Incidental pulmonary nodule — characterisation and follow-up

Fleischner Society 2017; BTS pulmonary nodule guideline

A nodule found by accident on a scan done for another reason. Almost every vetting decision here is about technique and interval rather than about whether to scan: an unenhanced thin-section acquisition reproducing the previous technique, at an interval set by size, morphology and risk.

A nodule reported on a CT performed for an unrelated indication, in a patient with no known malignancy and no symptoms attributable to it.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Immunosuppressed

Changes the differential rather than the modality.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Chest — Unenhanced

CT Chest

What we'd amend, and why

The question is growth, and growth is measured, not eyeballed — which makes reproducibility the whole protocol. Intravenous contrast adds nothing: a nodule is already surrounded by air, so the intrinsic contrast is as high as it can be, and enhancement only complicates comparison with an unenhanced prior. Thin sections in a consistent lung kernel matter because volume scales with the cube of diameter, so a partial-volume error of one millimetre on a 6 mm nodule is a large apparent volume change. Matching inspiratory effort and reconstruction to the previous study is what makes "stable" a measurement rather than an impression.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner
rulerule-pregnancy-ionising — Pregnancy status before an ionising exposure; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(2)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.
Pregnancy status before an ionising exposure
Make the pregnancy enquiry immediately before the exposure and record the answer. In the UK this is a statutory operator duty discharged at the time of exposure under the employer’s written procedures required by IR(ME)R 2017 — it is not something the vetting radiologist can perform or pre-empt, and a request is complete without it.
Radiographer at the scannerAt the scanner
Flags back if: The patient states that she is, or may be, pregnant AND the uterus is in or near the primary beam. The exposure is then paused for re-justification by the IR(ME)R practitioner before it proceeds.
Nodule surveillance is elective by definition. If the patient is pregnant, the correct action is almost always to defer the interval scan rather than to shield and proceed — a few months rarely changes the outcome for a nodule under surveillance, and no other question is being answered.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Immunosuppressed — a nodule that is infection until proven otherwise

Role	Study & protocol	Why this answers the question
First line	CT Chest CT Chest — Unenhanced usually appropriate	The acquisition is the same thin-section unenhanced study; what changes completely is the interval and the differential, and that is why this is a different pathway rather than a footnote. Fleischner states explicitly that its recommendations do not apply to immunosuppressed patients, so quoting a three-, six- or twelve-month interval to a transplant recipient, a patient on a biologic, or someone neutropenic after chemotherapy is applying a schedule to a population it was never derived in. In that population a new nodule is opportunistic infection until proven otherwise — angioinvasive fungal disease, nocardia, mycobacterial disease — and the tempo is days to weeks, judged against the clinical picture, the neutrophil count and the antifungal decision rather than against a surveillance calendar. The corollary for reporting is that the findings which are non-specific in an immunocompetent patient become actionable here: a halo of ground glass around a nodule, clustered or peripheral wedge-shaped nodules, and cavitation appearing as the neutrophil count recovers.

This fork deliberately carries one study. FDG PET-CT sits on the default ladder as the metabolic tie-breaker between benign and malignant, and that discrimination does not survive immunosuppression: infection and inflammation are avidly FDG-positive, so a hot nodule in this group separates nothing, and listing it here would imply a rung worth climbing.
Nothing here sets an interval. The point is that the interval belongs to the treating team and the infection question, not to a surveillance schedule — and that a request quoting a Fleischner interval for an immunosuppressed patient has usually misidentified which question is being asked.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Chest CT Chest — Unenhanced usually appropriate	The question is growth, and growth is measured, not eyeballed — which makes reproducibility the whole protocol. Intravenous contrast adds nothing: a nodule is already surrounded by air, so the intrinsic contrast is as high as it can be, and enhancement only complicates comparison with an unenhanced prior. Thin sections in a consistent lung kernel matter because volume scales with the cube of diameter, so a partial-volume error of one millimetre on a 6 mm nodule is a large apparent volume change. Matching inspiratory effort and reconstruction to the previous study is what makes "stable" a measurement rather than an impression.
Problem solving	FDG PET-CT FDG PET-CT — skull base to mid-thigh	Metabolic characterisation for a solid nodule large enough to be measured reliably by a PET scanner — conventionally around 8 mm and above, below which partial-volume effects make a low standardised uptake value uninformative rather than reassuring. It contributes most when it changes the estimated probability of malignancy enough to move the patient between surveillance, biopsy and resection. It is close to useless for pure ground-glass nodules, which are metabolically quiet even when malignant.

The 2017 revision raised the size threshold below which no routine follow-up is advised and expressed intervals as ranges rather than fixed dates, deliberately leaving room for individual risk and preference. The numbers are worth stating rather than gesturing at, because the commonest defect on this card is surveillance that should never have started. For a SINGLE SOLID nodule under 6 mm — equivalently under about 100 cubic millimetres by volume — no routine follow-up is recommended in a low-risk patient, and in a high-risk patient an optional single CT at 12 months is offered rather than a schedule. Between 6 and 8 mm the recommendation is a CT at 6 to 12 months and then, depending on stability and risk, at 18 to 24 months. Above 8 mm the options are a CT at 3 months, PET-CT, or tissue sampling, chosen on the estimated probability of malignancy. Multiple nodules follow the same size bands, driven by the largest.
Subsolid nodules are given longer initial intervals and longer total surveillance than solid ones, because indolent adenocarcinoma spectrum lesions can be stable for years and then grow. Pure ground-glass nodules under 6 mm need no routine follow-up; at 6 mm and above the schedule is a CT at 6 to 12 months and then every two years out to five years. A part-solid nodule under 6 mm needs no routine follow-up either; at 6 mm and above it is re-imaged at 3 to 6 months and then annually for five years, and a solid component reaching about 6 mm is the finding that moves it towards resection.
The schedules end, and the end point is part of the recommendation. A solid nodule unchanged over two years is resolved and comes off surveillance; a subsolid one needs the full five years, because the growth of an indolent adenocarcinoma is measured over that timescale. Nothing here is a substitute for judgement in a patient whose life expectancy or fitness means no result would be acted on — in that patient the correct number of follow-up scans is none, and saying so is the useful clinical act.

Pitfalls

Adding intravenous contrast because the request said "CT chest". It costs a cannula, a renal check and nothing gained, and it degrades comparison with the unenhanced prior.
Comparing across different slice thickness or reconstruction kernel and reporting the difference as growth or stability. This is the single commonest source of a false-positive interval change.
Applying the incidental-nodule schedule to a patient with a known extrathoracic primary, where the same nodule carries a different pre-test probability and belongs on a staging pathway.
Reading a low FDG uptake value in a sub-centimetre nodule as evidence of benignity — the scanner cannot resolve it, so the number is a technical artefact rather than biology.
Restarting the clock at every new radiologist. Surveillance is a schedule with an end point — two years for a solid nodule, five for a subsolid one — and repeatedly extending it is a harm of its own.
Starting surveillance that Fleischner does not ask for. A single solid nodule under 6 mm, or a pure ground-glass or part-solid nodule under 6 mm, needs no routine follow-up in a low-risk patient; putting one on a schedule commits the patient to years of scanning, dose and anxiety for a lesion whose malignancy risk is under one per cent. Over-investigation is a safety failure here in the same way under-investigation is, and the request that asks for a three-month interval on a 4 mm nodule should be answered with the guideline rather than with an appointment.
Quoting an interval without recording which risk group and which morphology it came from. Fleischner intervals are ranges, and a range applied without the smoking history, the morphology and the location is a number the next radiologist cannot check or safely stop.
Applying any of this to a patient in whom no result would change management. Life expectancy, frailty and fitness for any intervention are part of the vetting decision, and a surveillance programme nobody would act on is pure harm.

Priors — what to pull first

Hunt for older imaging before scheduling anything — a nodule demonstrably unchanged over two years on any prior study, including a CT done for trauma or renal colic, ends solid-nodule surveillance immediately.
Record the technique of the comparison study, not only its date. A 5 mm-section prior is not a valid comparator for a 1 mm-section current study.

What makes a good request

A good request states the nodule size and whether it is solid, part-solid or pure ground-glass, the date and technique of the study that found it, and the smoking history — those four items determine both the interval and whether follow-up is needed at all.
The Fleischner recommendations apply to incidental nodules in adults aged 35 and over. They do not apply to screening-detected nodules (which follow a structured reporting system), to patients with known primary malignancy, or to immunosuppressed patients, in whom infection dominates the differential.
Where a nodule was found on a screening study, the surveillance schedule belongs to the screening programme and not to this card.

Scoring this once it is done

The classification and risk tools this question ends in.

Fleischner Incidental Pulmonary Nodules Brock (PanCan) Pulmonary Nodule Malignancy Risk Herder Model (Mayo + FDG-PET) for SPN Malignancy Risk Mayo Clinic Solitary Pulmonary Nodule Model BTS 2015 Pulmonary Nodule Guideline Navigator Nodule Volume Doubling Time (VDT)Lung-RADS v2022 (Screening LDCT)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Chest — Unenhanced FDG PET-CT — skull base to mid-thigh

Confirm locally

CT Chest — Unenhanced: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.