Spectrum of tuberculosis infection with proposed relationship to FDG-PET findings. Following exposure to M. tuberculosis an unknown percentage will clear infection entirely, while the vast majority develop latency (adapted from , ). Treatment of TB may eradicate all bacteria or leave a small population in a dormant non-replicating state. Populations with occasional replication termed “percolating” can be held under immunological control (noted by the dotted line) , . Yet as bacterial burden increases, the risk of progression to active infection increases (noted by the hashed line). Cases 1–4 are presumptively placed along the proposed spectrum based on clinical, histopathological and microbiological studies and 18 F-fluorodeoxyglucose positron emission tomography (FDG-PET) avidity.