VALUE OF PERFUSION LUNG-SCAN IN THE DIAGNOSIS OF PULMONARY-EMBOLISM -RESULTS OF THE PROSPECTIVE INVESTIGATIVE STUDY OF ACUTE PULMONARY-EMBOLISM DIAGNOSIS (PISA-PED)

To assess the value of perfusion lung scan in the diagnosis of pulmona ry embolism, we prospectively evaluated 890 consecutive patients with suspected pulmonary embolism. Prior to lung scanning, each patient was assigned a clinical probability of pulmonary embolism (very likely, p ossible, unlikely). Perfusion scans were independently classified as f ollows: (1) normal, (2) near-normal, (3) abnormal compatible with pulm onary embolism (PE+: single or multiple wedge-shaped perfusion defects ), or (4) abnormal not compatible with pulmonary embolism (PE-: perfus ion defects other than wedge-shaped). The study design required pulmon ary angiography and clinical and scintigraphic follow-up in all patien ts with abnormal scans. Of 890 scans, 220 were classified as normal/or near-normal and 670 as abnormal. A definitive diagnosis was establish ed in 563 (84%) patients with abnormal scans. The overall prevalence o f pulmonary embolism was 39%. Most patients with angiographically prov en pulmonary embolism had PE+ scans (sensitivity: 92%). Conversely, mo st patients without emboli on angiography had PE- scans (specificity: 87%). A PE+ scan associated with a very likely or possible clinical pr esentation of pulmonary embolism had positive predictive values of 99 and 92%, respectively. A PE- scan paired with an unlikely clinical pre sentation had a negative predictive value of 97%. Clinical assessment combined with perfusion-scan evaluation established or excluded pulmon ary embolism in the majority of patients with abnormal scans. Our data indicate that accurate diagnosis of pulmonary embolism is possible by perfusion scanning alone, without ventilation imaging. Combining perf usion scanning with clinical assessment helps to restrict the need for angiography to a minority of patients with suspected pulmonary emboli sm.