Pulmonary thromboembolism with emphasis on angiographic-pathologic correlation

Subselective magnification angiography of experimental pneumonia

An experiment was designed to determine whether or not acute pneumococcal pneumonia in dogs is associated with intravascular thrombosis, or with angiographic features distinguishable from pulmonary embolism. In dogs with normal baseline chest radiographs and perfusion scans, pneumonia was produced by transbronchial instillation of type III pneumococcus. After 2 days, perfusion scans demonstrated discrete appropriate defects. In vivo magnification pulmonary arteriography, postmortem pulmonary arteriography, and histologic examination disclosed no evidence of thrombi.

Detection of experimental pulmonary emboli in dogs by sequential positron imaging after inhalation of 15O-carbon dioxide

After inhalation, C15O2 (T1/2 = 2 minutes) rapidly diffuses into pulmonary blood and is cleared from the lungs within 10 seconds. The purpose of this study was to determine whether impaired clearance of inhaled C15O2 from oligemic zones, distal to areas of obstructed pulmonary blood flow, could be detected by serial pulmonary imaging with a positron camera. Experimental obstruction of branches of the pulmonary artery was induced in 19 anesthetized dogs by inflation of balloon-tipped catheters (8-12 mm in diameter), injection of radiopaque silicone spheres (0.5-4.0 mm), and embolization with barium-impregnated autologous blood clots (1-5 mm) via the right external jugular vein. After a single bolus injection of 2 mCi of C15O2 into the endotracheal tube, serial lung images of 15O activity were obtained over 60-180 seconds. Obstruction of pulmonary arterial branches resulted in visualization of discrete zones of impaired 15O clearance which varied in area with catheter diameter. Location and size of these zones were confirmed by repeat imaging after direct injection of 15O-labeled blood through the distal catheter lumen. In dogs receiving autologous clots (n = 8), similar zones of impaired 15O clearance were consistently imaged, and single emboli as small as 2 mm in diameter produced regions of retained 15O activity. Zones of retained 15O activity corresponded to the location of radiopaque emboli on chest radiographs. This study introduces a new technique of radionuclide imaging for detection of pulmonary emboli that is noninvasive, safe, sensitive, and repeatable at short intervals.

Phlebography in the management of pulmonary embolism

The value of phlebography in the management of 102 patients presenting with clinical features suggestive of pulmonary embolism was assessed. Ascending phlebograms, chest x-rays and pulmonary perfusion scans were performed in all the cases. Of 33 patients with a high probability of pulmonary embolism, 29 (87 per cent) had thrombi in the peripheral veins shown by phlebography. Of 45 patients with no evidence of pulmonary emboli on lung scan, the deep veins were normal in 30, while in the remaining 15 (33 per cent), phlebograms showed the presence of thrombi. In all 7 patients where pulmonary angiography confirmed the presence of extensive emboli, phlebograms showed thrombi in the peripheral veins. Phlebography was of considerable help in deciding whether to give anticoagulant therapy.

The complementary roles of chest radiography, lung scanning, and selective pulmonary angiography in the diagnosis of pulmonary embolism

The chest X-ray, perfusion lung scan, and selective pulmonary arteriogram were independently reviewed in 104 patients with suspected pulmonary embolism. Thirteen patients also had 133 Xe ventilation studies. Of the 45 patients with angiographically-documented pulmonary emboli, 37 had perfusion scans interpreted as high probability of pulmonary embolism (82% sensitivity). Fifty of 59 patients without angiographic evidence of pulmonary embolism had perfusion scans interpreted as low probability of pulmonary embolism, other , or normal (85% specificity).

Of the 41 patients with acute pulmonary embolism, only three had normal chest X-rays. In 26 (63%) the abnormality on perfusion scan was more extensive than that on chest X-ray.

When both the scan and chest X-ray pointed strongly in the same direction, a correct diagnosis could usually be made, and accuracy was greater than when diagnosis was based on the perfusion scan alone. The lung scan was of limited value in patients with cardiomegaly or left heart failure. The differential role of the 133 Xe ventilation study remains unclear. On the basis of the present and other data, guidelines for the selection of patients for pulmonary arteriography are proposed.

The role of lung imaging in pulmonary embolism

The advantages of lung scanning in suspected pulmonary embolism are its diagnostic sensitivity, simplicity and safety. The ability to delineate regional pulmonary ischaemia, to quantitate its extent and to follow its response to therapy provides valuable clinical data available by no other simple means. The negative scan effectively excludes pulmonary embolism but, although certain of its features favour the diagnosis of embolism, the positive scan inherently lacks specificity and requires angiographic confirmation when embolectomy, caval plication or infusion of a thrombolytic agent are contemplated. The addition of simple ventilation imaging techniques with radioxenon overcomes this limitation by providing accurate analog estimation or digital quantitation of regional ventilation: perfusion (V/Q) ratios fundamental to understanding the pathophysiologic consequences of embolism and other diseases of the lung.