Anal Fistula

Anal fistulas are abnormal communications between the anorectal lumen and another body structure, often to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin. Anal fistulas often occur due to extension of anal abscesses but are also associated with specific diseases such as Crohn’s disease. Symptoms include pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain or irritation around the anus; abnormal discharge or purulent drainage; and swelling, redness, or fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever if an abscess is present. Management is primarily surgical, with fistulotomy, but can include antibiotics if infection is present. Treatment is surgical. Complications after surgery include recurrence and incontinence.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Definition and Epidemiology

Definition

  • Abnormal connection between the epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium of the anal canal and another body structure (often to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin
  • Also called fistula-in-ano

Epidemiology

  • Incidence: 9 per 100,000 adults per year
  • Sex: men > women
  • More common between the 3rd and 5th decades of life
  • 50% of patients with anorectal abscess will eventually develop a fistula.

Etiology and Pathophysiology

Etiology

  • Anorectal fistulas most often occur from:
    • An acute anal abscess → ruptures or is drained → epithelialized track forms that connects the abscess in the anus to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin (chronic process)
    • Anal abscesses (infected anal crypt glands often with reduced blood flow)
  • Other causes:
    • Rectal foreign bodies
    • Inflammatory bowel disease (Crohn’s disease)
    • Trauma (obstetric injury)
    • Anal fissures
    • Malignancy
    • Radiation proctitis

Pathophysiology

  • Obstruction of anal glands in the wall of the anal canal → stasis and overgrowth of the bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overviewanal abscess formation → extension of the abscess into adjacent perirectal spaces → fistula formation
  • May also occur secondary to disease states (e.g., Crohn’s disease)
  • Fistulas may remain open due to: 
    • Foreign body
    • Radiation
    • Infection
    • Epithelialization
    • Neoplasm
    • Distal obstruction
    • Other: 
      • Increased flow
      • Steroids

Clinical Presentation

History

  • Non-healing anal abscess, often associated with purulent drainage or malodorous discharge
  • Rectal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain

Physical exam

  • Inflamed perianal skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin
  • External fistula tract opening may be observed or palpated as an area of induration.
  • Associated with a palpable cord-like tract
    • Internal fistula tract opening may be palpated on digital rectal exam (DRE); however, anoscope or further imaging may be needed to identify the fistula tract.

Diagnosis and Management

Diagnosis

  • Based on history, physical exam, and radiology findings
  • Identification:
    • Internal opening on exam of the rectal area
    • Goodsall’s rule
      • Fistulas originating anterior to a transverse line through the anus will have a straight course and exit anteriorly.
      • Fistulas originating posterior to the transverse line will begin in the midline and have a curved tract.
    • Fistulous tract: can be detected by probing or fistulography under anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts

Management

  • Surgical management is 1st-line treatment
    • Goal: remove fistula without causing fecal incontinence
    • Fistulotomy: unroofs the fistula tract from the external to the internal opening
      • Allows drainage and healing by secondary intention
      • Low-lying fistula (does not involve external sphincter) → primary fistulotomy
      • High-lying fistula (involves external sphincter) → staged fistulotomy with Seton suture, a nonabsorbable suture placed through the tract to compress the fistula and encourage surrounding fibrosis
  • Post-operative measures:
    • Sitz baths and irrigation
    • Packing to ensure healing
  • Complications:
    • Recurrence
    • Worsening infection
    • Fecal incontinence (rare)

Mnemonic

Why fistulas stay open: “FRIENDS”

  • Foreign body
  • Radiation
  • Infection
  • Epithelialization
  • Neoplasm
  • Distal obstruction
  • Steroids

Differential Diagnosis

  • Anal carcinoma: neoplastic disease in which cancer cells form and grow in the anus. Symptoms include bleeding from the anus, anal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, anal mass. or itching. Risk factors include older age, infections including human papillomavirus Human papillomavirus Human papillomavirus (HPV) is a nonenveloped, circular, double-stranded DNA virus belonging to the Papillomaviridae family. Humans are the only reservoir, and transmission occurs through close skin-to-skin or sexual contact. Human papillomaviruses infect basal epithelial cells and can affect cell-regulatory proteins to result in cell proliferation. Papillomaviridae: HPV ( HPV HPV Human papillomavirus (HPV) is a nonenveloped, circular, double-stranded DNA virus belonging to the Papillomaviridae family. Humans are the only reservoir, and transmission occurs through close skin-to-skin or sexual contact. Human papillomaviruses infect basal epithelial cells and can affect cell-regulatory proteins to result in cell proliferation. Papillomaviridae: HPV), multiple sexual partners, and anal sex. Anal carcinoma is diagnosed by biopsy. Treatment can include surgery, radiation, or chemotherapy. In a chronic or atypical anal fissure Anal fissure An anal fissure is a painful superficial tear of the epithelial lining (anoderm) of the anal canal. Anal fissures most often occur secondary to local trauma or irritation from constipation, diarrhea, anal intercourse, or perineal lacerations during childbirth. Anal Fissure, anal carcinoma needs to be ruled out.
  • Hemorrhoids Hemorrhoids Hemorrhoids are normal vascular cushions in the anal canal composed of dilated vascular tissue, smooth muscle, and connective tissue. They do not cause issues unless they are enlarged, inflamed, thrombosed, or prolapsed. Patients often present with rectal bleeding of bright red blood, or they may have pain, perianal pruritus, or a palpable mass. Hemorrhoids: enlargement of anal cushions (submucosal vessels) at the distal rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal. Depending on the location of the veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, hemorrhoids can be internal or external. External hemorrhoids are painful, but internal hemorrhoids are painless; both can bleed and appear as a soft rectal mass on exam. Commonly caused by constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation, and diagnosed on exam. Treatment includes stool softeners, topical hydrocortisone, and sitz baths. For recurrent cases, rubber band ligation or surgical removal is indicated.
  • Perianal ulcerations: erosions in the perianal mucosa. Occur secondary to inflammatory bowel disease, most notably Crohn’s disease, infections, and cancer. Symptoms include pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, bleeding, and erosions in the lining of the mucosa. Treatment is aimed at the causative disease. Differentiated from anal fissures on physical exam by deeper erosions in mucosa and evidence of other causative disease.
  • Anal fissure: a painful superficial tear of the epithelial lining (anoderm) of the anal canal. Anal fissures most often occur secondary to local trauma or irritation from constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, anal intercourse, or perineal lacerations during childbirth. Treatment is generally conservative, including stool softeners, bulking agents, sitz baths, and/or topical vasodilators.

References

  1. Vogel, John D. Anorectal fistula: Clinical manifestations, diagnosis, and management principles. UpToDate. Retrieved Oct 12, 2020, from https://www.uptodate.com/contents/anorectal-fistula-clinical-manifestations-diagnosis-and-management-principles

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