Management of Small Triangular Opacity Adjacent to Anterior Oblique Fissure
No treatment is required for small triangular opacities adjacent to pulmonary fissures when they demonstrate characteristic benign morphology consistent with intrapulmonary lymph nodes or perifissural nodules. 1
Diagnostic Characterization
The key to management is proper radiographic characterization on CT imaging:
Benign Features (No Follow-up Required)
- Triangular or oval shape on transverse images with flat or lentiform configuration on sagittal/coronal reconstructions 1
- Location within 1 cm of a fissure (perifissural) or adjacent to pleural surface (subpleural) 1
- Fine linear septal extension to the pleura 1
- Smooth, homogeneous appearance without spiculation 1
When these morphologic criteria are met, follow-up CT is not recommended even if the average dimension exceeds 6 mm. 1 In the NELSON Lung Cancer Screening Trial, 20% of nodules were classified as perifissural, and while 16% grew during follow-up, none were malignant 1.
Features Requiring Surveillance
Certain characteristics override the benign perifissural location and mandate follow-up CT in 6-12 months: 1
- Spiculated borders
- Displacement of the adjacent fissure
- History of malignancy
- Lack of characteristic triangular/lentiform morphology
Imaging Recommendations
Initial Assessment
- Review on coronal and sagittal reconstructed images to confirm the elongated, triangular configuration that distinguishes benign scars from true nodules 1
- Use contiguous thin-section CT (≤2 mm collimation) for accurate characterization 1
- Measure using average of long- and short-axis diameters rounded to the nearest millimeter 1
When Imaging is Incomplete
For opacities detected on incomplete thoracic CT scans (neck, cardiac, or abdominal studies): 1
- <6 mm: No further investigation recommended
- 6-8 mm: Follow-up complete chest CT after 3-12 months depending on clinical risk factors
- >8 mm or suspicious features: Proceed with complete thoracic CT examination
Common Pitfalls to Avoid
Do not confuse with apical scarring: Pleural and subpleural apical scarring is extremely common and may appear nodular on transverse images. Look for pleural-based configuration, straight or concave margins, and presence of similar adjacent opacities. 1
Do not rely solely on transverse images: The triangular/lentiform shape that confirms benign perifissural nodules is best appreciated on coronal or sagittal reconstructions. 1
Do not apply volumetry thresholds: While perifissural nodules can be excluded from follow-up even when >6 mm in diameter, this applies only when the specific morphologic criteria are met—not simply based on size or volume measurements. 1
Risk Stratification Context
For nodules that do not meet benign perifissural criteria, management depends on size and clinical risk factors: 1
- ≤6 mm in low-risk patients: No routine follow-up
- 6-8 mm: Follow-up CT at 6-12 months based on risk factors (age, smoking history, upper lobe location)
- >8 mm: Consider PET-CT or biopsy depending on clinical context
The critical distinction is that true perifissural nodules with characteristic morphology bypass this algorithm entirely and require no follow-up regardless of size. 1