Tree-in-bud pattern: Frequency and significance on thin section CT

Purpose: Our goal was to describe those diseases of the airways that manifest the tree-in-bud (TIB) pattern on CT scan and to establish a differential diagnosis for this CT scan finding. Method: We prospectively collected cases with the TIB pattern on CT and reviewed the scans of patients with histories pertaining to small airway disease. CT scans were performed at 1 to 3 mm collimation. Results: Twenty-six of 27 cases with the TIB pattern had associated bronchiectasis or proximal airway wall thickening. One case with normal proximal airways had an acute aspiration. In addition, we reviewed 141 scans of patients with emphysema, respiratory bronchiolitis (RB), bronchiolitis obliterans (BO), bronchiolitis obliterans organizing pneumonia (BOOP), extrinsic allergic alveolitis (EAA), bronchiectasis, bronchitis, and pneumonia. Of the CT scans with bronchiectasis, 25.6% had TIB, and 17.6% of CT scans with acute infectious bronchitis or pneumonia had this pattern. None of the patients with emphysema, BO, BOOP, EAA, or RB had this pattern. Conclusion: The TIB pattern on CT scan is mostly associated with pulmonary infections that commonly involve the large airways. This pattern was present in 17.6% of cases with acute bronchitis or pneumonia and 25.6% of cases with bronchiectasis.