CT findings in apical versus basal involvement of pulmonary tuberculosis.

T uberculosis (TB) is a common infection worldwide and remains an important cause of morbidity and mortality, particularly in developing countries (1). In 2010, 8.8 million people developed overt disease; approximately 1.1 million deaths occurred among human immunodeficiency virus (HIV)-negative people and 0.35 million deaths occurred among HIV-positive people (2). Several host factors may contribute to radiologic manifestations of pulmonary TB, including prior exposure to TB, age, and underlying immune status (3). Radiologic manifestation of pulmonary TB has been divided into primary and postprimary TB, each with a characteristic radiologic pattern. Primary TB occurs most commonly in children without prior exposure to TB and without acquired specific immunity. Primary TB commonly presents as hilar or mediastinal lymphadenopathy, airspace consolidation, or pleural effusion. Postprimary TB is considered to be a reactivation of a previous TB lesion. Radiographically, postprimary TB usually presents as focal or patchy heterogeneous consolidation involving the apical and posterior segments of the upper lobes and less frequently in the superior segments of the lower lobes. On computed tomography (CT) scans, the most common findings of postprimary TB are centrilobular small nodules, branching linear and nodular opacities (tree-in-bud sign), patchy or lobular areas of consolidation, and cavitation (1, 3–6). Isolated involvement of basal segments of the lower lobes in pulmonary TB cases is unusual, and often causes great confusion in the diagnosis of pulmonary TB (3, 7). Because early diagnosis of pulmonary TB plays an important role in the treatment of TB, proper understanding of atypical radiologic manifestation is critical (8, 9). To the best of our knowledge, the CT findings of pulmonary TB involving basal segments have not been widely investigated. The present study compared clinical features and CT findings of pulmonary TB in basal segments and apical or apicoposterior segments, and assessed the frequent radiologic findings of TB in basal segments.