• Etymology
  The term “tree-in-bud” is derived from its resemblance to budding trees, symbolizing the growth and renewal of spring.
• AKA
  None.
• What is it?
  • A radiological finding characterized by:
    • Branching linear opacities resembling a budding tree, and
    • Small centrilobular nodules representing impacted or dilated small airways.
  • Typically indicates endobronchiolar inflammation or obstruction, often seen in infectious and inflammatory processes.
• Characterized by
  • Involvement of:
    • Bronchioles,
    • Alveolar ducts, and
    • Small airways within the centrilobular region.
  • Reflects distal airway disease with intraluminal filling by mucus, pus, or fluid.
• Anatomically affecting
  • Terminal bronchioles, extending to the alveolar ducts.
  • Centrally distributed within the secondary pulmonary lobule, often in the lower lobes or peripheral lung zones.
• Causes include
  • Most Common Causes
    • Infection:
      • Tuberculosis (including post-primary/endobronchial TB).
      • Mycobacterium avium complex (MAC).
  • Other Causes include
    • Infection:
      • Viral: Respiratory syncytial virus (RSV), measles.
      • Fungal: Aspergillosis, bronchocentric histoplasmosis.
    • Inflammation:
      • Bronchiolitis (including respiratory and follicular types).
    • Immune:
      • Allergic bronchopulmonary aspergillosis (ABPA).
    • Aspiration:
      • Recurrent inhalation of gastric contents or foreign materials.
• Pathophysiology
  • Distal airway obstruction and inflammation lead to dilation of bronchioles.
  • Intraluminal filling by inflammatory cells, mucus, or pathogens causes the tree-in-bud appearance.
• Histopathology
  • Histological findings include:
    • Lymphocytic infiltration and peribronchiolar inflammation.
    • Intraluminal debris, such as mucus, pus, or infectious material.
• Imaging Radiology
  • Applied Anatomy to CT
    • Parts: Terminal bronchioles and alveolar ducts.
    • Size: Centrilobular nodules typically measure 2–3 mm.
    • Shape: Branching, tree-like structures with nodular buds.
    • Position: Centrilobular, predominantly in the lower lobes or peripheral lung zones.
    • Character: Soft-tissue attenuation nodules and linear opacities.
    • Time: Acute or chronic, depending on the etiology.
  • CXR
    • Rarely detects tree-in-bud findings due to their small size.
    • Advanced cases may show diffuse or focal nodular opacities suggesting small airway disease.
  • MRI
    • Limited role in small airway disease.
    • T2-weighted sequences may highlight fluid-filled airways as hyperintense signals.
  • PET-CT
    • Primarily used for unclear etiologies or suspected malignancy.
    • Increased FDG uptake may indicate active infection or inflammation.
  • Other
    • Bronchography (historical): Reveals dilated bronchioles with terminal filling defects.
• Differential Diagnosis
  • Bronchiectasis: Larger airway dilation without the characteristic nodular opacities.
  • Pulmonary fibrosis: Reticular patterns with architectural distortion.
  • Miliary nodules: Random distribution without branching.
• Recommendations
  • Perform CT imaging for detailed evaluation of small airway involvement.
  • Evaluate for infections with sputum analysis, AFB staining, and cultures.
  • Consider bronchoscopy for direct sampling.
  • Use PET-CT if masses or neoplasms are suspected.
• Key Points and Pearls
  • The tree-in-bud pattern is a hallmark of endobronchial infection, particularly tuberculosis and MAC.
  • The finding is diagnostic of small airway disease and reflects distal bronchiolar involvement.
  • Chronic cases suggest immune dysfunction, aspiration, or non-infectious inflammation.
• Parallels with Human Endeavors
  • Examples in Social and Societal Equivalents
    • The tree-in-bud pattern mirrors spring’s renewal, symbolizing a mix of growth and obstructions along pathways.
    • The branching opacity highlights the tension between vitality and impairment, much like life cycles where struggles precede renewal.
  • Art: The tree-in-bud pattern is reminiscent of blossoming trees depicted in classical spring paintings.

Le Printemps (Springtime). Monet, Claude (French, 1840-1926). Oil on canvas,  1886. Purchased With a contribution from the National Art Collections Fund.

Sculpture: Branching structures in sculptures symbolize interconnectedness and growth.

Le_Printemps 1911 – Aristide_Maillol
Spring

Music: Melodic compositions with branching motifs reflect renewal and progression.

Vivaldi 4 Seasons 

Dance: Movements echoing budding and branching represent spring’s energy.

Mark Morris Dance Group Spring, Spring, Spring

Chinese Traditional Dancing – Recall That Spring

Literature: Spring often symbolizes new beginnings and the resolution of blockages.

Shakespeare
Henry VI, Part II
Now ’tis the spring, and weeds are shallow-rooted;
Suffer them now, and they’ll o’ergrow the garden

 

Quotes by famous people: “Spring is nature’s way of saying, ‘Let’s party!'” — Robin Williams.

Poetry: Poems often compare spring’s renewal to life’s potential.

Architecture: Designs inspired by trees, such as branching structures, signify resilience and connection.

The Tree-in-Bud (TIB) sign is a radiological finding observed on high-resolution CT (HRCT) of the chest. It represents centrilobular branching opacities with a nodular appearance, resembling budding tree branches. This sign typically indicates a pathological process within the small airways, such as bronchioles, and is often associated with infectious or inflammatory diseases.

 

Tree-in-bud is a radiological pattern seen on high-resolution CT
scans of the lungs, characterized by small, branching opacities that
resemble budding branches of a tree. This appearance is caused by
the impaction of mucus, pus, or other material within the small
airways (bronchioles), often due to infection, inflammation, or
aspiration. The pattern is commonly associated with conditions
such as bronchiectasis, tuberculosis, bacterial or viral
bronchiolitis, cystic fibrosis, and mycobacterial infections. The
pathogenesis involves the filling of the bronchioles and nearby
alveolar ducts with infectious or inflammatory material, leading to a
localized airway obstruction and subsequent peripheral opacities
on imaging. Diagnosis relies on the characteristic tree-in-bud
pattern seen on CT, along with clinical evaluation and sometimes
sputum cultures or bronchoscopy to identify the underlying cause. (Neelou)

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Anatomical Basis
The Small Airways

Alveolar Ducts and Alveolar Sacs

Pathophysiology

The Tree-in-Bud pattern results from:

1. Endobronchial spread of material:
   • Mucus, pus, or other substances accumulate within the bronchioles.
2. Peribronchiolar inflammation:
   • Thickening of the walls of small airways and their surrounding structures.
3. Distal airway obstruction:
   • Often due to infection or inflammatory debris.

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Radiological Features

1. Appearance:
   • Centrilobular, branching opacities resembling a tree with buds on its branches.
   • Composed of:
     • Linear structures (the “branches”): Reflect dilated or inflamed bronchioles.
     • Small nodules (the “buds”): Represent impacted bronchioles or peribronchiolar inflammation.
2. Location:
   • Centrilobular distribution: Centered within secondary pulmonary lobules.
   • Predominantly affects the lower lobes but may involve other areas depending on the underlying disease.
3. Associated Findings:
   • Ground-glass opacities.
   • Consolidation or airspace filling in advanced stages.

 

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Common Causes

1. Infectious Causes:
   • Bacterial:
     • Tuberculosis (particularly in active or post-primary stages).
     • Nontuberculous mycobacterial infections (e.g., Mycobacterium avium complex).
   • Fungal:
     • Aspergillosis.
   • Viral:
     • Viral pneumonias can rarely mimic this appearance.
   • Parasitic:
     • Parasitic infections like ascariasis or strongyloidiasis can rarely cause TIB.
2. Inflammatory Conditions:
   • Bronchiectasis:
     • Associated with chronic airway inflammation and infections.
   • Cystic Fibrosis:
     • TIB is common due to recurrent infections.
   • Hypersensitivity Pneumonitis:
     • Inflammatory reaction causing small airway involvement.
3. Aspiration:
   • Recurrent aspiration leading to chronic bronchiolar inflammation.
4. Diffuse Panbronchiolitis:
   • Seen primarily in East Asian populations, associated with chronic infection.
5. Connective Tissue Diseases:
   • Rheumatoid arthritis-associated bronchiolitis.

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Reactivation TB with Transbronchial Spread

Mycobacterium Avium Complex (MAC)

 

Aspergillus

Bronchopneumonic Form

ABPA

 

Bronchiectasis

HP

 

CT in the axial (upper)and coronal plane (lower panels) show most prominent changes in the anterior segment of the left upper lobe
The findings are characterized and best appreciated in the upper right panel by evidence of small airway disease including tree in bud and centrilobular nodules most prominent in the periphery
Ashley Davidoff MD TheCommonVein.net 135835

Aspiration

 

Differential Diagnosis

Conditions that may mimic the tree-in-bud sign include:

1. Miliary Nodules:
   • Random distribution, not branching.
2. Vascular Disease:
   • Centrilobular vascular opacities (e.g., pulmonary hemorrhage).
3. Sarcoidosis:
   • Perilymphatic distribution of nodules rather than centrilobular.

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Clinical Significance

• The Tree-in-Bud sign indicates a small airway disease, often with infectious or inflammatory pathology.
• It is important to correlate the radiological findings with clinical symptoms (e.g., cough, fever, dyspnea) and laboratory tests (e.g., sputum culture, serology).

---

Imaging Modalities

1. High-Resolution CT (HRCT):
   • Gold standard for identifying and characterizing the TIB sign.
2. Chest X-Ray:
   • Often non-specific and may miss subtle airway pathology.

• Is a
  • radiologic finding on chest CT
  • Characterised by
    • small, peripheral nodules,
    • originating from a centrilobular location extending into
    • distal smaller airways as
    • soft tissue nodules
    • connected to
      • multiple contiguous,
      • linear branching opacities.
      • reminiscent of a tree in bud in the spring
  • Representing
    • mucous plugging,
    • bronchial dilatation, and
    • wall thickening of bronchiolitis.
    • histopathological correlate
      • small airway plugging with
        • mucus,
        • pus, or
        • fluid, with
        • dilated intralobular bronchioles,
        • peribronchiolar inflammation, and
        • wall thickening.
•  Cause
  • • commonly associated with
    • infectious etiologies
      • aspiration
      • endobronchial spread of Mycobacterium tuberculosis,
      •  Pneumocystis jiroveci (Pneumocystis carinii) pneumonia
      • Also other infections
        •  bacterial,
        • fungal,
        • viral, or
        • parasitic
      • invasive pulmonary aspergillosis.
        • various
          • immunodeficiency states,
          • congenital disorders (cystic fibrosis),
          • malignancy (lymphoma),
          • panbronchiolitis,

Respiratory bronchioles, alveolar sacs, and alveoli
This drawing shows about 3-4 respiratory bronchioles that serve to make a secondary lobule. Alveolar sacs and individual alveoli are also seen. The yellow border represents the visceral pleura on the surface.
Courtesy of: Ashley Davidoff, M.D.

Infection

• small (2–4-mm) centrilobular nodules and
• branching linear opacities of similar caliber
• originating from a single stalk
  • bronchial wall thickening with or without
  • bronchiectasis.
• Active TB

• 

   

• TB

• 

  

  

• Aspergillus and Tree in Bud Sign

 

Other Infections

Staphylococcus Aureus

Hemophilus  Influenza

 

CMV

 

Respiratory Syncytial Virus

 

Inflammatory Diseases

Aspiration and Tree in Bud

 

Asthma

 

Inhalation Bronchiolitis

 

Obliterative Bronchiolitis aka (bronchiolitis obliterans is also known and constrictive bronchiolitis) association to lung transplant and bone marrow  transplant

 

Circulatory

 

Tree in Bud with

 

 

References and Links

Rossi, SE et al Tree-in-Bud Pattern at Thin-Section CT of the Lungs: Radiologic-Pathologic Overview RadioGraphicsVol. 25, No. 3 2005

 

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