Radiologic Findings

CT images show peripheral, dependent, confluent, and somewhat patchy opacities in the mid and lower lung zones. Recurrent pneumonias suggest various etiologies, including bronchial obstruction, bronchiectasis, repeated aspiration, and immunosuppression [1]. Bronchial obstruction and bronchiectasis are suggested when the pneumonias recur in the same location. Peripheral consolidations can be seen in eosinophilic pneumonia and bronchiolitis obliterans organizing pneumonia, among other etiologies. Dependent bibasilar pneumonias suggest aspiration.

This image has a focal density in the middle lobe.

Question: Which description best fits this density? 1. focal, patchy consolidation, 2. clustered, ill-defined, tiny nodules connected by faint lines, 3. focal ground-glass density, 4. reticular densities, 5. multiple serpiginous densities. Answer

Just below the carina, the lungs show bilateral, ill-defined consolidations in the lower lobes posteriorly as shown in the next three images. A few opacities were present in the apices.

Clinical summary Image 1

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Answer: 2. Clustered, ill-defined, tiny nodules connected by faint lines, also known as "tree-in-bud."

Centrilobular densities with a "tree-in-bud" appearance are usually due to endo- and peribronchiolar infection/inflammation. In this case, the combination of recurrent dependent densities and a focal region of "tree-in-bud" suggests the possibility of aspiration, although other etiologies are considered. See the excerpt from Case 10 below.

"Tree-in-bud": Centrilobular densities can best be appreciated on high-resolution CT scans, but can also sometimes be seen on regular CT images, as in this case. The location of the nodules can be inferred as centrilobular if they are near small vascular branches, surround or obscure the centrilobular artery, or are centered 5-10 mm from the pleural surface. These densities may appear as a rosette of small opacities, and if associated with filling or thickening of the bronchiole will result in a "tree-in-bud" appearance.

The differential diagnosis for centrilobular densities generally falls into the category of peribronchiolar disease, but may include perilymphatic or perivascular disease. Centrilobular densities with a "tree-in-bud" appearance are usually due to endo/peribronchiolar diseases and may be seen with bronchopneumonia (particularly in regions peripheral to frank consolidation), bronchiectasis and cystic fibrosis, bronchogenic spread of tuberculosis, bronchiolitis obliterans and bronchiolitis obliterans organizing pneumonia, respiratory bronchiolitis, and hypersensitivity pneumonia [2].


1. Slone R. Differential diagnosis for the chest. In: R Slone, F Gutierrez, A Fisher (eds): Thoracic imaging: a practical approach, New York, 1999, McGraw-Hill, p 38.

2.Webb W, Müller N, Naidich D. High-resolution CT of the Lung, 2nd ed., Philadelphia, 1996, Lippincott-Raven Publishers, pp 98-103.

Clinical summary Image 1

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