Frequencies of segmental perfusion and ventilation abnormalities in lung scintigraphy

The segmental ventilation-perfusion mismatch is almost invariably a sign of pulmonary embolism (PE). As ventilation scintigraphy is an expensive and time-consuming procedure, it is rarely performed in patients presenting as emergencies. In such patients PE is diagnosed by the presence of a segmental perfusion defect (SPD) in combination with a normal chest X-ray. However, little is known about SPD frequencies in different groups of patients or its value in predicting a mismatch. To determine this frequency, as well as its predictive value for a mismatch (PVM), we examined 764 patients with suspected Pe (PE? group), 359 patients at low risk for PE (low risk group), and 234 patients without suspected PE but at high risk for PE (high risk group), all by perfusion and ventilation scintigraphy. Frequencies of SPD were determined in each group as a function of age. PVM was calculated for each age subgroup using Bayes' theorem. In the low risk group the frequency of segmental mismatches (SM) was about 4%, while one-third of patients at high risk had a SM. This was not age dependent in contrast to the PE? group, where the frequency decreased with age. In the youngest subgroups the PVM for a SPD was higher than 0.9 as well as in a subgroup of the PE? group with a known thrombo-embolic disease. In these subgroups a ventilation scintigraphy is not required for the scintigraphic diagnosis of PE; in all other patients an additional ventilation study is necessary.(ABSTRACT TRUNCATED AT 250 WORDS)