Basic HRCT Patterns: Nodules

Definition: A nodule is a rounded density that does not correspond to a vessel. It represents either a spherical structure or a linear structure cut in cross section.

Location of Nodules: The anatomic distribution of nodules--centrilobular, random, or interstitial--helps to identify potential causes; for example, bronchopneumonia gives nodules in a centrilobular distribution.

In image 1, multiple nodular densities of varying size are seen in the right lung. Note that they are clustered in a line following the course of a bronchus in this example of bronchopneumonia. The larger nodular densities represent foci of lobular consolidation (1 to 2.5 cm in size).

The tiny nodules (1 to 2 mm in size) represent distal bronchiolar inflammation. The location of the nodules is centrilobular (see next page).

Image 1

 

 

"Tree-in-bud" Pattern

Some of the tiny centrilobular nodules are connected by thin, branching, linear structures. This appearance, which is referred to as "tree-in-bud," represents inflammation in branching bronchioles.

Look at images 1 and 2.

Is disease bilateral or unilateral?

Answer

In each image find 3 centrilobular nodules that fill a lobule.

Find a tree-in-bud pattern in each image.

tib1nfl1

Image 2

Find 3 small centrilobular nodules.

Causes of nodules include tumor, infectious and non-infectious granulomas, pneumoconioses, mucous plugs, endobronchial disease, and hypersensitivity pneumonia.

  tib2nfl2cln1cln2

Gross Appearance of Bronchopneumonia

This lung shows a more diffuse bronchopneumonia than is seen in the HRCT above. Large arteries and airways may be seen cut in cross section or longitudinally. Distributed fairly uniformly in the intervening parenchyma are small, pale nodules and lines, some of which are branching. These represent centrilobular airways filled with pus, which extends into the alveoli to a variable degree, accounting for the mild size differences.

Histologic Section of Bronchopneumonia

A section of one of the centrilobular nodules shown above has an airway (center) filled with exudate, which is also present in the surrounding alveoli.

By definition, bronchopneumonia is confined to the centrilobular region, and the presence of air in the adjacent lung gives the nodular appearance on HRCT.

When the exudate fills the whole lobule, the resulting HRCT pattern is that of larger nodules as seen above.

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Unilateral. Disease is confined to the right lung.

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Tree-in-bud pattern

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Centrilobular nodule filling a lobule

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Small centrilobular nodule

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