Incidental lung nodule

Fleischner 2017 covers nodules found incidentally on CT in adults 35 or older. The tables assume a complete chest CT. For a nodule seen only on a partial chest CT (abdominal, neck or cardiac), Fleischner says: under 6 mm, no further investigation; 6–8 mm, a complete chest CT at 3–12 months depending on clinical risk, or a prior study showing stability may suffice; large or very suspicious, proceed to a complete chest CT. This tool treats "large" as over 8 mm. For a nodule seen only on a chest X-ray, ACCP 2013 recommends reviewing prior imaging and getting a chest CT. Fleischner allows radiograph follow-up for larger, clearly visible, low-risk solid nodules.

The guideline is not intended for:

• Lung cancer screening CTs. Use ACR Lung-RADS (current version v2022). This tool does not apply Lung-RADS.
• Known primary cancer with risk of metastases. Nodules are managed within the cancer care plan. Fleischner does not address remote or low-risk cancers.
• Immunosuppressed patients. Consider active infection; short-term follow-up may be appropriate. Decide case by case with the treating team.
• Under 35. Lung cancer is rare and infection is more likely. Decide case by case and keep serial CT to a minimum.

If any of these applies, the tool shows no Fleischner interval.

Always compare with prior imaging, including the earliest available study.

• Solid nodule unchanged for 2 years or more: no further evaluation (ACCP 2013, 2.3.2, grade 2C). Fleischner calls 2-year stability reliable for solid nodules.
• Subsolid nodule unchanged: persistence is already shown, so the tool leads with the step after persistence: ground-glass, CT every 2 years until 5 years; part-solid with a solid component under 6 mm, annual CT until 5 years; solid component 6–8 mm, highly suspicious, so discuss PET/CT, biopsy or resection; over 8 mm, PET/CT, biopsy or resection; multiple, CT at 2 and 4 years, or manage by the most suspicious nodule. All timed from the first scan.
• Unchanged for less than 2 years: continue the original schedule, timed from the first scan. The tool does not work out how much of a schedule is left. For a subsolid nodule, persistence counts only if the prior scan is at least 3 months old (6 months for a single pure ground-glass nodule), the start of the Table 1B confirm-persistence window. Some subsolid lesions are transient (Fleischner Figures 11–12). If the prior scan is more recent, the confirm-persistence CT is timed from the first study.
• Growth, or a new or growing solid component: refer for work-up with radiology or pulmonology. Fleischner 2017 sets no numeric growth threshold. For solid nodules, Am Fam Physician 2023 calls significant growth on follow-up imaging presumptive evidence of malignancy.
• Prior scan thick-section: get a short-term follow-up CT with contiguous thin sections as the new baseline, and compare it with the earliest study too.

Size is the average of the long and short axes, measured on the same transverse, coronal or sagittal image (the one showing the largest dimension), then rounded to the nearest millimeter. Fleischner does not recommend fractional millimeters. "Under 6 mm" means a rounded size of 5 mm or less.

This tool rounds an exact half up (5.5 mm becomes 6 mm, 8.5 mm becomes 9 mm), toward the more cautious category. Examples: 5 × 6 mm averages 5.5 and rounds to 6, so it is 6–8 mm. 5.4 × 5.5 mm averages 5.45 and rounds to 5, so it is under 6 mm. 8 × 9 mm averages 8.5 and rounds to 9, so it is over 8 mm.

Solid component of a part-solid nodule: measure the longest diameter of the largest solid component on lung windows (Fleischner measurement statement). It is rounded the same way. If it rounds to 6 mm or more, it decides the recommendation even when the averaged size rounds under 6 mm. A solid component as long as the whole nodule means the nodule is solid.

Sources size the solid component differently. Lung-RADS v2022 sizes nodules by mean diameter and states no separate method for the solid component. The Fleischner measurement statement uses the long axis, and so does this tool.

Use thin contiguous sections (typically 1 mm, no thicker than 1.5 mm), and a technique similar to the earlier scan for follow-up (section thickness and reconstruction filter matter most). Compare with all prior imaging, including the earliest available study. Fleischner also gives volume equivalents of 100 mm³ for 6 mm and 250 mm³ for 8 mm. They depend on the software, so this tool uses diameters only.

Nodules 3 mm or smaller should not be measured (Fleischner measurement statement). A decimal comma is accepted (5,5 is read as 5.5).

Entry limits: each axis from 1 to 30 mm (0.1–3 cm). A lung opacity over 3 cm is a mass, not a nodule. It needs diagnostic evaluation and pulmonology referral (Am Fam Physician 2023).

Patient risk splits only the solid-nodule recommendations. The subsolid recommendations do not depend on risk.

No revision of the 2017 nodule guideline was found in PubMed or on the RSNA site from 2024 to October 2026. The 2024 Fleischner glossary updated terminology but gave no new intervals.

Not included: Lung-RADS categories, volumetric entry, malignancy-probability calculators, PET/CT or biopsy choices, a numeric growth threshold, and the time left on a partly completed schedule.

• Endobronchial or airway nodule: not covered. Discuss with radiology or pulmonology (Lung-RADS treats airway nodules separately).
• Cavitary or cystic nodule: not reassuring. Fleischner counts cystic components as suspicious morphology, and Lung-RADS manages cavitary nodules as solid nodules. Not handled by this tool's inputs.
• Pregnancy: Fleischner does not address it. Leave the timing of elective CT to radiology.

Every surveillance or work-up result also carries the ACCP 2013 caution: if the patient is not a candidate for, or does not want, curative treatment, biopsy and aggressive CT surveillance may not make sense.

• Tools: PE pathway · COPD management · Pulmonary function tests
• Topics: Chest X-ray · COPD · Pulmonary function tests