Ground-glass nodule (GGN) is a CT finding defined as a hazy increase in lung parenchymal density that does not obscure the underlying bronchovascular structures, typically representing preinvasive and early invasive lesions within the adenocarcinoma spectrum. Atypical adenomatous hyperplasia (AAH), adenocarcinoma in situ (AIS), and minimally invasive adenocarcinoma (MIA) are parts of this spectrum. The lepidic growth pattern — tumor cells spreading along existing alveolar walls — is the histopathologic correlate of the ground-glass appearance. The presence and size of a solid component predict the degree of invasiveness.
Age Range
40-70
Peak Age
55
Gender
Female predominant
Prevalence
Common
The histopathologic basis of ground-glass nodules is the lepidic growth pattern. In this pattern, neoplastic cells proliferate in a single layer along existing alveolar walls without destroying alveolar architecture, but causing alveolar wall thickening. Since alveolar spaces remain air-filled, ground-glass density rather than complete opacification occurs on CT — alveolar wall thickening creates partial density increase while air-filled alveolar spaces maintain low density. Therefore, underlying bronchovascular structures remain visible. When a solid component develops — indicating invasive growth — tumor cells fill alveolar spaces or form fibrous stroma, producing complete opacification (solid density). The size of the solid component directly correlates with invasion depth: ≤5mm solid = MIA (nearly 100% cure rate), >5mm solid = invasive adenocarcinoma. Pure ground-glass nodules grow slowly (mean volume doubling time 800+ days) because the lepidic pattern is associated with low proliferation rates.
In ground-glass nodules, solid component size is the most reliable predictor of invasiveness: no solid component = preinvasive (AAH/AIS), ≤5mm solid = MIA (nearly 100% cure), >5mm solid = invasive adenocarcinoma. This principle forms the basis of Lung-RADS classification and Fleischner Society follow-up guidelines.
Pure ground-glass nodule: a round/oval lesion with homogeneous ground-glass density that does not obscure underlying bronchovascular structures. Contains no solid component. Compatible with AAH (<5mm) or AIS (≤30mm).
Report Sentence
A pure ground-glass nodule is identified in the lung parenchyma that does not obscure underlying bronchovascular structures and contains no solid component; a preinvasive lesion (AAH/AIS) in the adenocarcinoma spectrum should be primarily considered.
Part-solid nodule: a nodule containing a solid (soft-tissue density) component within a ground-glass component. Solid component size determines the degree of invasiveness — ≤5mm solid suggests MIA, >5mm solid suggests invasive adenocarcinoma. Evaluated in the highest risk category in Lung-RADS (4X).
Report Sentence
A part-solid nodule containing a solid component within a ground-glass component is identified; minimal invasive adenocarcinoma or invasive adenocarcinoma should be considered based on solid component size.
Bubble lucency sign (pseudocavitation): small air-density areas within a ground-glass nodule. Corresponds to patent bronchioles or cystic alveolar spaces. Reflects preservation of bronchiolar structures in the lepidic growth pattern and is a supportive finding for the adenocarcinoma spectrum.
Report Sentence
Small air-density lucencies (bubble lucency/pseudocavitation) within the ground-glass nodule are observed, supporting the adenocarcinoma spectrum with lepidic growth pattern.
Air bronchogram: visibility of air-filled bronchi within a ground-glass nodule or consolidation. In lepidic growth, airways remain patent, creating contrast between bronchial structures and surrounding ground-glass/solid tissue. May be particularly prominent in mucinous adenocarcinoma.
Report Sentence
Air bronchogram is observed within the ground-glass nodule, supporting patent airways and a lepidic growth pattern.
Pure ground-glass nodules typically show low FDG avidity (SUVmax <2.5) and may even be false-negative. This is due to the low metabolic activity and low cellular density of lepidic growth. FDG uptake increases as the solid component increases. PET-CT may be valuable in part-solid nodules when the solid component is >8mm.
Report Sentence
No significant FDG uptake is observed in the ground-glass nodule on PET-CT (SUVmax <2.5); however, it should be noted that pure ground-glass nodules may be PET-negative due to low metabolic activity.
Multiple ground-glass nodules: presence of more than one pure or part-solid GGN. May represent synchronous multiple primary lung adenocarcinomas (MPLC) or AAH/AIS foci. Each nodule should be evaluated independently — the dominant nodule (largest or most solid component) determines management. Unlike metastases, multiple GGNs are generally independent primary lesions.
Report Sentence
Multiple ground-glass nodules are observed in both lungs, and synchronous multiple primary lung adenocarcinomas or preinvasive lesions (AAH/AIS) should be considered; each nodule should be evaluated independently.
The solid component in a part-solid nodule may show mild to moderate enhancement on contrast-enhanced CT. Enhancement indicates the presence of neoangiogenesis (tumoral vascularity) and correlates with invasive growth. Pure ground-glass nodules generally do not show significant enhancement.
Report Sentence
Mild to moderate enhancement is observed in the solid component of the part-solid nodule on contrast-enhanced series, suggesting an invasive growth component.
Criteria
≤5mm pure ground-glass nodule, no solid component. Preinvasive lesion — adenocarcinoma precursor.
Distinct Features
Very small size (≤5mm), may often be multiple, remains stable or grows very slowly on follow-up. Clinical significance is low but represents the starting point of the adenocarcinoma spectrum.
Criteria
≤30mm pure ground-glass nodule, no solid component. Entirely lepidic growth pattern, no invasion. 100% cure with surgery.
Distinct Features
Larger than AAH (5-30mm) but still no solid component. May show very slow growth on follow-up (VDT >800 days). Surgical resection is curative — 5-year disease-free survival is 100%.
Criteria
≤30mm part-solid nodule, solid component ≤5mm. Predominant lepidic growth + ≤5mm invasion. Nearly 100% cure with surgery.
Distinct Features
Appears as a part-solid nodule — small solid component within ground-glass. Solid component size ≤5mm is the critical threshold. Sublobar resection (wedge/segmentectomy) may be sufficient. 5-year disease-free survival is 97-100%.
Criteria
Part-solid nodule, solid component >5mm. Predominant lepidic pattern but >5mm invasion present. Lobectomy + lymph node dissection required.
Distinct Features
Distinguished from MIA by solid component >5mm. Has better prognosis than completely solid masses because ground-glass component is still present. 5-year survival is 80-90%. Adjuvant chemotherapy is considered based on stage and pathological features.
Distinguishing Feature
Invasive adenocarcinoma typically appears as a completely solid mass with spiculated margins and significant enhancement. A completely solid appearance without or with minimal ground-glass component, unlike GGN/AIS/MIA, suggests a more aggressive histological subtype (acinar, papillary, micropapillary).
Distinguishing Feature
Mucinous adenocarcinoma may appear as low-density consolidation or ground-glass but typically shows lower lobe predilection, air bronchograms, and low HU values due to mucin. Multilobar/bilateral spread (pneumonic form) and the CT angiogram sign (prominent vessels within consolidation) distinguish mucinous adenocarcinoma from pure ground-glass nodule.
Distinguishing Feature
Hamartoma contains fat (-40 to -120 HU) and/or popcorn calcification — findings not seen in ground-glass nodules. Hamartomas are generally well-defined, smooth-bordered solid nodules that do not show ground-glass density. The combination of fat and calcification is pathognomonic for hamartoma.
Distinguishing Feature
Granuloma is typically a solid, well-defined nodule that may show central/diffuse/laminar calcification. Does not show ground-glass density. Size stability on follow-up (unchanged for >2 years) and presence of calcification distinguish granuloma from GGN. Common in endemic areas (histoplasmosis, tuberculosis).
Urgency
surveillanceManagement
surveillanceBiopsy
Not NeededFollow-up
6-monthPure ground-glass nodules are generally slow-growing preinvasive lesions managed with size-based follow-up strategy. Per Fleischner Society guidelines: <6mm pure GGN requires no follow-up, ≥6mm pure GGN gets follow-up CT at 6-12 months then follow-up to 2 years. Part-solid nodules are evaluated more aggressively: if solid component ≥6mm, PET-CT and/or biopsy are considered. Surgery is typically planned for nodules showing growth or developing solid component. Sublobar resection (segmentectomy) provides equivalent outcomes to lobectomy for pure GGN and MIA.
Pure GGNs usually represent AIS or MIA and have excellent prognosis (nearly 100% 5-year survival). Pure GGNs >6 mm are followed with CT at 6-12 months. Surgery is considered if growth or solid component development occurs.