Tuberculosis, Post-Primary

Helen T. Winer-Muram, MD

Key Facts

Imaging Findings

Rim-enhancing enlarged mediastinal lymph nodes
Consolidation (100%)
- Lobular size and peribronchial
Cavitation (50%)
- Wall thickness variable: Thick > thin, shape may be irregular
Endobronchial spread
- Nodules: Centrilobular rosettes (Acinar), poorly defined, 2-10 mm in size
- Tree-in-bud appearance
CT more specific (rim-enhancing lymph nodes) and more sensitive for active disease (signs of endobronchial spread)

Top Differential Diagnoses

Chronic Fungal Infection
Ankylosing Spondylitis
Progressive Massive Fibrosis (PMF)

Pathology

Acid-fast bacilli located in macrophages, obligate aerobe

Clinical Issues

Chronic nonspecific symptoms: Cough, low-grade fever, malaise, weight loss

Diagnostic Checklist

Bronchogenic carcinomas (scar carcinoma) in patients with post-primary TB are usually advanced, because findings or progression are attributed to TB

Coronal CECT shows consolidation

and variable-sized cavities with thick walls

in the dorsal aspect of the lung.

Axial CECT in the same patient shows bronchiectasis

in the superior segment, right lower lobe. Centrilobular nodules

represent endobronchial spread.

TERMINOLOGY

Abbreviations and Synonyms

Tuberculosis (TB), post-primary TB, reactivation TB, recrudescent TB

Definitions

Indolent bacterial (Mycobacterium tuberculosis) infection, often relapsing course, associated with fibrosis, calcification, and adenopathy
- Varying appearance, depending on time course
  - Primary tuberculosis, initial infection
  - Miliary tuberculosis, overwhelming infection
  - Post-primary tuberculosis, recurrent infection

IMAGING FINDINGS

General Features

Best diagnostic clue: Rim-enhancing enlarged mediastinal lymph nodes
Patient position/location: Apical or posterior segments of upper lobes, superior segment of lower lobes (90%)
Morphology
- Combination
  - Consolidation + cavitation + endobronchial spread

CT Findings

Morphology
- Consolidation (100%)
  - Lobular size and peribronchial
- Cavitation (50%)
  - Wall thickness variable: Thick > thin, shape may be irregular
  - Air-fluid levels uncommon
  - Often surrounded by consolidated lung
- Endobronchial spread
  - Nodules: Centrilobular rosettes (acinar), poorly defined, 2-10 mm in size
  - Tree-in-bud appearance
  - Bronchial wall thickening
- Volume loss in affected lung
  - Usually from fibrosis (30%): Architectural distortion, bronchiectasis, emphysema
Distribution
- Often segmental in distribution
- Apical and posterior segments of upper lobes, superior segments of lower lobes
- Bronchogenous spread: Gravity dependent lobes
Adenopathy (30%)
- Classic appearance: Low-density center with peripheral rim enhancement
- Mean size 3 cm in diameter
Pleural effusions (20%)
- Usually small; if air, consider complicating bronchopleural fistula
- Pleural thickening common in advanced cavitary disease
Evolution
- With successful treatment, consolidation and nodules will resolve, usually over 9-12 months
  - Signs of fibrosis may increase with increasing volume loss in affected lung
- Calcification in lung (Ghon lesion) and lymph nodes (Ranke complex) may be from previous primary disease
Active vs. inactive disease
- Activity
  - Signs of endobronchial spread
  - Cavitation
  - Consolidation
- Inactivity
  - Requires stability over 6 months
Complications
- Bronchopleural fistula
- Mycetomas-saprophytic aspergillus colonization in cavities
- Fibrosis and retraction can cause secondary bronchial obstruction
- Bronchostenosis
- Broncholithiasis, erosion of calcified hilar or mediastinal lymph node into bronchus
- Fibrosing mediastinitis
- Empyema, may burrow into chest wall (empyema necessitatis), may involve breast (tuberculous mastitis)
- May involve spine (Pott disease)
- Pericardial involvement may give rise to constrictive pericarditis
- Hemoptysis may be due to Rasmussen aneurysm, mycetomas, bronchiectasis, or broncholithiasis
In immunosuppressed patients, may progress to
- Miliary disease: Profuse uniform distribution of 2-3 mm nodules, indicating hematogenous spread
- Adult respiratory distress syndrome
- Extrathoracic dissemination to breast, spine, kidney, meninges, bone
Post-primary TB in AIDS patients
- Will manifest as primary TB pattern when CD4 count < 200 cell/mm³, absence of cavities, cannot form granulomas
- Airspace consolidation, miliary dissemination, lymphadenopathy, effusions
- No lobar predilection
Accuracy of diagnosis (90%)

Radiographic Findings

Primary: Airspace consolidation in 1 lobe; may be lobar or segmental, any lobe
- If untreated, can spread to other lobes (bronchogenic spread)
- Cavitation uncommon
- ± Adenopathy; unilateral hilar or mediastinal adenopathy may present with adenopathy alone
- Effusions common, may be small or large
Miliary: Diffuse, tiny, relatively well-defined, uniform nodules, 2-3 mm in diameter
- Evenly distributed but may appear more numerous and larger in upper lobes with chronic disease
- Multilobar involvement, no adenopathy or effusion
Post-primary TB
- Airspace consolidation, cavities, fibrosis, retraction, distortion, endobronchial spread to dependent lung, acinar nodular opacities
- Apical and apical posterior segments of upper lobes and superior segments of lower lobes

Imaging Recommendations

Best imaging tool
- Chest radiography for initial detection, usually sufficient for monitoring response to therapy
- CT more specific (rim-enhancing lymph nodes) and more sensitive for active disease (signs of endobronchial spread)
Protocol advice
- CT angiography indicated in patients with hemoptysis to identify source of bleeding
- Common sources
  - Related to bronchiectasis, cavities with mycetomas
  - Pulmonary artery aneurysm from cavity (known as Rasmussen aneurysm)
- Also useful to define bronchial artery anatomy for embolization