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Radiological imaging of the chest is one of the most important and most requested investigations in medicine. These tests include X-rays, CT scans, and MRI investigations which are performed in order to give the requesting physician a better idea of what is going on internally in a patient presenting with relevant complaints.

These investigations help to narrow down the possible diagnoses relating to any of the anatomy located in the chest cavity including muscles, the ribs, joints, the diaphragm, and the oesophagus and organs such as the heart, lungs, and even the upper part of the liver, the stomach, and the pancreas.

Interpreting X-rays of the chest can be quite a daunting experience so physicians are trained in order to be able to assess basic pathologies if they are situated in rural settings where specialist radiologists are not available. If there are any issues that one would need further help with then a radiologist in a larger centre can always be contacted to offer some advice and guidance. 

One of the most common pathologies seen on X-rays of the lungs includes fibrohazed/cotton wool opacities. They are named as such because of the hazy and patchy appearances they produce on X-ray images.

Causes of Lung Opacities

There are only three things that are present in the lungs. Therefore, any opacities in the lung fields are caused by any of these three and include:

  • The interstitium which is the solid lung tissue.
  • The blood vessels which run through the interstitium.
  • Airspaces of which the majority are represented by the alveoli (air sacs) in the lungs. 

Interstitial Opacity

These opacities are more linear and streaky and can be caused by the following issues:

  • Pulmonary edema.
  • Lymphangitis.
  • Fibrosis.
  • Sarcoidosis.
  • Pneumoconiosis.

Blood Vessel Opacity 

Blood vessels in and around the lungs can distend (such as with venous congestion) or become blocked (as happens with a pulmonary infarct due to an embolus blocking the vessel). These conditions can then cause a generalized hazy appearance across the lung fields.

Airspace Opacity

The opacities causes by airspace issues mostly resemble cotton wool/fuzzy patches which are also referred to as the fibrohazed opacities. The following are therefore the most common causes of these opacities.
  • Inflammatory exudate - this occurs as a result of an infection in the lung tissue causing fluid such as pus to be produced which then builds up in the alveoli.
  • Pulmonary oedema - the increased pressure in the pulmonary vessels causes fluid to leak out of them and this ends up in the surrounding tissue. The causes of pulmonary oedema can be cardiogenic or non-cardiogenic. 
  • Blood - this can occur in conditions such as cystic fibrosis or Goodpasture's disease where blood leaks into the alveoli.
  • Cancer cells - when patients have cancer of the lungs, the cancer cells usually produce opacities involving the interstitium but they can also fill up the airspaces. Lymphoma can also result in these opacities.


As can be seen, the causes of fibrohazed opacities are limited to a handful of possible problems but these do indicate serious issues that need to be managed further by healthcare professionals. 

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