2  DDx of Diffuse Tracheal Thickening

Diffuse tracheal thickening represents abnormal thickening of the tracheal wall, which can be caused by various pathological processes. Understanding the differential diagnosis is crucial for accurate interpretation of radiographic findings.

2.1 Common Causes of Diffuse Tracheal Thickening

2.1.1 Relapsing Polychondritis

  • Definition: Collagen vascular disease characterized by inflammation and progressive destruction of cartilage throughout the body
  • Affected areas: Ribs, trachea, earlobes, nose, joints
  • Radiographic features:
    • Diffuse narrowing of trachea (slit-like lumen)
    • Thickening of tracheal wall
    • Sparing of the posterior membranous trachea
  • Clinical criteria (more than three needed):
    • Recurrent chondritis of auricles
    • Inflammation of ocular structures
    • Chondritis of laryngeal/tracheal cartilage
    • Cochlear or vestibular damage
  • Distribution: Ear (90%), joints (80%), nose (70%), eye (65%), respiratory tract (55%), inner ear (45%)
  • Recognition: Airway involvement particularly the larynx and subglottic trachea is most common

[Primer_Chest Imaging, 40-41]

2.1.2 Tracheobronchopathia Osteoplastica (TPO)

  • Definition: Foci of cartilage and bone develop in the submucosa of the tracheobronchial tree
  • Clinical findings:
    • Dyspnea, hoarseness, expiratory wheeze/stridor
    • Hemoptysis (mucosal ulceration)
    • Cough and sputum production
    • Rarely atelectasis or pneumonia
  • Radiographic features:
    • Calcified tracheobronchial tree, nodules, osteocartilaginous growth
    • Thickening of tracheal cartilage
    • Characteristic: Sparing of the posterior membranous portion
    • Narrowed lumen
    • Commonly affects distal three-fourths of the trachea and proximal bronchi
  • Note: Benign, rare condition often discovered incidentally at autopsy

[Primer_Chest Imaging, 40]

2.1.3 Amyloidosis

  • Definition: Extracellular deposition of protein derived from light chains of monoclonal immunoglobulin
  • Types:
    • Primary amyloid: heart, lung (70%), skin, tongue, nerves
    • Amyloid associated with multiple myeloma
    • Secondary amyloid (liver, spleen, kidney)
    • Heredofamilial amyloidosis
    • Local amyloidosis in isolated organs
    • Amyloid associated with aging
  • Radiographic features (airway involvement):
    • Nodular and irregular thickening of the trachea
    • Important: The posterior membranous trachea is NOT spared (unlike TPO and relapsing polychondritis)
    • Adenopathy and calcifications are common
  • Diagnosis: Requires biopsy

[Primer_Chest Imaging, 35, 73] [Core_Thoracic_Imaging, 11]

2.1.4 Sarcoidosis

  • Definition: Systemic granulomatous disease of unknown etiology with non-caseating granulomas
  • Tracheal involvement:
    • Rare and usually seen in advanced disease
    • Variable appearance from smooth stenosis to nodular/mass-like appearance
    • Posterior membranous trachea is not spared
  • Pulmonary findings: Bilateral hilar adenopathy, perilymphatic nodules, upper lobe predominance
  • Other findings: Fibrocystic changes, aspergilloma in cavities, bronchostenosis with lobar/segmental collapse

[Core_Thoracic_Imaging, 11] [Primer_Chest Imaging, 32]

2.1.5 Wegener Granulomatosis (Granulomatosis with Polyangiitis)

  • Definition: Systemic vasculitis affecting small and medium-sized vessels
  • Airway involvement:
    • Seen in approximately 20% of patients
    • Most commonly manifests as subglottic tracheal stenosis
    • Circumferential mucosal thickening
    • Posterior membranous trachea is not spared
    • Calcifications are not seen
  • Classic triad: Upper respiratory tract involvement, lung involvement, glomerulonephritis
  • Radiographic findings: Multiple cavitating pulmonary nodules or masses

[Core_Thoracic_Imaging, 11] [AuntMinnie_THORACIC RADIOLOGY, 70]

2.2 Comparison Table of Diffuse Tracheal Thickening

Entity Involvement of Posterior Membranous Portion Calcification Distribution Key Features
Relapsing Polychondritis No (spared) No Diffuse tracheal thickening with slit-like lumen Affects multiple cartilages in body (ear, nose, joints); respiratory symptoms
Tracheobronchopathia Osteoplastica No (spared) Yes Distal 3/4 of trachea and proximal bronchi Foci of cartilage and bone in submucosa; nodular appearance
Amyloidosis Yes (involved) Possible Variable Irregular narrowing; may be associated with systemic amyloidosis
Sarcoidosis Yes (involved) No Variable Rare finding in advanced sarcoidosis; associated with hilar adenopathy
Wegener Granulomatosis Yes (involved) No Often subglottic Associated with other manifestations of Wegener’s; ANCA+

2.3 Additional Considerations

2.3.1 Malignancies

  • Primary tracheal tumors (squamous cell carcinoma, adenoid cystic carcinoma)
  • Metastatic disease

2.3.2 Infections

  • Tuberculosis and atypical mycobacterial infections
  • Fungal infections (particularly in immunocompromised patients)

2.3.3 Other

  • Tracheomalacia (decreased diameter on expiration)
  • Saber-sheath trachea (reduced coronal diameter)
  • Inflammatory bowel disease-related tracheobronchial involvement (rare)

2.4 Key Diagnostic Differentiating Features

  1. Posterior membranous trachea involvement:
    • Spared: Relapsing polychondritis, TPO
    • Involved: Amyloidosis, sarcoidosis, Wegener granulomatosis
  2. Calcification:
    • Present: Tracheobronchopathia osteoplastica
    • Usually absent: Relapsing polychondritis, Wegener granulomatosis, sarcoidosis
  3. Clinical context:
    • Multisystem involvement (cartilage): Relapsing polychondritis
    • Pulmonary-renal syndrome: Wegener granulomatosis
    • Hilar adenopathy: Sarcoidosis
    • Age and comorbidities may provide additional clues
  4. Imaging modality considerations:
    • CT is more sensitive for detection of tracheal wall abnormalities
    • MRI may add value in tissue characterization
    • PET/CT may help assess inflammatory activity and guide biopsy