Apical opacity associated with pulmonary tuberculosis: high-resolution CT findings

Area of Science:

• Radiology
• Pulmonology
• Medical Imaging

Background:

• Apical opacity, often termed "apical cap" or "apical pleural thickening," is a common finding in patients with tuberculosis.
• The exact nature of this opacity on plain radiographs has been a subject of clinical debate.

Purpose of the Study:

• To investigate the composition of apical opacities in patients with upper lobe tuberculosis using high-resolution computed tomography (HRCT).
• To differentiate between extrapleural fat and pleural thickening in the apical regions of the lungs.

Main Methods:

• HRCT scans were performed on 18 patients with upper lobe tuberculosis exhibiting homogeneous apical opacity (>1 cm thick) on chest radiographs.
• Scans were analyzed at apical, supra-aerated lung, and more caudal levels to assess parenchymal and pleural structures.

Main Results:

• HRCT demonstrated that extrapleural fat, interspersed with vessels, constituted the majority of the opacity seen on plain radiographs.
• At levels above aerated lung, peripheral extrapleural fat (3-25 mm) and central atelectasis were observed.
• At lower levels, HRCT revealed extrapleural fat (3-20 mm), thickened pleura (1-3 mm), and peripheral atelectasis, along with central emphysematous changes and bronchiectasis.

Conclusions:

• The common apical opacity in tuberculosis, the "apical cap," is predominantly composed of extrapleural fat, not solely pleural thickening.
• HRCT provides detailed anatomical information crucial for understanding radiographic findings in pulmonary tuberculosis.