What are the typical HRCT (High-Resolution Computed Tomography) lung findings in pulmonary amyloidosis?

HRCT Findings in Pulmonary Amyloidosis

Pulmonary amyloidosis presents with distinct HRCT patterns that vary dramatically based on whether the disease is localized or systemic, with the most common systemic form showing diffuse interstitial or reticulonodular patterns with or without pleural effusion, while localized disease typically manifests as solitary or multiple pulmonary nodules. 1, 2

Systemic Amyloidosis with Pulmonary Involvement

Diffuse Alveolar Septal Pattern (Most Common)

• Interstitial or reticulonodular pattern is the predominant finding in primary systemic amyloidosis involving the lungs 2
• Diffuse irregular lines or interlobular septal thickening occurs in approximately 50% of systemic cases 1
• Reticular opacities represent amyloid deposition along the alveolar septa and interstitium 3
• This pattern reflects diffuse alveolar septal amyloidosis, which is usually associated with systemic AL amyloidosis and may affect gas exchange depending on the degree of interstitial involvement 4

Nodular Pattern

• Multiple pulmonary nodules occur in approximately 50% of systemic amyloidosis cases 1
• Nodules can present as multiple nodular opacities or patch shadows on chest radiography 3
• Some nodules may demonstrate a "halo sign" (ground-glass opacity surrounding the nodule), which correlates with severe inflammatory activity at the margins of amyloidomas and predicts faster progression and earlier response to chemotherapy 5

Pleural Involvement

• Pleural effusions are common, occurring as a presenting feature in systemic disease 1, 2
• Pleural thickening may be detected on HRCT 3
• Recurrent pleural effusions can occur in systemic amyloidosis 1

Lymphadenopathy and Mediastinal Findings

• Widespread noncalcified mediastinal and/or hilar adenopathy occurs in approximately 75% of systemic cases 1
• Infiltrative soft-tissue processes in the mediastinum may contain thick linear and focal calcifications, which is a characteristic finding 1
• Mediastinal lymphadenopathy represents another form of lung involvement in systemic amyloidosis 3

Localized Pulmonary Amyloidosis

Nodular Amyloidosis (Amyloidomas)

• Solitary pulmonary nodules are most common (60% of nodular cases), though multiple nodules can occur 1
• Nodules range in size from 8 mm to 3 cm 1
• Typically have a smooth or lobular contour with frequent subpleural or peripheral location 1
• Calcification is uncommon, occurring in only 20% of cases 1
• Multiple nodules were present in one patient with 10 separate nodules 1

Tracheobronchial Amyloidosis

• Irregular luminal narrowing and airway wall thickening with calcifications are characteristic CT findings 3
• Soft tissue shadows in the airway lumen may be visible 3
• Diffuse concentric soft-tissue thickening within the trachea can occur 1
• Focal thickening of laryngeal structures (such as the aryepiglottic fold) may be present 1
• Chest X-rays are typically normal in tracheobronchial amyloidosis, making CT essential for detection 3

Critical Diagnostic Pitfalls

Imaging Sensitivity Issues

• Chest radiography is not sensitive for detecting tracheobronchial lesions, and CT is required for adequate visualization 3
• Localized respiratory tract amyloidosis most commonly affects the trachea and bronchi but may be missed on plain films 3

Distinguishing Localized from Systemic Disease

• The presence of diffuse interstitial patterns, pleural effusions, or lymphadenopathy strongly suggests systemic rather than localized disease 1, 2
• Solitary nodules without other findings favor localized disease with a benign prognosis 2
• Bronchoscopic or surgical lung biopsy is often required for definitive diagnosis, particularly in localized disease 3, 2

Pattern Recognition for Prognosis

• The halo sign around nodules indicates active inflammatory disease with faster progression but also predicts better response to chemotherapy 5
• Diffuse interstitial patterns associated with primary systemic amyloidosis carry a poor prognosis with median survival of 16 months after diagnosis 2
• Localized amyloidomas follow a benign course and are not associated with systemic disease progression 2