MISLEADING ISOTOPE LUNG SCANS IN THE DIAGNOSIS OF PULMONARY EMBOLISM

Abstract

Pulmonary embolism (PE) remain a common yet poorly diagnosed condition with significant mor-bidity and mortality. Accurate diagnosis is impor-tant as treatment with anticoagulants which can cause significant problems itself, is associated with a major improvement in survival of patients with pulmonary embolism. Pulmonary angiography is an underused gold stan-dard in the diagnosis of pulmonary embolism; most clinicians preferring the simpler isotope V/Q scan-ning which is more readly available. While it is ac-cepted that an abnormal perfusion scan may be due to many causes other than pulmonary embolism, it is also widely accepted that a normal perfusion scan excludes this diagnosis. In Derbyshire Royal Infir-mary, we conducted a retrospective study of all pa-tients who were diagnosed as having pulmonary embolism during the period 1987-90. Results of V/ Q scans and pulmonary angiography were com-pared a total 402 patients were suspected as P.E. and undergone a V/Q lung scan & 206 patients from the same group also under went pulmonary angiog-raphy. Out of 402 V/Q scan, 162 (37.8%) were reported as normal, 101 (25.1%) as low probability, 66 (16.4%) as intermediate probability and 73 (18.1%) as high probability scans for P.E. Pulmonary an-giography was performed on 167 patients (101 low probability V/Q scan and 66 high probability V/Q scan). An extra 37 angiographies were performed in patients whose V/Q scan were reported as nor-mal but they continued to have persistent symptoms highly suggestive of P.E. In this group 3 pulmo-nary angiogrames were highly abnormal confirming the presence of major PE. We recommend that a normal isotope perfusion scan is only accepted as evidence for the absence of pulmo-nary embolism if there is no overwhelming clinical support for the diagnosis.