Clinical Utility of CAT Body Scans

Christopher Baker, MD, San Francisco, California

Lawrence W. Way, MD, San Francisco, California

Computerized axial tomography (CAT) has revolu- t ionized diagnostic neuroradiology. Evidence has accumulated that widespread use of CAT has de- creased the performance of cerebral angiography and pneumoencephalography, and has thereby decreased hospital admissions for diagnostic evaluation. It appears to most observers that CAT scanning of the head is highly cost-effective [I].

Application of CAT scanning to the rest of the 19ody had to await technologic improvements that would decrease the time needed to perform the ex- amination, and thereby decrease motion artifacts from respiration [2]. Many physicians anticipated that CAT body scans would produce results as dra- matic as those in neuroradiology, and announce- ments to that effect soon were forthcoming as the initial experience was accumulated. Many abdominal lesions that previously had been difficult to delineate could be outlined on CAT body scans, and numerous articles appeared detailing the CAT appearances of lesions of the pancreas, retroperitoneum, kidney, liver, pelvis, lung, and mediastinum [3-I I].

What has not yet been shown, however, is the clinical utility of the information provided by CAT l9ody scans. Our experience with CAT scans in the I9ast two and a half years has been promising and enlightening, but hardly as dramatic as the prelimi- nary reports would lead one to expect. Consequently, we attempted to assess systematically our experience with the overall accuracy and utility of CAT scans of the body.

Material and Methods

The case histories of 202 randomly selected patients hospitalized at the University of California and Veterans Administration Hospitals, San Francisco, who had one or more CAT body scans between January 1976 and No- rrember 1977 were analyzed. The scans were performed on sn EMT CT 5000 model with a 22 second scanning time per

From the Department of Surgery, Veterans Administratlon Hospital and University of California, San Francisco, California. This work was supported ir part by the Medical Research Service of the Veterans Administration.

Reprint requests should be addressed to Lawrence W. Way, M), Swgical Service (112). Veterans Administration Hospital, 4150 Clement Street, San F,xncisco, California 94121.

Presented at the Forty-Ninth Annual Meeting of the Pacific Coast Surgical Association, Newport Beach, California, February 19-22, 1978.

slice. Scans were ordinarily obtained at 1 to 1.5 cm intervals and had a thickness of 1.3 cm. Oral or intravenous contrast agents were used in selected cases at the discretion of the radiologist. It was the policy of the Radiology Department to screen requests for CAT scans to eliminate examinations that were unlikely to be useful. The body scanner had been operational for more than one year before the first of the patients included in the present report were studied.

Our study was restricted to hospitalized patients. Details of the clinical findings, provisional diagnoses, diagnostic and therapeutic plans, and the results of relevant diag- nostic tests were extracted from the charts and recorded. Accuracy of the CAT examinations was determined by comparing the results of the CAT reports with those of other tests, with the findings at laparatomy or autopsy, and with the patient’s clinical course.

Utility was measured in terms of how the results of the CAT examination, exclusive of other tests (1) improved the accuracy of the diagnosis, (2) obviated (actually or theo- retically) the need for more complex diagnostic procedures such as angiography or exploratory laparotomy, (3) altered treatment, (4) affected the outcome of the disease, and (5) affected the monetary cost of the workup.

An arbitrary scale of efficacy was devised, and each of us rated each CAT scan on its overall impact on the pa- tient’s illness. If the results of the scan were incorrect and seemed tD have a negative effect on the patient’s manage- ment, the extent of the negative effect was recorded on a similar scale. If a plan of management had been agreed upon before the CAT scan was performed, we gauged the impact of the scan to be small if it failed to change the plan, even if the scan provided details that were previously un- available. CAT scans obtained to follow patients receiving radiotherapy or chemotherapy were accepted as useful on the basis of the opinions of those working in this field [12,14] even though an effect on the outcome of treatment has not been shown.

The following statements explain in greater detail our rating policy. A positive rating of minimal value (score, 7-9) was assigned when the scan was correct but accomplished no more than confirmation of a diagnosis that was already obvious fro? clinical findings and less complex laboratory tests. The value was considered to be moderate (score, p6) when the scan clearly showed a strongly suspected but heretofore unproved lesion, such as an adrenal pheochro- mocytoma. A high rating (score, l-3) was assigned when the examination demonstrated a lesion that was unde- tectable by other means or whose discovery led to treat- ment that significantly affected the outcome of a serious disease. The discovery on CAT scan of a retroperitoneal

Volume 136, July 1978 37

Baker and Way

abscess in one patient was scored 1, since it appeared to have possibly saved the patient’s life.

Conversely, negative effects were considered to be of little consequence (score, 11-12) when a false-negative or false-positive CAT scan had no appreciable adverse impact on patient management because other findings prevented the physician from being misled. A negative impact of in- termediate severity (score, 13-15) was considered to have occurred if the CAT scan gave incorrect information that led to the performance of other expensive or complex tests, led to inappropriate treatment, or extended the hospital stay appreciably (that is, for a week or more). Unnecessary laparotomies were given a score of 16-1’7, the absolute rating depending on the magnitude of the procedure and the occurrence of complications. The worst category (score, 18) was to be assigned if the results of a CAT scan led to the patient’s death, a circumstance that did not happen. If the scan was of no value, a score of 10 was assigned.

Although it required subjective (value) judgments about the usefulness of the CAT scan, the rating system was easy to use and the correlation between the independent as- sessments was close (mean difference, 0.4 points). Of the 202 scans, a difference in rating of more than two points occurred in only five cases. When these five cases were re- viewed, it was evident that in each case one of the raters had misconstrued the clinical problem, and the rating was corrected.

We recognize that others might weigh the absolute values of the individual scans somewhat differently, but the distinction between a positive and a negative effect (which reflected accuracy) and whether there was a major or minor impact on the patient’s care seemed obvious in almost every case.

The ages of the patients ranged from three to eighty- three years; 70 per cent of the patients were more than forty years old. There were 114 men (56 per cent) and 88 women (44 per cent). The racial distribution was as follows: Cau- casian 88 per cent; black 6 per cent; and oriental 5 per cent.

TABLE I Indications for CAT Body Scan

System

Biliary (duct dilatation) Liver (mass) Pancreas

R/O cancer Pseudocyst

Retroperitoneum Tumor or lymph nodes Abscess Adrenals Other

Kidney (mass) Pelvis (mass) Abdomen (screening) Miscellaneous

Chest Other

No. of Patients

17 (8%) 20 (10%) 26 (13%) 20 (10%) 6 (3%)

45 (22%) 34 (17%)

5 (2%) 2(1%) 4 (2%) 9 (5%)

16 (8%) 32 (16%) 37 (18%) 24 (12%) 13 (6%)

Total 202 (100%)

Results

The indications for obtaining the CAT scans are

listed in Table I. The frequency of CAT scans per-

formed to examine the liver, retroperitoneum, and miscellaneous areas increased, and the frequency of CAT scans of the pancreas decreased over the

twenty-two months of the study. The miscellaneous

category comprised scans of the thorax, extremities, and vertebral column for the most part.

The reason for ordering the CAT scan was usually

obvious from reading the chart. In 30 per cent of cases there was no explicit statement in the chart de-

scribing the clinical assessment of the problem at the time the CAT scan was ordered. In many instances the clinicians seemed to have no clear expectation

that the CAT scan could affect management. The most common example occurred when a patient with

disseminated cancer was admitted to the hospital in a terminal state. CAT scans were often ordered along

with a battery of other tests apparently on the as- sumption that maximal information about the extent

of disease was needed. Rarely did the results of the CAT scan affect the management of these patients

who often succumbed from their disease within a few weeks of entering the hospital.

It is also of interest that in 41 per cent of cases the

CAT scan was ordered before less expensive tests which might have given the relevant diagnostic in-

formation. The test most often bypassed was the ultrasound scan. Many times ultrasound and CAT scans were ordered simultaneously rather than se-

quentially. Tables II and III demonstrate the diagnostic ac-

curacy of the CAT and ultrasound scans in these patients. .The sensitivity of a test is defined as the ratio of true-positive results to all patients with dis-

ease (true-positive plus false-negative) in the popu- lation under study [IS]. Specificity is defined as the ratio of true-negative results of the test to all dis-

ease-free patients (true-negative plus false-positive). ACCLLFUCY of a test is defined as the ratio of all correct results (true-positive plus true-negative) to all pa- tients being studied.

The sensitivity of the CAT body scans was 80 per

cent, the specificity was 70 per cent, and the accuracy was 77 per cent, similar to the rates in other reports [2,4,7,8,16]. The incidence of false-positive results was 10 per cent, and the incidence of false-negative results was 13 per cent. The relatively high sensitivity indicates that CAT scans have a high likelihood of demonstrating a lesion when one is present.

The specificity of the CAT scans between the various organ systems differed more than the sensi-

38 The American Journal of SurWV

Utility of CAT

tivity, perhaps partly because there were relatively

few t,rue-negative studies in each category. We con- sider it desirable to minimize the number of dis- ease-free people examined when a test is as expensive

as, CAT scanning and our success in this regard may reflect the screening of requests by radiologists. Nevertheless, the overall specificity of 70 per cent

suggests t,hat there may have been a tendency to try tcl read more into the CAT scans than was actually present with a resulting increase in false-positive

reports. One hundred nine (54 per cent) of the 202 patients

studied by CAT scanning also underwent ultrasound

scanning of the same area. As shown in Table III the sensitivity (84 per cent), specificity (86 per cent), accuracy (84 per cent), and the false-positive (6 per

cent) and false-negative (10 per cent) rates for ul- trasound were as good, or better than, for CAT. Many of’ the patients not examined by ultrasound were

included in the miscellaneous category of CAT scans, which covered areas in which ultrasound is not often

useful (for example, lung and extremities). Excluding this category, ultrasound was used in 67 per cent of the situations also studied by CAT.

Comparing the incorrect results by either CAT or u’ trasound, or both (Table IV), ultrasound was cor-

TABLE II Accuracy of CAT Body Scan

No. of Sensitivity Specificity

rect in eight (47 per cent) of the forty-six cases in

which CAT was incorrect. However, in only half of

these forty-six cases was an ultrasound study per- formed. Note that in only nine cases (8 per cent) in which both tests were ordered were they both

wrong. In addition to accuracy, the usefulness of the CAT

scan depends on how it affects patient management and the outcome of the disease. Figure 1 and Table

V list the distribution of the utility ratings of all 202 CAT scans. In 169 (84 per cent) the test was judged

to have either very little value (that is, verified a di-

agnosis (obvious from other tests), no value, or a negative value. In sixty-seven patients (33 per cent) the CAT scan provided diagnostic information not

available from other examinations. In thirty-three

cases (16 per cent) the results of the CAT scan were

used in the clinical management. Even here, however, efficacy was somewhat uncertain since this group included sixteen patients in whom the results of the

CAT sca.n were being used to plan radiotherapy or chemotherapy, and no proof has been presented that planning treatment in this way actually improves

results. The results of the CAT scan definitely im-

proved slhort-term outcome of the disease in only two patients (1 per cent).

System Patients TP TN FP FN (%) (%)

Biiiary 17 8 5 Lilfer 20 11 3 Pancreas 26 11 11 Retroperitoneum 45 22 15 Kidney 9 4 3 Pelvis 17 9 3 Abdomen 31 11 9 Miscellaneous 37 27 4

73 83 78 50 85 85 88 75

100 60 82 50 58 75 87 67

Total 202 (100%) 103 (51%) 53 (26%) 21 (10%) 25 (13%) 80 70

Note: TP = true-positive; TN = true-negative; FP = false-positive; FN = false-negative.

TABLE III Accuracy of Sonography -

Per Cent No. of Total Sensitivity Specificity

Svstem Patients Patients l TP TN FP FN I%) (%)

Biliary 16 94 9 4 3 1 90 57 Liver 12 60 8 3 0 1 89 100 Pancreas 20 77 10 8 0 2 83 100 Retroperitoneum 24 53 12 8 1 3 80 89 Kidney 8 89 4 3 1 0 100 75 Pelvis 6 35 4 0 1 0 100 N/A Abdomen 16 52 3 9 0 4 43 100 Miscellaneous 7 19 6 1 0 0 100 100 Total 109 (100%) 54 56(51%) 36 (33%) 6 (6%) ll(lO%) 84 86

Note: TP = true-positive; TN = true-negative: FP = false-positive; FN = false-negative. l See Table II, column 2 for total number of patients.

Volume 136, July 1978 39

Baker and Way

TABLE IV Comparison of Incorrect CAT Scans and Sonograms

Sonogram Not

CAT Scan TP TN FP FN Bone Total

TP - - - 6 - 6 TN - - 2 - - 2 FP 4 5 4 - 12 25 FN 5 - - 5 11 21

Total 9 5 6 11 23

Note: TP = true-positive; TN = true-negative; FP = false-positive; FN = false negative.

Forty-three per cent of the studies were judged to be superfluous because simpler tests had already fully elucidated the problem. These were CAT scans ordered because an interest was expressed in com- paring its results with ultrasound, or when test or- dering had been “shotgun” instead of selective.

In twelve patients (6 per cent) the results of CAT scanning had a truly negative effect on management, and in three of these cases (1.4 per cent) the patient’s health was seriously threatened in the process. Six of these involved unnecessary operations occasioned by false-positive findings on the CAT scan. There were six other cases in which the results were false- negative when the CAT scan would have been ex- pected to find a lesion if one existed, and an impor- tant delay occurred in reaching the correct diagnosis. Other methods, including laparotomy, were required in these cases to determine the nature of the problem. Examples of several of these situations are given in the following section.

bO-

I I I I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 lb 17 18

EFFICACY RATINGS

-l

Flgure 1. Distribution of effkacy rat/n@? for CAT body scans in 202 individual patients. A rating of 10 Indicated a neutral effect of the scan on patlent care. A rating of 1 was used to indicate the greatest positive effect and a ratbtg of 18 the greatest negative effect.

40

The costs of the diagnostic workup (exclusive of blood and urine tests) are shown in Table VI. The average expense for special diagnostic studies (x-ray films, CAT and ultrasound scans, and nulcear med- icine scans) was $770 per patient. We were not able from the information available to determine if CAT scans eliminated the performance of arteriography or other expensive and invasive tests. Our impression was that, unlike diagnostic neuroradiology, few sav- ings can be expected in this area from the use of CAT body scans. It should be noted, however, that the present study excluded outpatients, and it is possible that the performance of CAT body scans on outpa- tients has decreased hospital admissions for diag- nosis. Savings in this category would have been missed by our analysis. Of the total costs for special diagnostic tests listed, the CAT scan contributed 42

per cent. The cost-effectiveness calculations were performed

according to the usual methods with modifications to fit the rating system. Table VII gives the cost- effectiveness values for the CAT scans according to organ system. The differences between the categories are insignificant and the average result suggests that, in general, the value of the scans to medical care in relation to the costs of the scans was low.

The total cost of special diagnostic tests was cal- culated as the sum of the cost of CAT scans, plus other special diagnostic tests, plus the extra hospital days devoted to the performance of the examinations. If an unnecessary operation resulted from a false- positive CAT scan, its costs were also included. The denominator of the cost-effectiveness ratio was the clinical value rating from our arbitrary scale. The cost-effectiveness ratios for the CAT and ultrasound scans were calculated separately. According to this system, the lower the cost-effectiveness ratio, the more efficient is the test.

The results (Table VII) show that the cost-effec- tiveness ratios for ultrasound scans are substantially lower than for CAT scans (p <O.Ol, Wilcoxen signed

TABLE V Distribution of Efficacy Ratings

Rating No. of Patients

Saved life 1(0.5%) Quite valuable 4 (2%) Moderate value 28 (14%) Minimal value 118(58%) No value 39 (19%) Obscured diagnosis 9 (4%) Seriously threatened 13 (2%)

patient’s health Led to patient’s death 0 Total 202

The American Journal of Surgery

Utility of ( 4T

rank test ). The reason is that although the two tests

were of about equal clinical value in any given sit- uation, an ultrasound scan costs only one-fourth as much as a CAT scan. There were no significant dif- ferences in cost-effectiveness ratios between CAT

scans performed for the different organ systems ( Kruskal-Wallis test).

Case Reports

The following case reports are presented as represen- t;itive of the most striking positive and negative effects of the CAT scans in our series, and they provide illustrations

of how we rated the impact of the results.

Case I. True-Positioe. A sixty-one year old white man

~+as transferred to the University of California, San Fran- CISCO with a diagnosis of superior mesenteric artery aneu-

rysm. At operation the patient was found to have cho- lcdocholithiasis, hemorrhagic pancreatitis, and a pancreatic pseudocyst which had eroded into the superior mesenteric artery creating a false aneurysm. The aneurysm was re- paired, cholecystectomy was performed, and the area of the pancreas was drained. The patient’s postoperative course

nas extremely stormy with several episodes of hypovolemic aznd septic shock which were nearly fatal. A CAT body scan demonstrated a right psoas abscess which was drained. From that point the patient improved rapidly, and within

three weeks he was discharged from the hospital in excel- lent condition. (Rating, 1.)

TABLE VI Cost of Tests

Test -

CAT scan $325 202 (100%) $65,650 KUB film 37 97 (48%) 3,589 Sonogram 78 109 (54%) 8,502 OCG 60 25 (12%) 1,500 IVC 125 11(5%) 1,760 UGI series 79 83(41%) 6,557 IVP 81 84 (42%) 6,804 BE 76 66 (33%) 5,016 Arteriogram 350 31(15%) 10,850 Liver-spleen scan 135 92 (46%) 12,420 Bone scan 175 60 (30%) 10,500 Gallium scan 245 29 (14%) 7.105 Lymphangiogram 450 22(11%) 9,900 ERCP 650 7 (4%) 4,550 THC 166 4 (2%) 664 Renal scan 150 3 (2%) 450

cost No. of

Patients Total cost

Note: Eighty-two patients (41 per cent) had CAT scans obtained before one or more less expensive diagnostic tests which were appropriate. The subtotal costs of all the tests except the CAT body scan was $90,167, compared with $65,650 for the CAT body scan alone.

KUB = kidney, ureter, and bladder; OCG = oral cholecystogram; WC = intravenous cholangiogram; UGI = upper gastrointestinal series; IVP = intravenous pyelogram; BE = barium enema; ERCP = endoscopic retrograde cholangiopancreatogram; THC = trans- hepatic cholangiogram.

Case 111. Ehlscl-l)osititlc~ A sixth--six year old C’hinese man

who had previously undergone partial gastrectomy was

noted to have a left renal mass on intravenous pyelography. Although sonography showed a cystic mass, the CAT scan indicated that the mass was solid. Arteriography was per- formed, but the solid and cystic masses could not be dis-

tinguished. At exploratory laparotomy a simple thin-walled cyst was found which contained clear fluid. Postoperatively

the patie.nt developed stress ulcers which bled. and he re- quired transfusion of 3 units of blood. (Rating. 16.)

Case III. Fais+Xegn!icr>. 4 seventy f;,ur hear old white

man with partial urinary and large &)we! obstruction

caused by a sigmoid adenocarcinoma was found to have metastases to the pelvis and left testicle. He was treated with 6,lO~O r to the pelvis plus chemotherapy. One month later he presented with increasingly severe large bowel obstruction. and a CAT scan was done to assess metastatic

intraabdominal disease. The szan was read as showing no retroperii.oneal or mesenteric tumor and a normal liver. At operation a large pelvic tumor mass was found with wide-

spread metastatic disease in the retroperltoneal and mes- enteric lymph nodes. The patient expired one month later. Had the CAT scan demonstrated the obviously advanced

disease, surgery would not have been performed. (Rating, 16.1

Case IV. False-Negatiue. An eighty-one year old white

man presented with right lower quadrant pain. A barium enema showed polyps and diverticula. I!ltrasound and

CAT scans showed no right, lower quadrant mass or ab- scess. A right lower quadrant abscess was suspected from

clinical signs, and a gallium scan was positive. Operation was performed which revealed a perforated cecal carcinoma which was resected. After resection the patient recovered. The false-negative CAT scan delayed operation for five days. (Rating, 15.)

Case V. True-Negative. A fifty-five year old black male

with sarcoidosis was noted to have medial deviation of the ureters on intravenous pyelography, and the question of

a pelvic mass was raised. Computerized tomography re- vealed pelvic lipomatosis and conceivably saved the patient from unnecessary laparot.omy. (Rating, ti.i

TABLE VII Cost-Effectiveness Ratios

Svstern

Cost-Effectiveness Ratio CAT Sonog- Efficacy

Total CAT raohv Rating

Biliary 151.33 107.9 36.4 8.4 Liver 155.3 95.4 34.7 8.8 Pancreas 187.36 132.0 35.9 8.53 Retroperitoneum 220.01 142.65 37.9 8.07 Kidney 145.2 97.79 36.7 8.33 Pelvis 122.46 97.33 34.6 8 82 Abdomen 190.96 120.79 35.5 ( il Miscellaneous 153.16 112.22 38.0 b 15 Total 175.37 118.94 36.5 8.39

Volume 138, July 1978 41

Baker and Way

Comments

With the marked proliferation of CAT scanners in the United States [I 71 and the pressure to use this test, it is crucial for clinicians to define the proper indications for CAT scans of the body, especially in light of its significant costs. CAT scans have been shown to be capable of giving a wealth of diagnostic information about problems involving the liver [7,18], biliary tract [19,20], kidney [II], pancreas [8,21], retroperitoneum [10,22], and pelvis [9]. In addition, CAT is now being extended to aid in the staging of lymphoma [23], to examine breast, lung, and medi- astinal lesions [4,5,23,24], to guide percutaneous bi- opsy instruments [25], and to plan and gauge the effects of radiotherapy [12-141.

The technology of CAT scans is evolving rapidly. The studies analyzed in the present report were performed on a machine with a 22 second scanning time per slice, but faster machines are becoming available and will probably give superior detail. In addition, radiologists are still in the process of be- coming familiar with the capabilities of CAT scan- ning machines; when erroneous results are discov- ered, diagnostic criteria are reexamined and appro- priately revised. Clinicians are also in the early stages of learning what CAT scans can contribute to patient care. It seems certain, therefore, that this assessment of the utility of CAT body scans performed over the past two years will require revision in the near fu- ture.

Nevertheless, evaluation of the efficacy of CAT body scans is not premature, especially since so much useful information had been expected from them. Despite the many potential uses of CAT body scans, most reports on indications for this test have come from radiologists and, if they discuss efficacy at all, they deal almost exclusively with accuracy. Abrams and McNeil [26] noted that estimates of efficacy should also consider the impact of CAT scans on the therapeutic plan, health outcomes, and financial costs, questions which have so far been addressed by very few studies [27,28].

Our data verify that CAT scans are technically impressive, that the studies are acceptably accurate, and that they often provide anatomic detail which would otherwise be unavailable. Clinicians, however, are primarily concerned with the clinical efficacy of this test [26]. In our experience, CAT scans were of great help in a few cases and were very misleading in others, with the majority having a marginal impact, either positive or negative. In this last group, con- sisting of 78 per cent of all the scans, patient man- agement would not have been appreciably changed if the CAT scan had not been performed.

Frankly, it seems illusory to assign a positive value to test results that alter treatment but cannot be shown to improve outcome, and of these 202 CAT body scans, only two (1 per cent) appeared unequi- vocally to benefit the patient. The reason is that in most conditions in which CAT body scans are infor- mative, insufficient morphologic information is not a major limiting factor in the success of therapy. Spratt [29] has noted that in many areas medical practice has reached a point of diminishing returns for increased dollar input, and CAT body scans may be an example of this phenomenon. The results of this retrospective study are hardly conclusive, but they do underscore the need for scientific evidence that CAT body scans are worth the enormous ex- penses that will follow their widespread use.

Another fact that has received insufficient atten- tion is the extent to which ultrasound scans have become diagnostically useful in many of the areas in which CAT scans are thought to perform best [18,21,30,31]. For example, ultrasound scans now seem superior to CAT scans for the appraisal of bil- iary disease (that is, when looking for gallstones or dilatation of the bile ducts) or for diagnosing mass lesions of the liver [18,30,32]. Our data support these findings and suggest that for most abdominal dis- eases ultrasound scans should precede CAT scans, and the latter should be ordered only if the results of ultrasound are equivocal or technically inadequate [32]. Furthermore, hospitals should probably con- centrate on developing ultrasound capabilities before they purchase the more expensive, less cost-effective, and rapidly evolving CAT body scan equipment.

Thus, CAT body scans should only be ordered if (1) more information would truly affect management, (2) more cost-effective tests have failed, and (3) the likelihood of disease is high. Screening for uncommon problems with an expensive test can be exorbitant [ 33-361.

Certainly, CAT technology is unique and fasci- nating. Despite their potential, however, CAT body scans do not appear to have resulted in a substantial improvement in the care of patients. Perhaps this will come with time, but it seems appropriate to temper the enthusiasm and to proceed with prospective studies of efficacy.

Summary

The results of 202 computerized axial tomography (CAT) body scans performed on hospitalized pa- tients were analyzed for their accuracy and clinical utility. The sensitivity (80 per cent), specificity (70 per cent), and accuracy (77 per cent) were high but not superior to ultrasound examinations of the same

42 The American Journal of Surgery

Utility of CAT

area. The results of the CAT body scan affected pa-

tient management in 16 per cent of patients and af-

fected the success of treatment in 1 per cent of pa- tients. We conclude that for many abdominal con-

ditions ultrasound scans are equally as accurate and substantially more cost-effective than CAT body scans, and that the clinical value of CAT body scans

needs support from controlled clinical trials.

Acknowledgments: We wish to thank Mrs. Doro- th:y Archbold and Mrs. Judy Barbee for their expert help in preparation of the manuscript.

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Discussion

Ronald K. Tompkins (Los Angeles, CA): Drs. Baker and Way are to be congratulated for their diligent efforts to estimate the clinical utility of CAT scans of the abdo- men. This new diagnostic tool has met with enthusiastic endorsement by physicians and has been endowed with an aura of infallibility by patients. The authors’ report helps to put the use of the CAT scan in patients with abdominal disease in better perspective.

We shou.ld remind ourselves that retrospective studies such as this one do have certain important limitations, many of which have been pointed out. First, the technology has been developing at a rapid rate during the less than three years since the extension of the scanner to abdominal examination, and the quality of the examinations as well as the expertise of the interpreters has been improving. Second, in this study access to the test was controlled al-

Volume 136, July 1978 43

Baker and Way

most completely by the radiologist, and hence the popu- lation was highly selected. In some instances, unwarranted tests were excluded but in many others the test was ordered “for interest” to compare with a positive ultrasound or radionuclide scan, so that the new information offered by the CAT scan was nil. The findings that CAT scanning provided diagnostic information not available from other tests in only one third of patients would have been different if these “duplicate tests” had been excluded from the study. Similarly, the observation that CAT scanning im- proved short-term outcome in only 1 per cent of the cases might have been altered by eliminating indications “of interest” from the study population. We agree with the authors that less expensive tests, such as ultrasound, should be utilized in most instances prior to CAT scanning of the abdomen. Abrams and McNeil ]26] have just pub- lished an extensive review of the subject of CAT scanning and have concluded that at present there is no evidence that CAT scanning has demonstrated significant short- term or long-term health benefits over other test modalities used in patients with abdominal disease.

What is required is a prospective, controlled study of the efficacy of the CAT scan, compared to that of less expen- sive tests, in the diagnosis of abdominal problems. The Blue Shield of California Medical Policy Committee stated recently that “physicians in their enthusiasm to perfect the depth and accuracy of their diagnosis must re-evaluate the relationship of advancing technical ability in regard to the final outcome of the disease in question . . . and apply medical and moral judgment to [their] decisions with re- spect to each patient.” CAT scans are here to stay. My hope is that the authors and others will now design and carry out the prospective studies needed to provide us with the proper indications for use of this fascinating new tool in the near future.

Edward Passaro, Jr (Los Angeles, CA): I would like to report a personal experience in which extension of the use of the CAT scan was attempted. We have patients who have undergone total gastrectomy for malignant gastri- noma. At operation we noted that tumor was present in and around the pancreas in some of these patients. When the CAT scan became available to us, we attempted to use it

to see whether there was progression of the tumor. We abandoned the study after eight patients simply because tumors, which we knew were present as a result of the op- eration, could not be detected.

Lawrence W. Way (closing): At the time we initiated our retrospective review, we also polled 1’75 surgeons throughout the United States and Canada as to their ex- perience with CAT scans. Replies were received from 150 surgeons, 100 of whom had been using CAT scans for varying lengths of time. In general, there appeared to be an inverse correlation between the enthusiasm of the re- spondents for CAT scans and the length of time CAT had been available for use in that institution. Most people have been disappointed with the ability of CAT scans to find tumors in the pancreas. There is tempered optimism for their value in other retroperitoneal lesions, including tu- mors of the adrenal gland.

The point of our analysis is not to discourage the use of CAT scans in medical diagnosis, but to emphasize that scans should be ordered selectively, that the technic at present has marked limitations in improving care, and that discussions about how many scanners are needed are ap- propriate in view of their utility and costs.

In response to Dr. Tompkins, our utility ratings inevi- tably reflected the accuracy of the scans plus the indica- tions for ordering them. As Dr. Tompkins remarked, the utility scores would increase if tests that could be predicted to be of little value were not ordered. This goal would be partly achieved if ultrasound scans were ordered before CAT scans and if CAT scans were ordered for specific questions whose answers would be of importance in de- ciding therapy. Nevertheless, there were still very few pa- tients in this study in whom the CAT scan had a substan- tial effect on outcome.

The difficulty with the CAT scanner is that it provides morphologic information on abdominal diseases when morphologic information is not often the factor limiting the success of care. CAT scans might truly have improved care if they had been able to detect abdominal tumors at an earlier stage so surgical cures would increase. Even the brief experience to date shows that this has not been pas-

sible.

44 The American Journal of Surgery