| Definition |
A deprecated descriptor for a pulmonary opacity presumed to represent the invasion of the lung parenchyma by cellular or fluid components.
Current Recommendation: The Fleischner Society discourages the use of this term due to its lack of specificity and the conflation of a radiographic observation with a pathophysiologic process. The preferred terminology is Opacity, further characterized by attenuation as Consolidation or Ground Glass Opacity. |
| Etymology |
- Infiltrate: From Latin in (“in”) + filtrum (“to strain through”).
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| Also Known As (AKA) |
Pulmonary Opacity (Preferred), Airspace Opacity. |
| Imaging Signs (Historical Usage) |
- Ill-defined Opacity: Poorly demarcated area of increased attenuation.
- Vascular Obscuration: Silhouetting of pulmonary vascular margins.
- Non-segmental Distribution: Often described as patchy or coalescent.
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| Imaging Modalities |
- CXR: The context where the term “infiltrate” is most frequently misapplied (e.g., “RLL infiltrate”).
- CT: Cross-sectional imaging mandates precise characterization (e.g., distinguishing Ground Glass from Consolidation), rendering the non-specific term “infiltrate” obsolete.
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| Structural Changes |
The displacement of alveolar air by pathological substrates.
Blood: Alveolar hemorrhage.
Pus: Exudative pneumonia.
Water: Transudative edema.
Cells: Lepidic predominant adenocarcinoma or Lymphoma. |
| Assessment (The Fleischner Rule) |
- Avoid: The term “Infiltrate.”
- Evaluate: Assess the visibility of underlying vascular markings.
- Reclassify:– Obscured vessels = Consolidation.
– Visible vessels = Ground Glass Opacity.
– Discrete opacity = Nodule/Mass.
– Linear/interstitial opacity = Reticular Opacity.
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| Differential Diagnosis |
(Due to the non-specificity of “Infiltrate,” the differential is extensive)
- Infectious Pneumonia: The most common clinical correlate.
- Atelectasis: Resorptive collapse (frequently mislabeled as infiltrate).
- Pulmonary Edema: Hydrostatic or permeability (ARDS).
- Neoplasm: Pneumonic-type adenocarcinoma or Lymphoma.
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| Causes |
- Infectious: Bacterial, Viral, Fungal etiologies.
- Inflammatory: Vasculitides, Organizing Pneumonia (COP).
- Neoplastic: Invasive Mucinous Adenocarcinoma.
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| What Next? |
- Clarify Terminology: Convert the finding to specific descriptors (Consolidation vs. Opacity).
- Differentiate: Distinguish volume loss (Atelectasis) from space-occupying processes (Pneumonia), as this fundamentally alters clinical management (e.g., bronchoscopy vs. antimicrobial therapy).
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| Key Points and Pearls |
- “Infiltrate” vs. “Pneumonia”: While clinicians often use “infiltrate” as a synonym for pneumonia, radiologists must describe the morphologic finding (e.g., “RLL airspace opacity”) before offering a diagnostic impression (e.g., “compatible with pneumonia”).
- Pathophysiologic Implication: “Infiltrate” implies active invasion. Atelectasis represents collapse, not infiltration, yet presents as an opacity. Using “infiltrate” for atelectasis may precipitate inappropriate antibiotic administration.
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| References |
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