A 45-year-old woman from Delhi with known sputum-positive pulmonary tuberculosis undergoes high-resolution CT (HRCT) chest. All of the following CT findings are characteristic of active pulmonary TB EXCEPT:

## HRCT Findings in Active Pulmonary Tuberculosis ### Characteristic CT Patterns **Key Point:** Active TB shows specific patterns of airway involvement and parenchymal disease. Smooth, homogeneous ground-glass opacification without bronchial involvement is NOT characteristic of TB. | HRCT Finding | Typical in Active TB | Pathophysiology | |--------------|---------------------|------------------| | Tree-in-bud opacities | Yes | Centrilobular nodules from endobronchial spread and small airway inflammation | | Cavitary lesions | Yes | Central necrosis with irregular thick walls; often with surrounding consolidation | | Endobronchial nodules | Yes | Direct spread of infection along bronchi; nodules along segmental/subsegmental airways | | Smooth ground-glass (homogeneous, no bronchi) | No | Suggests diffuse alveolar process (e.g., viral pneumonia, ARDS, drug toxicity)—not TB | | Bronchial wall thickening | Yes | Inflammation and edema of airways from endobronchial disease | ### Why Smooth Homogeneous Ground-Glass is Wrong **High-Yield:** TB is fundamentally a **bronchocentric** disease. Active TB consolidation and ground-glass opacification are characterized by: - Visible bronchi within the opacified areas (bronchial sign) - Associated bronchial wall thickening - Nodular opacities along bronchi (endobronchial spread) Smooth, homogeneous ground-glass without these features suggests: - Atypical pneumonia (viral, PCP) - Acute respiratory distress syndrome (ARDS) - Drug-induced pneumonitis - Hypersensitivity pneumonitis **Clinical Pearl:** The presence of bronchi within consolidation (bronchial sign) is a hallmark of TB and helps distinguish it from non-TB causes of ground-glass opacification. ### Correct TB Findings 1. **Tree-in-bud opacities** — centrilobular nodules with branching; from small airway inflammation and endobronchial spread 2. **Cavitary lesions** — irregular thick-walled cavities with surrounding consolidation; classic in upper lobes 3. **Endobronchial nodules** — nodular opacities along segmental/subsegmental bronchi; indicates active spread **Mnemonic: BEAT-TB** — Bronchocentric, Endobronchial spread, Airway involvement, Tree-in-bud, Thick-walled cavities [cite:Hansell et al. Imaging of Diseases of the Chest 5e Ch 5]