“…Since the initial report of endobronchial spread of pulmonary tuberculosis ( 1 ), the “tree-in-bud sign” has been reported in a wide variety of health conditions including infectious diseases, aspiration pneumonia, congenital disorders, idiopathic disorders, inhalation, immunologic disorders, connective disorders ( 2 3 4 5 6 ) and central lung cancer involving the peripheral airways ( 7 ). Subsequently, metastatic diseases showing “tree-in-bud sign” caused by tumor cells in and around the intralobular pulmonary artery were also reported ( 8 9 10 11 ).…”