Imaging of pulmonary tuberculosis

Tuberculosis, more than any other infectious disease, has always been a challenge, since it has been responsible for a great amount of morbidity and mortality in humans. After a steady decline in the number of new cases during the twentieth century, due to improved social and environmental conditions, early diagnosis, and the development of antituberculous medication, a stagnation and even an increase in the number of new cases was noted in the mid-1980s. The epidemiological alteration is multifactorial: global increase in developing countries; minority groups (HIV and other immunocompromised patients); and elderly patients due to an altered immune status. Other factors that may be responsible are a delayed diagnosis, especially in elderly patients, incomplete or inadequate therapy, and the emergence of multidrug-resistant tuberculosis. The course of the disease and its corresponding clinicoradiological pattern depends on the interaction between the organism and the host response. Classically, pulmonary tuberculosis has been classified in primary tuberculosis, which occurred previously in children, and postprimary tuberculosis, occurring in adult patients. In industrialized countries, however, there seems to be a shift of primary tuberculosis towards adults. Furthermore, due to an altered immunological response in certain groups, such as immunocompromised and elderly patients, an atypical radioclinical pattern may occur. The changing landscape, in which tuberculosis occurs, as well as the global resurgence, and the changed spectrum of the clinical and radiological presentation, justify a renewed interest of radiologists for the imaging features of pulmonary tuberculosis. This article deals with the usual imaging features of pulmonary tuberculosis as well as the atypical patterns encountered in immunodepressed and elderly patients.