Anal Fistula Symptoms, Types, Differential Diagnosis, Treatment

Article by Dr Raghuram Y.S. MD (Ay) and Dr Manasa B.A.M.S
Anal fistula can be described in simple terms as ‘a narrow tunnel with its internal opening in the anal canal and its external opening in the skin near the anus or anal opening (outside the anal canal)’. Thus it is a tunnel between the outside and inside layers of anal canal.

In medical terms ‘Anal fistula is a chronic abnormal communication between the epithelialised surface of the anal canal and (usually) the peri-anal skin’.

Anal fistula is also called as Anal Fistulae (when there are more than one or multiple fistulae). Its other name is ‘fistula-in-ano’.

Formation of fistula

How is anal fistula formed?
It is commonly said to occur in the people with a history of anal abscesses. They are formed when the anal abscesses are not treated properly or when they do not heal properly.

The fistulae occurring in the anal region originate from the ‘anal glands’. These glands are located in between the ‘internal anal sphincter’ and ‘external anal sphincter’. They drain into the anal canal. Thus, the course of anal fistulae can be said to occur through the length between the anal glands and anal canal. If the outlet of these glands becomes blocked an abscess or pocket containing infected fluid can form. This abscess eventually extends to the skin surface. This tract is called a ‘fistula’.

Abscesses and fistulae are inter-linked phenomenon –
If abscess doesn’t heal properly, it can cause fistula. On the other hand, if the fistula seals over, the abscesses can recur, allowing the accumulation of pus. The abscess then can extend to the surface again and again, repeating the process. Therefore any abscess should be thoroughly treated so as to abort the possibility of the formation of anal fistulae.

How bothering is rectal fistula occurring in anus?
Rectal fistulae are generally not harmful. But they are very painful. They can be irritating because they are associated with frequent drainage of pus. There is also a possibility that the stools be passed through the fistulae and repeatedly contaminate them. Since fistulae are formed in the anal region and are continuously exposed to stools, they are in the vicinity of regular contamination and subsequent infection. This will lead to the formation of abscesses and fistulae in due course of time.

Additionally, recurrent abscesses may lead to significant short term morbidity from pain, importantly, create a starting point for systemic infection. The infection and contamination from this region can ascend and spread all over.

Treatment, especially surgery is considered essential to allow drainage of fistulae of its contaminants and also to prevent infections. Repair of fistulae itself is considered an elective procedure which is opted by many patients due to the discomfort and inconvenience associated with an actively draining fistula.

Types of Fistula-in-ano

Fistulae occurring in the anal region are classified into 5 types. They are:

Extra-sphincteric fistulae
They begin at the rectum (part of colon above anal canal) or sigmoid colon (part of colon above rectum). From here they proceed downward through the levator ani muscle and open into the skin surrounding the anus.

This type of fistula doesn’t arise from the dentate line (where the anal glands are located).
Causes may be from rectal, pelvic or supralevator (above the level of levator ani muscle) origin.

They are usually secondary to Crohn’s disease or an inflammatory process such as abscesses occurring in the appendix or diverticulae.

Supra-sphincteric fistulae
They begin between the internal and external sphincteric muscles.
From here, they extend above and cross the pubo-rectalis muscle.
From here, they proceed downwards between pubo-rectalis and levator ani muscles.
They open an inch or more away from the anus.

Trans-sphincteric fistulae
They begin between the internal and external sphincter muscles or behind the anus.
They cross the external sphincter muscle and open an inch or more away from the anus.
They may take a ‘U’ shape and form multiple external openings.
This is also called as ‘horseshoe fistula’.

Inter-sphincteric fistulae
They begin between the internal and external sphincter muscles
From here, they pass through the internal sphincter muscle. They open very close to the anus.

Sub-mucosal fistulae
They pass beneath the sub-mucosa
The fistulae do not cross either sphincter muscles

Signs and Symptoms

Skin maceration
Pus, serous and or faeces (rare) discharges
Bloody or purulent discharges at times
Pruritis ani (anal itching)
Pain around the anal region
Swelling around the anal region
Redness of the skin around anal opening
Tenderness
Fever

Diagnosis

Diagnosis of Fistula is usually done under anaesthesia. This is referred to as EUA i.e. Examination Under Anaesthesia.
The examination is also done in outpatient setting.
The fistula is explored with the help of a narrow instrument which can be pushed into the tunnel (fistula) called fistula probe. In this way, it is possible to find both outer and inner openings of the fistulae.
The examination can also be done through anoscopy.
Diagnosis may be aided by performing a fistula-gram, proctoscopy and or sigmoidoscopy.

Possible findings –
The opening of the fistula onto the skin may be observed
The area may be painful on examination
It may be associated with redness
Discharges may be observed
An area of induration (thickening due to chronic infection)

Treatment

The treatment of fistula depends on the location of fistula and which parts of the internal and external anal sphincters it crosses. Below mentioned are the treatment options –

Doing nothing – Without doing much, a drainage set on can be left in place for long term to prevent problems. This will keep draining the secretions. This is the safest option although it is not a definitive cure for the fistula.

Lay-open of fistula – Here, an operation is done to cut the fistula open. It is then packed on daily basis to ensure wound healing from inside out. This operation leaves behind a scar and can cause incontinence.

Cutting set-on – A cutting Seton may be used if the fistula is high in position and if it passes through a significant portion of sphincter muscle. In this, a thin tube is inserted through the fistula tract and its ends are tied together outside the body. The Seton is tightened over time, gradually cutting through the sphincter muscle and healing as it goes on. Chances of scar are less but incontinence (flatus) can still occur.

Seton stitch – In this, a length of suture material is looped through the fistula which keeps it open and allows pus to drain out. Here, the Seton is referred to as ‘draining seton’.

Fistulectomy – cutting off the fistula till ano-rectal ring
Colostomy – to allow healing
Fibrin glue injection – Here, fistula is injected with bio-degradable glue. It is believed to heal the fistula from inside out and allows healing in natural way. It avoids risk of incontinence.

Fistula plug – In this, the fistula is plugged with a device made from small intestinal sub-mucosa. The fistula plug is positioned from the inside of the anus with suture. It has a good success rate (65-75%) and does not carry any risk of bowel incontinence.

Endo-rectal advancement flap – It is a procedure in which the internal opening of the fistula is identified and a flap of mucosal tissue is cut around the opening. The flap is lifted to expose the fistula, which is then cleaned and the internal opening is sewn shut. After cutting the end of the flap on which the internal opening was, the flap is pulled down over the sewn internal opening and sutured. The external opening is cleaned and sutured. Success rates vary. Recurrences have been seen.

LIFT Technique (Ligation of Inter-sphincteric Fistula Tract) – it is based on secure closure of the internal opening and removal of infected crypto-glandular tissue, through the inter-sphincteric approach.

Fistula clip closure (OTSC Proctology) – is a surgical procedure in which the opening of the internal fistula is closed with a super-elastic clip made of nitinol (OTSC).

PERFACT (Proximal superficial cauterization Emptying Regularly Fistula tracts And Curettage of Tracts) Procedure – It is a procedure used to treat complex and highly complex fistula-in-ano. It is a minimally cutting procedure as both the anal sphincters are not cut / damaged at all. The risk of incontinence is thus minimal.

Other strategies:

• Soak in a warm bath for 3-4 times in a day
• Wear a pad over your anal area until healing is complete
• Resuming normal activities only when you are cleared by your surgeon
• Eat fibre-rich diet and drink plenty of fluids
• Use a stool softener or bulk laxative

Association with infection –
Some people will have an active infection when they present with a fistula. This infection has to be dealt with and cleared before any definitive treatment of fistula has been decided.

Antibiotics can be used to treat infections. The best way of healing infection is to prevent the build up of pus in the fistula / fistulae which leads to formation of abscess. This can be done with the help of a Seton.

Differential diagnosis

Differential diagnosis of Anal Fistula
Acute Proctitis – Proctitis is inflammation of the lining of the rectum called the rectal mucosa. It can be short term (acute proctitis) or long term (chronic). Proctitis involves an inflammatory change of the rectum. It can cause rectal pain and the continuous sensation that you need to have a bowel movement (frequent urge to defecate). It is common in people who have inflammatory bowel diseases.

Anal Carcinoma (anal cancer) – It is a malignant tumour which arises from the anus, the distal opening of gastrointestinal tract. Symptoms of anal cancer can include pain or pressure in the anus, a change in bowel habits, a lump near the anus, rectal bleeding, itching, or discharge. Bleeding may be severe.

Ano-rectal abscess (anal / rectal abscess) – is an abscess which occurs adjacent to the anus. It arises from an infection at one of the anal sinuses which leads to inflammation and abscess formation. It presents with pain in the perianal area. The pain may be dull, aching or throbbing. It is worst when the person sits down and right before a bowel movement. Other symptoms include constipation, drainage from the rectum, fever and chills or a palpable mass near the anus.

Constipation – It is a condition in which there is difficulty in emptying the bowels, usually associated with hardened faeces. Symptoms include few bowel movements, trouble having a bowel movement (straining at defecation), hard or small stools, a sense that everything did not come out (feeling of incomplete evacuation), swollen belly or belly pain and throwing up.
Read related: Constipation Causes, Ayurvedic Treatment, Home Remedies

Diverticulitis (Diverticulosis) – It is the inflammation of the diverticula in the digestive tract. It occurs when the bulging sacs (diverticula) that appear in the lining of your large intestine or colon, get acutely infected or inflamed. The most common and severe symptom is sudden pain in the lower left side of the abdomen. The other symptoms include bloating, constipation, fever, nausea and change in bowel habits.

Inflammatory bowel disease – It involves chronic inflammation of all or part of your digestive tract. It includes 2 conditions i.e. ulcerative colitis and Crohn’s Disease. Both usually involve diarrhoea, pain, and fatigue and weight loss. It can be debilitating and sometimes leads to life-threatening complications.

Pilonidal cyst – It is an abnormal skin growth located at the tailbone that contains hair and skin. The cyst is usually located near the tailbone and can become easily infected. Symptoms include pain, reddened skin or drainage of pus or blood.

Pilonidal Sinus – Pilonidal sinus is a small hole or tunnel in the skin. It usually develops at the end of the tailbone, at the cleft of the buttocks. It becomes commonly infected. Symptoms include pain, reddened skin or drainage of pus or blood.

Anal Fissure – It is a small tear or crack in the lining of the anus. It can cause sharp pain and bleeding during and after bowel movements.

Haemorrhoids – They are swollen veins in the lowest part of your rectum and anus. Symptoms include pain, severe itching, difficulty in sitting, constipation and bleeding.
Read related: Haemorrhoids: Ayurvedic Treatment, Medicines, Remedies

Risk factors

Who is at risk of developing anal fistula?
If you develop an anal abscess you have about 50% chance of developing an anal fistula. Even if your abscess drains on its own, you have about the same risk for a fistula. Certain conditions that affect your lower digestive tract or anal area may also increase your risk.

These include:
Colitis
Crohn’s disease
Chronic diarrhoea
Radiation treatment for rectal cancer
Anal abscess
Click to Consult Dr Raghuram YS MD (Ayu)