This thin-section computed tomography scan obtained in a 29y old man with acute myeloid leukemia after bone marrow transplantation. The patient had a history of fever and cough. Image shows multiple, small, centrilobular nodules of soft-tissue attenuation connected to linear branching opacities (arrows). Note the morphologic similarities to the photograph of the tree in bud . At serologic examination, an infection with Mycoplasma pneumoniae was confirmed.
Explanation of the tree-in-bud sign
The tree-in-bud pattern represents bronchiolar luminal impaction with mucus, pus, or fluid, which demarcates the normally invisible branching course of the peripheral airways . In addition, dilated and thickened walls of the peripheral airways and peribronchiolar inflammation can contribute to the visibility of affected bronchioles . In histopathologic studies, the tree-in-bud appearance correlates well with the presence of plugging of the small airways with mucus, pus, or fluid; dilated bronchioles; bronchiolar wall thickening; and peribronchiolar inflammation .
