Pathophysiology of the tree-in-bud pattern is the impaction of dilated terminal bronchioles which are normally less than 2mm in size, so, invisible on CT images. They are indirectly visible when filled with mucus, pus, aspirated material, cells or fluid.
They characteristically spare the subpleural lung parenchyma, including adjacent to interlobar fissures, since they are centrilobular.
1. Acute or acute on chronic/ chronic?
a. Acute
-Infection
-Diffuse panbronchiolitis
-Inhalational/ aspiration
b. Acute on chronic/ Chronic
-Cystic fibrosis
-Kartagener's syndrome
-Obliterative panbronchiolitis
-Aspiration/ inhalation
-Allergic bronchopulmonary aspergillosis
-Rheumatoid arthritis
-Sjogren's syndrome
2. Pattern/pathology?
a. Tracheobronchitis
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859455?maxheight=300&maxwidth=300)
Fig. 3: Tracheobronchitis (central airways' wall thickening)
References: Adam Kenji Yamamoto, Judith Lynn Babar (2012)
-Viral infection
-bacterial (rare)
-Aspergillus fumigatus
b. Bronchiolitis (Bronchial wall thickening, atelectasis, air trapping)
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859321?maxheight=300&maxwidth=300)
Fig. 4: Thickened bronchial wall (bronchiolitis) with mucus plugging and segmental air space consolidation with tree-in-bud opacities
References: Department of Radiology, Chettinad hospital and research institute
-Viral infection
-Bacterial
-Inhalation/ aspiration
-Diffuse panbronchiolitis
c. Lobar pneumonia (peripheral alveolar air space opacities rapidly evolving into confluent, homogeneous consolidation conforming to fissural boundaries; non segmental)
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859373?maxheight=300&maxwidth=300)
Fig. 6: lobar pneumonia (S. pneumoniae infection)
References: Department of Radiology, Chettinad hospital and research institute
-S. pneumoniae
-K. pneumoniae
d.Bronchopneumonia (small airway destruction; segmental; multifocal and bilateral)
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859352?maxheight=300&maxwidth=300)
Fig. 5: Bilateral segmental bronchopneumonia pattern (S. aureus infection)
References: Department of Radiology, Chettinad hospital and research institute
-S. aureus
-Gram negative organisms like Pseudomonas
e. Bronchiectasis with bronchiolitis
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859380?maxheight=300&maxwidth=300)
Fig. 7: Bronchiectasis with bronchiolitis and mucus plugging with segmental patchy consolidation and few tree-in-bud opacities in a Cystic Fibrosis patient
References: Department of Radiology, Chettinad hospital and research institute
-Congenital causes
-Obliterative panbronchiolitis
-Chronic aspiration
-ABPA
-RA
f. Follicular bronchiolitis (Peribronchial lymphoid hyperplasia with minimal infiltration of alveolar septae)
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859406?maxheight=300&maxwidth=300)
Fig. 8: Follicular bronchiolitis involving interstitium with NSIP pattern and few tree-in-bud opacities in a Rheumatoid arthritis patient
References: Department of Radiology, Chettinad hospital and research institute
-RA
-Lymphoid interstitial pneumonia
-Sjogren's syndrome
g. Severe immunosuppression?
i. Focal airspace opacities
- Bacterial infection
ii. Multifocal airspace opacities
-Fungal infection
-Mycobacterium tuberculosis
iii. Linear interstitial opacities
-P. jirovecii infection
-Virus
iv. Cavitations
-Fungal
-Necrotizing pyogenic pneumonia
v. Lymphadenopathy
-Mycobacterial tuberculosis
vi. Pleural effusion
-Fungal infection
-Mycobacterial TB
-Pyogenic bacterial infection
vii. Airway pathology or a mimic?
Mimic- Vascular tumor emboli (Beading of vessels)- carcinomatosis endarteritis.
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859408?maxheight=300&maxwidth=300)
Fig. 17: Beading of vessels due to tumor emboli in a choriocarcinoma patient
References: Department of Radiology, Chettinad hospital and research institute
Primary maliganancy
-Choriocarcinoma
-breast carcinoma
-Liver carcinoma
-Gastric carcinoma
-Renal carcinoma
Ancillary findings of above-mentioned differentials of TIB pattern
1. Infection
A.Bacterial infection
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859467?maxheight=300&maxwidth=300)
Fig. 9: Thick walled cavitations with segmental patchy consolidation and few tree-in-bud opacities in bilateral upper lobes (TB)
References: Department of Radiology, Chettinad hospital and research institute
i. Mycobacterium tuberculosis
-centrilobular nodules
-cavitary nodules
-interlobular thickening
-pleural effusion
-lymphadenopathy
-upper lobe predominance
ii. Atypical Mycobacterium avium complex
- Classic- elderly male with underlying chronic obstructive
pulmonary disease
- Non classic- elderly Caucasian female without underlying disease; lingula and middle lobe predominance
iii. Others
-centrilobular nodules
-pleural effusion
-lymphadenpathy
-bronchopneumonia/ lobar pneumonia
-bronchiolitis
B. Viral
i. Children (
- tracheobronchitis
- narrowing of subglottic trachea
- patchy, asymmetric, upper lobe, bilateral centrilobular nodules
and ground glass opacities
- bronchiolitis
ii. Adults
- viral infection with a superimposed bacterial infection
- immunocompromised. Ex: CMV
C. Fungal
-immunocompromised
-bronchopneumonia pattern
-bronchiolitis
2. Cystic Fibrosis
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859411?maxheight=300&maxwidth=300)
Fig. 10: Bronchiolitis with bronchiectasis
References: Department of Radiology, Chettinad hospital and research institute
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859419?maxheight=300&maxwidth=300)
Fig. 11: GB sludge, Chronic liver disease features (irregular liver surface with ascites and splenomegaly), atrophic body and tail of pancreas in a Cystic fibrosis patient
References: Department of Radiology, Chettinad hospital and research institute
-clinical history of recurrent infection
-bronchiolitis+bronchiectasis+/-atelectasis
-early- upper lobe predominance
-atrophic pancreas
-hepatic steatosis with multilobular cirrhosis
-cholelithiasis
3. Kartagener's syndrome
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859421?maxheight=300&maxwidth=300)
Fig. 12: Bronchiectasis with mucus plugging and resultant tree-in-bud opacities in a Kartagener's syndrome patient
References: Department of Radiology, Chettinad hospital and research institute
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859422?maxheight=300&maxwidth=300)
Fig. 13: situs inversus
References: Department of Radiology, Chettinad hospital and research institute
-Triad consists of situs inversus+sinusitis+pneumonia
-bilateral bronchiectasis- basal predominance
-bronchiolitis +/- pneumonia
-air trapping
4. Obliterative panbronchiolitis (Irreversible fibrosis)
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859427?maxheight=300&maxwidth=300)
Fig. 14: Obliterative panbronchiolitis
References: Department of Radiology, Chettinad hospital and research institute
-Air trapping
-bronchiolitis
-central and peripheral bronchiectasis
5. Diffuse panbronchiolitis
-Japan and Eastern Asia
-non-smokers
-bronchiolitis and centrilobular nodules
-bronchiectasis
-large cystic opacities with dilated proximal bronchi
air trapping
6. Aspiration/ Inhalation
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859429?maxheight=300&maxwidth=300)
Fig. 15: Bilateral basal confluent, non segmental opacities due to chronic aspiration
References: Department of Radiology, Chettinad hospital and research institute
-structural abnormalities of pharynx, esophageal disorders, neurologic deficit, chronic illness
Acute- pulmonary edema, bronchiolitis, atelectasis, pneumonia
Chronic- bronchiectasis+ other cute manifestations
7. ABPA
-asthma/ Cystic fibrosis
-central bronchiectasis
-upper lobe predomihnance
8. Rheumatoid arthritis
![](https://epos.myesr.org/posterimage/esr/ecr2020/155499/media/859443?maxheight=300&maxwidth=300)
Fig. 16: Fibrosing type of NSIP with few tree-in-bud opacities in a Rheumatoid arthritis patient
References: Department of Radiology, Chettinad hospital and research institute
- F>M, however, lung manifestations are more common in men.
- Pleural effusion+pleural thickening+reticular opacities+
groung-glass opacities in posterior and subpleural lung and
lung base
- Smokers undergo bronchiectasis which makes them vulnerable
to pneumonia and other infections
- Interstitial pneumonia
9. Sjogren's syndrome
- Triad consists of xerostomia+keratoconjunctivitis
+parotitis
- reticulonodular pattern with a basal predominance
- lymphoid interstitial pneumonia
- Lung cysts