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]

  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.
  2. A Rich focus develops within the choroid plexus or ventricular walls as a result of haematogenous dissemination.
  3. 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.
  4. Direct extension from an adjacent structure such as the vertebrae results in development of meningitis.
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References
  1. Donald PR, Schaaf HS, Schoeman JF (April 2005). "Tuberculous meningitis and miliary tuberculosis: the Rich focus revisited". J. Infect. 50 (3): 193–5. doi:10.1016/j.jinf.2004.02.010. PMID 15780412.
  2. Rich AR, McCordock HA (1933). "The pathogenesis of tuberculous meningitis". Bull. Johns Hopkins Hosp. 52 (1): 2–37.


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