficient and less expensive test for gallstone recognition exists. Sonography has been available for this purpose for more than 25 years, but its use has to be justified before third-party payers will reimburse for it as a screening test for cholelithiasis. Not so with the CT screening now being promoted across the United States—because the usual transaction for services rendered is immediate and payment is made directly to the physician, with no third party involved.

Unenhanced CT is not limited to the observation of disease in the viscera. Unenhanced CT can also readily reveal calcification in the aorta and in the iliac arteries. Some proponents of CT screening regard abnormalities in these vessels as a surrogate for concomitant disease in the arteries that supply the heart and brain. However, it is not necessarily true that the absence of calcification in the abdominal arteries can serve as indicator of vascular health elsewhere in the body. Moreover, negative findings on unenhanced abdominal CT may limit the desire by patients to concern themselves with the detection of heart or cerebral artery disease that could present imminent or at least prospective problems for individuals who have risk factors for those conditions.

Even without contrast infusion, abdominal CT screening can reveal aneurysms of the aorta and the iliac arteries. Often these aneurysms are asymptomatic. Surely, here is one distinct benefit of unenhanced CT of the abdomen. However, in patients younger than 60 years and, especially in such patients with no known risk factors such as hypertension, arteriosclerosis, or a history of smoking, the likelihood of an aneurysm is very low. Even in men older than 60 years, the prevalence of dangerous aneurysms (those > 4 cm in diameter) is only 2-3% [5, 6]. Also, high blood pressure by itself, if being treated, does not pose an increased threat of mortality [6, 7]. Moreover, sonography is as likely as CT to reveal aneurysms and therefore is a better choice as the initial test for their recognition.

Certainly CT screening can reveal arthritis and degenerative disease in the appendicular and axial skeletons. However, what is the value of this knowledge in a symptom-free individual? Does one really need to acquire such information, which is usually trivial to the maintenance of health?

Popularity with the Public

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
These concerns are now entering the debate in the lay press about CT screening. Moreover, the American College of Radiology has asserted that CT screening has no known scientific value [8]. The most current announcement from the Food and Drug Administration also dismisses the purported benefits of CT screening [9]. Despite the disclaimers, the public remains interested in CT screening, as shown by the rapid growth of private centers offering this service in both urban and rural areas.

I believe four reasons exist for the popularity of CT screening. First, Americans seem to be fond of technologic innovation in medicine in all its many guises, especially when such innovation is portrayed as pain-free and quick, even if it is expensive. The examination that is offered in screening centers may appeal to us with the power of its diagnostic incisiveness, the promise of certainty, and the assurance of minimal discomfort during the procedure. The prospect that nothing wrong will be found after spending 10 minutes on an imaging table, with the results promptly available, is certainly compelling to some individuals.

Second, we have been told that we must take responsibility for our bodies. To be healthy we must not only refrain from excessive use of alcohol, stop smoking, eat right, wear a seat belt, and exercise, we should also participate as equal partners with our physicians and other care-givers in prevention and surveillance. What could be more congenial to the assumption of personal responsibility than a self-referral to a screening CT center? Is there no more optimal example of patient empowerment than this?

Third, individuals know they cannot live forever, but most believe that they will not die soon. A screening CT examination with negative findings is an affirmation of the little bit of Superman remaining in everyone's fantasy. "I may pass on someday, but, as my scan shows now, I don't have to think about it for a while. In the interval at least, I will be immortal."

Finally, a supplementary psychologic factor exists that propels some people to subscribe to CT screening as a health measure. The technique supports the notion that not only will we not die soon, we wish to stay young nearly forever. More persuasive than numbers on a chart is a picture of intact interior organs that many people might conclude is where the vital determinants of longevity reside. Thus, screening CT is a twenty-first-century version of a flattering photograph, a portrait to be treasured perhaps more than a picture of the face or the figure. Receiving such a beautiful portrait could be regarded as a gift purchased by the customer at a CT screening center. It is a reassuring gift because a negative examination provides a sense of solace that the aging process, although inevitable, is deferred for the time being. Of course, at the same time, the cellular derangements in vessels and the immune system may be inexorably progressing despite the notion of what "I cannot see, I do not have," which can be a comforting deception as the processes of decrepitude quietly roll on.

Lack of Scientific Verification

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 
The debate about screening CT lends itself to comparison with the current controversy concerning mammography. Radiologists are central to both contentious agendas. The emergence and growth of mammography as a screening examination occurred in conjunction with a series of population-based investigations that have been conducted since the mid 1960s. Even if the conclusions of these studies remain in question today, mammography developed under an umbrella of scientific inquiry in which data obtained during controlled studies led to conclusions about age of commencement and frequency of testing [10]. Screening CT of the abdomen is based not on an accumulation of data, but on the exploitation of fear and hope. No agreement exists as to the age of commencement or the proper interval between follow-up studies. Clinical trials are underway for calcium scoring CT, pulmonary nodule detection on CT, and CT colonography, but no comparable investigations have been instituted for abdominal screening [9]. For CT screening of the abdomen, considerations of the interplay among cost, risk, and benefit have been bypassed.

Thus, once screening CT is shown not to measure up to the hype—an eventuality that seems inevitable—the blame will rest on radiologists alone, unlike mammography for which the current controversy has not depicted radiologists as avaricious opportunists but rather as concerned providers who are trying to do right. Collectively, our specialty will bear the onus created by a few who profit from screening CT.

Indeed, one may make a healthy profit by operating a CT screening center [11], but all those hospitals and radiology groups that choose not to participate in the rapid growth of CT screening will be squeezed by the need to raise salaries to meet increasing demand resulting from labor scarcity accentuated by the displacement of an increasing number of radiologists from traditional practice venues to these centers [12]. Hence, the diffusion of CT screening is not an isolated phenomenon confined only to enthusiasts who encourage the anxieties of individuals who can afford to buy the test. For these reasons, the consequences of screening, which seeks to bring radiology directly to the consumer, should engage the attention of everyone involved in the provision of diagnostic imaging.

References

Top Introduction Limitations Detection of Cancer Renal Carcinoma Nonmalignant Conditions Popularity with the Public Lack of Scientific Verification References

 

1. Cancer facts and figures. Atlanta: American Cancer Society, 2002
2. Peterson MS, Baron RL, Marsh JW Jr, Oliver JH 3rd, Cunfer SR, Hunt LE. Pretransplantation surveillance for possible hepatocellular carcinoma in patients with cirrhosis: epidemiology and CT-based tumor detection rate in 430 cases with surgical pathologic correlation. Radiology 2000;217:743 -749[Abstract/Free Full Text]
3. Walsh PC, Retik AB, Stamey TA, Vaughan ED. Campbell's urology, 6th ed. Philadelphia: Saunders, 1992: 2283-2326
4. American Gastroenterological Association Web site. Available at: www.gastro.org/public/brochures/gallstones.html. Accessed June 10, 2002
5. Thompson RW. Detection and management of small aortic aneurysms. N Engl J Med 2002;346:1484 -1486[Free Full Text]
6. Cronenwett J, Murphy T, Zelenock G, et al. Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985;98:472 -483[Medline]
7. Lindholm L, Ejlertsson G, Forsberg L, Norgren L. Low prevalence of abdominal aortic aneurysm in hypertensive patients. Acta Med Scand 1985;218:305 -310[Medline]
8. American College of Radiology Web site. Available at: www.acr.org/publications Accessed November 1, 2002 (accessible only to ACR members)
9. United States Food and Drug Administration Web site. Screening studies. Available at: www.fda.gov. Accessed April 17, 2002
10. Zylak CJ. Clinical epidemiology and radiology: the need to bridge the gap—breast screening, a case study. Radiology 1992;184:607 -611[Free Full Text]
11. Davis RJ. Full-body scans: are they worth it? Wall Street Journal, Apr 30, 2002;personal journal section: 4
12. Bhargavan M, Sunshine JH, Schepps B. Too few radiologists? AJR 2002;178:1075 -1082[Abstract/Free Full Text]

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				T. W. Rooke Controversies in vascular screening art versus science Vascular Medicine, August 1, 2007; 12(3): 235 - 242. [Abstract] [PDF]

				C. D. Furtado, D. A. Aguirre, C. B. Sirlin, D. Dang, S. K. Stamato, P. Lee, F. Sani, M. A. Brown, D. L. Levin, and G. Casola Whole-Body CT Screening: Spectrum of Findings and Recommendations in 1192 Patients Radiology, November 1, 2005; 237(2): 385 - 394. [Abstract] [Full Text] [PDF]

				G. M. Kalish, M. Bhargavan, J. H. Sunshine, and H. P. Forman Self-referred Whole-Body Imaging: Where Are We Now? Radiology, November 1, 2004; 233(2): 353 - 358. [Abstract] [Full Text] [PDF]

				R Iannaccone, A Laghi, C Catalano, F Mangiapane, D Marin, and R Passariello Computed tomography colonography: colon examination or Pandora's box Gut, June 1, 2004; 53(6): 915 - 915. [Full Text]

				R. Levatter Screening CT and Modern Economics Am. J. Roentgenol., November 1, 2003; 181(5): 1191 - 1193. [Full Text] [PDF]

				S. R. Baker Screening CT and Modern Economics Am. J. Roentgenol., November 1, 2003; 181(5): 1195 - 1196. [Full Text] [PDF]

				J. T. Ferrucci Virtual Colonoscopy for Colon Cancer Screening: Further Reflections on Polyps and Politics Am. J. Roentgenol., September 1, 2003; 181(3): 795 - 797. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Baker, S. R. Search for Related Content PubMed PubMed Citation Articles by Baker, S. R. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?