Post-primary cavitating tuberculosis. False-colour Chest X-ray showing extensive fibrosis in both lungs (blue areas), the consequences of primary pulmonary tuberculosis. In most chest diseases, including tuberculosis, the appearance on X-rays mirrors the pathology. The primary tuberculous infection, due to the bacterium Mycobacterium tuberculosis, results in areas of pneumonitis (inflammation). In the post-primary stage cavitation may occur, followed by progressive fibrosis.