What a lung CT scan shows: ground glass, nodules and how to read the report

Your doctor says, "Let's do a CT scan." An hour or two later you hold a report full of phrases like "ground-glass areas", "S6" or "small nodules". What do they mean? How serious is it? And why a CT if you already had an X-ray?

Here we explain in plain words what a chest CT can see, what healthy lungs look like on the scan, what the common report phrases mean and how the scan itself goes. This article does not replace a doctor's visit. It will help you come to that visit with the right questions.

A CT scan is still an X-ray. The difference is that you get hundreds of images instead of one. The X-ray tube spins around your body, and a computer builds thin slices into a 3D picture. The doctor can look at your lungs layer by layer, from any angle, and measure changes down to a millimetre.

On a plain X-ray, parts of the lungs hide behind the heart, ribs and diaphragm. A CT has almost no blind spots like that. So it finds what an X-ray misses: small spots, early inflammation and subtle changes in lung tissue.

According to the MedlinePlus medical encyclopedia, a chest CT helps doctors find:

• pneumonia and other infections or inflammation, including viral ones
• tumours, nodules and cysts, as well as cancer that has spread to the lungs
• emphysema and scarring after past illness
• interstitial lung disease, where lung tissue gets inflamed and then stiff
• bronchiectasis, which means damaged and widened airways
• fluid around the lungs (pleural effusion) and bleeding
• enlarged lymph nodes in the centre of the chest

A CT has limits too. A standard scan without contrast does not show blood clots in the lung arteries well. For that, doctors order a separate contrast scan called CT angiography. And small changes inside the airway wall are sometimes easier to see during a bronchoscopy.

At Oberig Clinic, chest scans are done in the Diagnostic Department on one of three CT scanners, and radiologists read them. The scanners produce slices as thin as 1 mm, so spots from 2-3 mm can be seen. The department is headed by radiologist Taras Matsiievskyi. You can read more on our chest CT page.

It sounds alarming. "Ground glass" worries people more than any other phrase in a report, yet it is a description of the picture, not a diagnosis. Radiologists use it for an area where lung tissue looks a little lighter and hazier than the tissue around it, while vessels and airways inside it are still visible. That is how the radiology reference Radiopaedia defines it.

So what happens? Why does the tissue get hazy? The alveoli, tiny air sacs, partly fill with fluid, inflammatory cells or blood, or the walls between them get thicker. There is less air, so the tissue looks denser.

There are many causes. Here are the main ones. The most common is viral pneumonia, including after COVID-19. Others include fluid in the lungs from heart failure, bleeding and interstitial lung disease. Sometimes a slow-growing tumour looks like this. There is also a harmless cause: if you did not breathe in fully during the scan, part of the lung can simply look denser.

So your doctor looks at the context, not the term alone. How many areas are there and where? Do you have a fever or a cough? Has the picture changed since your last scan? After you recover from pneumonia, ground-glass areas often clear up. A single area of this kind that does not go away needs follow-up.

Spots and nodules

A small round shadow in the report is called a spot or a nodule. Most are left over from old infections, scars or benign growths. The radiologist notes the size, edges and density, and your doctor decides if you need a repeat scan later. We cover nodules in a separate article. The key point here: a single small nodule is almost never a reason to panic.

Emphysema and bullae

In emphysema, the walls of the air sacs break down. Instead of a fine sponge, the lung forms larger air pockets. On a CT they show up as darker, overinflated areas, sometimes with large bullae. Emphysema is most often linked to smoking and is part of chronic obstructive pulmonary disease. Learn how to spot this condition in our COPD article.

Consolidation, fibrosis and fluid

Consolidation is an area where the air in the alveoli has been fully replaced by fluid or inflammatory material. It is the typical picture of bacterial pneumonia. Fibrosis looks like a net, strands and a honeycomb pattern, when normal tissue turns into scar tissue. Fluid in the pleural space appears as a band along the chest wall. A collapsed lung (pneumothorax) shows as air where it should not be.

Healthy lung tissue looks dark on a CT because it is almost all air. Against this dark background you see thin, light branches of blood vessels that taper evenly towards the edges, and the openings of the airways. The lining of the lungs is thin and smooth, there is no fluid around the lungs, and the lymph nodes in the centre of the chest are small.

A normal report usually says something like "no focal or infiltrative changes" or "lung fields without abnormalities".

Keep in mind that small findings are common in healthy people too. A single calcified spot, a small scar or slight thickening of the lung lining after an old infection often means nothing at all. Your doctor judges them together with your symptoms, not by one line in the report.

You lie on a narrow table that slides into the ring of the scanner. The scanner is not a long tube like an MRI machine, so even people who fear tight spaces usually feel fine. During the scan you need to lie still and briefly hold your breath when asked, so the images are not blurred.

According to MedlinePlus, the scan itself takes from 30 seconds to a few minutes. It does not hurt, and there is no recovery time: you can go back to your normal day right away.

If you need contrast, a dye containing iodine goes into a vein before the scan. It makes vessels and some growths easier to see. You may feel warm or notice a metallic taste in your mouth for a few seconds. After a contrast injection, our clinic asks you to stay under observation for up to 30 minutes. The doctor who refers you decides whether contrast is needed.

Bring your referral and the results of earlier tests, especially old CT scans. Pregnant women have CT only when it is vital. What to bring and how to prepare is described on our CT preparation page.

The lungs are divided into lobes: three on the right and two on the left. Each lobe is split into segments, and each segment has its own airway and blood vessels. According to Radiopaedia, the right lung has 10 segments, and the left lung usually has 8, because some segments share an airway.

Reports label segments with the letter S and a number: S1-S3 sit at the top, S4-S5 in the middle part on the right or the lingula on the left, and S6-S10 at the bottom. "Nodule in S6 of the right lung" is simply an exact address. It matters. A surgeon plans an operation by it. A bronchoscopist picks the airway for a biopsy. The next radiologist finds the same spot and compares its size.

A report has two parts. In the findings, the radiologist lists everything they saw. The impression, or conclusion, sums it up. Here are the most common terms in plain words.

Do not let the jargon scare you. Start simple. Read the conclusion first, not single words from the findings. Keep the disc with your images and your earlier results. Comparing with a previous scan often matters more than any single term: a nodule that has not changed in two years and a brand-new one are judged very differently.

A radiologist's report describes images. It is not a diagnosis. The diagnosis comes from the doctor who referred you, who also weighs your symptoms, tests and exam. If the wording is unclear, ask a pulmonologist to explain it.

The most common reasons are a long-lasting cough, shortness of breath, chest pain, coughing up blood, and suspected pneumonia or its complications. A CT is also used to check a shadow seen on an X-ray, to assess the lungs after an infection, before surgery and to see how treatment is working. For long-term smokers, a doctor may suggest a low-dose scan to find cancer early. We cover that in a separate article.

Radiation from a modern CT is low, but you should not have one "just in case". The scan should answer a specific question from your doctor.

Can a CT show pneumonia if the X-ray was normal?

Yes, quite often. A CT picks up inflammation early and in areas that the heart or diaphragm hide on an X-ray. So if your symptoms are strong and your X-ray looks clear, your doctor may order a CT to check.

How long will I wait for the report?

It depends on how complex the scan is and whether it needs to be compared with older images. Staff will tell you the exact time when you book.

Can I eat before the scan?

A standard chest CT needs no special preparation. If contrast is planned, your doctor or the front desk will tell you how many hours to fast and if you need a kidney function test first.

Does ground glass mean COVID?

Not necessarily. Many viral pneumonias, fluid in the lungs, bleeding and chronic lung diseases look the same. COVID-19 is only one possible cause, and your doctor makes the final call with your test results.

Can a CT show lung cancer?

CT is one of the most accurate ways to look for lung tumours. It can see nodules just a few millimetres across. But finding a shadow and making a diagnosis are two different things. The nature of a growth is confirmed with a biopsy and other tests.

Do I need to repeat the scan?

Only if your treatment or a finding needs follow-up, such as a nodule or pneumonia. Your doctor sets the timing, not a standard schedule.

If you have a cough or shortness of breath, an X-ray showed an unclear shadow, or your CT report raises questions, come to Oberig Clinic. The scan is done in our Diagnostic Department, radiologists read it, and a pulmonologist explains the results. Our pulmonologists include Anton Sadomov, PhD, associate professor and physician of the highest category. If needed, you can have spirometry and a bronchoscopy here too.

Book by phone at +38 044 521 30 03 or online.