Lung Bases Are Clear – What Does It Mean?

Lung bases are clear is a common term in radiology reports which means that the lower part of the lungs is free of abnormalities.   This is a term that is most commonly used in CT of the abdomen.  CT of the abdomen which is commonly done with CT of the pelvis includes the lung bases.  The lung bases are the lowest part of the lungs.

What are some conditions found at the lung bases?

Lung bases is a common site for abnormalities.  We often find abnormalities even if you don’t have chest symptoms.  Most commonly  there is atelectasis.  This is when a small part of your lung collapses and is airless.  This is usually not a cause for symptoms unless more extensive.

Lung nodules

Lung bases are a common site for small nodules under a centimeter.   Many patients who undergo CT of the abdomen and pelvis may have at least one nodule under a centimeter.  Often we recommend follow up or chest CT for these nodules.  These nodules are most likely to be benign, but many still require follow up to make sure.  There are established guidelines for following nodules under a centimeter.  Those nodules found which are around a centimeter need workup with further testing to exclude cancer.


Lung bases are a common site for pneumonia.  Sometimes pneumonia can present in an unusual manner.  This can present as flank pain, or upper abdominal discomfort.  Sometimes we see pneumonia when we scan patients for abdominal pain.  The patient may complain of pain in the upper abdomen when the pneumonia is at the very bottom of the lungs.

Lung bases are clear are mostly used in CT of the abdomen and pelvis

Lung bases are also included on CT of the chest or lungs.  I don’t see the term lung bases are clear used for chest CTs very much.  Radiologists may describe abnormalities at the lung bases but I don’t see the phrase lung bases are clear very much.  Sometimes you may see the phrase the lungs are clear.

What happens if the lung bases are not clear?

When we do see an abnormality at the lung bases, this means they are not clear.  Sometimes an abnormality of the lung bases may need a dedicated chest CT to further evaluate.   This may be because we want to see the full extent of the abnormality or because we only see part of it.  A big nodule at the lung base may need a PET scan to see if it is more likely to be cancerous.

Lung bases are clear is a term most commonly used on abdominal CTs in my experience.  The radiologist is mentioning that he looked at the bottom of the lungs on the CT and saw nothing,  The lungs are clear instead of having a spot or some whiteness to them which can mean collapsed lung or pneumonia.    The radiologist will comment on the lung bases being normal in the body of the report.

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