Atelectasis — What It Means on Your Imaging Report

Quick Answer

Atelectasis is a partial collapse or incomplete expansion of lung tissue — it is one of the most common incidental findings on chest imaging and is usually not a cause for concern.

What Is Atelectasis?

Atelectasis occurs when a portion of the lung does not fully expand with air. The word comes from the Greek "ateles" (incomplete) and "ektasis" (expansion). When a section of lung tissue is not inflated, it becomes denser and appears as a white streak or hazy area on imaging — because collapsed tissue blocks X-rays more than air-filled tissue does.

It is important to understand that atelectasis is not a disease itself — it is a physical finding that describes what the lung tissue is doing. Think of it like a balloon that is not fully inflated. The lung tissue is still there and is usually perfectly healthy; it simply is not filled with air at the moment the image was taken.

There are several types of atelectasis that radiologists describe:

• Subsegmental atelectasis (also called plate-like or linear atelectasis) — thin, horizontal white lines at the lung bases. This is the most common type and is almost always benign. It results from shallow breathing and is frequently seen after surgery, during hospitalization, or even during a routine scan if the patient was not taking deep breaths.
• Bibasilar atelectasis — atelectasis at the bases of both lungs. This is extremely common and typically results from lying flat, shallow breathing, or mild compression from abdominal contents pushing up on the diaphragm.
• Compressive atelectasis — occurs when something outside the lung, such as a pleural effusion (fluid around the lung) or an enlarged heart, pushes on the lung tissue and prevents it from expanding fully.
• Obstructive atelectasis — caused by a blockage in the airway, such as a mucus plug, that prevents air from reaching a section of lung. This type is less common as an incidental finding and may require further evaluation.

When You Might See This on Your Report

Atelectasis is one of the most frequently reported findings on chest imaging:

• Chest X-rays — this is where atelectasis is most commonly reported. You may see phrases like "bibasilar atelectasis," "linear atelectasis at the left lung base," or "subsegmental atelectasis." On a chest X-ray, it appears as faint white lines or streaky densities, most often at the bottom of the lungs.
• CT scans — CT is more sensitive than X-ray and can detect smaller areas of atelectasis. It also provides more detail about the type and cause. Dependent atelectasis — collapse of lung tissue in the part of the lung closest to the ground due to gravity — is very commonly seen on CT scans taken while the patient is lying on their back. This is a normal physiological finding.

Common situations that cause atelectasis:

• Post-surgery — especially after abdominal or chest surgery, when pain limits deep breathing
• Hospitalization or bed rest — prolonged lying down leads to shallow breathing and dependent atelectasis
• During the imaging study itself — if you were not taking deep breaths during a chest X-ray or CT, mild atelectasis may appear
• Obesity — increased abdominal weight can compress the lung bases
• Pleural effusion — fluid around the lung can compress adjacent lung tissue
• Mucus plugging — mucus blocking a small airway, often temporary

Should I Be Worried?

In the vast majority of cases, no. Atelectasis is one of the most common incidental findings in all of chest imaging, and subsegmental or bibasilar atelectasis is almost always clinically insignificant. It is so common that many radiologists consider it a near-normal finding, particularly on imaging performed in the hospital or post-operative setting.

Here is what to consider:

• Subsegmental and bibasilar atelectasis are rarely a concern. They are typically caused by shallow breathing and often resolve simply by taking a few deep breaths or changing position. If you see these terms on your report, they are almost certainly not the reason your doctor ordered the imaging study.
• Dependent atelectasis on CT is a normal physiological finding. It occurs because gravity causes the lowest parts of the lung to partially deflate when you lie on your back. This happens to virtually everyone.
• Atelectasis that is persistent, involves a large area, or is new compared to previous imaging may warrant follow-up, as it could occasionally be caused by an airway obstruction that needs evaluation.
• Your symptoms matter. If you have no respiratory symptoms, incidental atelectasis on imaging is almost certainly benign. If you are experiencing shortness of breath or cough, your doctor will determine whether the atelectasis is contributing to your symptoms or is simply an unrelated finding.

What Should I Do Next?

1. Read the Impression section of your report. If the radiologist considers the atelectasis clinically significant, they will typically mention it in their summary and may recommend follow-up. If it is not mentioned in the Impression, it is likely considered incidental.
2. Discuss with your doctor if you have questions, but know that mild atelectasis rarely changes your treatment plan. Your doctor may not even mention it because it is so common and typically insignificant.
3. Practice deep breathing exercises. If you are recovering from surgery or have been on bed rest, deep breathing (incentive spirometry) is one of the simplest and most effective ways to resolve atelectasis. Your care team may already have recommended this.
4. Stay mobile when possible. Walking and upright positioning help your lungs expand fully. If you are hospitalized, getting out of bed and walking — even short distances — helps prevent and resolve atelectasis.
5. Follow up if recommended. In the uncommon situation where the radiologist recommends follow-up imaging for atelectasis, it is usually to confirm that the area re-expands and to rule out an underlying airway obstruction. Keep the follow-up appointment for your peace of mind.