Abstract
2535
Objectives To provide an alternative imaging maneuver when performing lung perfusion scan in a patient with superior vena cava obstruction and systemic to pulmonary venous shunt.
Methods 5 mCi Tc-99m MAA was administered in the right antecubital vein. Planar chest images were acquired in the anterior, posterior and oblique projections. Planar images were also acquired of the brain and the kidneys. As the lungs were poorly visualized, 2.6 mCi Tc-99m MAA was administered through a femoral catheter. Planar chest images were then acquired in the anterior, posterior and oblique projection. Chest CTA images were evaluated after the scanning procedure was completed and reviewed by a radiologist.
Results The lungs were poorly visualized after 5 mCi Tc-99m MAA was administered in the right antecubital vein. Radiotracer uptake was observed in the myocardium, spleen, brain, and right lateral chest. 2.6 mCi Tc-99m MAA administered through the femoral catheter resulted in improved pulmonary perfusion images. Review of a chest CTA performed earlier in the department showed evidence of early pulmonary venous contrast enhancement during pulmonary artery imaging phase. An extensive collateral network of vessels was visualized on the MIP Chest CTA image.
Conclusions The hemodynamic pathway of Tc-99m MAA may be altered in the presence of chronic SVC obstruction and systemic to pulmonary venous shunt. Commonly, the shunting of Tc-99m MAA into systemic circulation may lead to the visualization of the kidneys, spleen, and brain. Tc-99m MAA is rarely visualized in the myocardium. In this case, the systemic to pulmonary venous shunt and the extensive network of collaterals may explain the unusual Tc-99m MAA visualization in the myocardium. The lower extremity veins should be used for Tc-99m MAA dose administration in suspected cases of superior vena cava obstruction and systemic to pulmonary venous shunt.