What is the diagnostic and treatment approach for perifissural nodules?

Diagnostic and Treatment Approach for Perifissural Nodules

Perifissural nodules (PFNs) can be safely managed conservatively without follow-up imaging when they demonstrate typical morphological features, as they represent intrapulmonary lymph nodes with virtually no risk of malignancy.

Definition and Characteristics of PFNs

Perifissural nodules are small solid nodules commonly seen on CT images with specific characteristics:

• Location: Adjacent to pleural fissures or pleural surfaces
• Shape: Triangular, oval, or lentiform (flat) on transverse images
• Morphology: Homogeneous solid nodules with smooth margins
• Appearance: Often have a fine linear septal extension to the pleura
• Size: Typically small (<10 mm)

Diagnostic Algorithm for PFNs

Step 1: Identify Typical PFN Features

• Assess nodule location (adjacent to fissure or pleural surface)
• Evaluate morphology (triangular, oval, or lentiform shape)
• Check for smooth margins and homogeneous density
• Look for fine linear septal extension to the pleura

Step 2: Risk Stratification

1. Typical PFNs (<10 mm):

   • No follow-up required 1
   • These represent intrapulmonary lymph nodes

2. Atypical PFNs (features raising concern):

   • Spiculated borders
   • Displacement of adjacent fissure
   • Size >10 mm
   • History of extrapulmonary cancer
   • Follow-up CT in 6-12 months recommended 1

Step 3: Management Based on PFN Classification

For Typical PFNs:

• No follow-up imaging required, even if >6 mm 1
• Document as benign finding (intrapulmonary lymph node)

For Atypical PFNs:

• Follow standard pulmonary nodule management protocols
• Consider CT surveillance according to size and risk factors
• For nodules ≥8 mm, consider risk assessment using Brock model 1, 2

Evidence Supporting Conservative Management

Multiple studies support the benign nature of typical PFNs:

• In the NELSON lung cancer screening trial, 794 of 4,026 nodules (19.7%) were classified as PFNs. While 8.3% showed growth with volume doubling time <400 days, none were malignant after 5 years of follow-up 1.

• A study of 16,850 patients who underwent routine chest CT found that 21% of non-calcified nodules were PFNs, and none developed into lung cancer over a median follow-up of 4.5 years 3.

• In an oncologic population study, 95.2% of PFNs remained stable or decreased in size over a median follow-up of 5.6 years, suggesting benign etiology even in cancer patients 4.

Special Considerations

PFNs in Patients with Known Malignancy

• While typical PFNs are generally benign even in oncologic patients, caution is warranted with:
  • PFNs >10 mm
  • Atypical features
  • History of extrapulmonary cancer 1, 4

Reducing False Positives in Screening

• Classifying typical PFNs as benign (Lung-RADS category 2) can significantly reduce false-positive results in lung cancer screening programs 5, 6
• This approach maintains high sensitivity while improving specificity 6

New PFNs on Follow-up Imaging

• New fissure-attached nodules with typical PFN morphology are also highly unlikely to represent malignancy 7
• Apply the same morphological criteria as for baseline PFNs

Potential Pitfalls

1. Misclassification of nodules: Not all nodules adjacent to fissures are PFNs; they must have the characteristic morphology.

2. Size considerations: While most studies focus on PFNs <10 mm, larger PFNs should be approached with caution, especially with history of extrapulmonary cancer.

3. Atypical features: Spiculation, fissure displacement, or irregular margins should prompt standard nodule evaluation rather than PFN classification.

4. Overdiagnosis: Failure to recognize typical PFNs may lead to unnecessary follow-up imaging and patient anxiety.

By following this structured approach to PFN evaluation, unnecessary follow-up imaging can be avoided while maintaining patient safety and reducing healthcare costs.