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Pulmonary Nodules — Assessment, Imaging & Follow-Up

Registrar quick reference · Fleischner 2017 (incidental) · BTS · Lung-RADS / NLCSP (screening)
Compiled Jun 2026
Incidental ≠ screening
Solid vs subsolid first
Decision support only — not a substitute for the Fleischner 2017 guideline, BTS, local radiology, or your respiratory/MDT team. Fleischner applies to incidentally detected nodules in adults ≥35 — not to screening-detected nodules (use Lung-RADS), and not to patients with known cancer or immunosuppression. Always compare with prior imaging. Verify thresholds against the source.
1 Fleischner 2017 — solid nodule follow-up at a glance
Benign morphologyany size
Fat (hamartoma); benign calcification (central, popcorn, laminated, diffuse); perifissural/triangular node.
No follow-up. Don't surveil a confidently benign nodule.
Solid <6 mm<100 mm³
Single, indeterminate.
Low risk → no routine follow-up. High risk → optional CT at 12 months.
Solid 6–8 mm100–250 mm³
Single, indeterminate.
CT at 6–12 months, then consider CT at 18–24 months (sooner/firmer if high risk).
Solid >8 mm>250 mm³
Single, indeterminate.
CT at 3 months, PET-CT, or tissue sampling — quantify malignancy risk and take to MDT.
Subsolid ≥6 mmGGN / part-solid
Ground-glass or part-solid (part-solid carries the highest malignancy risk).
The long game: GGN → CT 6–12 mo to confirm persistence, then 2-yearly to 5 years. Part-solid → CT 3–6 mo; solid component ≥6 mm = suspicious → sample/resect.
Use the most suspicious nodule to drive management when there are several. "High risk" = heavy smoking (≥30 pack-years, quit <15y), older age, upper lobe, spiculation, emphysema/fibrosis, family history. Subsolid nodules grow slowly (lepidic adenocarcinoma) — hence the 5-year tail, and why PET is unreliable for them.
2 Characterise the nodule

Density & size

  • TypeSolid vs subsolid (pure ground-glass, or part-solid). Part-solid = highest cancer risk.
  • SizeMean of long/short axis on thin-section (1 mm) CT; volumetry preferred for tracking growth (BTS).
  • Thresholds6 mm and 8 mm are the decision points for solid; ≥6 mm for subsolid.

Morphology

  • BenignFat, benign calcification, smooth perifissural/triangular (intrapulmonary node).
  • MalignantSpiculation, lobulation, upper-lobe, pleural tag, bubbly lucency, a growing solid component.
  • MultipleOften infective/granulomatous — but manage by the most suspicious.

Compare priors

  • SolidStable ≥2 years → benign; stop surveillance.
  • Subsolid2 years isn't enough — they need up to 5 years.
  • GrowthAny unequivocal growth → act, regardless of where you are in the schedule.
3 Stratify the malignancy risk

Patient factors

  • StrongAge, smoking pack-years (and time since quitting), prior cancer, family history.
  • LungEmphysema, fibrosis, asbestos exposure raise risk.
  • CombinePatient risk + nodule features together — not size alone.

Use a model, not gestalt

  • BrockBrock / PanCan model McWilliams NEJM — malignancy probability from CT + clinical data.
  • HerderAdds PET avidity to refine intermediate-probability solid nodules.
  • WhyQuantified risk guides the PET/biopsy/surveillance decision better than impression.
4 Imaging & sampling

CT

  • ProtocolThin-section (1 mm), low-dose for surveillance.
  • GrowthVolumetry detects growth earlier and more reliably than diameter.

PET-CT — know its limits

  • UseSolid nodules >8 mm, low–intermediate probability.
  • False −Subsolid/GGO, carcinoid, <8 mm — a low SUV doesn't reassure here.
  • False +Infection, granuloma, inflammation light up.

Tissue & MDT

  • BiopsyCT-guided (peripheral) or navigational bronchoscopy (central) for accessible suspicious nodules.
  • MDTAnything >8 mm suspicious, growing, or part-solid with a solid component → lung MDT.
5 Pick the right framework — and the pitfalls

Which set of rules?

  • IncidentalFleischner 2017 — adults ≥35, nodule found on a scan done for another reason.
  • ScreeningLung-RADS — for LDCT screening. Australia's NLCSP (from Jul 2025): 50–70 y, ≥30 pack-years, current or quit <10 y, 2-yearly LDCT.
  • SpecialKnown cancer or immunocompromised → not Fleischner; lower threshold, often PET/biopsy/MDT directly.
  • <35 yCase-by-case — infection far more likely than cancer; limit serial CT.

The traps

  • Wrong rulesApplying Fleischner to a screening or known-cancer patient is the classic error.
  • SubsolidNeed a 5-year tail and PET is unreliable — don't false-reassure on a low-SUV GGO.
  • Over-workDon't chase confidently benign morphology (fat, granuloma calcification, perifissural node).
  • Anxiety/costThe 2017 raise to a 6 mm threshold exists to spare unnecessary scans — respect it.
Sources. Fleischner Society 2017 — MacMahon et al, "Guidelines for Management of Incidental Pulmonary Nodules Detected on CT," Radiology 2017 (solid & subsolid, 6 mm threshold, follow-up ranges). British Thoracic Society 2015 pulmonary nodule guideline (volumetry, Brock/Herder, PET). ACR Lung-RADS (screening). Cancer Australia — National Lung Cancer Screening Program (commenced July 2025).   Models / evidence: Brock/PanCan model (McWilliams, NEJM 2013); Herder model (PET-augmented); NLST & NELSON (screening efficacy, volumetric growth).   Caveats: Fleischner is for incidental nodules in adults ≥35 only — not screening, known cancer, or immunosuppression. Intervals are ranges, individualised by risk and patient preference. NLCSP eligibility/intervals are program-defined — confirm current criteria. Always read against prior imaging and your local MDT pathway. Companion to the respiratory set.