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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. Skin: Structure and Functions. Anal fistulas often occur due to extension Extension Examination of the Upper Limbs of anal abscesses but are also associated with specific diseases such as Crohn's disease. Symptoms include pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways or irritation around the anus; abnormal discharge or purulent drainage; and swelling Swelling Inflammation, redness Redness Inflammation, 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 Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease is present. Management is primarily surgical, with fistulotomy, but can include antibiotics if infection is present. Complications after surgery include recurrence and incontinence.

Last updated: 11 May, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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: Histology 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. Skin: Structure and Functions
  • Also called fistula-in-ano

Epidemiology

  • Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 9 per 100,000 adults per year
  • Sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria: men > women
  • More common between the 3rd and 5th decades of life
  • 50% of patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with anorectal abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease will eventually develop a fistula.

Etiology and Pathophysiology

Etiology

  • Anorectal fistulas most often occur from:
    • An acute anal abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease → ruptures or is drained → epithelialized track forms that connects the abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease 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. Skin: Structure and Functions (chronic process)
  • Other causes:
    • Rectal foreign bodies
    • Inflammatory bowel disease (Crohn’s disease)
    • Trauma (obstetric injury)
    • Anal fissures Anal fissures A painful linear tear at the margin of the anus. It appears as a crack or slit in the mucous membrane of the anus and is very painful and difficult to heal. Constipation
    • Malignancy Malignancy Hemothorax
    • Radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma proctitis Proctitis Inflammation of the mucous membrane of the rectum, the distal end of the large intestine. Chronic Granulomatous Disease
    • Infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease ( lymphogranuloma venereum Lymphogranuloma venereum Subacute inflammation of the inguinal lymph glands caused by certain immunotypes of Chlamydia trachomatis. It is a sexually transmitted disease in the U.S. But is more widespread in developing countries. It is distinguished from granuloma venereum, which is caused by calymmatobacterium granulomatis. Chlamydial Infections)

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. Bacteriologyanal abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease formation extension Extension Examination of the Upper Limbs of the abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease 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 Foreign Body Foreign Body Aspiration
    • Radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma
    • Infection
    • Epithelialization
    • Neoplasm
    • Distal obstruction
    • Other: 
      • Increased flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure
      • Steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors

Clinical Presentation

History

  • Non-healing anal abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease, often associated with purulent drainage or malodorous discharge
  • Rectal pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways

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. Skin: Structure and Functions
  • External fistula tract opening may be observed or palpated as an area of induration Induration Dermatologic Examination.
  • Associated with a palpable cord-like tract
    • Internal fistula tract opening may be palpated on digital rectal exam ( DRE DRE A physical examination in which the qualified health care worker inserts a lubricated, gloved finger of one hand into the rectum and may use the other hand to press on the lower abdomen or pelvic area to palpate for abnormalities in the lower rectum, and nearby organs or tissues. The method is commonly used to check the lower rectum, the prostate gland in men, and the uterus and ovaries in women. Prostate Cancer Screening); 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 Identification Defense Mechanisms:
    • 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.
    • Exception to the Goodsall rule: fistulas > 3 cm from the anal verge
    • Fistulous tract:
      • Can be detected by probing or fistulography under anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts
      • A fistula probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography) must be used with care to prevent penetration Penetration X-rays of the fistula wall.
      • Rectal involvement requires the use of a sigmoidoscope.
  • Preferred imaging: MRI of the pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy (with and without contrast) and endosonography

Types of fistula

  • Parks classification:
    • Intersphincteric Intersphincteric Perianal and Perirectal Abscess (most common): 
      • Fistula between the external and internal sphincters, terminating in the 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. Skin: Structure and Functions
      • Spares the external sphincter
    • Transsphincteric: The track is through the external sphincter into the ischiorectal Ischiorectal Perianal and Perirectal Abscess fossa.
    • Suprasphincteric: The fistula starts at the anal crypt, penetrates the internal anal sphincter Internal anal sphincter Rectum and Anal Canal: Anatomy, and goes superiorly above the intersphincteric Intersphincteric Perianal and Perirectal Abscess plane.
    • Extrasphincteric: 
      • High in the anal canal and tracks through the sphincter complex, going lateral to the sphincters before ending in 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. Skin: Structure and Functions
      • Results from trauma, Crohn disease, or foreign bodies
  • Not included in the Parks classification: superficial or submucosal (does not involve the sphincter muscles)

Management

  • Surgical management is 1st-line treatment
    • Goal: remove fistula without causing fecal incontinence Fecal incontinence Failure of voluntary control of the anal sphincters, with involuntary passage of feces and flatus. Pediatric Constipation
    • Fistulotomy: unroofs the fistula tract from the external to the internal opening
      • Allows drainage and healing by secondary intention Secondary intention When there are significant tissue losses and the wound surface cannot be brought together (e.g., lacerations, burns, and ulcers) Wound Healing
      • Low-lying fistula (does not involve external sphincter) → primary fistulotomy
      • High-lying or complex fistula (involves external sphincter) → staged fistulotomy with Seton suture, a nonabsorbable suture placed through the tract to compress the fistula and encourage surrounding fibrosis Fibrosis Any pathological condition where fibrous connective tissue invades any organ, usually as a consequence of inflammation or other injury. Bronchiolitis Obliterans
  • Post-operative measures:
    • Sitz baths and irrigation
    • Packing to ensure healing
  • Complications:

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 An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, anal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast, or itching. Risk factors include older age, infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease 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. Papillomavirus (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. Papillomavirus (HPV)), multiple sexual partners, and anal sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria. Anal carcinoma is diagnosed by biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma. Treatment can include surgery, radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma, or chemotherapy Chemotherapy Osteosarcoma. In a chronic or atypical anal fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes, 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: Anatomy. 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: Histology, 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 can be internal or external. External 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 are painful, but internal 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 are painless; both can bleed and appear as a soft rectal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast 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 Hydrocortisone The main glucocorticoid secreted by the adrenal cortex. Its synthetic counterpart is used, either as an injection or topically, in the treatment of inflammation, allergy, collagen diseases, asthma, adrenocortical deficiency, shock, and some neoplastic conditions. Immunosuppressants, and sitz baths. For recurrent cases, rubber band ligation Band ligation Mallory-Weiss Syndrome (Mallory-Weiss Tear) or surgical removal is indicated.
  • Perianal ulcerations: erosions Erosions Corneal Abrasions, Erosion, and Ulcers in the perianal mucosa. Occur secondary to inflammatory bowel disease, most notably Crohn’s disease, infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease, and cancer. Symptoms include pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, bleeding, and erosions Erosions Corneal Abrasions, Erosion, and Ulcers in the lining of the mucosa. Treatment is aimed at the causative disease. Differentiated from anal fissures Anal fissures A painful linear tear at the margin of the anus. It appears as a crack or slit in the mucous membrane of the anus and is very painful and difficult to heal. Constipation on physical exam by deeper erosions Erosions Corneal Abrasions, Erosion, and Ulcers in mucosa and evidence of other causative disease.
  • Anal fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes: a painful superficial tear of the epithelial lining (anoderm) of the anal canal. Anal fissures Anal fissures A painful linear tear at the margin of the anus. It appears as a crack or slit in the mucous membrane of the anus and is very painful and difficult to heal. Constipation 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 Anal intercourse Hemorrhoids, or perineal lacerations during childbirth. Treatment is generally conservative, including stool softeners, bulking agents, sitz baths, and/or topical vasodilators Vasodilators Drugs used to cause dilation of the blood vessels. Thromboangiitis Obliterans (Buerger’s Disease).

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
  2. Turner, S.V., Singh, J. (2021). Perirectal Abscess. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507895/
  3. Carr, S., Velasco, A.L. (2021). Fistula In Ano. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557517/

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