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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Pulmonology

Decoding Your Diagnosis: Imaging and Genetic Testing

At a Glance

Diagnosing Birt-Hogg-Dubé (BHD) syndrome requires a High-Resolution CT (HRCT) to spot characteristic lower-lung cysts and precise genetic testing of the FLCN gene. Ensure your genetic testing includes deletion/duplication analysis so mutations aren't missed.

Getting a definitive answer for recurring lung collapses requires a “two-key” approach: specialized imaging of the lungs and precise genetic testing of your DNA. Because Birt-Hogg-Dubé (BHD) syndrome is rare, standard reports might miss the subtle clues that point toward a genetic cause [1][2].

The Gold Standard: High-Resolution CT (HRCT)

A standard chest X-ray can show a lung collapse, but it cannot see the thin-walled cysts that cause it. A High-Resolution CT (HRCT) is essential [3]. Unlike “typical” lung collapses (Primary Spontaneous Pneumothorax) which usually involve blisters at the top of the lung, BHD has a very specific “signature” on a scan:

  • Basal Distribution: The cysts are primarily found in the lower lobes (the base) of the lungs [4][5].
  • Paramediastinal Location: Cysts often appear near the heart and the middle of the chest [3][6].
  • Variable Shapes: Unlike the perfectly round cysts seen in other diseases, BHD cysts can be “floppy,” oval, or multi-chambered [3][7].

Genetic Testing: The Definitive Proof

While imaging can strongly suggest BHD, a blood or saliva test for the FLCN gene is the only way to confirm the diagnosis [8][9]. A complete genetic workup should include:

  1. Sequence Analysis: This “reads” the gene letter-by-letter to find small typos [10].
  2. Deletion/Duplication Analysis (MLPA): This looks for large missing or extra “chapters” of the gene. About 10% of BHD cases are missed if this step isn’t included [11][12].

Report Completeness Checklist

When you receive your medical records, check for these specific details to ensure your care team has all the information they need.

Radiology Report (HRCT) Genetic Test Report
[ ] Number and size of cysts (e.g., >40 cysts) [13] [ ] Gene tested: FLCN [14]
[ ] Specific location (Basal vs. Apical) [4] [ ] Variant classification (e.g., “Pathogenic”) [15]
[ ] Presence of “paramediastinal” cysts [3] [ ] Deletion/Duplication analysis performed [11]
[ ] Comparison to previous scans (if any) [16] [ ] Specific mutation name (e.g., c.1285dup) [17]

Decoding Your Reports: Technical Terms

  • Basal: Located at the bottom of the lungs [4].
  • Apical: Located at the top of the lungs [18].
  • Subpleural: Located just beneath the outer lining (pleura) of the lung [18][3].
  • Paramediastinal: Located in the area near the heart and great vessels in the center of the chest [3].
  • Blebs: Tiny blisters under 1cm, typically found at the top of the lung [18].
  • Bullae: Larger air pockets over 1cm within the lung tissue [19].
  • Pathogenic Variant: A genetic change that is known to cause disease [15].
  • Variant of Uncertain Significance (VUS): A genetic change where it is not yet clear if it causes disease or is just a normal human variation [20].
  • Bilateral: Affecting both the left and right lungs [21].

If your reports use these terms, it is a sign that your clinical team is looking for the specific patterns associated with Familial Spontaneous Pneumothorax [5][22].

Return to Home | Next: Taking Action: Surgical Strategies and Precautions

Common questions in this guide

Why do I need a High-Resolution CT (HRCT) instead of a standard chest X-ray?
While a standard chest X-ray can show a lung collapse, it cannot clearly show the thin-walled cysts that cause it. A High-Resolution CT scan is essential for seeing the specific size, shape, and location of cysts in the lungs.
What is the specific pattern of lung cysts in Birt-Hogg-Dubé (BHD) syndrome?
Unlike typical lung cysts found at the top of the lungs, BHD cysts are primarily located in the lower lobes and near the center of the chest. They also often appear in variable shapes, such as floppy, oval, or multi-chambered.
What genetic test confirms Birt-Hogg-Dubé syndrome?
BHD is confirmed through a blood or saliva test that checks the FLCN gene for mutations. This testing should include both sequence analysis and deletion/duplication analysis to ensure no genetic changes are missed.
What if my FLCN genetic sequencing comes back negative?
If standard genetic sequencing is negative, you must ensure the lab also performed Deletion/Duplication Analysis, sometimes called MLPA. Without this extra step, about 10 percent of BHD cases are missed.
What does a "Pathogenic Variant" mean on my genetic report?
A pathogenic variant means the laboratory found a specific genetic change in the FLCN gene that is known to cause disease. This finding confirms the genetic diagnosis of Birt-Hogg-Dubé syndrome.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.My imaging shows cysts in the lower lobes; how common is this pattern in primary spontaneous pneumothorax versus a genetic syndrome like BHD?
  2. 2.If my FLCN sequencing comes back negative, will the lab automatically perform a 'Deletion/Duplication analysis' or MLPA to look for larger genetic missing pieces?
  3. 3.Can you confirm if the cysts are located in the 'paramediastinal' region, and does that change my diagnostic score?
  4. 4.Do I need to see a genetic counselor to discuss how these results might affect my siblings or children?
  5. 5.Now that we have these imaging results, what is the recommended schedule for screening my kidneys?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

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This page explains imaging and genetic testing for Birt-Hogg-Dubé syndrome for educational purposes only. Always discuss your specific CT scans and genetic test results with your pulmonologist or medical geneticist.

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