fistula is an abnormal, tube-like passage that forms a connection between two internal organs, between two blood vessels, or between an internal organ and the exterior of the body (the skin). Unlike a sinus tract, which is a blind-ending channel that opens to only one surface, a fistula connects two distinct epithelialized surfaces. The underlying pathological mechanism typically involves chronic inflammation, infection (such as an unresolved abscess that ruptures into adjacent structures), surgical trauma, ischemic injury, or penetrating trauma, which causes tissue necrosis and subsequent abnormal healing. While the vast majority of fistulas are pathological (e.g., anal fistula, vesicovaginal fistula), they can also be physiological/iatrogenic when surgically created for therapeutic purposes (e.g., an arteriovenous fistula created for hemodialysis access). The clinically relevant subtypes most commonly encountered in coding include anal fistulas (K60.3), vesicovaginal fistulas (N82.0), enterocutaneous fistulas (K63.2), and surgically created arteriovenous fistulas (Z99.2 for presence/dependence). Fistulas are commonly confused with fissures; however, a fissure is simply a tear or crack in the mucosal lining or skin, whereas a fistula is a complete tunnel connecting two separate spaces.
Noun-forming suffix — “state or condition of”
The word entered English in the 1390s as fistula (noun), borrowed directly from Latin fistula — literally “pipe, tube, or ulcer.” The root fistula (“pipe/tube”) connects fistula to the entire fistul- family: fistulotomy (surgical incision of a pipe/tract), fistulectomy (surgical excision of a pipe/tract), and fistulization (the process of forming an abnormal tract).
🔀 ALIASES / ALTERNATE TERMS
Fistulous(adjective form — e.g., “fistulous tract,” “fistulous disease,” “fistulous communication”)
Abnormal tract(lay and clinical synonym; often used in radiology reports describing contrast extravasation)
Incomplete fistula / Sinus tract(a partial or blind-ending tract that has not yet connected to a second surface; often a precursor to a true fistula)
Arteriovenous fistula (AVF)(vascular connection between an artery and a vein; can be congenital, acquired via trauma, or surgically created for dialysis)
Enterocutaneous fistula (ECF)(abnormal connection between the intestinal tract and the skin; highly morbid, often a complication of abdominal surgery)
Vesicovaginal fistula (VVF)(abnormal connection between the bladder and the vagina; causes continuous urinary incontinence, often obstetric or surgical in origin)
Colovesical fistula(abnormal connection between the colon and the bladder; commonly caused by diverticulitis, presenting with pneumaturia or fecaluria)
Tracheoesophageal fistula (TEF)(connection between the trachea and esophagus; can be congenital [Q39.x] or acquired [J86.0])
Anal fistula / Fistula-in-ano(epithelialized track connecting the anal canal to the perianal skin; almost always arises from a cryptoglandular abscess)
Branchial cleft fistula(congenital anomaly of the neck; Q18.0)
Carotid-cavernous fistula (CCF)(abnormal communication between the carotid artery and the cavernous sinus; presents with pulsatile exophthalmos)
Lacrimal fistula(abnormal tract from the lacrimal sac or gland to the skin surface; H04.61x)
đź”— RELATED TERMS
Anastomosis — the opposite of a pathological fistula in intent; a deliberate, surgically created connection between two tubular structures (e.g., bowel loops or blood vessels) to restore continuity.
Sinus tract — shares the characteristic of an abnormal channel, but is a blind-ending tract that opens to only one epithelial surface (often draining an underlying abscess cavity).
Fissure — a linear tear or crack in the mucosal lining (e.g., anal fissure, K60.2); often confused with a fistula but lacks a tunneling tract.
Abscess — a localized collection of pus; the rupture and incomplete healing of an abscess is the primary physiological mechanism that creates a fistulous tract.
Epithelialization — the cellular mechanism where epithelial cells migrate to line the abnormal tract, preventing it from closing spontaneously and making the fistula chronic.
Crohn’s disease — inflammatory bowel disease characterized by transmural inflammation, making it a primary causative disease entity for enteroenteric, enterocutaneous, and perianal fistulas (K50.x).
Diverticulitis — inflammation of colonic outpouchings; the most common underlying disease entity causing colovesical fistulas (K57.x).
Fistulogram / Sinogram — primary diagnostic fluoroscopic procedure involving the injection of radiopaque contrast into the external opening to map the tract’s course and internal opening.
CODING CORNER
🏥 ICD-10-CM CODES
Gastrointestinal & Anal Fistulas (General Surgery / GI)
Injection of sinus tract; diagnostic (sinogram) (Requires radiological supervision and interpretation code 76080)
⚠️ Coding Note: When coding fistulas in the inpatient profee setting, sequencing depends heavily on the etiology and the reason for admission. If the fistula is a manifestation of an underlying disease (e.g., Crohn’s disease, diverticulitis, or radiationcystitis), the underlying condition is typically sequenced first, followed by the specific fistula code. A common undercoding alert involves colovesical fistulas; coders often see “pneumaturia” or “fecaluria” documented but fail to query for the presence of a colovesical fistula (N32.1) and its underlying cause (e.g., K57.20Diverticulitis). For surgically created AV fistulas for dialysis, do not code them as a complication or disease unless they are failing, infected, or bleeding; a functioning AV fistula is captured simply by Z99.2 (Dependence on renal dialysis). When coding surgical closures (e.g., CPT 44661), ensure the operative report clearly documents whether a resection of the bowel or bladder was required, as this significantly impacts the RVU and code selection.