How is pulmonary arterial blood flow affected by pulmonary venous obstruction in children? A phase-contrast magnetic resonance study

Hemodynamic changes within a stenosed pulmonary vein might not reflect the severity of the obstruction if redistribution of pulmonary artery flow occurs. The purpose was to investigate flow changes in branch pulmonary arteries in the presence of pulmonary vein stenosis. Twelve children (age range 3-180 months) who had undergone MRI for pulmonary vein stenosis were identified. The severity of vein stenosis was assessed from percentage diameter reduction. Pulmonary artery flow distribution was correlated with the severity of pulmonary vein stenosis. Nine of the patients had unilateral stenosis; three had bilateral involvement. Unilateral vein stenosis was associated with diastolic reversal in the ipsilateral branch pulmonary artery (mean flow reversal 12.3%, range 2.4-42%) and continuous diastolic forward flow in the contralateral pulmonary artery in seven of nine patients. Severe stenosis was associated with decreased systolic flow to the ipsilateral lung. The ratio of net forward flow through pulmonary arteries correlated well with the cross-sectional area ratio of pulmonary arteries (r=0.75, P=0.006). Severe pulmonary vein obstruction results in redistribution of pulmonary arterial flow. When investigating pulmonary vein stenosis by MR, an evaluation of the pulmonary arterial system should be included to assess the functional importance of an obstruction.