Fistula in - ano : Why do they persist?
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Idiopathic anal fistulas constitute the majority of anal fistulas Unlike fistulas in other sites, idiopathic anal fistulas never close spontaneously. The reason for that is still unknown recent studies showed that chronic bacterial inflammation is not responsible for persistence of anal fistulas. We hypothesize that presence of a pressure gradient between the anal canal lumen and the intersphincteric space together with or without epithelialization of part of the track may play a role in idiopathic anal fistula persistence. 28 consecutive patients with clinical diagnosis of idiopathic anal fistulas were studied to establish whether or not a pressure gradient across the internal sphincter is present and for the prevalence of epithelialization of the fistula tracks. The intersphincteric pressure and the anal canal lumen pressure were consecutively measured in Lithotomy position under general anaesthetic (without muscle paralysis and prior to any instrumentation ) using the standard technique of normal saline infused cannula connected to anaesthetic Siemens monitor through a pressure transducer. Pressures were recorded after insertion of the cannula at a depth of 1.5 cm from the anal verge (at the level of dentate line). Thereafter, core out fistulectomy was done in all patients and the specimen was fixed in 10% formaline saline after marking the internal opening and the intersphincteric component of the track and sent for histology. The results showed that the intersphincteric pressure was significantly lower than the anal canal lumen pressure [(intersphincteric median pressure 30.5 mmHg (q, q3 25-34) vs. Anal canal median pressure 54.5 mmHg (qi q3 40-68)] (p<0.00001 Wilcoxon). Histological examination showed epithelialization of 20 tracks (71%) while the rest had no evidence of epithelial lining. We conclude that there is a pressure gradient across the internal sphincter of median value of 24mmHg. This pressure gradient can play a role in idiopathic anal fistula persistence by driving the anal canal lumen contents through the intersphincteric component the fistula track keeping it open. Epithelialization of the fistula track may have a role in fistula persistence as well.