Ground glass opacities in lungs is a common finding on lung imaging which means that the normally dark lung now has ground glass in it. Ground glass is a technique in glassmaking where the surface of glass is roughened and looks white or frosted.
Ground glass on chest X-ray and CT
Ground glass is found on X-rays and CT of the lungs. Ground glass looks hazy or cloudy compared to the normal dark lung. The finding can be one small spot all the way to involve the lungs throughout on both sides. You can see the lung blood vessels and bronchi through the ground glass. There are many causes of ground glass opacity from benign and requiring no treatment all the way to cancer.
What causes ground glass attenuation in the lungs?
Ground glass opacities or attenuation forms when the alveoli or air spaces are partially filled with infection, fluid, blood, or cancer. They can also form when the air spaces of the lung collapse which is called atelectasis. Inflammation of the lung, scarring, thickening around airspaces are additional causes. The appearance on imaging, the clinical history and additional testing helps us narrow the diagnosis.
Ground glass opacity causes
In practice, ground glass opacification of lungs is most common with infections, fluid or edema in the lungs, interstitial diseases, drug toxicity and cancer. The appearances of these conditions vary and the clinical history can be very important to differentiate the conditions. Many diseases that have ground glass can have additional abnormalities which help with the diagnosis as well.
Diffuse ground glass opacities
Fluid or bleeding in lungs
Diffuse ground glass opacities throughout the lungs has a more limited set of possibilities. Most commonly I see this with fluid or edema in the lungs. This is most common from heart conditions but has other non heart related causes as well. Bleeding throughout the lungs can cause diffuse ground glass opacities.
Infections of the lungs
ground glass opacities or patchy ground glass opacities can be found in infections. COVID infection is the most common cause of diffuse ground glass opacities in the current pandemic. Patients who’s immune system is compromised can have other infections like pneumocystis pneumonia or CMV.
Acute respiratory distress syndrome
This is damage to the lungs which can occur from lung causes and those outside the lungs. Infections of the lungs, smoke inhalation and near drowning are some causes from lung injury. Causes that are not related to the lungs can include burns, trauma, pancreatitis and shock. The damage to the lung results in fluid accumulation. The condition is serious and leads to respiratory failure, chronic scarring of lungs and possible death.
Less common causes of diffuse or multi focal ground glass
Less common causes of diffuse ground glass can include lung disease from allergic lung disease or an external agent called hypersensitivity pneumonitis. Interstitial pneumonias of unknown cause can lead to diffuse ground glass opacities. Drug toxicity can cause diffuse ground glass opacities. Connective tissue diseases like scleroderma and rheumatoid can cause ground glass opacities.
Focal ground glass opacity
A smaller area of ground glass can also be caused by some of the conditions outlined above.
Additionally, cancer can sometimes look like a focal area of ground glass. Particularly adenocarcinoma of lung or lesions which have cancerous potential.
Infections described above can also be limited to a smaller part of the lung. One example is fungal infection with aspergillosis.
Bruising of the lung called contusion can look like a ground glass opacity.
Smaller areas of scarring can look ground glass. This is commonly seen by the spine in the lower lungs when there is arthritis.
Ground glass opacities opacities in lungs therefore look hazy, like frosted glass. They can be in one spot or involve the lungs throughout. The appearance, clinical history and other testing is critical to arriving at a diagnosis. Ground glass opacities can range from benign and requiring no treatment all the way to life threatening conditions. The radiologist will often provide a diagnosis he thinks is most likely in the report.