Incidental Pulmonary Nodules & Other Incidental Chest CT Findings

 

NP CHRONICLES Incidental Pulmonary Nodules & Other Incidental Chest CT Findings A practical framework for the nodule you weren't looking for — plus the thyroid, coronary, and abdominal findings that come along for the ride

Clinical education for NP students and new graduates  •  Board-relevant  •  Based on a Pri-Med CME lecture by Stephen Bujarski, MD (Baylor College of Medicine / Michael E. DeBakey VA Medical Center)

A patient falls off a step stool, bruises a rib, and walks out of the ER with a lung nodule nobody was looking for. It happens constantly: incidental pulmonary nodules are detected on roughly 30% of all chest CT scans, translating to about 1.6 million people per year in the U.S. who are handed a result they never expected — and a clinician (often you) who has to decide what to do about it. The good news: 90–95% of these nodules are benign. The job is figuring out, systematically, which ones aren't — and knowing what to do with the thyroid nodule, the coronary calcification, or the liver lesion that showed up in the same scan.

CLINICAL BOTTOM LINE

●        An incidental pulmonary nodule (IPN) is a well-defined lesion <3 cm, completely surrounded by lung parenchyma, unrelated to the reason imaging was ordered. ●        Management hinges on nodule size, morphology (solid vs. subsolid), and the patient's individual risk — not on reflexive anxiety about cancer. ●        The Fleischner Society 2017 guidelines govern truly incidental nodules; Lung-RADS governs nodules found on formal lung cancer screening LDCT — know which framework you're in. ●        Small nodules aren't the only incidental finding worth your attention: thyroid nodules, coronary calcification, aortic aneurysms, and abdominal organ lesions are common stowaways on chest CT.

CASE FROM PRACTICE — Case 1

A 66-year-old man is seen in clinic after an ER visit for chest pain following a fall off a step stool. A chest X-ray showed no rib fracture but a vague opacity in the right upper lobe, prompting a CT chest. He's told the scan is abnormal and to follow up with his primary care clinician. History: former smoker, quit ~6 years ago, smoked 1 pack/day since age 15 — a ~45 pack-year history. The nodule: 16 mm, right upper lobe, solid, spiculated. Using a validated risk calculator (Mayo Clinic model — age, nodule diameter, smoking status, extrathoracic cancer history, upper lobe location, spiculation, and optional PET uptake), his probability of malignancy came back at 60.1%, placing him solidly in the intermediate-to-high risk range. He proceeded to VATS wedge and frozen resection; cancer was detected intraoperatively, so the surgeon completed a lobectomy with lymph node dissection. Pathology: non-small cell carcinoma, invasive adenocarcinoma, poorly differentiated. Pathologic stage pT1b, pN0, M0 — Stage I. He was placed on post-operative surveillance.

Defining the Incidental Pulmonary Nodule

●        Incidental: a finding unrelated to the chief complaint and not pertinent to the immediate reason for the visit.

●        Lung nodule: a well-defined lesion, completely surrounded by pulmonary parenchyma, measuring less than 3 cm in size.

Because only about a quarter of these nodules turn out to be cancer-adjacent concerns, the instinct to reflexively chase every finding with more imaging or biopsy isn't just inefficient — it can drive unnecessary invasive procedures. A systematic, risk-stratified approach is the whole point of the guidelines below.

Causes of pulmonary nodules

The differential is broad. Malignant neoplasia (bronchogenic carcinoma, carcinoid/neuroendocrine tumors, metastasis, lymphoma) sits alongside benign neoplasia (hamartoma, chondroma, fibroma, neural tumor, hemangioma), infectious causes (tuberculosis, fungal infection, lung abscess, round pneumonia, nontuberculous mycobacteria, nocardia, septic embolus), inflammatory disease (granulomatosis with polyangiitis, rheumatoid nodule, sarcoidosis), vascular lesions (AV malformation, hematoma, pulmonary artery aneurysm, pulmonary infarct), and bronchial lesions (bronchogenic cyst, mucocele, sequestration).

Three Pathways to Discovery — Three Different Frameworks

How a nodule was found determines which guideline applies. Conflating these pathways is a common source of over- or under-management.

●        Incidental discovery (imaging obtained for an unrelated reason) → Fleischner Society 2017 guidelines, or the parallel American College of Radiology (ACR) incidental findings algorithm.

●        Lung cancer screening low-dose CT → Lung-RADS 2022, a distinct structured reporting and management system.

●        Symptom-driven evaluation (hemoptysis, unexplained weight loss, persistent cough) → managed on its own clinical merits, generally with a lower threshold for tissue diagnosis regardless of nodule size.

Nodule morphology

Nodules are first sorted as solid or sub-solid (SSN). Sub-solid nodules are further divided into part-solid (semi-solid) and pure ground-glass (GGO) nodules. This distinction matters because solid and sub-solid nodules carry different natural histories and follow different Fleischner follow-up schedules — ground-glass and part-solid nodules, in particular, can be slow-growing and require longer surveillance windows before a decision point is reached.

Fleischner Society 2017 Guidelines

The Fleischner Society is an international multidisciplinary group — radiology, pathology, pulmonary medicine, epidemiology, and thoracic surgery — founded in 1969 to build consensus recommendations for chest imaging. Their solid-nodule guidelines were first published in 2005 and most recently updated in 2017. These guidelines apply specifically to nodules discovered outside the context of formal lung cancer screening, and require the clinician to classify the patient as low risk (<5% annual chance of lung cancer) or high risk (>5%) based on factors like older age, heavy smoking history, nodule margin characteristics, and upper lobe location.

A: Solid nodules

Nodule type	<6 mm (<100 mm³)	6–8 mm (100–250 mm³)	>8 mm (>250 mm³)
Single, low risk	No routine follow-up	CT at 6–12 mo, then consider CT at 18–24 mo	Consider CT at 3 mo, PET/CT, or tissue sampling
Single, high risk	Optional CT at 12 mo	CT at 6–12 mo, then CT at 18–24 mo	Consider CT at 3 mo, PET/CT, or tissue sampling
Multiple, low risk	No routine follow-up	CT at 3–6 mo, then consider CT at 18–24 mo	CT at 3–6 mo, then CT at 18–24 mo
Multiple, high risk	Optional CT at 12 mo	CT at 3–6 mo, then CT at 18–24 mo	CT at 3–6 mo, then CT at 18–24 mo

 

Comments: nodules <6 mm generally don't require routine follow-up, but certain high-risk patients with suspicious morphology, upper lobe location, or both may still warrant a 12-month follow-up scan. For multiple nodules, use the most suspicious nodule to guide management — follow-up intervals may vary by size and risk.

B: Sub-solid nodules

Nodule type	<6 mm (<100 mm³)	≥6 mm (>100 mm³)
Single, ground glass	No routine follow-up	CT at 6–12 mo to confirm persistence, then CT every 2 years until 5 years
Single, part-solid	No routine follow-up	CT at 3–6 mo to confirm persistence. If unchanged and solid component <6 mm, annual CT for 5 years
Multiple	CT at 3–6 mo; if stable, consider CT at 2 and 4 years	CT at 3–6 mo. Subsequent management based on the most suspicious nodule(s)

 

Comments: in certain suspicious nodules <6 mm, consider follow-up at 2 and 4 years — if a solid component or growth develops, consider resection. Part-solid nodules cannot truly be classified as such until the solid component is ≥6 mm; persistent part-solid nodules with a solid component ≥6 mm should be considered highly suspicious. Multiple pure ground-glass nodules <6 mm are usually benign, but selected high-risk patients may warrant follow-up at 2 and 4 years.

Source: MacMahon H, Naidich DP, Goo JM, et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology 2017;284:228-243.

Practical Guidance at the Point of Care

●        Individual and nodule risk factors: age, smoking history, personal or family history of cancer; nodule size, shape, morphology, and whether it's single or multiple.

●        Prior imaging: is there anything to compare against? If so, is the nodule new, growing, or stable?

●        Ask yourself whether there are corresponding signs or symptoms pointing toward cancer, infection, or systemic disease — the nodule rarely exists in isolation from the rest of the history.

Risk predictor models

Multiple validated models estimate the probability that a given nodule is malignant, using overlapping independent predictors: age, smoking history, personal cancer history, nodule diameter, spiculation, and nodule location. Models differ by the population they were derived from — the Mayo Clinic model, the Brock model, and a VA-derived model are commonly cited, built respectively from general clinical populations, screening cohorts, and veterans. Many clinicians also estimate probability intuitively — a reasonable approach when validated against these formal models, though studies suggest gestalt alone often under- or over-estimates risk compared to a structured calculator.

Risk category	Probability of malignancy
Low	<5%
Intermediate	5% to 65%
High	>65%

 

NUANCE TO REMEMBER

Risk stratification isn't just three buckets — it should change what you do next. One commonly cited approach: consider watchful waiting only at very low post-test probabilities (<2%), biopsy at lower post-test probabilities (2–20%), and surgical evaluation at higher post-test probabilities (>70%). Shared decision-making belongs at every step in between.

Sampling options

●        Bronchoscopically — including newer robotic-assisted bronchoscopic biopsy platforms for peripheral lesions.

●        Percutaneously, via interventional radiology (CT-guided biopsy).

●        Surgical resection — including VATS wedge biopsy with intraoperative frozen section, which can be extended to lobectomy and lymph node dissection if malignancy is confirmed on the table.

The ACR Approach to Incidental, Asymptomatic Solid Nodules

The American College of Radiology's Incidental Findings Committee publishes a parallel white paper and decision algorithm for managing incidental thoracic CT findings. For patients with limited life expectancy, significant comorbidities, or age under 35, management depends on the individual clinical scenario rather than a fixed protocol. For the general population age 35 and older, nodules are first sorted by risk (low risk <5%, high risk ≥5%) and then by size:

Risk category	<6 mm	6–8 mm	>8 mm
Low risk (<5%)	No further workup	CT at 6–12 mo; then consider at 18–24 mo	CT at 3 mo or PET/CT and/or tissue sampling
High risk (≥5%)	No follow-up, or CT at 12 mo	CT at 6–12 mo; then at 18–24 mo	CT at 3 mo or PET/CT and/or tissue sampling

 

Source: Managing Incidental Findings on Thoracic CT: Lung Findings. A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2021;18(9):1267-1279.

Shared Decision-Making

Hearing the words "lung cancer" — even in the context of an incidental nodule with a low probability of malignancy — is stressful, and it's normal for patients to be anxious even when the actual risk is small. Patient education materials, such as the American Thoracic Society's "What is a Lung Nodule?" handout, are a useful anchor for these conversations: covering why the finding was flagged, how common nodules are, whether they cause symptoms, what determines the size-based follow-up interval, and what active surveillance will actually look like going forward. Framing next steps as a shared decision — not a unilateral order for more scans or a biopsy — improves both understanding and follow-through.

CASE FROM PRACTICE — Case 2

A 63-year-old woman comes to clinic for an incidental lung nodule found on a CT chest obtained for persistent cough following a COVID-19 diagnosis. Former smoker, quit ~5 years ago, 0.5–1 pack/day for 33 years. A repeat CT chest around 6 months later shows interval growth of approximately 3 mm. Growth on a follow-up scan is itself a significant data point, independent of the original size or morphology classification, and generally escalates the management pathway toward tissue sampling. She underwent robotic-assisted bronchoscopic biopsy. Pathology: adenocarcinoma, moderately to poorly differentiated, with acinar and lepidic growth patterns.

CASE FROM PRACTICE — Case 3

A 73-year-old male veteran is found to have a nodule on chest X-ray during a pre-operative evaluation, prompting a CT chest. He describes a chronic "smoker's cough," is a former smoker (quit ~1 year ago, 48 pack-years), and reports an unintentional 10-lb weight loss over 6 months. The nodule was 13 mm; a risk calculator using his age, smoking history, and nodule characteristics returned a 64.5% probability of malignancy — high enough to warrant tissue sampling rather than watchful waiting. Interventional radiology performed a CT-guided biopsy of the left upper lobe nodule. Pathology: caseating granulomatous inflammation with acid-fast positive organisms. Sputum AFB cultures later returned positive for non-TB mycobacteria (Mycobacterium avium complex, MAC) — not cancer. This case is a useful counterweight to Cases 1 and 2: even a nodule with a high calculated malignancy probability and a compelling clinical story (weight loss, smoking history, chronic cough) can turn out to be granulomatous infection. High-probability doesn't mean certain, and tissue sampling exists precisely to settle that distinction rather than to confirm a preconceived diagnosis.

Incidentally detected nodules on incomplete thoracic CT scans

Not every CT that captures part of the lung was intended as a chest CT — abdominal or cardiac CTs frequently image lung bases incidentally. General guidance for nodules found this way:

●        Small nodules (<6 mm): no further investigation is generally recommended.

●        Intermediate size (6–8 mm): recommend a dedicated full CT chest, with timing based on risk profile (roughly 3–12 months), then follow Fleischner guidelines from there.

●        Nodules >8 mm: obtain a full CT chest promptly and follow Fleischner guideline recommendations.

Lung Cancer Screening and Lung-RADS

Formal lung cancer screening is a distinct pathway with its own eligibility criteria and its own structured reporting system — don't apply Fleischner incidental-nodule intervals to a screening-detected nodule, and vice versa.

USPSTF SCREENING CRITERIA (GRADE B)

The USPSTF recommends annual screening for lung cancer with low-dose CT (LDCT) in adults aged 50 to 80 years who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. Screening should be discontinued once a person has not smoked for 15 years, or develops a health problem that substantially limits life expectancy or the ability or willingness to undergo curative lung surgery.

Lung-RADS (American College of Radiology, 2022 version) is the structured category system applied to screening LDCT findings, from Category 0 (incomplete) through Category 4X (highest suspicion). Two categories are worth knowing by name:

Lung-RADS category	Estimated population prevalence	Management
0 — Incomplete	~1%	Comparison to prior CT needed, additional imaging needed, or short-interval (1–3 mo) LDCT if findings suggest an inflammatory/infectious process
S — Significant or potentially significant	~10%	Modifier applied to any category for clinically significant findings unrelated to lung cancer; managed as appropriate to the specific finding

 

Source: Adapted from JAMA. 2021;325(10):962-970, and American College of Radiology Lung-RADS v2022 (release November 2022).

Beyond the Nodule: Other Incidental Findings on Chest CT

Category S exists because a chest CT frequently captures more than lungs. Some of these findings need real follow-through of their own:

Symptom-worthy pulmonary findings

●        A patient reporting cough, upper respiratory symptoms, dysphagia, or recurrent bronchitis deserves a direct conversation about symptoms alongside the imaging review — not just a nodule follow-up plan.

●        Chronic undiagnosed findings are sometimes uncovered this way, including non-TB mycobacterial infection (as in Case 3), tree-in-bud opacities, and bronchiectasis — findings a patient may have been living with under a label of "smoker's cough."

Other structures commonly flagged

●        Pulmonary: emphysema, pleural effusion, pulmonary fibrosis / interstitial lung disease.

●        Thyroid nodule.

●        Coronary artery calcification, aortic aneurysm.

●        Pancreatic, hepatic, or renal lesions.

●        Lymphadenopathy.

None of these are the primary reason the scan was ordered, but each carries its own downstream workup — and each is a reminder to actually read the full radiology report, not just the line about the lung nodule.

Key Takeaways

●        Define it correctly: an IPN is <3 cm, well-defined, surrounded by parenchyma, and unrelated to why the scan was ordered — and roughly 90–95% of these are benign.

●        Match the guideline to the discovery pathway: Fleischner 2017 for truly incidental nodules, Lung-RADS for screening-detected nodules, and clinical judgment for symptom-driven workups.

●        Risk-stratify using validated models (Mayo, Brock, VA) rather than gestalt alone, and let the resulting probability — not anxiety — drive the choice between surveillance, biopsy, and surgical referral.

●        Growth on interval imaging is a management-changing finding in its own right, independent of the original size or morphology category.

●        A high pretest probability of malignancy doesn't guarantee cancer — granulomatous infection, NTM, and other benign causes remain on the differential until tissue says otherwise.

●        Read the whole report: incidental thyroid, cardiac, and abdominal findings on chest CT are common and often need their own referral.

References

MacMahon H, Naidich DP, Goo JM, et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology. 2017;284(1):228-243.

Managing Incidental Findings on Thoracic CT: Lung Findings. A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2021;18(9):1267-1279.

US Preventive Services Task Force. Screening for Lung Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2021;325(10):962-970.

American College of Radiology. Lung-RADS v2022. Release date November 2022.

Evaluating the Patient with a Pulmonary Nodule. JAMA. 2022;327(3):264-273.

Tanner NT, et al. Physician Assessment of Pretest Probability of Malignancy and Adherence with Guidelines for Pulmonary Nodule Evaluation. Chest. 2017;152(2):263-270.

Baldwin DR, et al. Solid and Subsolid Nodule Classification. Thorax. 2015;70:794-798.

Lazarus, Ost. The Solitary Pulmonary Nodule — Deciding When to Act? Seminars in Respiratory and Critical Care Medicine. 2013;34(6).

American Thoracic Society Patient Education Series. What is a Lung Nodule? Am J Respir Crit Care Med. 2016;193:P4-P54 (updated June 2020).

Bujarski S. Incidental Pulmonary Nodules & Other Incidental Findings on Chest Imaging. Pri-Med Institute CME, Baylor College of Medicine / Michael E. DeBakey VA Medical Center.

NP Chronicles — Clinical education for NP students and new graduates. For educational purposes; always practice within your scope and consult current full-text guidelines for patient-specific decisions.