Aspiration refers to the inhalation of foreign material (e.g., food, liquid, gastric contents, or other substances) into the airways and lungs, leading to pulmonary complications visible on imaging. In bedridden patients in the supine position, aspiration typically involves the posterior segments of the upper lobes and the superior segments of the lower lobes, as these are the most dependent areas of the lungs when lying flat.

Radiological Features

1. Chest X-Ray (CXR):
   • Localized Opacities:
     • Alveolar infiltrates in the dependent lung regions:
       • Posterior segments of the upper lobes.
       • Superior segments of the lower lobes.
     • Consolidation with air bronchograms is common if significant inflammation occurs.
   • Ground-Glass Opacities:
     • Suggests early aspiration or mild inflammation.
   • Atelectasis:
     • Focal lung collapse due to obstructive aspirated material.
2. High-Resolution CT (HRCT):
   • Acute Aspiration:
     • Ground-glass opacities or consolidations in the same dependent regions (posterior upper lobes and superior lower lobes in supine patients).
   • Chronic Aspiration:
     • Fibrotic changes, bronchiectasis, or recurrent consolidations in dependent areas.
3. Specific Imaging Patterns by Material:
   • Gastric Contents:
     • Acute pneumonitis with ground-glass opacities and consolidation.
   • Particulate Food:
     • Centrilobular nodules, focal consolidation, or airway obstruction.
   • Lipoid Aspiration:
     • Fat-density consolidations or nodules, often in dependent areas.

Common Locations in Bedridden, Supine Patients

1. Posterior Segments of the Upper Lobes:
   • The most gravity-dependent portions of the upper lobes in the supine position.
2. Superior Segments of the Lower Lobes:
   • These segments are posteriorly positioned and also gravity-dependent.

Differential Diagnosis

• Infectious Pneumonia: May not have the same gravity-dependent distribution.
• Pulmonary Edema: Diffuse findings, not segment-specific.
• Pulmonary Hemorrhage: Can be diffuse but lacks focal aspiration features.

Clinical Relevance

Aspiration in bedridden, supine patients typically involves the posterior segments of the upper lobes and superior segments of the lower lobes. Recognizing this distribution helps differentiate aspiration from other causes of lung opacities on imaging and guides management in vulnerable patients.

Dependent Segment Involvement

• Superior Segments of the Lower Lobes:
  • Most commonly involved in supine aspiration due to their posterior and gravity-dependent location.
• Posterior Segments of the Upper Lobes:
  • Frequently affected in aspiration while lying flat.
• Medial Basal Segments:
  • May be involved when aspiration extends further into the basal areas of the lower lobes in a supine patient.
  • Typically more involved than the anterior basal segments (which are higher and less gravity-dependent).
• Lateral Basal Segments:
  • Involvement is less likely in supine aspiration but can occur if the patient shifts position laterally.

Why Medial Basal Segments Are Less Commonly Affected

• Aspiration typically follows the path of least resistance to the most gravity-dependent lung regions:
  • Supine Position: This directs material to the superior segments of the lower lobes and the posterior segments of the upper lobes, which are anatomically more posterior than the medial basal segments.
  • Medial basal segments are anatomically dependent relative to anterior and lateral basal segments but less so than the superior segments.

Key Takeaway

In supine aspiration:

1. Superior segments of the lower lobes and posterior segments of the upper lobes are most commonly involved.
2. Medial basal segments may be involved but are less commonly affected than the superior segments of the lower lobes.
3. Anterior and lateral basal segments are typically spared unless aspiration occurs in an upright or lateral position.