Unilateral VQ mismatch from pulmonary embolism detected on VQ scintigraphy with SPECT/CT: a case report

Background We describe a case of unilateral whole-lung VQ mismatch caused by a right main pulmonary artery PE, equivocal on pseudoplanar VQ scintigraphy, highly suspected on VQ SPECT/CT scintigraphy and confirmed on CT angiography. This case confirms the well-established notion that SPECT and SPECT/CT provide significant improvement in diagnostic performance compared to planar imaging in such cases. Case presentation Pseudoplanar VQ scintigraphy identified a unilateral right lung VQ mismatch and was doubtful on the presence of a left-sided subsegmental mismatch, ultimately equivocal for pulmonary embolism given the vast differential of unilateral VQ mismatches. SPECT allowed for definitive identification of a contralateral lung VQ segmental mismatch, and low-dose CT did not reveal an alternative diagnosis to explain the unilateral right-sided whole-lung VQ mismatch. Conclusion In our case, pseudoplanar imaging alone was insufficient to make a certain diagnosis of PE. However, SPECT confirmed a significant contralateral lung VQ mismatch and low-dose CT did not reveal an alternate cause of the VQ mismatch, together highly suggestive of PE, supporting the potentially added value of SPECT and CT in such cases.