Authors: Curtis BR et al., Emerg Radiol 2017 Apr 12;
VQ scan rarely identifies pulmonary embolism after indeterminate computed tomography pulmonary angiography.
Investigators studied the incidence of pulmonary embolism (PE) diagnosed by ventilation and perfusion (VQ) scan after suboptimal computed tomography pulmonary angiography (CTPA). They retrospectively analyzed data from one academic institution that used modified prospective investigation of pulmonary embolism diagnosis (PIOPED) or prospective investigative study of acute pulmonary embolism diagnosis (PISAPED) criteria to diagnose pulmonary embolism. Of 300 consecutive CTPA studies, 122 were determined to be “suboptimal,” and the patients then proceeded to VQ scan. Of these, 98% were negative for PE. An alternative diagnosis was made in 28% of suboptimal CTPA cases (59% pneumonia). On review, contrast injection timing was the factor responsible for most (80%) of the suboptimal CTPA studies. The authors conclude that the incidence of PE diagnosed on VQ imaging performed after suboptimal CTPA is very low.
CTPA is now the gold standard for diagnosing PE (Am J Roentgenology 2017; 208:485). The current study should not change practice, and it seems highly unlikely that progression to VQ after a suboptimal CTPA study will ever be useful.