Computed Tomography in the Evaluation of Lung Cancer

Correlative Anatomy, Pathology

and Imaging

Chairman:Joseph Aisner; M.D.

Computed Tomography In the Evaluation

of Lung cancer

Stuart S. Sagel, M.D., Wahington University Medical Center, St. Louis

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mputed tomography (CO can substantialIy influence the diagnostic evaluation and therapeutic plan in many patients with known or suspected bronchogenic carcinoma. Because cr provides a detailed view of the segmental and subsegmental bronchi in cases where the suspected neoplasm in relatively small, precise depiction of the location of an endobronchial mass may be a helpful adjunct in directing the bronchoscopist to the appropriate biopsy site. When sputum analysis and fiberoptic bronchoscopy both yield negative results in a patient with a pulmonary mass, the findings on the cr examination can be valuable in directing further diagnostic evaluation. The next appropriate test may be suggested, be it a transcervical mediastinoscopy, anterior parasternal mediastinotomy, percutaneous needle biopsy, or conventional thoracotomy. Computed tomography has a very high accuracy in predicting the likelihood of curative surgical resection in the majority of patients with bronchogenic carcinoma. At most, 40% of patients with newly diagnosed bronchogenic carcinoma are amenable to surgical resection with curative intent. Surgery should be restricted for complete tumor resection; incomplete resection in patients with stage III disease should be avoided. Staging by CT is clearly superior to conventional radiologic techniques for the demonstration of direct extension of the primary neoplasm into the mediastinum or chest wall and the detection of enlarged mediastinal lymph nodes. However, a staging cr examination need not be performed in all patients with bronchogenic carcinoma. Those with clinically evident metastatic disease or unequivocal mediastinal lymphadenopathy on the plain chest radiograph precluding resection usually do not require a study. The exceptions would be to pinpoint the exact location if necessary for biopsy planning or for radiation therapy planning. Also, the patient with a newly discovered small, irregular peripheral pulmonary nodule and a normal appearing mediastinum on plain chest radiographs is unlikely to benefit from a cr examination. Contiguous extension of a primary bronchogenic carcinoma into the mediastinum, particularly when mediastinal vascular invasion has occurred, precludes successful surgical resection for cure. With conventional tomography, it is frequently difficult to determine whether a centrally situated pulmonary mass invades the mediastinum or merely lies in close proximity to it. Computed tomography can establish that the mediastinum is involved by direct extension when invasion of the mediastinal fat or around the mediastinal vessels is demonstrated. It should be emphasized that a neoplastic mass simply contacting the mediastinal pleura, with the lack of a well-defined fat plane between the lesion 318S

and the mediastinum, does not necessarily indicate mediastinal invasion. The tumor mass must infiltrate into (interdigitate with) the mediastinal fat or extend around the great vessels or major bronchi before extension can be confidently diagnosed. Scanning after a bolus injection of intravenous contrast media is often beneficial in confirming mediastinal vascular involvement. The presence of mediastinal lymph node metastases secondary to bronchogenic carcinoma, constituting Nt, stage III cancer; presages a very poor prognosis and usually indicates . incurable disease. In most medical centers it is a contraindication to surgery. Computed tomography can be very valuable in detecting mediastinal lymph node enlargement and can serve as a useful guide for selection of the optimal tissue sampling staging procedure (mediastinoscopy) before attempting curative resection of a bronchogenic carcinoma. Although the presence of ipsilateral hilar lymph node enlargement alters the stage and ultimate prognosis of the patient, it neither makes him unresectable nor accurately predicts the presence of mediastinal lymph node involvement. Therefore, rigorous efforts at hilar staging are usually not warranted. Enlarged lymph nodes around the innominate vessels, in the pretracheal and aortopulmonary region, and in the subcarinal area around the azygoesophageal recess can be more easily seen than with the standard roentgenographic techniques. The demonstration of enlarged mediastinal lymph nodes in the patient with bronchogenic carcinoma does not automatically imply metastatic disease. Computed tomography cannot absolutely distinguish lymph node enlargement due to in8ammatory disease from that due to neoplasm. Also, cr will fail to detect microscopic metastatic disease in normal size lymph nodes. Recognizing these limitations, our diagnostic criteria on cr scans are that mediastinal lymph nodes less than a centimeter in diameter are considered unlikely to harbor metastatic disease. Those nodes 1 to 2 em in diameter are considered indeterminate; such mild enlargement can be caused by either neoplasm or granulomatous disease. Mediastinal lymph nodes more than 2 cm in diameter in a patient with a known primary bronchogenic carcinoma almost certainly are due to neoplastic involvement. An ROC curve, which relates the true positive ratio (sensitivity) to the false positive ratio could be prepared for the cr assessment of mediastinal nodal involvement. 1£10 mm is used, sensitivity will be over 95%, but the false positive ratio will rise to 40%. Using 15 mm as an indication of nodal abnormality, sensitivity will fall to about 60%, although specificity becomes greater than 90%. Some patients thought to be resectable for cure have metastatic disease present outside the thorax. The adrenal is the most frequent site, followed by the liver: An adrenal mass is not synonymous with metastasis; many represent incidental adenomas. Most lesions exceeding 3 cm in diameter represent metastases. The detection of an enlarged mediastinal lymph node, or an enlarged adrenal gland, by cr alone generally should not constitute sufficient indication for inoperability. Histologic corroboration of neoplasm within the enlarged node or adrenal is strongly recommended in patients otherwise considered operative candidates. Based upon cr localization of abnormally enlarged lymph nodes, the appropriate biopsy procedure and access route can be determined. This may be IV VVortd Conference on Lung Cancer

accomplished by transcervical mediastinoscopy, anterior parasternal mediastinotomy, percutaneous needle biopsy, or transbronchoscopic needle aspiration biopsy. H cr indicates a stage I or II lesion, generally the surgeon can proceed directly to thoracotomy without the use of mediastinoscopy. While there willalways be a small percentage of false negative cr scans due to microscopic metastases within normal size lymph nodes, this may have no clinical significance. A favorable prognosis may be achieved in patients with limited intranodal disease, detected by routine biopsy of normal appearing mediastinal lymph nodes draining the tumor; when high dose postoperative mediastinal irradiation is administered. . REFERENCES Baron RL, Levitt RG, Sagel SS et al. Computed tomography in the preoperative evaluation of bronchogenic carcinoma. Radiol 1983; 145:727-32 Breyer RH, Karstaedt N, Mills SA, et al. Computed tomography for evaluation of mediastinal lymph nodes in lung cancer: correlation with surgical staging. Ann Thor Surg 1984; 38:215-20 Ekholin S, Albrechtsson U, Kugelberg 1 et al. Computed tomography in preoperative staging of bronchogenic carcinoma. J Comput Asst Tomog 1980; 4:763-65 Fating LJ, Pugatch RD, Iung-Legg Y, et al. Computed tomographic scanning of the mediastinum in the staging of bronchogenic carcinoma. Am Rev Respir Dis 1981; 124:690-95 Glazer GM, Orringer MB, Gross BR, et al. The mediastinum in non-small cell lung cancer: CT-surgical correlation. AJR 1984; 142:1101-05 Lewis JW, Madrazo BL, Gross SC, et al. The value of radiographic and computed tomography in the staging of lung carcinoma. Ann Thorac Surg 1982; 34:553-58 Libshitz HI. CT of mediastinal lymph node in lung cancer: Is there a "state of the art"? AJR 1983; 141:1081-84 Mathews MJ, Kanhouwa S, Peckren J, et al. Frequency of residual and metastatic tumor in patients undergoing curative surgical resection for lung cancer. Chem Rep 1973; 4:63-7 Modini C, Passariello R, Iascone C, et al. TNM staging in lung cancer: Role of computed tomography, J Thorac Cardiovasc Surg 1982; 84:569-74 Oliver 1W Jr, Bernardino ME, Miller JI, et al. Isolated adrenal masses in non small-cell bronchogenic carcinoma. Radiology 1984; 153:217-18

Prasad S, Pilepich M~ Perez CA. Contribution ofCT to quantitative radiation therapy planning. AJR 1981; 136:123-1.28 Sander MA, Perlberg JL, Madrazo BL, et al. Computed tomographic evaluation of the adrenal gland in the preoperative assessment of bronchogenic carcinoma. Radioll982; 145:733-36 Whitley NO, Fuks jz, McCrea ES, et al. Computed tomography of the chest in small cell lung cancer: potential new prognostic signs. AJR 1984; 142:885-92

Early Radiologic Detection of Lung

tal, Memorial Sloan-Kettering Cancer Center; and The Mayo Clinic) have all independently come to similar conclusions regarding the sensitivity and specificity of early lung cancer detection. The sensitivity of screening for lung cancer is relatively poor with almost 50% of the tumors that occurred in this study being initially undetected by radiographic screening. The small ill-defined lesions are frequently overlooked, often being hidden by overlying bone and mediastinal structures. The chest radiographs of older men frequently have other abnormalities which can distract the reader's attention from a small cancer in another portion of the radiograph. Sensitivity is improved by double reading, either by a second physician or by a specially trained technologist. Double reading also tends to increase the false positive rate; however; this increase can be held to a respectable level by the addition of a referee. The lateral view can be considered another form of double reading as the tumor may first be consciously or unconsciously recognized on the lateral view and then documented on the PAview. In addition, from the Johns Hopkins Hospital ann of the study, lung cancer was better seen or only seen on the lateral view in 7 and 2% respectively. There appear to be 2 types of lung cancer: (1) very rapidly growing, generally central tumors that arise between screenings and are extensive at the time of discovery and, (2) slowly growing tumors, generally peripheral, and frequently missed early in radiographic screening but when finally detected are still resectable. Once a pulmonary lesion is detected, differentiation between benign and malignant disease also becomes a problem. In all 3 centers, approximately half of the lesions initially coded as cancer by radiographic screening were subsequently found to be due to benign disease. The problem is 2fo1d. First, the radiographic appearance of early lung cancer is protean. Second, elderly patients and especially those who smoke, frequently develop benign pulmonary lesions that may mimic early or even advanced lung cancel: The relatively poor differentiation between benign and malignant disease is generally of secondary clinical importance as sputum cytology, cr densitometry, 6beroptic bronchoscopy, and percutaneous needle aspiration biopsy can often separate benign from malignant disease. Although the overall sensitivlty of radiographic detection in all the 3 centers was low, there was a significant portion of localized lesions that once detected were still resectable. A careful search of the PAand lateral chest radiographs in both male and female smokers is urged. REFERENCES Stitik F~ Tockman MS. Radiographic screening in the early detection of lung cancer. Bad Clin ofN Amer 1978; 3:347

Cancer

Stitik F~ Tockman MS, Khouri Nit: Chest radiography. In: Miller AB, ed. Screening for cancer. New York: Academic Press, 1985

Frederick P. Stitik, M.D., F.C.C.P., DePaul Hospital, Norfolk,

Fontana RS, Sanderson DR, 1kylor WK, et al. Early lung cancer detection: results of the initial (prevalence) radiologic and cytologic screening in the Mayo Clinic study. Am Rev Respir Dis 1984; 130:561

Virginia

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n the NIH-NCI Cooperative Early Lung Cancer Detection Group, radiologic techniques detected most of the lung cancers in this 5-year study of over 30,()()() smoking men. The 3 clinical centers involved (Johns Hopkins HospiI

Flehinger B], Melamed MR, Zaman MB, et al. Early lung cancer detection: results of the initial (prevalence) radiologic and cytologic screening in the Memorial Sloan-Kettering study. Am Rev Respir

Dis 1984; 130:555 CHEST I 89 I 4 I APRIL, 1986 I Supplement

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