Differentiation of Pulmonary Vascular from Parenchymal Diseases by Ventilation/Perfusion Scintiphotography

Defects observed in pulmonary perfusion scintiphotography often have been equated with a diagnosis of pulmonary embolism. In fact, such defects have lacked diagnostic specificity because many other disease processes can reduce regional lung blood flow. Physiologic-anatomic considerations suggest that specificity might be gained by combining ventilation with perfusion radionuclide studies. The experience of several investigators with combined ventilation/perfusion scintiphotography now has proved this to be the case. Their experience has identified two major patterns of diagnostic significance: absent or reduced blood flow to a lung zone with preservation of homogeneous ventilation; and marked reduction or absence of both blood flow and ventilation. The first pattern consistently has reflected the presence of congenital or acquired pulmonary vascular obstruction, including thromboembolic occlusion. The second pattern has indicated the presence of primary parenchymal diseases including emphysema, bullous lesions, infiltrative-consolidative processes, and endobronchial obstruction. These combined ventilation/perfusion patterns provide an interpretive framework that permits diagnostic conclusions not possible on the basis of perfusion studies alone.