Pleuroparenchymal Fibroelastosis (PPFE) is a mouthful, but for radiologists, it’s a diagnosis worth knowing. Often overshadowed by more common interstitial lung diseases (ILDs) like IPF, PPFE presents a distinct and often challenging pattern of fibrosis, primarily affecting the upper lobes. This article will guide you through its unique HRCT features, help differentiate it from other ILDs, and provide a clear reporting framework.
Why PPFE Matters: It’s a progressive, debilitating condition that can lead to respiratory failure and is associated with complications like recurrent pneumothorax. Accurate and timely diagnosis is crucial for patient management.
What Exactly is Pleuroparenchymal Fibroelastosis?
Imagine your lungs’ outer lining (the pleura) and the tissue just beneath it becoming stiff, scarred, and thick, particularly at the top. That’s essentially PPFE. Pathologically, it’s characterized by the deposition of dense, elastic fibers and collagen in the subpleural parenchyma and visceral pleura.
Unlike many ILDs that “gravitate” towards the lung bases, PPFE has a striking upper-lobe predominance, making it an exception to many rules in interstitial lung disease.
Key Clinical Associations:
While some cases are idiopathic, PPFE is increasingly recognized in association with:
- Bone marrow transplantation
- Chemotherapy
- Autoimmune conditions
- Familial predisposition
- Recurrent infections
The HRCT Hallmark: What to Look For
High-Resolution Computed Tomography (HRCT) is the cornerstone of diagnosing PPFE. When reviewing scans, keep these critical features in mind:
1. Striking Upper Lobe Predominance
This is the single most important diagnostic clue. The fibrosis is either exclusively or significantly more severe in the apical and posterior segments of the upper lobes. You’ll see:
- Thickened Visceral Pleura: A clear, often irregular, thickening of the pleura in the upper zones.
- Subpleural Fibrosis: A distinct band-like or linear pattern of fibrosis running parallel to the pleura.
2. Progressive Volume Loss
As the disease advances, the fibrotic process causes the upper lobes to shrink. This leads to:
- Hilar Elevation: The hila (where vessels and bronchi enter the lung) are pulled upwards.
- Tracheal Deviation: The trachea can be pulled towards the fibrotic areas.
- “Flattened Thorax Index” (Platypnea): The chest wall itself can be affected, showing a reduction in its anteroposterior diameter, giving a “flattened” appearance. This is a subtle but important sign of chronic volume loss.
3. Traction Bronchiectasis and Bronchiolectasis
The fibrotic pull on the airways results in:
- Dilated Bronchi: Bronchi within the fibrotic upper lobes appear widened and distorted.
- Dilated Bronchioles: Small airways also show evidence of traction.
4. Recurrent Pneumothorax
This is a frequent and often presenting complication due occurring to the rigid, inelastic pleura and subpleural lung. Always look carefully for a pneumothorax, especially in patients with acute dyspnea.
Differentiating PPFE from Other Interstitial Lung Diseases
Mistaking PPFE for other ILDs can lead to inappropriate management. Here’s a quick comparison:
| Feature | Pleuroparenchymal Fibroelastosis (PPFE) | Idiopathic Pulmonary Fibrosis (IPF / UIP Pattern) | Nonspecific Interstitial Pneumonia (NSIP) |
| Primary Location | Upper Lobes Predominant | Lower Lobes & Peripheral Predominant | Diffuse, often subpleural |
| Fibrosis Pattern | Subpleural linear, fibroelastic | Honeycombing, reticulation, traction bronchiectasis | Ground-glass opacities, reticulation |
| Pleural Involvement | Marked visceral pleural thickening | Minimal to none | Minimal to none |
| Thoracic Shape | Flattened Thorax (Platypnea) | Usually normal | Normal |
| Volume Loss | Significant upper lobe volume loss | Lower lobe volume loss | Variable |
| Honeycomb Cyst Formation | Less common, often peripheral linear | Common, typically subpleural, basal | Absent |
The Radiobite Reporting Template: PPFE
Clear, concise reporting for PPFE is essential to communicate findings effectively to referring clinicians. Use this template to standardize your reports:
FINDINGS:
Lungs:
- Upper Lobes: Marked subpleural fibroelastotic-like opacities and pleural thickening noted in the bilateral upper lobes, demonstrating a clear upper-lobe predominance. Associated traction bronchiectasis and bronchiolectasis are present within these regions.
- Lower Lobes: [Spared / Demonstrate mild reticulation/ground-glass opacities / Evidence of basilar honeycombing (suggesting an overlap syndrome or secondary changes)].
- Lung Volumes: Evidence of significant bilateral upper lobe volume loss, manifested by bilateral hilar elevation and crowding of upper lobe vessels.
- Thoracic Configuration: Flattening of the anteroposterior diameter of the chest is observed, consistent with a “Flat Thorax” morphology.
Pleura:
- Visceral pleural thickening is prominent in the upper and middle lung zones. No significant pleural effusions. [Evidence of apical pleural caps].
Associated Findings:
- Pneumothorax: [Absent / Present on the (right/left) side, with approximate size/extent].
- Pulmonary Vasculature: [No evidence of pulmonary hypertension / Normal caliber pulmonary arteries].
- Mediastinum: [No significant mediastinal lymphadenopathy].
IMPRESSION:
- HRCT imaging pattern highly suggestive of Pleuroparenchymal Fibroelastosis (PPFE), characterized by progressive upper-lobe-predominant subpleural fibrosis, pleural thickening, and associated volume loss.
- [Mention any complicating factors, e.g., “Note: Small (right/left) pneumothorax also identified.”]
- [Clinical correlation recommended, particularly regarding prior bone marrow transplant, chemotherapy, or autoimmune conditions.]
Conclusion: Don’t Miss the Upper Lobe Enigma
PPFE might be rare, but its distinct upper-lobe distribution and association with complications like pneumothorax make it a crucial diagnosis for every radiologist. By recognizing the specific HRCT features – the striking upper lobe fibrosis, pleural thickening, volume loss, and the “flat thorax” – you can accurately diagnose PPFE and contribute significantly to patient care.
