Scintigraphic evaluation of small pulmonary right-to-left shunt and therapeutic effect in pulmonary arteriovenous malformation

Purpose: Right-to-left shunts of pulmonary arteriovenous malformation (PAVM ) can be detected and measured by pulmonary perfusion scans using Tc-99m MA A. In PAVM with a relatively small right-to-left shunt, however, measuremen t of the shunt ratio may not be reliable. This study re-evaluated pulmonary perfusion scans for a small right-to-left shunt of PAVM. Methods: Tc-99m MAA lung scans were performed in five patients with proved PAVM before and after percutaneous transcatheter embolization. The right-to -left shunt ratio was calculated and extrapulmonary uptake was assessed on total-body images. Results: Lung perfusion scans obtained before embolization revealed brain u ptake in four patients, and the shunt ratio ranged from 4.4% to 22.9%. In t wo patients with a small single PAVM, the shunt ratio was less than 15% bef ore treatment and did not change significantly after successful embolothera py. The brain uptake, which had been clearly visible before therapy, disapp eared after embolization. Renal uptake was seen on pre- and post-therapy sc ans. Conclusions: Changes in brain activity visible on Tc-99m MAA scans might be a more reliable sign than a decreased shunt ratio or a change in renal upt ake when evaluating embolization therapy in patients with PAVM who have a s mall right-to-left shunt.