What are the High-Resolution Computed Tomography (HRCT) criteria for diagnosing Pleuroparenchymal Fibroelastosis (PPFE)?

HRCT Criteria for Pleuroparenchymal Fibroelastosis (PPFE)

The diagnostic HRCT features of PPFE consist of dense subpleural consolidation with traction bronchiectasis, architectural distortion, and upper lobe volume loss, predominantly affecting the upper lobes with characteristic pleural-based opacities and reticular patterns. 1

Primary HRCT Features

The hallmark imaging findings include:

• Irregular pleural-based opacities in the upper lobes with associated reticular patterns and parenchymal distortion 1
• Dense subpleural consolidation with traction bronchiectasis as the defining characteristic 1
• Architectural distortion of the underlying lung parenchyma 1
• Upper lobe volume loss with bilateral upward shift of hilar structures 2, 3
• Pleural thickening involving the visceral pleura with subpleural fibrosis 3, 4

Distribution Pattern

The distribution is critical for diagnosis:

• Upper lobe predominance is the defining feature, though lower lobe involvement may occur 1, 2
• The pleura and lungs in the lower lobes may appear normal or show only subtle subpleural reticular patterns 1
• PPFE may be seen in 6-10% of IPF cases as a coexistent finding 1

Diagnostic Categories Without Surgical Biopsy

When surgical lung biopsy is not performed, three radiological categories exist 2:

• Radiologically possible PPFE: CT lesions present in both lung apexes, regardless of lower lobe involvement 2
• Radiologically probable PPFE: Requires chest radiograph findings of bilateral upward shift of hilar structures and/or CT findings of upper lobe volume loss 2
• Radiologically and physiologically probable PPFE: Adds physiological criteria including RV/TLC %predicted ≥115% and BMI ≤20 kg/m² plus RV/TLC %predicted ≥80% 2

Key Distinguishing Features

PPFE must be differentiated from other upper lobe fibrotic processes:

• The subpleural and pleural-based distribution with elastotic fibrosis distinguishes PPFE from typical UIP patterns 1
• Scattered pleuroparenchymal opacities with distortion of underlying parenchyma are characteristic 1
• PPFE can occur as an isolated entity or coexist with other interstitial lung diseases, particularly IPF 1, 5

Clinical Context and Associated Findings

Important clinical associations include:

• Pneumothorax is common and should raise suspicion for PPFE 1
• Approximately half of patients have experienced recurrent infections 1
• PPFE is strongly associated with lung transplantation (7.54% prevalence) and hematopoietic stem cell transplantation (0.28% prevalence) as late complications 4
• When PPFE is present in IPF patients, it is associated with more rapid decline in lung function, higher risk of pneumothorax and pneumomediastinum, and poorer survival 1

Diagnostic Pitfalls

Critical considerations to avoid misdiagnosis:

• Do not confuse the upper lobe predominance with sarcoidosis or hypersensitivity pneumonitis, which have different parenchymal patterns 3
• The definite PPFE pattern (concentrated in upper lobes with less marked lower lobe involvement) must be distinguished from consistent PPFE (not concentrated in upper lobes or with features of coexistent disease elsewhere) 5
• CT-guided transthoracic core lung biopsy can be considered when surgical biopsy is contraindicated, though pneumothorax requiring chest tube placement is common 6