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 patients. 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. 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.