A New Anatomical Pathway of Spread of Pus/Sepsis in Anal Fistulas Discovered on MRI and Its Clinical Implications

Abstract

Background: In the anal sphincter complex, the intersphincteric space between the internal and external sphincters is the only conventionally recognized pathway for the spread of sepsis. However, there is another unrecognized space discovered on MRI, the "outersphincteric space", between the external anal sphincter and its lateral fascia along which pus can spread. An abscess in the intersphincteric space is easily drained into the rectum via the transanal route and is more likely to spread into the supralevator space. Conversely, an abscess in the outer-sphincteric space is difficult to drain transanally into the rectum and is more likely to become a transsphincteric abscess/fistula. Methods: The MRIs of anal fistula patients operated over four years on intersphincteric abscesses were analyzed. The pattern of spread into the ischiorectal fossa and/or supralevator space and ease of drainage into the rectum through the transanal route were studied. Results: Thirty-six patients were operated on to drain their intersphincteric abscesses through the anal canal. Two distinct patterns were noted. Twenty patients had abscesses in the intersphincteric space, which were easily drained into the rectum. Of them, 6/20 had supralevator extension, while only 1/20 had spread to the ischiorectal fossa. In 16/36 patients, the abscess was in the outer-sphincteric space and could not be drained into the rectum. In 9/16 of these patients, pus spread into the ischiorectal fossa but supralevator spread did not happen in any patient. Conclusion: Apart from the intersphincteric space, there is perhaps another unrecognized anatomical space -the outer-sphincteric space -discovered on MRI, through which pus can spread in anal fistulas or abscesses.

Chronic Cryptoglandular Anal Fistulas: Surgical Outcomes; A Retrospective Case Control Study In 148 Patients with No Risk Factors for Recurrence

“…In our patients studied with SAF, we didn't use cutting-settons techniques; a more popular procedure in past with excellent healing rates at 85% [29], but with minor continence problems and some times more severe, ranging from 12 to 26% of patients with SAF [30] Finally simple AF, are not so simple, at least in the field of correct diagnosis; due do advances in MRI studies we give attention in the estimation of the peripheral segment of simple low intersphincteric AF. This segment is located in a new recognized anatomical space, so called outer-sphincteric(between external sphincter and it's fascia).It's a space parallel to intersphincteric space, and a new pathway of the spread of cryptoglandular infection; infection may proceed upwards, remaining in outer-sphincteric and sublevator space and finally may result a complex fistula [31].Finally the estimation of intersphicteric space by MRI, is crucial in simple and complex AF, as it is the initial space of cryptoglandular infection; despite the surgical treatment of complex fistulas, if this space is affected, the surgical therapy of complex fistula must be helped by transanal openining of this space: a new operation, TROPIS(Transanal Opening of the Intersphincteric Space), seems to increase the outcomes of surgery for complex AF [32].…”

Anal Fistula of Crypto-Glandular Etiology: A Review of the Literature with a Step-by-Step Approach for Diagnosis and Surgical Management

“…The improvement in MRI techniques, allowed recently the identification of a new anatomical pathway of spread of infection in a recently recognized anatomical space called "outer-sphincteric space", between the external anal sphincter and its fascia. The inflammatory collection progresses along this space, in a parallel route to the inter-sphincteric space, without the ability to extent in the supralevator space, to be drained into the intra-anal canal and may probably forms a trans-sphincteric fistulous tract [7] . The surgical anatomy of the anorectal canal and the main types of cryptoglandular anal fistulas are shown in the figure of the text.…”

Endoscopic Ultrasound-Guided Botox Injection for Refractory Anal Fissure

“…Acute anal fissures are commonly managed by conservative medical treatment, while chronic anal fissures are refractory to such treatment. Surgical treatment, such as sphincterotomy, is commonly required for the treatment of chronic anal fissures or abscesses, providing symptomatic relief [ 6 , 7 ]. However, this procedure requires sphincter injury and has been associated with permanent complications ranging from incontinence of gas in up to 45% of patients to stool incontinence in up to 22% [ 8 , 9 ].…”