[Differential diagnosis of pneumonia and pulmonary infarct based on lung scintigraphy]

The etiology of radiologic signs of circumscript parenchymatous lesions is multivarious. In some instances infarction of the lung has to be distinguished from pneumonia. The differential diagnosis has important therapeutic consequences for the patient. An important criterion for primary pneumonic infiltration is Xe-trapping within the area lacking perfusion, which can only be demonstrated by perfusion scintigraphy with Xe-133-NaCl. However, infarction of the lung lacks this pathologic feature. Pathophysiologically the various changes may occur as the result of obstruction of the vessel i.e. due to alveolar hypoxia and embolism. In order to improve the diagnostic methods a combination of perfusion scintigraphy using Xe-133-NaCl and Tc-99-macroaggregate and ventilation scintigraphy with Xe-127 was employed. We retrospectively evaluated 20 patients with the nuclear medical diagnosis of either pneumonia (n = 10) or infarction of the lung (n = 10). The following criteria were adopted: history, risk factors, X-ray of the chest, blood chemistry, ECG, phlebography, pulmonary angiography and histopathological diagnosis, as well as the course of the disease. According to our results the specificity of the scintigraphic diagnosis of pneumonia and infarction of the lung was 90%. However these results will have to be verified in a prospective study using pulmonary angiography as the reference method.