Radiological diagnosis and follow-up of pulmonary tuberculosis

Mycobacterium tuberculosis, the causal organism of tuberculosis (TB), is one of the oldest and still one of the deadliest pathogens known to man. Approximately 1 in 10 people with primary pulmonary tuberculosis (PTB) present clinically; of untreated cases, approximately 1 in 10 reactivate usually at a time of relative immunodeficiency. The spectrum of radiologic manifestations of PTB can pose a variety of diagnostic and management challenges. PTB infection often leaves long term sequelae of infection, particularly granulomatous nodules, cavitation, and fibrosis; distinguishing dormant disease from reactivation is not always clear-cut. The radiologic presentation of primary PTB infection tends to differ from that of post-primary PTB, but there is significant overlap in the appearances. Primary PTB typically presents with consolidation and regional lymphadenopathy, whereas post-primary PTB more often results in cavitation. The pathology and therefore the radiology of TB infection will be altered based on the efficacy of the immune response and will therefore vary depending on the immune competency. Clinically, in the presence of infection, the main questions are whether M tuberculosis is the infecting organism and, if treated, does the radiology indicate response to treatment. In order to interpret the radiology of TB one needs to be aware of the spectrum of presentation, the expected reaction to treatment, and the myriad of non-pulmonary sites of infection that may prove to be more clinically significant than the pulmonary infection.