46 years old male with fever, cough and weight loss. He has a history of alcoholism.
Plain radiograph (A) of the chest shows irregular opacities including larger consolidations and smaller nodules. In the middle and upper parts there are hyperlucencies indicative of cavitations. Transverse sections of a chest CT (B, C) demonstrate large cavitations with irregular borders and thick walls located in the upper lobes. Moreover, there is wall-thickening of bronchi and diffuse nodularization with innumerous small centrilobular nodules and centrilobular branching lines producing a tree-in-bud pattern. These centrilobular nodules often coalesce into larger consolidations, in which again cavitations are observable. The minimum intensity projection (D) clearly illustrates the communication of the large airways with the cavitations.
Active pulmonary tuberculosis with cavitation and bronchiolitis from endobronchial dissemination.
The combination of coalescing cavitations and bronchiolitis is highly suggestive of pulmonary tuberculosis. Cavitations are usually observed in postprimary tuberculosis and are a result of caseous necrosis of lung parenchyma getting connection to large airways.
Primary tuberculosis is often clinically inapparent in immunocompetent individuals and consists of small focal infiltrates. Lymphatic spread (to hilar and mediastinal lymph nodes) and hematogenous spread (in particular to the apical lung regions, Simon Spitzenherde) may occur even in subclinical cases. Development of immunity leads to healing of the lesions resulting in often calcified pulmonary and hilar granulomas. If immunity is inadequate to contain the primary infection, a chronic progressive primary tuberculosis may develop. The radiological features of progressive primary tuberculosis are similar to those of postprimary tuberculosis.
Postprimary tuberculosis is a chronic progressive disease that results from reactivation of a dormant primary infection in 90% of cases. Reactivation usually occurs in the secondary foci of primary hematogenous spread and begins with patchy alveolar infiltrations if the lung is the site of reactivation (Assmann Frühinfiltrat). Progression of these early infiltrates leads to cavitations, which are the hallmark of postprimary tuberculosis and concern approximately 40% of affected adults. Bronchogenic dissemination from cavitation into the airways is the most common form of spread in postprimary tuberculosis and manifests radiologically as bronchiolitis with centrilobular nodules and centrilobular branching lines (tree-in-bud pattern).
The tree-in-bud pattern is the best indicator of disease activity and is more reliably identified on CT imaging. However, bronchiolitis and tree-in-bud pattern are not specific for tuberculosis and may occur in a variety of other conditions. Other signs of disease activity in patients in whom lung changes suggest old scarring of pulmonary tuberculosis are larger nodules and consolidations.
Beigelmann et al.
CT of parenchymal and bronchial tuberculosis
European Radiology (2000) 10(5):699
Zumba et al.
NEJM (2013) 368(8):745
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