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

Here's how COVID-19 can damage a person's lungs.

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

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

While it's important to note that ground-glass opacities aren't specific to COVID-19, meaning they can show up in other conditions and infections, they are common among those infected with SARS-CoV-2. Here's what you need to know.

What Are Ground-Glass Opacities?

According to Isabel Oliva Cortopassi, MD, senior associate consultant at Mayo Clinic and former chief of thoracic imaging at Yale Medicine, ground-glass opacities (GGOs, for short) indicate abnormalities in the lungs. "Ground-glass opacities [are] a pattern that can be seen when the lungs are sick," said Dr. Cortopassi. Dr. Cortopassi added that, while normal lung CT scans appear black, an abnormal chest CT with GGOs will show lighter-colored or gray patches.

Those lighter patches don't completely obscure the other structures in the lungs, said Jennifer Possick, MD, a Yale Medicine pulmonologist—that 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, or glass that is still transparent but has a matte finish.

What Do Ground-Glass Opacities Indicate?

It's important to keep in mind 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 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 respiratory syncytial virus (RSV), cytomegalovirus, herpes simplex virus, and coronavirus.

In terms of COVID-19, Dr. Cortopassi explained that GGOs on a CT scan indicate COVID-19-related pneumonia or lung inflammation caused by the viral infection. It's important to note, however, that not all patients with COVID-19 will go on to develop pneumonia, stressed Dr. Cortopassi.

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. Other studies also done early on in the pandemic showed similar findings.

A 2021 study published in the journal The Lancet Respiratory Medicine took people who had been hospitalized for COVID-19 and had GGOs on initial lung scans; they rescanned their lungs at three and nine months following hospital discharge. Researchers found that 78% of patients still 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 journal Lancet, researchers looked at one-year outcomes in COVID-19 hospital survivors. They found that while GGOs had decreased by 12 months, 78% of patients still had some GGOs showing up on lung scans. Of note: Both 2021 studies showed 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.

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 it as well—including consolidation (a white portion on a lung CT that signifies fluid is present) and 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 important to know, especially if your doctor 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 some people will have no imaging abnormalities at all," said Dr. Cortopassi.

As always, if you are experiencing symptoms of COVID-19—dry cough, fever, fatigue—the CDC recommends several things, including 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.

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