Infiltrative Pulmonary Tuberculosis: Key CT Imaging Features and Patterns

Understanding Infiltrative Pulmonary Tuberculosis on CT Scans

Infiltrative pulmonary tuberculosis (TB) presents a wide spectrum of radiological features on computed tomography (CT), often varying from subtle early signs to more advanced structural changes. These imaging patterns are critical for accurate diagnosis, treatment planning, and monitoring disease progression. While some patients may exhibit a single dominant pattern, it is more common to see a combination of multiple imaging findings coexisting within the lungs.

Common Radiological Signs of Infiltrative TB

One of the most frequently observed manifestations is localized patchy consolidation, typically located in the apical or posterior segments of the upper lobes or the dorsal segment of the lower lobes. Interestingly, involvement tends to be more prevalent in the right lung compared to the left, possibly due to anatomical and airflow dynamics. This asymmetric distribution can serve as an important clue during radiological evaluation.

In more extensive cases, infiltrative TB can progress to lobar involvement characterized by large areas of dense parenchymal consolidation—often referred to as caseous pneumonia. These regions appear as bulky, ill-defined opacities affecting an entire lobe or segment, reflecting significant necrotic inflammation within the affected tissue.

Granulomatous and Nodular Patterns

Another hallmark of tuberculosis is the presence of proliferative lesions, which appear as well-defined nodular or punctate shadows on CT imaging. These nodules are often arranged in distinctive patterns such as flower-like clusters or tree-in-bud configurations, especially along the bronchovascular bundles. The tree-in-bud appearance is particularly suggestive of endobronchial spread and active infection, indicating small airways filled with inflammatory debris or pus.

Additionally, tuberculomas—rounded or oval-shaped masses—are commonly detected, typically measuring between 2 to 3 centimeters in diameter. These lesions usually have sharp margins and high density, with internal calcifications visible in many cases. Surrounding these tuberculomas, smaller satellite nodules or fibrotic foci may be present, representing residual or ongoing granulomatous activity—an important diagnostic clue that helps differentiate them from malignant tumors.

Cavitary Changes and Their Diagnostic Significance

Cavitary formation is a key feature in the evolution of infiltrative TB. On CT scans, these cavities appear as rounded or oval lucencies within areas of consolidation. They are generally thin-walled with smooth inner linings, although irregular thickened walls may also occur, especially in chronic or complicated cases. Irregular cavities may suggest secondary infection or delayed healing processes.

Patterns of Bronchogenic Dissemination

CT imaging often reveals evidence of endobronchial spread, where infectious material travels through the airways, leading to scattered parenchymal involvement. This appears as small, acinar-type nodules distributed along bronchial pathways, sometimes merging into larger confluent opacities confined to individual pulmonary lobules. This pattern underscores the importance of airway-centered disease propagation in active TB.

Fibrotic and Calcified Residual Lesions

As part of the healing process, granulomatous lesions may undergo fibrosis and calcium deposition. These healed areas manifest as sharply demarcated, hyperdense foci on CT scans. In advanced stages, complete calcification can result in bone-density-like patches or small nodules, indicating inactive or quiescent disease. Identifying these calcified remnants is essential for distinguishing past TB infection from active disease.

Interlobular Septal Thickening and Reticular Patterns

In certain patients, interlobular septal thickening may be evident, appearing as linear or reticular opacities across the lung fields. This finding may reflect lymphatic spread of infection or associated interstitial inflammation. When combined with other typical TB-related changes, such patterns contribute to a comprehensive radiological profile that supports clinical diagnosis.

Overall, recognizing the diverse CT manifestations of infiltrative pulmonary tuberculosis enables earlier detection and better management. Radiologists and clinicians should remain vigilant for classic signs such as upper lobe predominance, cavitary lesions, tree-in-bud opacities, and satellite nodules—all of which play a vital role in differentiating TB from other pulmonary conditions like pneumonia or lung cancer.