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Perianal Abscess and Fistula in ano disease

Summary of Pathophysiology and Operative management

Health & Medicine◦
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Perianal Abscess/Fistula- in-Ano Tom Tiang
Perianal - Anatomy From The Anatomy of General Surgical Operations: G Jamieson
Perianal - Anatomy • Rectum is ~ 15cms in length. Inner mucosa, submucosa then inner circular and outer longitudinal muscle layers • The internal sphincter is continuation of the inner circular muscle layer, External sphincter continuation of the outer longitudinal muscle layer. • Superior border of external sphincter fuses with puborectalis forming a sling originating at the pubis and coming around the rectum. • Intersphincteric groove is the space between internal and external sphincter, fibrous continuation of the longitudinal smooth muscle rectum • 6-10 anal glands lie in this space, each gland has a duct that discharges into the anal crypt of the dentate line. • Dentate line union between embryological ectoderm and endoderm and is transition between rectal mucosa above and transitional epithelium below. Also the division between neurovascular and lymphatic supply into two routes.
Perianal Abscess Pathophysiology Acute anorectal abscess Chronic anal fistula Incidence • 1 in 10 000 M:F 3:1 most common in 30-50s Aetiology • Cryptoglandular hypothesis anal fistulae (Parks & Eisenhammer) • Associated conditions: e.g. Crohn’s disease, trauma, TB, malignancy. • Acute anorectal non-cryptoglandular abscesses (Eisenhammer)
Anorectal Sepsis 56% 21% 3% 3% Superficial fistula 16% (% from Marks & Ritchie 1977, Classification of 769 fistulae) (% from Prasad, Read & Abrican 1981, 506 patients) 9% 48% 22% 12% Submucos al abscess 4%
Diagnosis of Anorectal Sepsis • History Anorectal Abscess Anal fistula Pain (93%) Discharge (65%) Swelling (50%) Pain (34%) Bleeding (16%) Swelling (24%) Fever Bleeding (12%) Purulent discharge, diarrhoea Diarrhoea (5%) Vasilevsky & Gordon, Dis Colon Rectum 27: 126-130 1984
Diagnosis of Anorectal Sepsis • Examination • Signs of inflammation • EUA • Proctosigmoidoscopy • Investigation • Proctoscopy & sigmoidoscopy (+/- under anaesthesia) • EUA under anaesthetic as 10 diagnostic procedure.
Diagnosis of Anorectal Sepsis • Techniques useful in the assessment of complicated fistulous disease. • Fistulography • CT • Anal endoultrasound • MRI: High concordance with operative findings (St Mark’s study 86%)
Abscess - Management • Perianal, Ischiorectal • Incision and Drainage • Packs, drains • Salt baths • Intersphincteric • Lay open internal sphincter • Up to dentate line, higher if extension
Abscess - Management • Supralevator • Origin • Intersphincteric – via rectum • Ischiorectal – via skin • Pelvic – rectum/skin/abdo • Horseshoe Abscess • Posterior drainage • Counterincisions
Anal Fistula - Classification • Parks • Intersphincteric 45%- 70% • Transsphincteric 23-30% • Suprasphincteric 5-20% • Extrasphincteric 2-5% • Horseshoe extension 8.8%
Evaluation • Digital assessment (<85% accurate) • H2O2 (97% accuracy) • Dyes • Goodsall’s rule (59% accuracy) • Anterior external opening – radial track • Posterior external opening – posterior midline • Exception – long anterior
Evaluation - Imaging • Fistulography • <25% accuracy • CT • abscess • U/S • assess sphincters • MRI • 86% concordance with operative findings for presence of 1o track, 2o extensions and abscess, 97% for horseshoeing
Surgical Treatment of Anal Fistula • Fistulotomy • Setons • Advancement flaps* • Other techniques • Fibrin glue* • Fistulotomy & immediate reconstruction of the divided musculature, with 10 wound closure*. • Fistulectomy • Defunctioning colostomy • *Need to eradicate acute sepsis before more complex procedures undertaken for anal fistula
Setons • Potential actions of the seton • Act as a drain for acute sepsis • To allow resolution of inflammation prior to definitive fistula surgery • Role in staged fistulotomy • Delineation of the amount of muscle caudal to the fistulous track • Cutting & Chemical setons: • Controlled division of the enclosed sphincter mechanism with minimal separation of the transected ends.