LUNG SCAN PATTERNS IN PULMONARY EMBOLISM VERSUS THOSE IN CONGESTIVE HEART FAILURE AND EMPHYSEMA

¹ Division of Nuclear Medicine, University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada.
² Director of Radiology Research Laboratory, Johns Hopkins Medical Institutions, Baltimore, Maryland.

A summary of the lung scan patterns in pulmonary embolism versus those in congestive heart failure and emphysema is given in Table v.

The following conclusions may be drawn:

1. Pulmonary emboli most frequently cause focal segmental or lobar defects. Ninety per cent of individual emboli resulted in this pattern.

2. Congestive heart failure usually presents as: (a) an irregular inhomogeneous perfusion pattern; (b) focal nonsegmental perfusion defects superimposed on the irregular pattern with the focal defects corresponding to the alveolar pattern on the concurrent chest roentgenogram; (c) a reversal of the normal perfusion ratio between upper and lower lobes; (d) cardiac enlargement; and (e) changes due to pleural effusion.

3. The most common pattern in emphysema is an irregular inhomogeneous distribution of perfusion. Focal, nonsegmental defects are the next most common pattern. In contrast to pulmonary emboli, focal segmental and lobar defects occur infrequently. The perfusion lung scan is as sensitive as the pulmonary angiogram in determining areas of vascular involvement in the lung by the emphysematous process. In addition, it has the advantage that quantification of the degree of regional perfusion can easily be achieved.

4. In those few cases, where the lung scan pattern and chest roentgenogram together cannot satisfactorily differentiate between pulmonary embolism, congestive heart failure and emphysema, selective pulmonary arteriography should be performed, using the lung scan defects as a guide in the selection of the arteries to catheterize.

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