Lung-RADS (Lung Imaging Reporting and Data System), is a classification system to aid interpretation of findings in low-dose CT screening exams for lung cancer, and standardize follow-up and management decisions. The system is similar to the Fleischner criteria, but designed for the subset of patients intended for low-dose screening studies. The classification was updated in 2019 (Lung-RADS version 1.1 ⁵) and 2022 (Lung-RADS v2022 ⁶).

Classification system

Category 0 (incomplete)

• prior CT studies were performed but are not available

• lungs incompletely imaged

• findings suggest inflammation or infection

Category 1 (negative, <1% chance of malignancy)

• no lung nodules

• lung nodule(s) with specific findings favoring benign nodule(s)

  • complete calcification

  • central calcification

  • popcorn calcification

  • calcification in concentric rings

  • fat-containing nodules

Category 2 (benign appearance or behavior, <1% chance of malignancy)

• juxtapleural nodule <10mm mean diameter at baseline OR new and smooth, solid, oval, lentiform, or triangular

• solid nodule(s)

  • <6 mm at baseline

  • new nodule <4 mm

• part-solid nodule < 6 mm total mean diameter at baseline

• ground glass nodule(s)

  • <30 mm (version 1.1 change previously 20 mm)

  • ≥30 mm and unchanged or slowly growing (version 1.1 change previously 20 mm)

• subsegmental airway nodule at baseline or stable

• category 3 nodules that are stable or decreased at 6 months

• category 4B lesion that has a benign diagnosis on work up

Category 3 (probably benign, 1-2% chance of malignancy)

• solid nodule(s)

  • between 6 and 8 mm at baseline

  • new nodule between 4 mm and 6 mm

• subsolid nodule(s)

  • ≥6 mm total diameter with solid component <6 mm

  • new <6 mm total diameter

• ground glass nodule(s)

  • ≥30 mm on baseline CT or new (version 1.1 change previously 20 mm)

• atypical thick-walled lung cyst with enlarging cystic component (mean diameter)

• category 4A lesion, stable or decreased in size at 3-month follow-up (excluding airway nodules)

Category 4A (suspicious, 5-15% chance of malignancy) (version 1.1 change previously suspicious)

• solid nodule(s)

  • ≥8 mm to <15 mm at baseline

  • growing nodule(s) <8 mm

  • new nodule 6 mm to <8 mm

• part solid nodule(s)

  • ≥6 mm total diameter with solid component ≥6 mm to <8 mm

  • new or growing <4 mm solid component

• segmental or more proximal airway nodule at baseline

• thick-walled cyst OR multilocular cyst at baseline OR thin- or thick-walled cyst that becomes multilocular

Category 4B (very suspicious, >15% chance of malignancy)

• stable or growing airway nodule, segmental or more proximal

• solid nodule(s)

  • ≥15 mm at baseline

  • new or growing, and ≥8 mm

• part-solid nodule(s)

  • solid component ≥8 mm

  • new or growing ≥4 mm solid component

• atypical pulmonary cyst: thick-walled cyst with increasing wall thickness/nodularity OR growing multilocular cyst (mean diameter) OR

  multilocular cyst with increased loculation or new/increased opacity (nodular, ground glass, or consolidation)

• solid or part solid nodule growing slowly over multiple screening exam

Category 4x (very suspicious, >15% chance of malignancy)

• category 3 or 4 nodules with additional features or imaging findings that increase the suspicion of malignancy

• includes:

  • spiculation

  • ground glass nodule(s) that double in size in 1 year

  • enlarged regional lymph nodes

• for new large nodules that develop on an annual repeat screening CT, a 1 month LDCT may be recommended to address potentially infectious or inflammatory conditions. (version 1.1 addition)

Modified categories

• [X]S (e.g. "3S") if there is a clinically significant or potentially significant non-lung cancer finding

• (version 1.1 removal): [X]C (e.g. "3C") for a patient with a prior diagnosis of lung cancer who returns to screening

Changes 2022

Up to 9% of lung cancers present as an atypical pulmonary cyst and these are classified as 3, 4A or 4B lesions depending on the most concerning feature. Features of concern are wall-thickening, nodularity, multilocularity and associated opacity as well as an interval increase in any of these features. A cavitating solid nodule is a different entity and is classified according to mean diameter.

Juxtapleural replaces perifissural as a descriptor for typical intraparenchymal lymph nodes which can occur along any pleural surface.

Endobronchial nodules have been renamed ‘airway nodules’ and concerning features are location in a segmental or more proximal bronchus and stability or growth on follow-up.

Nodule growth now relies on mean diameter and applies to a 12 month follow-up interval.

Ground-glass nodules that grow no more than 1.5mm over 12 months are category 2. A higher growth rate or a new solid component triggers reclassification.

The timing of the next follow-up low-dose CT scan is now based on the grade of the findings.

Potentially benign infectious/ inflammatory findings can be allocated to category 0. These findings include more than 6 new nodules, rapid appearance of an 8mm or larger nodule and segmental or lobar consolidation. These need to be reclassified according to the most suspicious feature on the next follow-up CT scan after 1-3 months. Other potentially benign infectious/inflammatory findings such as new tree-in-bud nodules and a new ground-glass nodule less than 3cm diameter do not require short term follow-up and can be classified using existing size criteria based on the most suspicious nodule¹. Multiple endobronchial segmental abnormalities without a proximal obstructing lesion can be assigned to either category ⁴.

Recommended follow-up

Category 0:

• comparison with prior studies before assignment of Lung-RADS classification

Category 1: 

• continue annual screening with LDCT

Category 2: 

• continue annual screening with LDCT

Category 3: 

• 6-month follow-up with LDCT

Category 4A: 

• 3-month follow-up with LDCT

• PET-CT may be used if there is a ≥8 mm solid component

Category 4B and 4X: 

• chest CT with or without contrast, as appropriate

• PET-CT and/or tissue sampling depending on the probability of malignancy and comorbidities (PET-CT if solid component ≥8 mm)

• for new large nodules that develop on an annual repeat screening CT, a 1 month LDCT may be recommended to address potentially infectious or inflammatory conditions. (version 1.1 addition)

Practical points

• nodule measurement should be in lung windows

• to calculate nodule mean diameter, measure both the long and short axis to one decimal point, and report mean nodule diameter to one decimal point. [previously recommended rounding to nearest whole number version 1.0.]

• only a single measurement is necessary for round nodules

• "growth" is an increase in size of ≥1.5 mm

• assignment of a Lung-RADS status is based on the most suspicious nodule

• category 4B management is based on multiple factors including overall patient status and patient preference

• solid nodules with smooth margins, an oval, lentiform or triangular shape, and maximum diameter less than 10 mm (perifissural nodules) should be classified as category 2. (version 1.1 addition)

• for category x, the Lung-RADS is rendered as "Lung-RADS category x" or "Lung-RADS x".

External links

• Lung-RADS Calculator v. 2022 - Rad At Hand

If any of these links are broken or for other problems and questions, please contact editors@radiopaedia.org.

See also

• RADS (Reporting and Data Systems)