Background: Tree-in-bud (TIB) is a radiologic pattern seen on high-resolution chest CT reflecting bronchiolar mucoid impaction occasionally with additional involvement of adjacent alveoli. Its microbiologic significance has not been systematically evaluated.
Objectives: We aimed to establish the incidence of the TIB pattern as a proportion of all patients undergoing chest CT and to identify its etiology wherever possible.
Methods: We included all patients with TIB pattern detected on chest CT in our institution from January 2007 to June 2012 and correlated this radiologic finding to the microbiologic etiology, which were available, for each patient.
Results: During the study period, TIB pattern was described in 326 patients, which is 1.8% of all chest CTs. Of these, 220 (67.5%) patients had an infectious etiology and 34 (10.4%) had aspiration pneumonia. Other presumptive etiologies were in 13 (4%) lung malignancy, 31 (9.5%) other malignancies, 20 cases (6%) inconclusive etiology or incidental findings, and 8 (2.5%) had other inflammatory disorders. The relative incidence of the various organisms isolated reflected the overall incidence of these bacteria in community- or hospital-acquired populations independent of the TIB pattern. No correlation was found between distribution of TIB, the immune status, and the organism isolated.
Conclusions: TIB pattern reflects endobronchiolar inflammation due mainly but not exclusively to an infectious cause. The microbiologic etiology in patients with this finding is similar to that of the general population (community acquired versus hospital acquired).
Keywords: Chest CT; Endobronchiolar inflammation; Pulmonary infection; Tree-in-bud.