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Anal Fistula

DEFINITION : Anal Fistula, Fistula in Ano, Ano-Rectal Fistula are all related to the same condition. A “Fistula” is defined as an abnormal pathologic “track” which can affect any part of the body, from head to toeAnal Fistula is an abnormal channel (track) with two openings, one opening is inside the Anal Canal or Rectum and the other opening is outside the surface of the skin which surrounds the Anal Verge (Peri-Anal skin) and contains infected material.

SYMPTOMS : Anal Fistula can occur at any time during adulthood and rarely in childhood. The patient may or may not have a history of having a painful and tender abscess outside on the skin near the Anal Verge or deep seated pain around the Anus and Rectum, several weeks or a few months previously. The patient may feel a small, tender lump on the skin in the vicinity of the Anal Verge, a few centimetres up to several centimetres away from the verge. Usually, there is a watery, purulent (pus) discharge from the external opening of the Fistula which stains the undergarments. Sometimes, there is no discharge but a recurrent and exquisitely painful and tender swelling near the Anal Verge for a duration of a few days due to collection of pus in the cavity of an abscess in the Fistula Track which bursts suddenly with a profuse discharge of pus followed by relief of painThe external opening of the Fistula usually closes completely and may appear to the patient that the Fistula has healed, but then reoccurs with pain and tenderness several weeks or a few months later.

DIAGNOSIS : The diagnosis is made from both a detailed history which is pathognomonic (characteristic) and also from the physical examination of the patient in the left lateral Sim’s position with good lighting and good assistance. The outside opening of the Fistula Track will be visible even if it is a tiny dimple which may be covered with a scab, or there will be disfigurement and various degrees of fibrosis of the involved skin and subcutaneous tissue (tissues under the skin).

Sometimes, the Fistula is so chronic and the surrounding soft tissue feels indurated (hardened) with various degrees of pain and tenderness.Clinical examination is not complete without physical examination of the abdomen and considering the general look of the patient.

DIFFERENTIAL DIAGNOSIS All Ano-Rectal Abscesses and Fistulae are due to infection by purulent (pus forming) bacteria. Rarely, it may also be associated with other uncommon diseases such as Crohn’s Disease, Lower Rectal Cancer and Tuberculosis. In the pre-antibiotics era, one major hospital in London recorded nearly fifteen percent (15%) of all Ano-Rectal Fistulae were due to Tuberculosis. This high incidence of Tuberculosis Fistulae may still exist in underdeveloped countries.

TREATMENT : An established Anal Fistula will never heal spontaneously, although there may be remission and quiescent periods. The best and the only certain treatment for a permanent cure and no recurrence is the following elective surgical operation which is extremely effective if it is carried out accurately. It has stood the test of time. Briefly, under pre-medicationin the left lateral Sim’s position and infiltration of 15ml Lidocaine 2% with Adrenaline 1/100,000. With the aid of Allen Park’s retractor and Lockhart Mummery fistula director, the soft tissues of the track are all sharply divided and laid open by cutting on the groove in the fistula director with no. 11 Swan Morton Blade, curreting septic granulation and excision of the roof. The wound heals by granulation and epithelialization (second intention). The duration of complete healing will be between one to ten weeks, depending on the type of the Fistula, chronicity, whether the patient has had a previous surgical operation or operations on the same Fistula, the degree of fibrosis and the condition of the adjacent soft tissues. Any other type of treatment is doomed to fail and reoccurrence is almost certain.

Second Intention is a process  of healing, cure and restoration of integrity of the tissue where the wound closure takes place from the base and both sides of the wound towards the surface.

In my private surgical practice over the several years, and according to my records, I have performed eighty (80) surgical operations on Ano-Rectal Fistulae in the operation theatre of my surgical clinic in Dubai under pre-medication and local anaesthesia. The vast majority of the Fistulae were of the Inter-Sphincteric type and also several Trans-Sphincteric. Furthermore, I operated upon several patients with recurrent Fistulae and severe peri-anal fibrosis and induration which were operated upon elsewhere including countries outside the U.A.E. A few patients have had two to three surgical operations elsewhere for the same condition and the Fistula has reoccurred. All wounds healed soundly by granulation and epithelialization (second intention). All patients were followed up post-operatively for many months and up to several years.There has never been a recurrence. The ano-rectal sphincters worked normally with full control of wind and faeces.

I would like to emphasize that the surgeon must have very good and detailed knowledge of the surgical anatomy of the Anal Canal, the Rectum, the highly specialized sphincters and the surrounding soft tissues. Otherwise, there will be either recurrence of the Fistula or even partial or complete incontinence of wind and faeces and in such cases, repair of the damage is not possible.


An Anal Fistula is preceded by an abscess in the ano-rectal complex. If an abscess in this region is recurrent it is certainly due to an Anal Fistula, even if its track cannot be identified. Spontaneous healing of an established Ano-Rectal Fistula, if it ever happens, must be very rare. A neglected Fistula may flare up at any time causing repeated abscesses and considerable pain, tenderness and ill health. Sometimes, an abscess which is treated at an early stage by surgical drainage, without antibiotics, may heal completely without Fistula formationThe vast majority of Fistulae are due to infection with a purulent (pus forming) bacteria arising in the Anal Glands which open into the crypts in the Anal Canal at the level of the dentate line (Figure 1/4). Normally, the glands, six to eight in number, are thick and sticky mucus secreting. These glands branch out and tend to penetrate through the Internal Sphincter into the Inter-Sphincteric plane. Infection arising in these glands leads to abscess formation (Figure 2/4). If the acute abscess is drained surgically and early, it will heal.If the abscess is undrained surgically or it becomes chronic or partly sterilized by antibiotics, it becomes lined by granulation tissue and when it ruptures a Fistula results which becomes a well-established Chronic Fistula (Figure 3/4 and 4/4).

THE SEQUENCE OF EVENTS that takes place in the formation of Ano-Rectal Fistulae. Pyogenic infection in the deeper part of Anal Gland leads to an abscess cavity:


1) If the enlarged abscess track medially it causes a Sub-Mucous Abscess i.e.beneath the mucous membrane(Figure 1/3). The patient complains of a rapid onset of persistent deep seated ano-rectal pain which becomes unbearable after a day or soThe patient cannot sit, stand or walk.There are no external signs and no outside tenderness,but very careful digital rectal examination, if possible, will reveal extreme tenderness. MRI is preferable to confirm the diagnosis pre-operatively.

If it breaks spontaneously, it will lead to a secondary opening at a higher level than the primary opening of the Mucous Gland which is at the level of the crypts at the dentate line. The secondary opening may heal spontaneously.

2) Infection in the deeper part of the Anal Gland may lead to abscess cavity formation in the potential space between the Internal and External Anal Sphincters i.e. the Inter-Sphincteric plane (Figure 1/3). If the infection in the latter plane tracks directly downwards to the peri-anal skin it forms a Peri-Anal Abscess (Figure 1/3), and when it has discharged, a Fistula results and is called an Inter-Sphincteric Fistula (Figure 2/3) and its external opening is about two centimetres away from the anal verge. This is the most common type of Fistulae.

3) If the infection and abscess in the Inter-Sphincteric plane spreads laterally through the External Anal Sphincter it will infect the Ischio-Rectal Fossa with the formation of an Ischio-Rectal Abscess (Figure 1/3). The drainage of this abscess will be followed by a fistula, the opening of the track will be situated in the peri-anal skin, three centimetres up to several centimetres from the anal verge, even into the buttock. This type of Fistula is called Trans-Sphincteric Fistula (Figure 3/3).

Ano-Rectal Fistulae run through or between a variety of anatomical planes of the Anal Canal, the Rectum and the highly specialized adjacent muscles complex. They are either, Low, Intermediate, High, Sub-cutaneous, Sub-mucous, Inter-Sphincteric, Trans-Sphincteric or Extra-Sphincteric (Pelvirectalsupralevator). All these names are descriptive of the anatomical locations.


The Anal Canal is four centimetres long (4 cm). It is a tube made of two types of muscular sphincters.The “Internal Anal Sphincter and the “External Anal Sphincters” (Figure 2/4 and 3/4).These sphincters hold the Anal Canal continually closed except for the temporary passage of flatus and faeces.

The junction of the Rectum and Anal Canal is at the pelvic floor, i.e. at the level where the “Pubo-Rectalis Muscle” clasps the gut and angles it forwards (Figure 3/4 and 4/4). From this right-angled junction with the Rectum, the Anal Canal passes downwards and somewhat backwards to the skin of the Perineum where it forms the Anal Verge.

Muscles of continence of wind and faeces

1. Pubo-Rectalis
2. Levator Ani
3. Profundus
4. Superficialis


As above, the Anal Canal is four centimetres (4 cm) long and divided into three parts. Upper (15 mm), middle (15mm) and lower (10mm).

The upper part (15mm) is lined with mucous membrane and contain crypts and glands. These glands are atypical Apocrine Mucous Glands and are called Anal Glands. The Anal Gland opens into a crypt. A mucous membrane is a membrane that lines cavities or passages and secretes mucus which is a protective slimy secretion. The nerve supply of this membrane is Autonomic and sensitive to pressure only, for example, digital examination of the ano-rectum and rectal tubeIt also can distinguish between constipated faeces, soft faeces, diarrhoea and flatus. It is relatively insensitive to touch and pain.

The lining of the middle part (15mm) is lined by none keratinized stratified squamous epithelium which is a transitional zone and called Pecten.The junction of the mucous membrane to the Pecten is called the Pectinate Line.

The lining of the lower part (10mm) of the Anal Canal is lined by a thin, hairless true skin and contains sebaceous and sweat glandsIts nerve supply is Somatic and therefore very sensitive to pain like a fissure and a cut from trauma.

The junction of the lower part of the Pecten to the upper part of the hairless skin lining of the lower part is abrupt and called Hilton’s White Line(Mr John Hilton, FRCS England, 1805-1878, English Anatomist and General Surgeon).This landmark is very important from the surgical point of view during the surgical procedure of sphincterotomy for painful and tender Chronic Anal Fissure.

At this landmark, there is a “groove” or a “step” which is palpable.This groove separates the lower border of the Internal Anal Sphincter from the Subcutaneous External Anal Sphincter (Figure 1/4 and 2/4).

MUSCLE SPHINCTERS OF THE ANAL CANAL are Internal Anal Sphincter and External Anal Sphincters (Figure 2/4, 3/4 and 4/4).

1) THE INTERNAL ANAL SPHINCTER (FIGURE 2/4) is a continuation of the muscles of the Rectum. It is a smooth muscle and encircles the uppertwo thirds of the Anal Canal down to Hilton’s White Line and it is under voluntary controlIts nerves supply are autonomic, Parasympathetic and Sympathetic. Parasympathetic stimulation relaxes the muscleSympathetic stimulation contracts the muscle, but this contraction is not competent when acting alone, it needs another three muscles to have complete continence of flatus and faeces (see infra).

2) THE EXTERNAL ANAL SPHINCTER (FIGURES 2/4, 3/3 and 4/4) are striated muscles and encircles the lower two thirds of the Anal Canal.Therefore, the External Anal Sphincter overlaps the Internal Anal Sphincter at the middle third of the Anal CanalThe External Anal Sphincters consist of three separate parts. Each part is a ring of muscle lying adjacent to each other in a series. The lowest is called “Subcutaneous External Anal Sphincter”, the middle is called “Superficial External Anal Sphincter” and the uppermost which is the deepest is called “Profundus External Anal Sphincter”.

a) Subcutaneous External Anal Sphincter – This is a thick ring of muscle like a ribbon band. It lies immediately beneath the skin and is easily palpable by the examining finger-tip (see infra)It is an important landmark during the surgical operation of sphincterotomy for Chronic Anal Fissures.

The lowest end of the Internal Anal Sphincter is thickened and by digital palpation during the surgical operation of sphincterotomy for Chronic Anal Fissure, it is felt as a tight flat band especially when stretched by a bivalved Alan Park’s anal retractor. It is bulky in young healthy adult males (Figure 2/4). As mentioned above, there is a palpable “groove” or a “step” which separates the lower end of the Internal Anal Sphincter from the Subcutaneous External Anal Sphincter (Figure 2/4).

b) Superficial External Anal Sphincter This muscle contributes to the continence of wind and faeces.

c) Profundus External Anal Sphincter This is the uppermost and the deepest portion of the External Anal SphincterIt encircles the Internal Anal Sphincter in the highest part of the Anal Canal.

Corrugated Cutis of AniMuscle This small muscle consists of thin flat strip of smooth muscle fibres and is attached to the peri-anal skin. Its contraction expels the last drop(s) of faecal matter especially when the motion is loose and also, puckering of the peri-anal skin.                           

CONTINENCE OF FLATUS AND FAECES are essentially achieved by the four muscles which are the 1) “Pubo-Rectalis”, 2) “Profundus External Anal Sphincter”, 3) Superficial External Anal Sphincter and 4) part of the “Internal Anal Sphincter”.