Functional assessment of pulmonary venous obstruction with MR

Shi-Joon Yoo
Professor of Diagnostic Imaging and Paediatrics, University of Toronto
Section Head, Cardiac Imaging, The Hospital for Sick Children
Toronto, Canada

Pulmonary venous obstruction is rare but often lethal. Pulmonary vein stenosis can be congenital or develop postnatally. Obstruction also occurs as a complication of surgical treatment of abnormal pulmonary veins or radiofrequency ablation procedures. As the prognosis of pulmonary venous obstruction remains guarded, frequent follow-up studies are required. MR is best suited for anatomical and functional assessment of pulmonary venous obstruction.
　The anatomy of pulmonary vein pathology can be depicted using contrast-enhanced MR angiography and cine imaging. Flow pattern changes associated with stenosis can be assessed using phase-velocity mapping technique. The abnormal findings include loss of normal phasic changes, reduced flow velocity in upstream and accelerated velocity in downstream. As the pulmonary blood flow can be redistributed to the unaffected areas of the lung, assessment of the blood flow through branch pulmonary arteries provides information regarding the effect of pulmonary venous obstruction on pulmonary circulation. Unilateral pulmonary venous obstruction is associated with reduced systolic flow to the affected branch pulmonary artery, diastolic reversal in the ipsilateral branch pulmonary artery and continuous forward flow in the contralateral pulmonary artery, and findings of elevated pulmonary arterial pressures in the affected lung. The ratio of net forward flow through the pulmonary arteries correlates well with the cross-sectional area ratio of the pulmonary arteries. The pulmonary arterial size is highly predictive of the severity of pulmonary venous obstruction. The obstructed pulmonary vein can be drained to the unaffected pulmonary veins through the pulmonary venous-pulmonary venous collateral channels or very rarely through the pulmonary venous-systemic venous collaterals. Severe pulmonary venous obstruction results in recruitment of systemic arterial collateral arteries. When the systemic arterial collaterals are florid, the flow through the branch pulmonary artery can be reversed.
　This presentation will highlight the functional/hemodynamic consequences of the pulmonary venous obstruction seen at MR imaging.
References:
1.　Valsangiacomo ER, Barrea C, Macgowan CK, Smallhorn JF, Coles JG, Yoo SJ. Phase-contrast MR assessment of pulmonary venous blood flow in children with surgically repaired pulmonary veins. Pediatr Radiol 2003; 33: 607-613.
2.　Wiebe S, Maclusky I, Manson D, Holowka S, Yoo SJ. Hemoptysis: a rare cause can be related to a bronchial varix due to pulmonary venous obstruction. Pediatr Radiol 2003; 33: 884-886.
3.　Roman KS, Kellenberger CJ, Macgowan CK, Coles J, Redington AN, Benson LN, Yoo SJ. How is pulmonary arterial blood flow affected by pulmonary venous obstruction in children? A phase-contrast magnetic resonance study. Pediatr Radiol 2005; 35: 580-586.
4.　Grosse-Wortmann L, Al-Otay A, Goo HW, Macgowan CK, Coles JG, Benson LN, Redington AN, Yoo SJ. Anatomical and functional evaluation of pulmonary veins in children by magnetic resonance imaging. J Am Coll Cardiol 2007; 49: 993-1002.