The Ghon complex is the most frequent pathologic form of primary pulmonary tuberculosis. Mycobacterium tuberculosis first localizes in the lung parenchyma and then in the hilar lymph nodes. In both these locations, a granulomatous reaction takes place. These lesions usually heal by fibrosis, leaving only small scars at the sites of remote tuberculous infection. In some cases, owing to immunosuppression (e.g., AIDS, immunosuppressant treatment, and lymphomas), reactivation of dormant bacilli in old lesions or additional re-exposure leads to secondary tuberculosis, with progression of lesions. Sometimes, active lesions of the Ghon complex are discovered by chance at autopsy. More frequently, scars due to remote healed tuberculosis are found postmoem and listed in autopsy repos as incidental findings. Also know: Cavitary tuberculosis and miliary tuberculosis are expressions of secondary infection, following reactivation of old, usually clinically silent, lesions. The cavitary form is characterized by development of large areas of liquefactive necrosis that empty into the air spaces, leading to cavities within the lung parenchyma. The miliary form is due to lymphohematogenous dissemination and subsequent seeding of tubercle bacilli throughout the body, with myriad small granulomas forming in the lungs, spleen, liver, bone marrow, retina, and adrenals, for example. Acid-fast bacilli suggest tuberculosis, rather than an infection with a fungus such as Histoplasma. Ref:Raviglione M.C., O'Brien R.J. (2012). Chapter 165. Tuberculosis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds),Harrison's Principles of Internal Medicine, 18e