A pitfall of radioisotope quantification of the ratio of pulmonary blood flow to systemic blood flow (Qp/Qs) in a patient with severe postoperative pulmonary venous obstruction.

PURPOSE: We report a case with initial misinterpretation of the radionuclide angiocardiographic study that was obtained in a child with persistent tachypnea and concern for residual left to right shunt after prior repair of total anomalous pulmonary veins and an atrial septal defect.

MATERIALS AND

METHODS

Ultrasound, radionuclide angiocardiogram, and magnetic resonance imaging studies were obtained.

RESULTS

The radionuclide study was ordered after an unremarkable ultrasound. Unsuspected severely reduced left pulmonary arterial flow associated with high-grade ipsilateral pulmonary venous obstruction led to misinterpretation of the radionuclide study as a large residual shunt. Later replotting of the graphic data using each lung separately corrected the error. Magnetic resonance played a key role in making the correct diagnosis.

CONCLUSIONS

Significant asymmetric pulmonary flow due to vascular obstruction is an important additional potential pitfall to recognize in interpreting radionuclide angiocardiographic studies.