Diffuse tracheal pathologies
Overview
Differential diagnosis of diffuse tracheal abnormalities is a frequent theme in board exams. The primary discriminator is the involvement vs sparing of the posterior membranous wall.
- Posterior wall spared? Path process involves cartilage only (Tracheobronchopathia Osteochondroplastica, Polychondritis).
- Posterior wall involved? Path process is transmural or mucosal (Amyloidosis, GPA, Infection).
- Calcification present? Think Tracheobronchopathia Osteochondroplastica or Amyloidosis.
Tracheobronchopathia Osteochondroplastica (TBO)
Pathophysiology: Benign, rare condition. Submucosal osseous/cartilaginous metaplasia.
Demographics: Men >50 years.
Imaging features
- Nodule morphology: Multiple, sessile, calcified submucosal nodules (1–3 mm).
- Distribution: Distal 2/3 of trachea and proximal main bronchi.
- Key sign: Spares the posterior membranous wall (pathognomonic).
- Bronchoscopy: 'Cobblestone' or 'rock garden' appearance; hard on contact.
Clinical relevance
- Often incidental.
- Can cause chronic cough, haemoptysis.
- PFTs: May mimic asthma or show fixed obstruction.
Relapsing Polychondritis
Pathophysiology: Systemic autoimmune disorder affecting proteoglycans in cartilage.
Associations: Auricular chondritis (spares earlobes), nasal chondritis (saddle nose), arthritis.
Imaging features
- Morphology: Diffuse, smooth wall thickening and increased attenuation of cartilage.
- Key sign: Spares the posterior membranous wall.
- Complications: Tracheomalacia (dynamic expiratory collapse >50% lumen) and air trapping.
- Differentiation from TBO: Polychondritis causes smooth thickening/malacia; TBO causes discrete calcified nodules.
Tracheal Amyloidosis
Pathophysiology: Extracellular deposition of insoluble amyloid fibrils (AL type most common in respiratory tract).
Imaging features
- Morphology: Focal or diffuse submucosal thickening.
- Calcification: Common (partially ossified/calcified plaques).
- Key sign: Circumferential involvement (involves posterior membranous wall).
- Luminal narrowing: Can be severe.
Granulomatosis with Polyangiitis (GPA)
Pathophysiology: Necrotising granulomatous vasculitis (formerly Wegener's).
Serology: c-ANCA positive (PR3-ANCA).
Imaging features
- Morphology: Circumferential wall thickening, often irregular or ulcerated.
- Classic location: Subglottic stenosis is the characteristic airway manifestation.
- Posterior wall: Involved.
- Lung parenchyma: Cavitating nodules, masses, ground-glass opacity (alveolar haemorrhage).
Tracheal Papillomatosis
Pathophysiology: Human Papillomavirus (HPV) 6 and 11.
History: Recurrent laryngeal papillomatosis is the precursor.
Imaging features
- Morphology: Multiple polypoid soft tissue nodules encroaching on the lumen.
- Cavitation: Nodules may cavitate or form cysts (often with air-fluid levels).
- Posterior wall: Variable/random involvement.
- Malignant transformation: Squamous cell carcinoma (SCC) develops in <2% (look for rapid growth or invasion).
Differential diagnosis summary table
| Pathology | Morphology | Calcification | Posterior Wall | Key Associations |
|---|---|---|---|---|
| TBO | Discrete nodules | Yes (Bone) | Spared | Older men, incidental |
| Relapsing Polychondritis | Smooth thickening | Rare | Spared | Saddle nose, ear pain, tracheomalacia |
| Amyloidosis | Irregular plaques | Yes | Involved | Systemic amyloid signs |
| GPA | Irregular/Ulcerated | Rare | Involved | Subglottic stenosis, cavitating lung nodules |
| Tuberculosis | Irregular/Fibrotic | Variable | Involved | Long segment stenosis, mediastinal nodes |
| Sarcoidosis | Nodular/Plaque | Rare | Involved | Hilar nodes, perilymphatic nodules |
Exam tips
- "Rock garden" + spared posterior wall = TBO.
- Subglottic stenosis + cavities = GPA.
- Cystic lung nodules + tracheal polyps = Papillomatosis.
- Saber-sheath trachea: Marked coronal narrowing + sagittal widening of intrathoracic trachea. Assoc. with COPD. Not a wall thickening pathology.
