Medicine:Rich focus
A Rich focus is a tuberculous granuloma occurring within the cortex or meninges of the brain that ruptures into the subarachnoid space, causing tuberculous meningitis.[1] The Rich focus is named for Arnold Rice Rich, a pathologist at Johns Hopkins Hospital, who along with his colleague Howard McCordock first described the post-mortem finding of caseous foci within the cerebral cortex or meninges which appeared to predate the development of meningitis.[2] Prior to their research the prevailing view had been that meningitis occurred as a result of the dissemination of tuberculous bacilli associated with miliary tuberculosis and that these processes occurred at the same time.
Developments
More recently a more comprehensive classification of the pathogenesis of tuberculous meningitis has been proposed by Donald et al.:[1]
- A Rich focus develops as a result of haematogenous dissemination from the primary complex, including miliary tuberculousis, subsequently rupturing into the sub-arachnoid space.
- A Rich focus develops within the choroid plexus or ventricular walls as a result of haematogenous dissemination.
- The mechanism described by Rich and McCordock in which haematogenous dissemination at the time of infection, or later, results in development of a Rich focus which is initially controlled but later ruptures into the subarachnoid space.
- Direct extension from an adjacent structure such as the vertebrae results in development of meningitis.
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