• Etymology:
    Derived from the term “geographic,” meaning distinct areas or regions, used to describe patterns of lung involvement that are sharply demarcated or patchy, resembling a map-like distribution.
  • AKA:
    Patchy lung changes, Mosaic attenuation (in specific contexts).
  • What is it?
    Geographic changes refer to sharply demarcated areas of altered lung parenchyma, often with distinct differences in attenuation or density. These changes reflect heterogeneity in lung pathology and may result from variations in perfusion, ventilation, or structural integrity across different regions. Geographic changes can involve the interstitium, alveoli, or vascular structures, depending on the underlying disease.
  • Caused by:
    • Infection: Focal or multifocal bacterial pneumonia, fungal infections, or tuberculosis leading to patchy infiltrates or cavitations.
    • Inflammation/Immune: Sarcoidosis (perilymphatic nodules with patchy fibrosis), hypersensitivity pneumonitis (patchy ground-glass opacities).
    • Neoplasm: Metastatic disease presenting as sharply demarcated nodules.
    • Mechanical trauma: Pulmonary contusions resulting in localized hemorrhagic areas.
    • Metabolic: Pulmonary edema with dependent geographic changes.
    • Circulatory: Pulmonary embolism (mosaic attenuation due to perfusion defects).
    • Inherited: Lymphangioleiomyomatosis (LAM) with patchy cystic areas.
    • Congenital: Congenital lobar emphysema or bronchopulmonary sequestration.
    • Other: Post-radiation fibrosis or organizing pneumonia.
  • Resulting in:
    • Distinct regions of abnormal attenuation or density, often reflecting areas of disease activity or resolution.
    • Functional impairment based on the extent and distribution of affected lung regions.
  • Structural Changes:
    • Lung Parenchyma: Patchy ground-glass opacities, reticulations, or fibrosis in interstitial diseases.
    • Airspaces: Consolidation or cavitation in infections or neoplasms.
    • Vasculature: Perfusion defects or mosaic attenuation patterns in vascular diseases.
  • Pathophysiology:
    • Geographic changes result from uneven involvement of lung tissue due to localized or regional pathological processes.
    • Differences in perfusion, ventilation, or structural integrity create distinct areas of contrast, seen on imaging.
  • Pathology:
    • Gross: Sharply demarcated areas of abnormal lung tissue, varying from dense consolidation to cystic changes.
    • Microscopic: Focal inflammation, fibrosis, or neoplastic infiltration in affected regions.
  • Diagnosis:
    • Based on imaging patterns, clinical history, and correlation with laboratory and biopsy findings if needed.
  • Clinical:
    • Symptoms vary with the underlying cause but may include cough, dyspnea, or localized chest pain.
    • Physical exam findings can include crackles, wheezing, or reduced breath sounds over affected regions.
  • Radiology:
    • CXR:
      • Findings: Patchy opacities, regions of consolidation, or areas of hyperlucency.
      • Associated Findings: Volume loss, air bronchograms, or cavitation in certain cases.
    • CT (High-Resolution Computed Tomography):
      • Parts: Affects one or more lung lobes or segments with sharply demarcated abnormalities.
      • Size: Varies based on the extent of the pathological process.
      • Shape: Map-like or patchy patterns.
      • Position: Can involve dependent regions in pulmonary edema or subpleural areas in interstitial diseases.
      • Character:
        • Ground-glass opacities or consolidation in inflammatory or infectious conditions.
        • Mosaic attenuation in vascular or small airways diseases.
        • Nodules or cystic changes in neoplastic or congenital conditions.
      • Time:
        • Acute geographic changes seen in infections or edema.
        • Chronic changes reflect fibrosis or structural remodeling.
    • Other Relevant Imaging Modalities:
      • MRI: Limited role but may show vascular involvement.
      • PET-CT: Helpful in distinguishing active inflammation or malignancy.
      • Ultrasound: Can identify pleural-based abnormalities or guide interventions.
  • Pulmonary Function Tests (PFTs):
    • May show restrictive, obstructive, or mixed patterns depending on the underlying cause.
  • Management:
    • Treat underlying condition:
      • Antibiotics for infections.
      • Immunosuppressive therapy for inflammatory diseases.
      • Anticoagulation for thromboembolic conditions.
    • Supportive care: Oxygen therapy, pulmonary rehabilitation, and monitoring for progression.
  • Recommendations:
    • Early imaging to identify the pattern and extent of involvement.
    • Correlation with clinical and laboratory findings for accurate diagnosis.
    • Tailored treatment based on the underlying etiology.
  • Key Points and Pearls:
    • Geographic changes in the lungs reflect sharply demarcated areas of altered attenuation or density, often resembling a map-like distribution.
    • Common causes include infections, inflammation, and vascular diseases.
    • The hallmark radiological features are patchy ground-glass opacities, mosaic attenuation, reticulations, and focal consolidations, depending on the underlying condition.
    • High-resolution CT (HRCT) is essential for characterizing the pattern and distribution of changes.
    • Integration of imaging findings with clinical and pathological data is critical for accurate diagnosis and management.