Tuberculous meningitis and miliary tuberculosis: the Rich focus revisited.

Tuberculous meningitis (TBM) develops most often when a caseating meningeal or sub-cortical focus, the Rich focus, discharges its contents into the subarachnoid space. It is recognized that TBM is frequently accompanied by miliary tuberculosis, but the relationship between the development of the Rich focus and miliary tuberculosis remains controversial. The original descriptions of Arnold Rich and Howard McCordock are reviewed together with the work of other pathologists and the observations of the natural history of tuberculosis by astute clinicians such as Arvid Wallgren and Edith Lincoln. Rich and McCordock dissociated miliary tuberculosis from a role in the pathogenesis of TBM, and this view continues to appear in reviews and textbooks dealing with TBM. We suggest, particularly in childhood, that miliary tuberculosis is indeed directly involved in the pathogenesis of TBM in as much as that the overwhelming bacillaemia that accompanies miliary tuberculosis serves to increase the likelihood that a meningeal or sub-cortical Rich focus will be established, which may in its turn caseate and give rise to TBM.