Pulmonary embolism: increased ventilation in areas of decreased perfusion.

An abnormal finding that is considered characteristic of large or extensive pulmonary embolism has been observed on ventilation-perfusion (V-P) lung scans. This observation is a regional area of increased ventilation radioactivity in the embolized region of the lung that is more than the normal ventilation radioactivity in the adjacent or contralateral normally perfused lung. It has been designated the "enhanced V-P mismatch sign." This sign was noted in 15 cases among approximately 700 routine V-P lung scans interpreted by a nuclear radiologist. Of these, large or extensive emboli were confirmed in only 10 cases, nine by means of angiography and one by means of autopsy studies. The remaining five cases demonstrated clinical correlation only and are not included in this report. Of the 10 confirmed cases with enhanced V-P mismatch sign, increased ventilation radioactivity involved unilateral lung distribution in five and zonal or lobar distribution in five. The Westermark sign was seen in only seven of the 10 cases. It is hoped that this observation will prove useful in the diagnosis of large or extensive pulmonary emboli.