• Subpleural sparing is a
  • pattern of lung abnormality
  • best identified on a CT scan but
  • less frequently on CXR
  • where the
  • lung regions directly adjacent to the pleura
  • are preserved
  • showing little or no involvement
  • compared to the diseased lung parenchyma in other areas.
  • It can be a critical finding in the
    • differential diagnosis of
    • interstitial lung diseases (ILDs) since it is a characteristic in patients with NSIP.

    • 

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Causes

Subpleural sparing is typically associated with certain conditions, most notably:

Inflammation

1. Non-Specific Interstitial Pneumonia (NSIP):
   • Commonly shows subpleural sparing as a distinguishing feature from usual interstitial pneumonia (UIP), where the subpleural regions are heavily involved.

1. Connective Tissue Diseases:
   • Especially in systemic sclerosis, dermatomyositis, and other autoimmune diseases with pulmonary involvement.
2. Hypersensitivity Pneumonitis (HP):
   • In chronic HP, subpleural sparing may be seen as part of a diffuse pattern of ground-glass opacities and fibrosis.
3. Sarcoidosis:
   • Advanced stages may show relative subpleural sparing despite other fibrotic or granulomatous changes in the lung parenchyma.

1. Drug-Induced Lung Disease:
   • Certain chemotherapeutic agents and other medications can cause interstitial changes with subpleural sparing.
2. Other Conditions:
   • Early organizing pneumonia or pulmonary involvement in vasculitis can also display subpleural sparing.
3. Hemorrhage

 

 

 

 

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CT Diagnosis

Subpleural sparing is best detected on high-resolution CT (HRCT) of the chest, which provides fine details of lung parenchyma. Key features to look for include:

1. Appearance:
   • Relative preservation of the lung tissue immediately adjacent to the pleura.
   • Often seen as a “rim” of normal lung between the pleura and the diseased areas (e.g., ground-glass opacities, reticulations).
2. Distribution:
   • The sparing is usually uniform and circumferential but may vary depending on the underlying disease.
3. Key CT Findings in Associated Conditions:
   • NSIP: Bilateral ground-glass opacities with basal predominance, subpleural sparing, and minimal honeycombing.
   • Hypersensitivity Pneumonitis: Patchy areas of ground-glass opacities with relative subpleural sparing.
   • Sarcoidosis: Fibrotic changes in the midzones with relative sparing of the periphery.

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Radiological Implications

1. Differentiation of Interstitial Lung Diseases:
   • Subpleural sparing is a critical diagnostic clue to differentiate NSIP from UIP, where the latter typically shows subpleural involvement and honeycombing.
2. Management and Prognosis:
   • Diseases associated with subpleural sparing, such as NSIP, often have a better prognosis and are more responsive to immunosuppressive therapy compared to UIP.
   • Correct radiological identification ensures appropriate treatment pathways.
3. Radiological Mimics:
   • Awareness of conditions with subpleural sparing is crucial to avoid misdiagnosis, especially in distinguishing it from UIP or fibrotic hypersensitivity pneumonitis.

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Conclusion

Subpleural sparing is a significant radiological finding with diagnostic and prognostic value in various interstitial lung diseases. Recognizing its pattern on HRCT aids in narrowing the differential diagnosis, guiding appropriate treatment, and improving patient outcomes.