Lung patterns made easy!

Alveolar, interstitial or maybe bronchial?

Who does not know that feeling: you look at a chest radiograph and see a bit of every lung pattern and finally you end up with the diagnosis of bronchio-interstitial lung pattern with areas of alveolar infiltrate. To come to a final diagnosis based on this description is almost impossible.


But how do you get to a good radiological description of the lung pattern?


The first step: technique!

As for all other regions, the first step in evaluating chest radiograph or CTs is to look at the radiographic quality and patient related factors.

  • Has the correct exposure or algorithm been selected?
  • Is the patient emaciated or obese?
  • Has the radiograph been taken during inspiration or expiration?

In contrast to other body regions the phase of respiration has a significant influence on the radiologic appearance of the lung.

Obesity, expiration and underexposure lead to an artificial increase in lung opacity. Contrary to that emaciation, deep inspiration and overexposure decrease the lung opacity. If you are in doubt repeating the radiographs may be helpful.

The second step: increased, decreased or normal!

Based on the answers to the above questions you need to decide if the lung of your patient is abnormal. It is not about deciding if the lung changes you are dealing with are alveolar, interstitial or bronchial. Start with answering the following questions:

Is the lung opacity …

  • … increased?
  • … decreased?
  • … normal?

Are the changes affecting the entire lung or are the changes more pronounced in certain areas?

The third step: Alveolar, bronchial or interstitial


The alveolar lung pattern

The key to diagnose an alveolar lung pattern is the lung vasculature. Their visibility or better said the loss of their visibility decides on the changes being alveolar or not.


In the altered lung area …

  • … you don`t see lung vessels any more,
  • … you do see air bronchogramms, meaning dark lines on a white background, mirroring the normal appearance of the lung?

You are done! The lung pattern you are dealing with is an alveolar lung pattern. Contrary to the other lung patterns an alveolar lung pattern shows a typical distribution helping to choose a most likely diagnosis from the long list of differential diagnosis for alveolar lung pattern. A list of most likely differential diagnosis based on distribution can be found under the link “DD alveolar”. Consider also anamneses, other clinical symptoms and results of other diagnostic tests in your diagnosis.


Bronchial lung pattern

Bronchial lung changes can be divided in three groups.

  • Mineralisations/ sclerosis of the bronchial walls or bronchial glands
  • Soft tissue thickening of the bronchial walls
  • Bronchiektasia/ dilation of bronchi


Mineralisations or sclerosis of the bronchi is usually not difficult to detect. They can finely delineate the bronchial walls appearing as fine lines or present as cauliflower- like patches. For differential diagnosis check under the following link “DD bronchial” below or at the side.



Soft tissue thickened bronchial walls can ben the result of peribronchial infiltrates, that is the

  • accumulation of cells or fluid around the bronchi
  • accumulation of mucus in the lumen of the bronchi

Lung vessels are still visible, the lung shows tram lines or donuts.


 - Easier said as seen –


Tip: On first glance, the lung may look as if multiple small nodules are present. Close inspection shows a that small dark point is visible centrally in most of the nodules. Or the lung appears as if a net is spread over it. On close inspection the lines, causing the netlike impression, run parallel to each over some distance. For differential diagnosis check under the link “DD bronchial”.



Bronchiectasia can be difficult to detect. In general bronchi should decrease in size from the principle bronchi to the periphery. In bronchiectasia a bronchus shows an increase in diameter peripherally compared to a more centrally located part. Occasionally the lung parenchyma may appear bullous. Also for this type of bronchial pattern you find a list of differential diagnosis under the following link “DD bronchial”.

Interstitial lung pattern

Like the bronchial lung pattern also the interstitial lung pattern can be subdivided further

  • Nodular/ structured
  • Retrikulonodular/ miliar
  • Unstructured


A nodular or structured interstitial pattern does usually not cause any problems in diagnosing it. A single or multiple soft tissue opaque nodules are visible. The list of differential diagnosis is short and identical to the list for soft tissue opaque nodules at other sides of the body.


In a miliary or reticulonodular lung pattern the radiograph looks as if a snowstorm is blustering. You see multiple, small nodules less than 5mm in diameter.


The unstructured interstitial lung pattern is the most challenging lung pattern. And the most commonly over diagnosed lung pattern. The lung appears as if a white screen door is superimposed onto it. The lung vessels can still be delineated.

Before you diagnose an unstructured interstitial lung pattern lie back and reconsider: Is the lung opacity really increased?  Is the increased opacity really not related to underexposure, exspiration or any of the other artificial cause for an increased lung opacity.

The list of differential diagnosis is long. You find a list of differential diagnosis under the following link “DD interstitial”.

Test yourself – mixed breed dog Baloo, 5 months, coughing

Which lung pattern is visible on the radiograph and what are possible differential diagnoses. Click on the respective link and see if you are right.

Bilder mit freundlicher Genehmigung/ Image courtesy Tierklinik Hofheim. Dres Kessler, Kosfeld, Tassani-Prell, Bessmann, Rupp, Delfs, Schmohl, von Klopmann
Bilder mit freundlicher Genehmigung/ Image courtesy Tierklinik Hofheim. Dres Kessler, Kosfeld, Tassani-Prell, Bessmann, Rupp, Delfs, Schmohl, von Klopmann

No responsiblity is taken for the correctness of this information. 

© Antje Hartmann