000 Respiratory Syncytial Virus Pneumonia due to respiratory syncytial virus in a 23-year-old man with leukemia. Thin-section CT scan shows peripheral poorly defined centrilobular nodules and tree-in-bud opacities bilaterally. Note the scattered lung nodules surrounded by halos of ground-glass attenuation.Rossi, SE et al Tree-in-Bud Pattern at Thin-Section CT of the Lungs: Radiologic-Pathologic Overview RadioGraphics Vol. 25, No. 3 2005