Tree-in-bud Appearance:
The "tree-in-bud" pattern on HRCT is characterized by small centribular nodules (2-4mm) connected to multiple branching linear structures of similar caliber [5]. The findings occur secondary to abnormal dilated bronchioles filled with fluid, mucus, or pus which appear as the centrilobular tubular/branching structures ("trees") and the "buds" (nodular structures) are related to the filled alveoli. The pattern can be associated with centrilobular opacities if inflammation of the adjacent lung is present. This combination of fluid or pus filled bronchioles and surrounding inflammation produces the characteristic "tree-in-bud" appearance.
Differential considerations include:
Infection:
- Tuberculosis (endobronchial spread)/ Non-tuberculus mycobacterial infection: The presence of tree-in-bud opacities is highly suggestive of active TB infection [5].
- Bronchopneumonia
- Also: Fungal, viral, and parasitic infection
Bronchial Disease:
Congenital Disorders:
Immunologic disorders:
Mimics:
The combination of peribronchiolar nodules and thickening of adjacent lobular septa can mimic bronchiolar disease on CT
Lymphatic disease:
- Lymphangectic carcinomatosis
- Sarcoid
- Langerhans Cell Histiocytosis
Metastatic disease:
- Hematogeneous metastatses (Tumor thrombotic microangiopathy)- very rare cause [1,2,3]
REFERENCES:
(1) AJR 2001; 176: 1421-1422
(2) AJR 2002; 179: 897-899
(3) Radiographics 2003; Han D, et al. Thrombotic and nonthrombotic pulmonary arterial embolism: spectrum of imaging findings. 23: 1521-1539
(4) AJR 1998; Collins J, et al. CT patterns of bronchiolar disease: What is "Tree-in-bud"? 171: 365-370
(5) Radiographics 2005; Rossi SE, et al. Tree-in-bud pattern at thin-section CT of the lungs: radiologic-pathologic overview. 25: 789-801
(6) AJR 2009; Gosset N, et al. Tree-in-bud pattern. 193: 1473-1474