Tumor Imaging in Diagnostic Radiology

DAVID G. BRAGG, MD'

Medical imaging benefited from major technological advances during the decade of the 1970s. These newly evolving procedures have been accused of significantly adding to health care expenditures and confusing clinicians in the selection of the appropriate examination. The purpose of this presentation is to place these new technologies in their current perspectives, emphasizing the advantages and limitations of each. To illustrate the appropriate imaging technique, decision trees will be developed for each major anatomic site.

In many instances, the complementary rather than competitive nature of these imaging studies will become apparent. Average national charges for these procedures will be shown to illustrate the impact of cost on these decisions. Each imaging decision must still be individualized to the patient and disease, as well as the institution's equipment and professional expertise.

Cancer 47:1159- 1163, 1981.

HE INTRODUCTION OF computerized axial tomo- T graphic (CT) scanning technology in the 1970s has had significant impact on the field of medical imaging. Less dramatic but equally important advances have modified ultrasonic imaging and interventional radiog- raphy. In parallel with these exciting advances, con- cerns have been expressed regarding the cost, efficacy, and application of these new techniques. The purpose of this paper is to place the conventional and newer diagnostic tumor imaging procedures in the perspective of both accuracy and cost. To accomplish these goals, each major anatomic site is reviewed separately, with decision trees presented to illustrate the imaging recommendations. Cost comparisons will be provided, using average charges and ranges derived from samples of various institutions in the United States.

In developing the imaging recommendations which follow, assumptions have been made that in each diag- nostic encounter, all imaging modalities are available with balanced interpretive expertise. Each decision tree includes considerations of cost and detection effi- ciency. Obviously, the behavior of certain neoplasms must alter or modify the imaging approach in some instances; however, the recommendations are intended to be appropriate for the majority of tumor patients.

Presented at the American Cancer Society National Conference on Cancer Prevention and Detection, Chicago, Illinois. April 17- 19, 1980.

* Professor and Chairman, Department of Radiology, University of Utah Medical Center, Salt Lake City, Utah.

Address for reprints: David G. Bragg, M.D., Department of Radiology, University of Utah Medical Center, Salt Lake City, UT 84132.

Accepted for publication June 1 1 , 1980.

New Technology -Impact and Cost

Few would argue that the most important diagnostic medial advance in the decade of the 1970s was CT scanning. In a broader sense, the marriage of computer technology with medical imaging has greatly expanded diagnostic abilities in recent years, a process that will continue well into the 1980s.

Much of this new imaging technology was made available before application recommendations could be developed. Rapid improvement in these new diagnostic instruments, lack of experience in their application, as well as operator inexperience, has further complicated attempts to compare and evaluate these procedures. Finally, a paucity of well controlled clinical trials, com- paring conventional and new diagnostic techniques, has made even more difficult the development of recommendations for the prioritization of medical imaging procedures of body site.

Cost concerns have paralleled the confusion relating to recommendations of procedure choice. CT units in operation across the country today number approxi- mately 1,200- 1,500. Purchase prices for these systems vary from $100,000 to $1,500,000. In spite of these large acquisition costs, during 1978 these capital expendi- tures amounted to less than 0.5% of the entire national health care budget .s Regardless of these proportionally smaller costs than most people realize, each imaging choice must be placed in the perspective of benefit, risk, and cost.

In the discussion that follows, each major site is re- viewed separately, with recommendations presented to most efficiently image mass lesions in each respective area. The question of nuclear imaging will be touched

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FIG. 1. Decision tree-brain imaging.

upon in a comparative setting only, since this subject is covered separately in another article. The conclusions reached are not intended to be used in a screening set- ting but rather in the initial staging of a tumor and in the subsequent follow-up of the patient for metastatic disease.

Brain Imaging

A contrast enhanced CT scan should be the first imaging procedure selected in a patient having any of the symptoms of a brain tumor. Since enhancement with iodinated contrast material is essential in tumor imaging in the central nervous system (CNS), both procedure time and cost can be spared by eliminating the non- contrast enhanced CT scan. Using this imaging ap- proach, no false negative cases were encountered in a review of 100 consecutive patients. The advantages of this approach are in decreasing CT machine time and procedural cost, therefore, potentially increasing machine capacity by some 25-30%.3

Figure I outlines the decision tree for brain tumor imaging. CT has been shown to have the greatest sensi- tivity and specificity in detecting mass lesions, with both acceptable costs and risk factors. Radionuclide brain scans should be seldom necessary, having been virtually replaced by CT for tumor imaging. Nonethe- less, in a patient suspected of having a mass lesion in the brain but with a negative enhanced CT scan, a role still exists for the radionuclide brain study. Cerebral

angiography is infrequently required in the detection of CNS mass lesions. The angiographer’s role now is largely reserved for the further characterization of the previously detected lesion prior to its treatment. An exciting new application of CT technology lies in the stereotaxic localization, biopsy and treatment of CNS tumors.‘

Thoracic Imaging

Recommendations for thoracic tumor imaging are more complex than with the brain and must be further subdivided by compartments as summarized in Figure 2.

CT is the recommended imaging method to evaluate tumor involvement in the mediastinum and chest wall. The improved diagnostic return which results is further enhanced by the potential for application of these CT images in radiation treatment planning and occasion- ally, tissue characterization. As yet, mediastinal CT imaging has not been shown to be sufficiently accurate in the detection of nodal extension with primary lung tumors to obviate mediastinoscopy or surgical exploration. l 3

The pulmonary hilum is still best imaged by film tomography, with the patient placed in the 55-degree oblique position. Mass lesions and enlarged lymph nodes contiguous with the hilum may be difficult or impossible to evaluate with CT.H

Initial entusiastic reports suggested that CT would be the obvious choice in detecting pulmonary neoplasms. Whereas it is true that CT enjoys the greatest sensitivity in nodule detection, the technique suffers from a lack of specificity in the differentiation of tumor from non- neoplastic lesions.” An imaging strategy must therefore be developed which is appropriate for the patient and the tumor in question. Patients at high risk for pulmo- nary metastatic disease should be examined by CT be- fore undergoing definitive major surgery directed at the primary tumor ( e . g . , osteosarcoma patients). Routine radiographic films and linear tomography can ade- quately serve the lung nodule screening needs of the non-high risk patient.

Preliminary results from Johns Hopkins suggest the ability of CT to discriminate primary lung cancers from other, non-neoplastic lesions based on their average CT attenuation numbers.” This new approach to pulmo- nary nodule characterization is equipment limited and will need further evaluation.

Mammography

The controversy regarding both the role of mammog- raphy in screening as well as that of radiation increasing the spontaneous rate of breast cancer occurence has received a great deal of recent attention. The reader is

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referred to the bibliography for information summar- izing this discussion as well as other articles in this issue.'

Low-dose film mammography and xeromammog- raphy share a similar diagnostic accuracy. Xero- mammographic films are easier to view and have a wider exposure latitude, making this method more appropriate to the high patient volume setting than film mammography.

The decision as to the composition of the mammo- graphic screening population is indeed a complex, con- troversial topic. In general, the symptomatic woman over age 35, or the individual with a strong family his- tory should be examined both by physical examination and mammography. Women over age 50 should be fol- lowed by both physical examination and mammog- raphy. The frequency of these studies must be individ- ually determined. It should be remembered that some 20% of palpable cancers will not be detectable by mammography. Therefore, a normal mammogram should never alter the clinical decision to biopsy a breast mass.'"

Although some enthusiasts might disagree, thermog- raphy of the breast has no role in cancer screening at present, suffering from an unacceptably high false- positive and false-negative detection rate.

The liver imaging decision tree (Fig. 3) suggests the radionuclide scan be the first imaging study selected in individuals suspected of having aliver mass lesion. This recommendation is based on the similar sensitivity of radionuclide scanning with other imaging modal i t ie~ . '~ , '~ Ultrasound, CT and occasionally hepatic angiography may be necessary to further characterize the defect or abnormality detected by liver scintigraphy.

In the patient with j&undice, the imaging workup must be modified. Either ultrasound or CT may demon- strate the dilated ducts found in patients with obstruc- tive jaundice; not infrequently, these studies will also outline the obstructing process. Percutaneous trans-

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Abdominal Imaging

Abdominal tumor imaging recommendations will be separately discussed for the major organ sites of the liver, pancreas, kidney, and retroperitoneal lymph nodes.

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FIG. 3. Decision tree-liver imaging

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hepatic cholangiography using the “skinny” (Chiba) needle has proven to be a valuable diagnostic approach to the patient with obstructive jaundice, both to further characterize the obstructing lesion as well as in bypass- ing this site if surgical resection is not

Imaging recommendations for suspected pancreatic mass lesions are summarized in Figure 4. Ultrasound and CT share a similar detection efficiency when the pancreas can be adequately visualized sonographically. The use of pancreatic angiography in the diagnosis of pancreatic cancer is very limited but still plays a role in functioning tumors as well as in the preoperative evalu- ation of the neoplasm. Endoscopic retrograde cholan-

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I ERCP $ 3 0 0 - 7 0 0 I giopancreatography-(ERCP) may have a complemen- tary diagnostic role in these patients if the diagnosis is uncertain by CT and/or ultrasound. ERCP may also be used to aid in mapping the distal ducts, not visualized in the jaundiced patient at the time of percutaneous cholangiography . l4

Figure 5 summarizes the diagnostic approach to the renal mass lesion. The intravenous urogram (IVP) still remains the logical first imaging procedure. Mass le- sions detected on the IVP then should be further char- acterized with ultrasound to determine whether they are cystic or solid. The decision to subsequently punc- ture the cyst and analyze its contents must be tempered by the patient’s age and clinical setting, but can be easily accomplished with the aid of sonographic monitoring. Vascular procedures seldom are required for diagnosis but may be indicated prior to surgery, serving the role of either an anatomic “road map” or in further .tumor evaluation. Patients with large or central hilar renal tumors should undergo preoperative cavography to exclude venous extension. Both ultra- sound and CT will provide similar information as to ex- tent of disease prior to ~ u r g e r y . ~ ’ ~ “

Lymph node imaging is a more complex challenge. The development of an imaging strategy for nodal assessment must include considerations of anatomy, tumor histology, patient status as well as the usual factors of cost, benefit, and risk.

An understanding of the common patterns of nodal involvement by the tumor in question should be the initial consideration. Cancers and Hodgkin’s lympho- mas usually cause small filling defects in involved nodes, often less than 1 cm in size. Ultrasound and CT seldom can resolve defects of this size and will therefore

No. 5 TUMOR IMAGING . Bragg 1163

suffer from an unacceptable false-negative detection rate in comparison to lymphography. In contrast, many non-Hodgkin’s lymphomas and testicular tumors are responsible for bulky nodal disease. In these settings, CY and ultrasound would be logical first imaging choices, with lymphography reserved for the question- able or problem case^.'^.'^

Often, multiple-node imaging techniques used in combination will improve the diagnostic yield of any single study. Hypogastric, retrocrural and mesenteric lymph nodes usually can be visualized only by CT, since pedal lymphography does not opacify these groups of lymphatics. Tumors with patterns of nodal extension predilecting these sites, such as testicular primaries, prostatic and occasionally cervical cancers, therefore usually profit from combined CT and lympho- graphic studies. Patients with non-Hodgkin’s lym- phoma have a tendency to exhibit mesenteric node in- volvement which is not imaged during pedal lymphog- raphy. CT obviously can serve as a complimentary imaging procedure to view this anatomic site of involvement.

Plain film evaluation of the abdomen after lymphog- raphy affords a simple, cost-effective way of following the response to treatment. CT and ultrasound can pro- vide similar data if one tailors or limits the imaging sec- tions in these follow-up examinations in the interest of both cost and radiation.

No single, simple lymph node imaging algorithm can be outlined at present for all tumors. Consideration must be given to the variables of tumor type, patient status, anatomic sites, cost, benefit, and risk in defining the choice of the imaging procedure(s) to be utilized.’l

Skeletal Imaging

Recent changes in therapeutic concepts with several primary bone tumors have placed different demands on diagnostic imaging techniques. Survivals with both Ewing’s and osteogenic sarcomas have dramatically improved with combined therapy, and now approach 70%. Local erzhloc resection rather than radical ampu- tation is more frequently being utilized surgically to extirpate primary bone neoplasms. The treatment plan therefore demands much more precise definition of tumor extent.6

CT provides information as to medullary and cortical tumor extension as well as soft tissue involvement which correlates well with tumor boundaries subse- quently evaluated histologically.G In the axial skeleton, CT is particularly valuable in tumor definition and is the imaging procedure of choice in the evaluation of pri- mary neoplasms arising centrally.

Angiography no longer plays a significant role in the diagnosis of primary tumors of the skeleton. Possible

exceptions to this statement may be the occasional requirements for preoperative “road map” angiog- raphy as well as the use of interventional catheter occlusive techniques in the paliation of the inoperable bone cancer patient.

Summary

The emergence of new imaging techniques, more complex and precise treatment regimens, and better understanding of tumor behavior have placed new de- mands on diagnostic oncologic radiologists. A tumor- imaging strategy must be developed which should be biased by a knowledge of the tumor histology and ana- tomic location, as well as the advantages and limitations of each diagnostic technique. This article reviewed these variables and developed diagnostic decision trees for the major body sites to serve as guidelines.

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