Tuberculosis: epidemiology, manifestations, and the value of medical imaging in diagnosis.

Mycobacterial infections have been shown to be increasing in number worldwide, mainly due a global increase in developing countries, the increased number of patients with HIV infection and AIDS disease worldwide, an increasing number of elderly patients and the emergence of multidrug resistant tuberculosis. Inhalation is the predominant pathway of Mycobacterium tuberculosis (M. tuberculosis) infection, making pulmonary tuberculosis the most common form of tuberculosis. Tuberculosis may arise either from a recent infection with M. tuberculosis, or from the reactivation of dormant bacilli, years or decades after initial infection. Extrapulmonary tuberculosis mainly results from reactivation of a tuberculous focus after hematogenous dissemination or lymphogenous spread from a primary, usually pulmonary focus. Tuberculosis may demonstrate a variety of radiological features depending on the organ site involved and may mimick other pathologies. The final diagnosis of tuberculous disease mainly depends on the detection of the causative organism on histopathological examination, culture and polymerase chain reaction-based assay for mycobacterial DNA on material obtained during bronchoscopic washings, fine needle aspiration cytology (FNAC) or biopsy.