From the Guidelines
Radiographically distinguishing between tuberculosis (TB), coccidioidomycosis, pulmonary Kaposi sarcoma (KS), and Pneumocystis jirovecii pneumonia (PJP) requires a stepwise approach, starting with chest radiography as the initial test, as recommended by the American College of Radiology 1. To differentiate between these conditions, it is essential to consider specific imaging patterns:
- TB typically presents with upper lobe predominant nodules, cavitations, and fibrotic changes, often with hilar or mediastinal lymphadenopathy, and a classic finding is the "tree-in-bud" pattern representing endobronchial spread.
- Coccidioidomycosis commonly shows nodular infiltrates, thin-walled cavities, and hilar lymphadenopathy, with a predilection for the lower lobes.
- Pulmonary Kaposi sarcoma characteristically displays peribronchovascular nodular opacities, thickened interlobular septa, and pleural effusions, with lesions following bronchovascular bundles.
- PJP typically presents with diffuse, bilateral ground-glass opacities with a central or perihilar distribution, often sparing the lung periphery, and may show pneumatocysts in advanced disease. Clinical context is crucial for accurate diagnosis, as immunocompromised status (particularly HIV) increases risk for all these conditions, and definitive diagnosis usually requires microbiological or histopathological confirmation, as radiographic findings may overlap, especially in immunocompromised patients where atypical presentations are common 1. In cases where chest radiography is nonrevealing or nondiagnostic, CT may be appropriate to increase the specificity of the diagnosis of TB and to better show distinct findings such as cavitation or endobronchial spread with tree-in-bud nodules 1.
From the Research
Radiographic Distinction of TB, Coccidioidomycosis, Pulmonary Kaposi Sarcoma, and PJP
To distinguish between TB, coccidioidomycosis, pulmonary Kaposi sarcoma, and PJP radiographically, the following characteristics can be considered:
- TB:
- Primary TB: parenchymal consolidation, associated adenopathy, lack of systemic toxicity, failure to respond to conventional antibacterial therapy, and recent PPD conversion 2
- Postprimary TB: heterogeneous, often cavitary opacity in the apical and posterior segments of the upper lobes and the superior segments of the lower lobes, lymphadenopathy is rare 2
- Coccidioidomycosis:
- Acute disease: lobar or segmental consolidation, multifocal consolidation, and nodules, adenopathy and pleural effusions are also seen 3
- Chronic disease: residual nodules, chronic cavities, persistent pneumonia with or without adenopathy, pleural effusion, and regressive changes 3
- CT findings: multiple bilateral nodules, solitary nodules associated with consolidation, cavitation of nodules, coalescence, nodule-associated abnormalities, lymph node enlargement, and small pleural effusion 4
- Pulmonary Kaposi Sarcoma and PJP:
- There are no specific radiographic findings mentioned in the provided studies to distinguish these conditions from TB and coccidioidomycosis
Coinfection and Diagnostic Challenges
Coinfection with TB and coccidioidomycosis can occur, and radiologic studies may not be able to distinguish between the two conditions 5. In such cases, clinical and laboratory features, as well as antimicrobial treatments and outcomes, should be considered.
Imaging Modalities
Different imaging modalities can be used to diagnose and assess TB and other conditions, including:
- Chest radiography: mainstay for diagnosis of parenchymal disease in primary pulmonary TB 2, 6
- CT: more sensitive in detecting lymphadenopathy, revealing early bronchogenic spread, and characterizing infection as active or not 2, 6
- MRI: preferred modality in diagnosis and assessment of tuberculous spondylitis, and superior to CT for detection and assessment of central nervous system TB 6
- (18)F-FDG PET/CT: yields promising results in characterizing infection as active or not, and may play a major role in assessing response to anti-TB treatment 6