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

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.

Clustered micronodules as predominant manifestation on CT: A sign of active but indolently evolving pulmonary tuberculosis

“…Similarly, Lee et al [9] showed a representative case report of CMs in a patient with a minimal extent of disease and found that CMs presented as nodular aggregations of granulomas in the peribronchiolar interstitium. In contrast, when CMs were pathologically analyzed in patients with advanced TB disease, they corresponded to the aggregation of tree-in-bud lesions of impacted caseation material within the bronchioles and alveolar ducts [15]. The difference in pathologic nature of CMs between our series and previously reported cases [15] might come from the difference in the stage of TB infection.…”

“…In contrast, when CMs were pathologically analyzed in patients with advanced TB disease, they corresponded to the aggregation of tree-in-bud lesions of impacted caseation material within the bronchioles and alveolar ducts [15]. The difference in pathologic nature of CMs between our series and previously reported cases [15] might come from the difference in the stage of TB infection. All our cases were live subjects with an early stage, while the latter cases were a post-mortem lung in advanced stage.…”

“…Furthermore, granuloma formation on TB occurs in the interstitium rather than alveolar space at the initial stage [14]. In our study, CMs originated from few small peribronchiolar nodule which suspected as MTB granuloma [15]. The CMs indolently grew over months to years, and finally turned into a pattern of bronchogenic spread.…”

“…less frequently observed (54.5%, 12 of 22 patients; 40.0%, 4 of 10 patients with a total CT score smaller than 10) [3,15,18]. In addition, cavities which are seen in 20-45% cases of active TB were rarely seen [18].…”

3D microarchitecture of the human tuberculous granuloma

“…*Corresponding Author 28 29 Adrie JC Steyn, Ph.D. 30 asteyn@uab.edu or adrie.steyn@ahri.org 31 +27-31-260-4715 32 33 34 35 Our current understanding of the pathophysiology of human pulmonary TB is limited by the paucity 38 of human TB lung tissue for study and reliance on 2D analytical methods. Here, to overcome the 39 limitations of conventional 2D histopathology, we used high-resolution 3D X-ray imaging 40 (µCT/nCT) to characterize necrotic lesions within human tuberculous lung tissues in relation to the 41 airways and vasculature.…”