Ground Glass Opacity (GGO): What It Means

Ground glass opacity (GGO) is an abnormal finding that shows up on computed tomography (CT) scans in people’s lungs as a result of several diseases. These growths are described as an “opacity,” meaning they darken the CT, showing areas where the lung structure is denser than the tissue around it.

Some people can develop these lung nodules after COVID-19. GGOs can help diagnose and monitor complications from COVID, such as pneumonia (inflammation of the lungs).

GGOs are not specific to COVID. They can show up due to other health conditions and infections that affect the lungs. Read on to learn about GGO and what it means to have it.

GGOs indicate abnormalities in the lungs. A healthcare provider can detect GGOs on a chest CT scan as the result of a range of lung diseases.

GGOs point to increased density in the lungs, which might mean that fluid or other substances have filled air spaces. Research has shown that GGOs might also indicate the walls of alveoli (air sacs in the lungs) or spaces between the lungs have thickened.

Normal lung tissue appears black on a CT scan, but GGOs are lightly colored or gray patches. They resemble ground glass, which is still transparent but has a matte finish.

These lighter patches do not completely obscure the other structures in the lungs. This makes them different from cancerous lesions, which often appear solid. GGOs, in contrast, cause a haziness that overlays an area of the lung. A healthcare provider will still be able to identify underlying structures of the lung (e.g., airways, blood vessels, and lung tissue).

The shape, size, and number of GGOs may indicate the cause. Types of GGOs include:

• Centrilobular: Forms in one or multiple lobules, or small subdivisions within each lobe of the lungs
• Crazy paving: Appears in a linear pattern within enlarged lobules
• Halo sign: Permeates the space around the nodules, or a dense spot in the lung (which might also appear reversed)
• Diffuse: Forms in several lobes within one or both lungs if fluid fills air spaces
• Mosaic: Shows up if something blocks the bronchioles (small airways in the lungs) or pulmonary arteries
• Nodular: Dense spots in the lungs, which may indicate a cancerous or benign (non-cancerous) growth

GGOs tend to be more prevalent with lung damage caused by COVID infection than other lung conditions. These abnormalities can indicate COVID-related pneumonia or other lung inflammation.

A study published in 2021 looked at people hospitalized with COVID symptoms and who had GGOs on initial lung scans. The researchers rescanned their lungs at three and nine months after hospital discharge. They found that 78% of people had residual GGOs three months post-discharge, and 24% had GGOs nine months post-discharge.

Another study published in 2021 looked at one-year outcomes in people who were hospitalized with COVID. The study authors found a decrease in GGOs by 12 months and that 78% of people still had GGOs showing up on lung scans.

Both studies showed the people had other respiratory issues in addition to GGOs. The study authors urged long-term follow-up for anyone who had COVID, especially those who had severe illness.

Other COVID-19-Associated Changes on Chest CT Scans 

GGOs are some of the most common findings seen in people with COVID-related pneumonia. Other imaging appearances also can signal COVID, such as consolidation and septal thickening.

Consolidation is a white portion on a CT scan that signifies fluid is present. Septal thickening is a thickening of the connective tissue in the lung. This finding may also indicate fluid, fibrous tissue, or cell infiltration.

These terms are essential to know, especially if a healthcare provider mentions GGOs when treating you for COVID or another illness. Remember that a COVID diagnosis does not automatically lead to a worsened condition in which these GGOs show up in a CT scan. An abnormal scan likewise does not always signal COVID. Some people will have completely different radiologic findings, while others will have no abnormalities.

It’s important to remember that GGOs are not specific to COVID. A healthcare provider might detect GGOs in many different settings. Some of the most common causes include lung damage from congestive heart failure, diffuse alveolar hemorrhage, interstitial lung diseases, lung cancer, and viral pneumonia.

Congestive Heart Failure

Heart failure occurs if your heart is unable to pump blood throughout your body efficiently. As a result, your other organs may not work as they typically do. Heart failure may also cause fluid to gather in the air spaces in your lungs, known as pulmonary edema. This complication may show up as GGOs on a CT scan.

Diffuse Alveolar Hemorrhage

Alveolar hemorrhage is a life-threatening complication that causes bleeding into the alveoli. A study published in 2019 found that this complication appeared as diffuse GGOs on a CT scan.

Interstitial Lung Diseases

Interstitial lung diseases cause inflammation or scarring of the lungs, which makes it hard to breathe. These complications cause the air spaces in the lungs to become thickened. Research has shown that GGOs may indicate interstitial thickening in the lungs.

Lung Cancer

Research has found that GGOs are important indicators of lung cancer. Most cases of lung cancer start in cells that line the bronchi, or two tubes that carry air from the trachea (windpipe) to the lungs.

Viral Pneumonia

One of the most common diagnoses for GGOs is viral pneumonia, or inflammation of the lungs. Viruses that may cause pneumonia include coronavirus, cytomegalovirus, herpes simplex virus (HSV), influenza (flu) virus, and respiratory syncytial virus (RSV).

A healthcare provider can detect GGOs and their type using a chest CT scan. This diagnostic test uses X-rays to take detailed pictures of the inside of your chest, including the lungs. You may require further tests if abnormalities like GGOs show up on a chest CT scan.

Other diagnostic tests include:

• Bronchoscopy: A healthcare provider will insert a tube with a small camera and light (bronchoscope) through your nose or mouth to look down your throat and into your lungs.
• Chest magnetic resonance imaging (MRI): This uses magnets and radio waves to create pictures of the inside of your chest. A chest MRI can provide more detail than a CT scan.
• Lung function tests: These include pulse oximetry and spirometry, which measure how well your lungs work.

What percentage of ground glass opacities are cancerous? Not all GGOs are cancerous, but a high percentage of them are. Research has found that about 63% of GGOs are cancerous.

Treatment depends on the cause of GGOs. For example, a healthcare provider may prescribe antiviral drugs if you have COVID-related pneumonia. Some people with severe viral pneumonia require treatment at the hospital.

Other treatments may include:

• Medicines
• Lung transplant
• Oxygen therapy for low blood oxygen levels

Lung cancer treatment will depend on the type and severity of the cancer. You may require chemotherapy, radiation therapy, or surgery to remove cancer cells.

GGOs show up as lighter-colored or gray patches on chest CT scans of the lungs. This finding can indicate COVID-related lung conditions, such as pneumonia. Other causes of GGOs include congestive heart failure, diffuse alveolar hemorrhage, interstitial lung diseases, and lung cancer. Treatment depends on what’s causing GGOs but may include medicines, lung transplants, and oxygen therapy.

The information in this story is accurate as of publication. However, as the situation surrounding COVID-19 continues to evolve, it’s possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.