Metakaryotic cells linked to pediatric pulmonary vein stenosis.

•This is the first report identifying primitive stem cells called “metakaryotic cells” in pulmonary vein stenosis biopsy specimens.•Metakaryotic cells might serve as multi-potent stem cells creating both pathologic fibroid and smooth muscle cell proliferation and are the likely precursors to myofibroblasts.•Surgical pathology from five pediatric patients with pulmonary vein stenosis showed metakaryotic cells in all patients with progressive/persistent vein stenosis in three patients after attempts at surgical repair.•Metakaryotic cells may be a potential therapeutic target for treatment of pulmonary vein stenosis.