What is a fistula?

What is a Fistula?

A fistula is an abnormal connection or passageway between two epithelial surfaces—either between two organs, between an organ and the skin, or between an organ and another body cavity—that do not normally connect. 1

Core Definition and Pathophysiology

• A fistula forms when there is a loss of wall integrity from an underlying insult, leading to penetration of an adjacent organ or epithelialized surface 2
• The abnormal tract connects two surfaces that should remain separate, creating a communication pathway 3
• Fistulae are named based on the two structures they connect (e.g., enterocutaneous connects intestine to skin, enterovesical connects intestine to bladder) 1, 2

Types of Fistulae by Location

Gastrointestinal/Inflammatory Bowel Disease Context

• Intestinal fistulae: Abnormal connections involving the bowel, which can be between intestinal segments (enteroenteric), intestine to skin (enterocutaneous), intestine to bladder (enterovesical), intestine to vagina (enterovaginal), or rectum/anus to skin around the anus (perianal) 1
• Simple fistula: A single extra-enteric tract connecting to another bowel segment, organ cavity, or skin surface 1
• Complex fistula: Multiple extra-enteric tracts involving multiple structures, often showing an asterisk or star configuration, or high fistulae with extensions, multiple external openings, complicated by abscess, urogenital involvement, or anorectal stricture 1
• Perianal fistulae: Tracks linking the rectum (lower bowel) with the skin around the anus, classified as intersphincteric, transsphincteric, suprasphincteric, extrasphincteric, or superficial based on their relationship to the anal sphincter muscles 1

Vascular Access Context

• Arteriovenous fistula: An autogenous connection surgically created between an artery and vein (e.g., Brescia-Cimino radiocephalic fistula connecting radial artery to cephalic vein at the wrist) for hemodialysis access 1
• This represents an intentionally created therapeutic fistula, distinct from pathological fistulae 4

Common Etiologies

• Postoperative/surgical trauma: The most common cause in developed countries, occurring after gastrointestinal surgery due to anastomotic breakdown, inadvertent bowel injury, or foreign body 2, 3, 5
• Inflammatory bowel disease: Particularly Crohn's disease, where deep ulcers penetrate through the bowel wall to form connections with adjacent structures 1
• Infection/abscess: Fistulae typically develop after rupture or drainage of a perianal abscess 6
• Malignancy: Tumor invasion can erode through tissue planes 3, 5
• Radiation injury: Radiation-induced tissue damage 3
• Bowel diverticula: Diverticular disease complications 2

Clinical Significance and Complications

• Fistulae can lead to serious complications including infection, abscess formation, sepsis, fluid and electrolyte disturbances, malnutrition, and death 1, 3, 7
• High-output fistulae (>500 mL/day) cause significant fluid, electrolyte, and nutritional losses requiring aggressive replacement 7, 5
• Overall mortality rates for gastrointestinal fistulae remain high at up to 30% despite advances in management 3

Diagnostic Approach

• Imaging: CT is the initial imaging modality of choice; MRI provides excellent soft tissue detail for perianal fistulae with T2-weighted sequences showing fluid-filled tracts and post-contrast enhancement 1, 2
• Ultrasound: Can identify fistulae as hypoechoic duct-like structures with or without internal gas, particularly useful for perianal disease 1
• Endoscopy: Visualizes internal openings and mucosal pathology 2, 6