Can a lung nodule be located on the surface or inside the lung?

Lung Nodule Location: Surface vs. Interior

Lung nodules can be located both on the surface (pleural or subpleural) or inside (parenchymal) the lung, with specific characteristics that help distinguish their location and potential clinical significance.

Anatomical Location of Lung Nodules

Surface Nodules

• Pleural and Subpleural Nodules: These nodules are located on or adjacent to the pleural surface of the lung 1
• Perifissural Nodules: Small solid nodules commonly seen adjacent to pleural fissures, typically representing intrapulmonary lymph nodes 1
• Characteristics:
  • Often triangular or oval on transverse images
  • Flat or lentiform configuration on sagittal/coronal reconstructions
  • May have fine linear septal extension to the pleura
  • Typically have smooth margins 1

Interior Nodules

• Parenchymal Nodules: Located within the lung tissue, surrounded by aerated lung 1
• Definition: A pulmonary nodule is defined as a lesion ≤3 cm in diameter surrounded by normal lung tissue 1
• Characteristics:
  • Can be solid, part-solid, or ground-glass in appearance
  • May have various patterns of calcification if benign
  • Location within the lung affects risk (upper lobe nodules have higher malignancy risk) 1

Clinical Significance Based on Location

Surface Nodules

• Perifissural/Juxtapleural Nodules:
  • When showing typical morphology consistent with intrapulmonary lymph nodes, follow-up CT is generally not recommended 1
  • In one study from the NELSON Lung Cancer Screening Trial, 20% of nodules were classified as perifissural, and while 16% showed growth, none were malignant 1
  • Important caveat: Perifissural or juxtapleural location alone does not guarantee benignity; specific nodule morphology must be considered 1

Risk Factors for Malignancy

• Location within the lung: Upper lobe nodules have higher risk of malignancy than lower lobe nodules 1
• Warning signs regardless of location:
  • Spiculated border
  • Displacement of adjacent fissure
  • History of cancer 1
  • Growth over time 2

Imaging Evaluation

• CT Technique: Use thin sections (≤1.5mm) to accurately characterize nodules 2
• Viewing Planes: Review on coronal or sagittal reconstructed images can be helpful in characterizing pleural-based opacities 1
• 3D Geospatial Location: Recent research suggests that nodule location within the lung (superior-inferior distance, radial distance from carina) can help predict malignancy risk 3

Management Considerations

• Typical perifissural or subpleural nodules: No follow-up needed if <10mm and showing homogeneous, smooth, solid appearance with lentiform or triangular shape 1
• Atypical features: Consider follow-up for surface nodules with spiculated borders, displacement of adjacent fissure, or in patients with history of cancer 1
• Documented growth: Any change in a previously stable nodule (surface or interior) warrants further evaluation 2

Common Pitfalls

• Apical scarring: Can have nodular appearance, especially on transverse images. Features suggesting a scar include pleural-based configuration, elongated shape, and straight or concave margins 1
• Mischaracterization: Inadequate imaging technique can lead to mischaracterization of nodules 2
• Overlooking changes: Failing to notice growth or changes in previously stable nodules can lead to delayed diagnosis 2

Understanding the location of lung nodules is critical for appropriate risk assessment and management decisions, with both surface and interior nodules requiring careful evaluation of their specific characteristics to determine clinical significance.