Anal fistula
(1).Cause
Major: abscess (30–40% of abscesses will give rise to fistula in ano.)
Minor: IBD, TB, trauma, cancer, radiation
The majority of anal abscesses and fistulas originate from infected anal glands. Most people have 8 to 10 anal glands, which are located circumferentially within the anal canal at the level of the dentate line, penetrate through the internal sphincter, and end in the intersphincteric plane(anal glands分佈以肛門之後半部較前半部多). Blockage of anal glands permits the growth of bacteria, which may ultimately lead to an abscess.
(2). Anal abscess分類
1. perianal abscess：路徑是從intersphincteric groove進入perianal skin，表現方式為疼痛而會浮動的腫塊。
2. ischiorectal abscess：從external anal sphincter進入ischiorectal space，表現方式為廣泛疼痛堅硬而會浮動的腫塊。
3. intersphincteric abscess：出現在internal和external sphincter之間的4. intersphincteric groove。只佔2~5%，在perianal skin沒有任何的表現，但在做肛門指診時可能會在深部摸到浮動的腫塊。
5. supralevator abscess：有兩種來源。一種是cryptoglandular infection，自intersphincteric plane 到supralevator space。另一種來源則是源於diverticular disease或Crohn’s disease，屬於pelvic infection。
(3).Classification (examine the patient in the operating room under anesthesia or transanal ultrasound, MRI, fistulogram, 可參考harrison的圖較清楚)
1. Intersphincteric fistulas (70%,最常見, 沒經過external sphincter)travel along the intersphincteric plane to the perianal skin
-> primary fistulotomy
2. Transsphincteric fistulas (23%,穿過internal and external sphincter) encompass a portion of the internal and external sphincter, and terminate on the skin overlying the buttock
-> low: primary fistulotomy
-> high: cutting seton; partial fistulectomy and endoanal flap; injection of fibrin glue
3. Suprasphincteric fistulas (5%, 由Intersphincteric space上方繞行) encompass the entire sphincter apparatus
-> cutting setons; advancement flaps or sphincter reconstruction
4. Extrasphincteric fistulas (2%,沒經過Intersphincteric space) extend from an internal opening in the bowel proximal to the anus, encompass the entire sphincter apparatus, and open onto the skin overlying the buttock
-> internal openings low in the rectum: advancement flap
-> coming off a more proximal section of colon or small intestine:
treated by laparotomy to resect the involved segment of intestine
and curettage of the fistula tract
(4).symptomes
1.Pain(加重因子：cough, defecation), itching, discharge, Systemic symptoms(ex.fever) if abscess becomes infected
2.肛門鏡檢查則可見內口所在之肛腺口有向下凹的現象,叫 herniation sign，這是因為內口被廔管之結疤組織向下拉入而凹陷。
(5).Goodsall's rule
以transverse anal line為界，因為posterior midline 處有posterior anal space(為potential space)，所以源於後側的Anal fistula有空間可以延伸
1. anterior to this line 且external openings 小於 3 cm of the anal verge
→enter the anal canal in a radial fashion
2. anterior to this line 且external openings 大於 3 cm of the anal verge
→drawn through the Ischia spines travel in a curvilinear fashion to the posterior midline
3. posterior to a line
→drawn through the Ischia spines travel in a curvilinear fashion to the posterior midline
(6).Clinical manifestations
present with a "non-healing" anorectal abscess following drainage, or with chronic drainage and a pustule-like lesion in the perianal or buttock area pain during defecation, usually much less severe than fissures
對anal abscess而言，不需使用anti，除非以下4種情形
1. immunocompromise
2. diabetic
3. extensive cellulitis
4. valvular heart disease
(7).手術方法
1.廔管切開術(fistulotomy)：先用probe從fistula外口探查整條通道，接著將通道打開，將肉芽組織刮掉；再用可吸收縫線將打開通道之刀口邊緣縫起來(Marsupialization)。
2.廔管切除術(fistulectomy)：先沿fistula外口周圍劃開一圈，接著用組織鋏子挾住，沿著fistula之外緣用剪刀修剪，一直到齒狀線之內口，終於將整條廔管分出切除。廔管切除術比切開術會傷及更多的組織，傷口更大，因此大部份還是以廔管切開術為主。
3.如果是較高位或影響較多肌肉的fistula如Transsphincteric fistulas 或Suprasphincteric fistulas則可用「銑通」(seton tie)法：找到廔管通道後將五條不吸收線(粗的絲線)貫穿廔管，然後漸進式的將線綁緊，一週一條直到廔管完全被切開。此方法的好處是漸進式切開廔管，兩邊的括約肌不會分開，病人比較不會有失禁的危險。缺點是需時較長，同時治療過程中病人較不舒服。
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