Ground Glass Opacifications (GGOs) can pose a variety of challenges for physicians. Below is a short guide to help ensure proper diagnosis and management.
What are GGOs?
Ground Glass Opacifications are a subset of pulmonary nodules. Unlike solid nodules, GGOs occur with non-uniformity and less density, which can cause a hazy appearance. GGOs may be non-solid (referred to as “pure ground glass”) or part-solid (part of the ground-glass opacity completely obscures the tissue). Part-solid nodules are most strongly associated with lung cancer detected in CT or other imaging modalities.
The risks of GGOs
Knowledge of the causes and effects of GGOs as well as knowledge of patient history are critical in proper diagnosis and management. In malignant part-solid GGO nodules, the solid part histologically represents invasion, whereas the pure GGO areas are considered adenocarcinoma in situ (AIS) – which is the most common cancer manifesting with ground-glass opacity on CT. Because of this, solid transformation of GGO nodules is considered a strong indicator of malignancy. GGO nodules often grow slowly, and if malignant transformation from carcinoma in situ does occur, the process may take years. This means that a longer follow-up time is necessary. Apart from malignant disease, GGO changes can represent lung infections, lung edema with fluid in the interstitium, patchy increased parenchymal perfusion, or interstitial diseases.
The unique challenges of GGOs
In patients with pure GGO nodules, tumor growth can be slow and invasive disease is uncommon. Despite this, resection rates can be high. These unique features pose a challenge for physicians and patients managing GGOs over time. Similar to the management of solid nodules, the goal with GGOs is to identify and cure (usually through resection) all dangerous cancers, and to avoid resection in all benign tumors. With GGOs, the risks of observation with serial imaging are usually lower, but the observation periods may be significantly longer in order to achieve these goals.
Below is a limited summary of the 2017 Fleischner guidelines for GGO and subsolid pulmonary nodules.
Pure GGO Pulmonary Nodules
For pure GGO nodules ≤5 mm in diameter, no routine follow up is suggested. For suspicious pure GGOs ≤5 mm, a CT scan should be performed at 2 and 4 years. For pure GGO nodules >5 mm in diameter, a CT scan should be performed between 6 and 12 months in order to confirm persistence, and then another CT scan should be performed every 2 years until the 5-year mark. After 5 years, the physician and patient can assume benignity and stability and stop following the nodule.
Part Solid (Subsolid) Pulmonary Nodules
A general rule is that GGO cannot truly be defined as part solid until after the nodule is larger than 6 mm diameter. For subsolid nodules less than 6mm, no routine follow up is recommended. A suspicious nodule can be followed with a 2 and 4-year CT scan. For subsolid nodules greater than 6 mm, a CT scan should be performed between 3 and 6 months to confirm persistence. If the overall nodule size does not change and the solid component remains less than 6 mm, an annual CT scan should be performed for 5 years. After 5 years, the physician can assume stability and stop following the nodule.
Multiple Subsolid Nodules or GGO
The category of multiple subsolid nodules includes both pure GGO and part solid GGO. This category can often represent infectious or inflammatory processes. In patients with multiple subsolid nodules smaller than 6 mm, an initial follow up scan is recommended at 3-6 months, with the consideration of follow up at approximately 2 and 4 years to confirm stability depending on the clinical setting. In patients with multiple subsolid nodules with at least one nodule that is 6 mm or larger, management decisions should be based on the most suspicious nodule. If persistence is confirmed on CT scan after 3-6 months, then subsequent CT scans should follow the recommendations from the category of the most suspicious nodule. If multiple nodules are 6 mm or larger, physicians should use the one that is determined to be most suspicious to guide the timing of future scans.
Copeland S, Islam E. Management of Ground Glass and Subsolid Pulmonary Nodules: Review. Pulm CCM Website. Accessed September 2, 2018.
Pedersen JH, Saghir Z, Winkler Wille MM, Thomsen LH, Skov BG, Ashraf H. Ground-Glass Opacity Lung Nodules in the Era of Lung Cancer CT Screening: Radiology, Pathology, and Clinical Management. Modern Medicine Network Website. Accessed September 2, 2018.