Tissue tropism is a phenomenon by which certain host tissues preferentially support the growth and proliferation of pathogens. This concept is central to the radiological evaluation of infectious disease.
As infections that display tissue tropism will thrive in certain tissue locations, this characteristic can be helpful in making a diagnosis from radiological imaging. Findings of infection on imaging that are localised in a pattern typical for a particular microbial organism allow for. This is particularly useful when serological confirmation can take days or weeks, as in the cases for many of the viral encephalitides.
Radiological diagnosis of the underlying microbial pathogen responsible for presenting infection allows for the use of specific antimicrobial therapy much before the causative organism is eventually confirmed. This is particularly true for viruses which are confirmed through the use of PCR, which can take days to weeks.
Examples of tissue tropism include:
- bilateral thalamic involvement in Japanese encephalitis
- medial temporal and limbic involvement in herpes simplex encephalitis
- terminal ileum for gastrointestinal tuberculosis
The degree to which microbes display tissue tropism varies and indeed not all of them do.