The new pathways of spread of anal fistula and the pivotal role of MRI in discovering them

Conventionally, in the pathophysiology of anal fistulas, there is only one space considered significant for the spread of pus in the sphincter complex: the intersphincteric space. However, with increasing experience in the high-resolution MRI, and more focus being given on managing fistulas through the intersphincteric space, two additional pathways of fistula spread have been identified. First is a newly described space labelled as the outer-sphincteric space. Second is a known anatomical space (inner intersphincteric space), but this space was considered as irrelevant from the point of view of fistula spread. The conventional intersphincteric space is present in between these two spaces and is referred as ‘middle intersphincteric space’ in this paper. These three distinct spaces have significant clinical implications as the pattern of spread of pus is quite different in each space, and the management also differs for fistula tract in each of these spaces.