Extra pulmonary uptake of Tc 99m MAA perfusion lung scan as a result of right to left intra cardiac shunt

Extra pulmonary accumulation of Tc-99m-macroaggregate of albumin [MAA] is rarely seen on perfusion lung scan, and has been reported in less than 4% of a study population of nearly 380 patients1. It occurs when the agent bypasses the lungs due to a right to left [R-L] cardiac or pulmonary shunt, when it is shunted to the portal vein before reaching the right atrium and ventricle of the heart, and when the agent is degraded to a submicron particle size.2 When a pharmaceutical problem is excluded, extra-pulmonary uptake implies unusual hemodynamics with a shunt. A case is reported in which a clinically unsuspected shunt was diagnosed from the lung perfusion scintigraphy