Pneumonia does not always show up on X-rays. A classic pneumonia will look like a white area in the normal black lung. Pneumonia can be in one spot or throughout the lung. Often there are symptoms like cough, fever and fatigue. It is important to remember that not all pneumonias and infections are visible on chest X-rays for multiple reasons.
Pneumonias can hide in chest X-ray
Some pneumonias can not be seen because they are in blind spots. Pneumonias can hide in areas tough for the radiologist to see. This can be below the diaphragms, along the spine, near the heart and mediastinum to name some. They are there but simply too difficult to see and diagnose with certainty.
Ground glass pneumonias
Pneumonias can also be ground glass in appearance and not show on chest X-rays. An example of a ground glass pneumonia can be a viral infection like COVID. Pneumocystis pneumonia occurs in immunocompromised patients like those with AIDS. Ground glass density in general does not show up on X-ray very well. Ground glass is lighter then the white dense appearance of a classic pneumonia.
Pneumonias may have few imaging findings
Other lung infections like bronchitis or certain viral infections have few or subtle findings on chest X-ray. Some pneumonias are small and do not show on X-ray because they blend in with normal structures or hide behind ribs or the heart.
Technical factors and obesity
Pneumonias do not show on some chest X-rays because of large patients. X-rays are more limited in obese patients. This is particularly true when this is done using portable technique. The soft tissues and fat of the patients limits the ability to detect pneumonias in some cases.
Pneumonia can be hidden in chronic lung disease
Pneumonias can also look like other abnormalities or be hidden by chronic lung disease. Pneumonia is harder to diagnose in patients who have chronic lung disease on chest X-ray. This is especially true if there are no prior X-rays available to show change. Sometimes we can not tell if the chronic lung disease is worse or there is a pneumonia.
Not everything that looks like pneumonia is
Sometimes lung collapse or atelectasis can be misdiagnosed as pneumonia. Some cancers can look like pneumonia. That is why some radiologists will recommend follow up imaging to make sure the pneumonia clears after antibiotics. More chronic lung disease can also look like pneumonia, especially if we don’t have prior studies.
Pneumonia does not show up on chest X-rays in all cases. Sometimes further imaging with CT is needed if there is high suspicion for a pneumonia and a normal chest X-ray. Some pneumonias do now show up on X-rays for various reasons outlined above. There is also a possibility of an abnormality being diagnosed as a pneumonia which represents something else. Follow up imaging and further testing may be needed.