What Do 'Ground-Glass Opacities' Mean in Lung Scans of COVID-19 Patients?

The COVID-19 pandemic filled our vocabularies with more medical terms than most of us would ever hear about otherwise: flattening the curve, PPE, and active and passive immunity.

Another term—ground-glass opacities—refers to findings on computed tomography (CT) scans of people with COVID-19 that can help diagnose and monitor the infection.

Ground-glass opacities (GCOs) aren't specific to COVID-19—meaning they can show up due to other conditions and infections. But they are common among those infected with SARS-CoV-2. Here's what you need to know.

What Do Ground-Glass Opacities Look Like?

According to Isabel Oliva Cortopassi, MD, senior associate consultant at Mayo Clinic and former chief of thoracic imaging at Yale Medicine, ground-glass opacities indicate abnormalities in the lungs. "Ground-glass opacities [are] a pattern that can be seen when the lungs are sick," said Dr. Cortopassi. Normal lung tissue appears black on a CT scan, but GGOs are lighter-colored or gray patches, Dr. Cortopassi added.

Those lighter patches don't completely obscure the other structures in the lungs, said Jennifer Possick, MD, a Yale Medicine pulmonologist—which makes them different from lesions associated with lung cancer, which can often appear as solid. With GGOs, "there is haziness seen overlying an area of the lung, but the underlying structures of the lung (airways, blood vessels, lung tissue) can still be identified," said Dr. Possick. It resembles, well, ground glass, which is still transparent but has a matte finish.

COVID-19 and Ground-Glass Opacities

While GGOs can be seen on chest CT as a result of a range of lung diseases, they tend to be more prevalent with lung damage caused by COVID-19 infection than other lung conditions.

Researchers from the University of Michigan reported the prevalence of GGOs in chest imaging among COVID-19 patients in a case series published in February 2020 in Radiology: Cardiothoracic Imaging. Looking at three different cases of confirmed COVID-19 patients in China, researchers discovered GGOs in each patient's CT scan. Another study published in the journal Radiology in February 2020, earlier in the pandemic, showed similar findings.

In the context of COVID-19 infection, Dr. Cortopassi explained that GGOs on a CT scan indicate COVID-19-related pneumonia or lung inflammation caused by the viral infection. But not all patients with COVID-19 will go on to develop pneumonia, said Dr. Cortopassi.

Lung Disease and Ground-Glass Opacities

It's important to remember that GGOs aren't specific to COVID-19 and can be seen in many different settings, emphasized Dr. Possick. GGOs in chest CT scans can also indicate lung damage from congestive heart failure, inflammatory interstitial lung diseases, and diffuse alveolar hemorrhage (bleeding into the airspaces of the lungs), among other issues.

But one of the most common diagnoses for GGOs is viral pneumonia, most often caused by a respiratory syncytial virus (RSV), cytomegalovirus, herpes simplex virus, and coronavirus. A 2014 research article published in The European Journal of Radiology found that GGOs are a fairly uncommon finding. The most common causes are viral lung infections and pulmonary edema (fluid in the lungs).

Residual Ground-Glass Opacities

A 2021 study published in The Lancet Respiratory Medicine included people hospitalized for COVID-19 and had GGOs on initial lung scans; the researchers rescanned their lungs at three and nine months following hospital discharge. Researchers found that 78% of patients had residual GGOs at three months post-discharge, and 24% had GGOs still showing up on scans at nine months post-discharge.

In another 2021 study published in the Lancet, researchers looked at one-year outcomes in COVID-19 hospital survivors. They found a decrease in GGOs by 12 months and that 78% of patients still had some GGOs showing up on lung scans.

Of note: Both 2021 studies showed that patients still had other respiratory issues in addition to GGOs. And study authors from both 2021 studies urged long-term follow-up for anyone who had COVID-19, especially those who had severe illness.

Other COVID-19-Associated Changes on Chest CT Scans

While GGOs are some of the most common findings seen in patients with COVID-19-related pneumonia, Dr. Cortopassi pointed out that there are additional imaging appearances that can signal COVID-19 as well—including:

• Consolidation (a white portion on a lung CT that signifies fluid is present)
• Septal thickening (a thickening of the connective tissues within the lung, also indicative of fluid, fibrous tissue, or cell infiltration)

"These are terms we radiologists use to describe what we see when reading a chest CT and are not specific for one disease," added Dr. Cortopassi.

These terms are essential to know, especially if your healthcare provider mentions ground glass opacities while treating you for COVID-19 or another illness.

But Dr. Cortopassi reiterated that a COVID-19 diagnosis doesn't automatically lead to a worsened condition in which these GGOs will show up in a CT scan, nor does an abnormal scan definitively mean a coronavirus infection. "Some people will have completely different radiologic findings, and others will have no imaging abnormalities at all," said Dr. Cortopassi.

A Quick Review

Ground-glass opacities (GGOs) show up as lighter-colored or gray patches on chest CT scans of the lungs. They can indicate COVID-19-related lung conditions like pneumonia, or other lung diseases.

If you are experiencing symptoms of COVID-19—dry cough, fever, fatigue—the CDC recommends getting tested and staying at home and away from others. If you experience emergency warning signs, including trouble breathing, persistent pain or pressure in the chest, new confusion, inability to stay awake, or blue or grey tint to your skin, lips, or nail beds, call 911 immediately.

The information in this story is accurate as of press time. 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.