Fistula

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Fistula - Comprehensive Overview

Definition

A fistula is an abnormal communication between two epithelium-lined surfaces. The tract is usually lined by granulation tissue but may become epithelialised in chronic cases. Fistulae may be congenital (e.g., tracheo-oesophageal, branchial) or acquired (e.g., enterocutaneous from Crohn's disease or surgery, arteriovenous for dialysis access).

Bailey and Love's Short Practice of Surgery, 28th Ed.

Classification by Type

Type	Connection	Common Examples
Enterocutaneous	Bowel to skin	Post-operative, Crohn's
Rectovaginal	Rectum to vagina	Obstetric trauma, IBD, radiation
Vesicovaginal	Bladder to vagina	Obstetric injury, surgery
Arteriovenous (AV)	Artery to vein	Congenital, dialysis access, trauma
Tracheoesophageal	Trachea to oesophagus	Congenital, malignancy
Pharyngocutaneous	Pharynx to skin	Post-laryngectomy complication
Anal (fistula-in-ano)	Anal canal to perianal skin	Cryptoglandular abscess, Crohn's
Obstetric/Genitourinary	Genitourinary tract	Prolonged obstructed labour
Aortoenteric	Aorta to GI tract	Post-aortic graft, erosion

Fistula-in-Ano (Anal Fistula)

Pathogenesis

Fistula-in-ano results from persistent communication between the cryptoglandular complex in the anal canal (internal opening) and the perianal skin (external opening) after spontaneous or surgical drainage of a perianal abscess. Approximately 50% of patients with a perianal abscess will ultimately develop a fistula. - Sabiston Textbook of Surgery

Parks Classification

The standard classification system divides anal fistulae into four types based on their relationship to the anal sphincter complex:

Type	Name	Frequency	Description
Type 1	Intersphincteric	45%	Tracks between internal and external sphincters
Type 2	Transsphincteric	30%	Crosses the external sphincter
Type 3	Suprasphincteric	20%	Goes above the puborectalis
Type 4	Extrasphincteric	5%	Entirely outside the sphincter mechanism

Goodsall's Rule

External opening anterior to transverse anal line → track runs radially to the internal opening
External opening posterior → track curves to a posterior midline internal opening
Exception: anterior openings >3 cm from anal verge may curve posteriorly (horseshoe fistula)

Diagnosis

Clinical: chronic perianal drainage, cyclical pain/swelling relieved by discharge
Physical exam: cordlike subcutaneous structure, external opening(s)
"Watering can perineum" (multiple openings) suggests perianal Crohn's disease
MRI with anal fistula protocol is the gold standard for complex anatomy

MRI of anal fistulae - axial T2-weighted images:

(A) Intersphincteric fistula (white arrow) lying within the intersphincteric plane. (B) Transsphincteric fistula (white arrow) penetrating the external sphincter boundary.

Treatment Goals (Anal Fistula)

Treat any undrained infection
Define fistula anatomy
Remove or ablate epithelialised tracts
Avoid or minimise risk of fecal incontinence
Prevent recurrence

Surgical options:

Fistulotomy (lay-open): For low-lying fistulae involving <1/3 of the external sphincter (intersphincteric/low transsphincteric). Fecal incontinence risk <5% with normal preoperative sphincter function; recurrence rate 2-8%.
Seton: A suture/drain placed through the tract; used as a cutting or draining seton for complex/high fistulae to protect continence
Advancement flap: Mucosal or full-thickness flap to close the internal opening
LIFT procedure (Ligation of Intersphincteric Fistula Tract)
Bioprosthetic plug, fibrin glue, video-assisted anal fistula treatment (VAAFT)
Sabiston Textbook of Surgery

Enterocutaneous Fistula (ECF)

Causes

75-80% are post-surgical complications (anastomotic leak, inadvertent bowel injury)
Pre- or post-surgical malnutrition is a major risk factor
Crohn's disease, radiation, cancer, foreign body

Output Classification

Class	Output	Clinical significance
Low output	<200 mL/day	More likely to close spontaneously
Medium output	200-500 mL/day	Variable
High output	>500 mL/day	Significant fluid/electrolyte loss, skin excoriation from digestive enzymes, difficult to manage

Conservative Management ("SNAP" principles)

Skin care - protect surrounding skin from corrosive secretions
Nutrition - parenteral or enteral nutrition is critical; high-output fistulae worsen malnutrition
Anatomy - contrast sinogram/fistulogram, CT scan to delineate tract
Plan - identify spontaneous closure potential vs. need for surgery

Conservative measures:

Nil by mouth, nasogastric drainage
IV fluid and electrolyte replacement (especially for high-output)
Total parenteral nutrition (TPN)
Somatostatin analogues (octreotide) to reduce output
Wound/stoma care with collection devices

Contraindications to spontaneous closure (mnemonic FRIEND):

Foreign body in tract
Radiation damage
Inflammation (IBD, abscess)
Epithelialisation of tract
Neoplasm
Distal obstruction
Pye's Surgical Handicraft; Yamada's Textbook of Gastroenterology

Arteriovenous Fistula (AVF)

Types

Congenital AV fistulae - developmental malformations
Acquired AV fistulae - trauma (penetrating injury causing artery-to-vein communication), iatrogenic (post-catheterisation), neoplastic erosion
Surgically created AVF - for hemodialysis access

Hemodialysis AVF

The surgically created AVF is the preferred vascular access for hemodialysis ("fistula first" principle from KDOQI guidelines). Common configurations:

Radiocephalic (Brescia-Cimino) - wrist, first choice
Brachiocephalic - antecubital
Brachiobasilic - requires transposition

AVF advantages over AV graft (AVG):

Lower infection risk
Better long-term patency
No prosthetic material

However, AVF requires 6 months maturation time before use. Factors negatively affecting AVF maturation and patency: female sex, coronary artery disease, diabetes, obesity, elderly patients.

Key complications of AVF:

Stenosis/thrombosis (most common)
Steal syndrome causing distal ischemia
Venous hypertension
Aneurysm/pseudoaneurysm
Infection
High-output cardiac failure (rare, with large AV connections)
Sabiston Textbook of Surgery, 25th Ed.

Head & Neck Fistulae (Pharyngocutaneous)

Context

A common complication after laryngectomy, glossectomy, neck dissection, or other ablative head/neck surgery. Forms an abnormal connection between the pharynx/aerodigestive tract and the surrounding neck/skin.

Risk Factors

Prior radiation therapy
Malnutrition
Postoperative hypothyroidism

Consequences

Prolonged open wounds
Severe infections
Carotid blowout (most devastating - saliva and bacteria pooling near great vessels)

Management

Conservative: Local wound care, debridement, strict NPO with enteral feeding (NG or gastrostomy), dry packing. Barium swallow to confirm closure before resuming oral intake.
Surgical: Required for uncontrolled infection, systemic sepsis, or proximity to carotid. Pectoralis major muscle flap is the gold standard for large fistula closure.

Prevention: Use of vascularized tissue (pedicled pectoralis, radial forearm or anterolateral thigh free flap) to reinforce pharyngeal closure significantly reduces pharyngocutaneous fistula risk.

Sabiston Textbook of Surgery

Factors Preventing Fistula Closure (General)

Any fistula is unlikely to close spontaneously if:

There is distal obstruction to flow
A foreign body is present in the tract
The tract is epithelialised
There is active disease (malignancy, active IBD, radiation necrosis)
There is an abscess cavity that has not been drained
The fistula has a short, straight, wide-bore tract

Summary Table: Common Fistulae

Fistula	Aetiology	Key Investigation	Treatment
Fistula-in-ano	Cryptoglandular abscess, Crohn's	MRI pelvis	Fistulotomy, seton, advancement flap
Enterocutaneous	Post-operative, IBD	CT/sinogram	SNAP, surgery if no spontaneous closure
Rectovaginal	Obstetric, IBD, radiation	Examination, MRI	Advancement flap, colostomy
Vesicovaginal	Obstetric, gynaecologic surgery	Cystoscopy, CT urogram	Surgical repair (open/laparoscopic)
AVF (dialysis)	Surgical creation	Duplex USS	Maturation procedures, angioplasty if stenotic
Pharyngocutaneous	Post-laryngectomy	Barium swallow, CT neck	Conservative / pectoralis flap
Tracheoesophageal	Congenital, malignancy	Bronchoscopy, endoscopy	Stenting, surgical repair

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