Amyloidosis, Airways

Melissa L. Rosado-de-Christenson, MD, FACR

Key Facts

Terminology

Extracellular deposition of abnormal protein
Localized tracheobronchial amyloidosis; rare but most frequent form of 1° pulmonary amyloidosis

Imaging Findings

CT/HRCT
- Tracheal &/or bronchial involvement
- Focal or diffuse airway wall thickening
- Eccentric or circumferential; may involve posterior tracheal wall
- May exhibit calcification
- May produce tracheobronchial stenosis
MR
- Low signal intensity on T2WI
Nuclear medicine
- Radionuclide uptake on bone scan

Top Differential Diagnoses

Tracheal Stenosis
Tracheopathia Osteochondroplastica
Wegener Granulomatosis
Relapsing Polychondritis
Neoplasm

Pathology

Abnormal protein in airway wall submucosa
Stains with Congo Red; characteristic apple-green birefringence on polarized microscopy

Clinical Issues

Asymptomatic; cough, dyspnea, wheezing

Diagnostic Checklist

Focal or diffuse, eccentric or circumferential airway wall thickening ± calcification

Axial CECT of a patient with tracheobronchial amyloidosis shows asymmetric soft tissue thickening of the intrathoracic trachea, which affects the pars membranacea

and narrows the airway lumen.

Coronal CECT of a patient with tracheobronchial amyloidosis shows diffuse nodular soft tissue thickening

of the airway walls with scattered foci of calcification

and luminal narrowing.

TERMINOLOGY

Abbreviations and Synonyms

Amyloid light (AL) chain: May be associated with multiple myeloma and macroglobulinemia
Amyloid A (AA) chain: Inflammatory conditions (rheumatoid arthritis, inflammatory bowel disease), chronic infection, familial Mediterranean fever
Amyloid transthyretin (ATTR): Genetic mutation responsible for hereditary amyloidosis
Amyloid β-2 microglobulin (Aβ2M): Normal plasma component not cleared by hemodialysis; amyloidosis in patients on dialysis

Definitions

Amyloid
- Describes starch-like appearance of substance
- Group of molecularly diverse proteins composed of nonbranching fibrils arranged in sheets
  - Heterogeneity of amyloid related to diversity of fibril precursor peptide units
Amyloidosis = extracellular deposition of abnormal protein; resistant to proteolysis, stains with Congo Red
Biochemical classification based on specific fibrillar protein type
- Most respiratory amyloidosis due to AL subtype
Anatomic classification
- Systemic amyloidosis: AL proteins, frequent pulmonary involvement, may be asymptomatic
- Localized respiratory tract amyloidosis
  - Less common than systemic amyloidosis
  - AL proteins produced by lymphocytes and plasma cells
  - Focal and organ-limited amyloidosis without systemic disease
  - Large airway involvement typically seen in this form of disease
Systemic amyloidosis: Includes primary, secondary, and familial amyloidosis
Localized amyloidosis: Includes organ-limited and focal amyloidosis
- Calcification more common in localized deposits
Primary amyloidosis: No preceding or concurrent disease (except multiple myeloma and Waldenstrom macroglobulinemia)
Secondary amyloidosis: Concurrent infection, inflammation, neoplasia
Thoracic amyloidosis: Tracheobronchial, nodular parenchymal, diffuse alveolar septal, lymphadenopathy, pleural
- Tracheobronchial > pulmonary nodular > adenopathy > diffuse alveolar septal
Tracheobronchial amyloidosis: Rare, but most frequent form of primary pulmonary amyloidosis
- Amyloid deposits in tracheobronchial submucosa and muscle

IMAGING FINDINGS

General Features

Best diagnostic clue: Focal or diffuse nodular soft tissue thickening of airway walls ± calcification
Patient position/location: Focal or circumferential airway wall involvement
Size: Variable thickness; may obstruct airway lumen
Morphology: Nodular luminal surface; may exhibit calcification

CT Findings

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