Anal fistula: symptoms, causes, surgery and recovery

The NHS lists skin irritation around the anus, a constant, throbbing pain that may be worse when you sit down, move around, poo or cough, smelly discharge from near your anus, passing pus or blood when you poo, and swelling and redness around your anus with a high temperature if you also have an abscess. Difficulty controlling bowel movements (bowel incontinence) can occur in some cases.

The end of the fistula might be visible as a hole in the skin near your anus, although this may be difficult for you to see yourself, according to the NHS. University Hospitals Sussex says it may appear as a small opening or sore near the anus, and that symptoms may improve when the fistula drains but often return if it does not heal.

• Pain around the anus, often throbbing and worse on sitting.

• Smelly discharge, pus or blood.

• Itching or skin irritation.

• Swelling, redness and fever if an abscess forms.

The NHS says surgery is often needed to treat anal fistulas because they do not usually heal by themselves, and there are several different procedures. The best option depends on the position of your fistula and whether it is a single channel or branches off in different directions. Sometimes you may need an initial examination under general anaesthetic to help determine the best treatment.

The aim of surgery is to heal the fistula and avoid damaging the sphincter muscles, the ring of muscles that open and close the anus, because damaging them could result in loss of bowel control. The surgeon will talk to you about the options. Surgery is usually carried out under general anaesthetic, and in many cases it is not necessary to stay in hospital overnight.

An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the opening of the bottom, according to the NHS. It is usually caused by an infection near the anus that results in a collection of pus (an abscess) in the nearby tissue. When the pus drains away, it can leave a small channel behind.

University Hospitals Sussex says fistulas vary in complexity. Low (simple) fistulas are close to the skin and involve little or no muscle, and are easier to treat. High (complex) fistulas pass through or near important muscles, are more difficult to treat and may need staged treatment. It adds that some fistulas form between the bowel and the vagina, which may cause passing gas through the vagina, discharge or stool from the vagina and recurrent infections.

It says anal fistulas are not usually life-threatening, but they rarely heal on their own.

The NHS says most anal fistulas develop after an anal abscess, and you can get one if the abscess does not heal properly after the pus has drained away. University Hospitals Sussex says around 3 in 4 fistulas develop after an abscess, that small glands in the anal canal can become blocked and infected, and that when the abscess drains a tunnel may remain.

Less common causes listed by the NHS include Crohn's disease, diverticulitis, hidradenitis suppurativa, infection with tuberculosis (TB) or HIV, and a complication of surgery near the anus. University Hospitals Sussex also lists previous injury, radiotherapy, some sexually transmitted infections and, rarely, cancer.

The NHS says to see a GP if you have persistent symptoms. The GP will ask about your symptoms and whether you have any bowel conditions, and may ask to examine your anus and gently insert a finger inside it (a rectal examination) to check for signs of a fistula.

If the GP thinks you might have a fistula, they can refer you to a specialist called a colorectal surgeon. Tests you may have include a further physical and rectal examination, a proctoscopy, where a special telescope with a light is used to look inside your anus, and an ultrasound, MRI or CT scan.

An abscess near the anus is the usual starting point for a fistula. The NHS lists swelling and redness around your anus and a high temperature among the symptoms if you also have an abscess. University Hospitals Sussex says that if there is an abscess urgent treatment is required, which may include drainage of the abscess and placement of a seton, and that at this stage the focus is on controlling infection rather than closing the fistula.

It says to seek medical advice urgently if you develop increasing pain not relieved by medication, fever or chills, heavy bleeding, signs of infection such as redness, swelling or warmth, or new or worsening symptoms, and that you can contact your GP, NHS 111 or urgent care services.

University Hospitals Sussex says a seton does not cure the fistula but helps control symptoms while further treatment is planned. After placement you may have mild discomfort, a feeling of a small knot or tugging, and ongoing discharge, which it describes as normal. Pain is usually managed with paracetamol or ibuprofen, and you may be advised to gently move the seton while washing to prevent blockage. It may stay in place for several months.

It says most people recover quickly, walking normally the next day and returning to light activities within a few days and work within a few days to a week, and to avoid heavy lifting or strenuous activity for 1 to 2 weeks. To stay comfortable it suggests warm baths for 10 to 15 minutes, keeping the area clean and dry, using soft gauze or pads, barrier cream if the skin is irritated, a high-fibre diet and plenty of fluids.

It says even with treatment fistulas can sometimes recur. If a seton falls out or breaks, contact your surgical team for advice rather than trying to replace it yourself. Recovery times differ with the procedure and your own trust's advice takes priority.

On the NHS the route is usually a GP appointment and then referral to a colorectal surgeon. An abscess is treated urgently. The NHS says many people do not need to stay in hospital overnight after surgery, although some may need to stay for a few days.

Private colorectal surgery is also available for assessment and procedures. Whichever route you use, ask which procedure is proposed and why, what the risk to bowel control is, and whether staged treatment is likely.