TIB opacities represent a normally invisible branches of the bronchiole tree (≤1 mm in diameter) that are severely impacted with mucous, pus, or fluid, with resultant dilatation and “budding” of the terminal bronchioles ( ≥2 mm in diameter)¹ (photo).

Although initially described in 1993 as a thin-section chest CT finding in active tuberculosis, TIB opacities are by no means restricted to a specific lung entity, and may be of infectious as well as non-infectious causes.

TIB is most commonly seen with infectious bronchiolitis caused by bacteria (particularly Staphylococcus aureus, Hemophilus influenzae), mycobacteria (including atypical mycobacteria), viruses (eg, respiratory syncytial virus, cytomegalovirus), and fungi (eg, Pneumocystis jirovecii, Aspergillus sp.)^1,2.

Non-infectious causes include inhalation of toxic gases, connective tissue disorders (eg, rheumatoid arthritis, Sjögren syndrome), cystic fibrosis, Kartagener syndrome, and non-infectious bronchiolitis (eg, obliterative bronchiolitis). Malignancy-related causes include chronic lymphocytic leukemia and pulmonary tumor embolism in breast, liver, kidney, stomach, prostate and ovarian cancers³.

References

1. Collins J, Blankenbaker D, Stern EJ. Ct patterns of bronchiolar disease: What is “tree-in’bud”? AJR 1998;171:365-70.
2. Rossi SE, Franquet T, Volpacchio M, et al. Tree-in-bud pattern a t thin-section CT of the lungs: radiologic-pathologic overview. RadioGraphics 2005;25:789-801.
3. Terhalle E, Gunther G. “Tree-in-bud”: thinking beyond infectious causes. Respiration 2015;89:162-165.

Photo: TIB opacities in a 50 year old man with productive cough and shortness of breath caused by infectious bronchiolitis.