Hemiazygos vein "steal hypoxic-syndrome" after hemi-Fontan operation: comprehensive four-dimensional flow magnetic resonance visualisation.

A 2-year-old boy with hypoplastic left heart syndrome and previous hemi-Fontan palliation surgery was referred for cardiovascular magnetic resonance evaluation because of progressive cyanosis. This case report illustrates the advantages of non-invasive four-dimensional magnetic resonance imaging for comprehensive identification and quantification of venovenous collaterals in patients with palliated hemi-Fontan staged surgery.