Lung-RADS (Lung Imaging Reporting and Data System), is a classification proposed to aid with findings in low-dose CT screening exams for lung cancer. The goal of the classification system is to standardise 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 original classification was updated in 2019 and 2022 in the light of new knowledge.
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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 favouring benign nodule(s)
complete calcification
central calcification
calcification in concentric rings
fat-containing nodules
Category 2 (benign appearance or behaviour, <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
Recent 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 current findings.
Potentially benign findings can be allocated to category 0 or 2 with option for 1-month follow-up. Category 0 findings are more than 6 new nodules, rapid appearance of an 8mm or larger nodule and segmental or lobar consolidation. Category 2 benign findings are new tree-in-bud nodules and a new ground-glass nodule less than 3cm diameter. 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".
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