Korean J Radiol.  2018 Oct;19(5):859-865. 10.3348/kjr.2018.19.5.859.

Tree-in-Bud Pattern of Pulmonary Tuberculosis on Thin-Section CT: Pathological Implications

• Im JG
• Itoh H

• KMID: 2418548
• DOI: http://doi.org/10.3348/kjr.2018.19.5.859

Abstract

The "tree-in-bud-pattern" of images on thin-section lung CT is defined by centrilobular branching structures that resemble a budding tree. We investigated the pathological basis of the tree-in-bud lesion by reviewing the pathological specimens of bronchograms of normal lungs and contract radiographs of the post-mortem lungs manifesting active pulmonary tuberculosis. The tree portion corresponds to the intralobular inflammatory bronchiole, while the bud portion represents filling of inflammatory substances within alveolar ducts, which are larger than the corresponding bronchioles. Inflammatory bronchiole per se represents the "tree" (stem) and inflammatory alveolar ducts constitute the "buds" or clubbing. "Clusters of micronodules", seen on 7-mm thick post-mortem radiographs with tuberculosis proved to be clusters of tree-in-bud lesions within the three-dimensional space of secondary pulmonary lobule based on radiological/pathological correlation. None of the post-mortem lung specimens showed findings of lung parenchymal lymphatics involvement.

Keyword

Tree-in-bud; Pulmonary tuberculosis; Cluster of micronodules; Radiology-Pathology correlation; Centrilobular nodules

MeSH Terms

Bronchioles
Lung
Trees
Tuberculosis
Tuberculosis, Pulmonary*

Figure

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  Fig. 1 Post-mortem bronchiologram. Respiratory bronchioles and central part of alveolar duct are demonstrated. Respiratory bronchioles are equipped with alveoli. Diameter of alveolar duct is larger than that of respiratory bronchiole, because diameter of alveoli is added to that of ductal lumen (arrow).

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  Fig. 2 Post-mortem bronchiologram. Two types of bronchiolar branching, cm and mm pattern, are demonstrated. Latter (boxed area) is morphological basis of tree-in-bud lesions in pulmonary tuberculosis. Extreme end of mm pattern is ballooned-out with fuzzy outline, which indicates alveolar ducts (circle).

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  Fig. 3 Post-mortem radiograph of patient with active pulmonary tuberculosis demonstrating tree-in-bud lesion (boxed area) with smooth marginated bronchiole (tree) and distal clubbed end (bud). Bud measures 1–2 mm in diameter and is definitely bigger than parent bronchiole (tree). Slice thickness is 1 mm. PV = pulmonary vein

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  Fig. 4 Pathologic basis of tree-in-bud lesion. Post-mortem radiograph (A) and gross photograph (B) of same specimen in patient with pulmonary tuberculosis. Impacted cheesy material within smooth-marginated bronchiole (arrows) continues to larger, rather ill-defined alveolar ducts (arrowheads). Bar indicates 1 mm. Reprinted with permission from authors' reference 1. Adapted from Im et al. Radiology 1993;186:653-660

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  Fig. 5 CT image of tree-in-bud lesions in patient with active pulmonary tuberculosis. Note that tree ends in terminal clubbing (bud) (arrow). Note also that tree-in-bud lesions appear dense and well-defined even with small size; standard window setting (width 1600, level 250 HU).

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  Fig. 6 Comparison of centrilobular branching nodules seen in bacterial pneumonia (A) and tuberculosis (B). Note that marginal clarity of centrilobular nodules (arrows) are much greater in pulmonary tuberculosis (B) than in bacterial pneumonia (A).

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  Fig. 7 Post-mortem radiographs of cluster of micronodules (galaxy appearance described in sarcoidosis) and corresponding microscopic findings in patient with endobronchial spread of tuberculosis. A. Micronodules ≥ 2 mm are clustered within secondary pulmonary lobule, demarcated by interlobular septa (interrupted line) and PV. Bronchiole enters central portion of lobule (Br). PA indicates pulmonary artery. Bar indicates 10 mm; slice thickness is 7 mm. B. Serial thin-section radiographs reveal separation of each clustered nodule, with occasional continuity and branching. In lower right image, branching linear lesions occur predominantly at periphery of lobule abutting interlobular septa (arrowheads). If this plane were imaged by CT, it might have erroneously been interpreted as perilymphatic location. Bar indicates 5 mm; slice thickness is 1 mm. C. Close-up view of lower central section shows centrilobular patent bronchiole (Br) continuing into smooth marginated impacted bronchioles (tree), terminating in irregular marginated clubbed ends (buds). These findings suggest that cluster of small nodules observed on CT of patients with tuberculosis represent aggregates of tree-in-bud lesions. D. Pathologic specimen of same region shows central patent bronchiole, which continues into respiratory bronchiole with cheesy material; peripherally located cheesy material with inflammatory debris extending into surrounding alveoli (H&E, ×10).

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