A fistula-in-ano (FIA) is a track that arises from the last part of the rectum, and goes through the tissues to open in the skin around the anus. It is an extremely common surgical disorder, and much prone to recurrences after surgery.
The rectum is the last part of the large
intestine, and ends in a 4 cm tube called the anal canal,
which itself opens into the anus. During embryonic
development, the large intestine moves outwards to end in the anus, and the anal
skin moves inwards to join the large intestine. Thus the
rectum does not actually end in the anus, but ends a
short distance before the anus. The inner layer (mucosa)
of the rectum is of the intestinal type, while the mucosa
of the anal canal resembles the skin in structure. The
point where the two mucosae join is called the dentate
line, and at this point are present numerous glands
called anal glands.
A fistula is an abnormal
communication between two hollow organs, or between one
organ and skin. A fistula in ano is the best known of the
fistulas in the body. It is a narrow track, often no more
than a millimeter in diameter, and travels from the anal
canal towards the skin. The path may be a straight line
or a gentle curve, but is genererally more tortuous, and
branching is quite common. Tiny particles of stool may
enter the fistula, and cause infection to develop in the
track. This leads to recurrent inflammation and pain. On the skin the track
opens on a small elevation that the patient can usually
feel as a nodule. In a few patients there may be more
than one opening.
Most fistulas develop as a consequence of anal gland infection. The infected gland bursts outwards into the skin, but retains its connection with the anal canal. This form of fistula often first forms an abscess near the anus ("perianal abscess") and then either discharges into the skin to form a fistula, or is drained surgically and heals with the formation of a fistula.
Other causes. Infections like large intestinal tuberculosis, lympho-granuloma venereum, certain fungal infections and amebiasis may cause fistula in ano. Chronic inflammatory diseases like Crohn's disease and ulcerative colitis may develop a fistula. An injury near the anal canal, including an operation (eg for piles) may heal with the formation of a fistula. Cancers of the rectum and anal canal can also result in fistulas, which are extremely difficult to manage. Rarely, some children are born with anal fistulas (congenital fistulas)
Fistulas are commoner in males. Most patients complain of the passage of pus, sometimes with blood, from an opening near the anus. They usually complain that there is increasing pain over a period of a few days, followed by the discharge of a small amount of pus, with relief of pain. Itching and soreness may be present. Patients usually are able to feel a small nodule, which is the external opening of the fistula. The examining doctor will also search for the internal opening by inserting a finger into the rectum. This can also be done by means of a metallic probe, or by injection of a dye such as methylene blue.
Investigations. A fistula is a clinical diagnosis, and investigations are rarely needed to diagnose it. Some patients may need an X-ray to mark out the fistula and confirm that the track is a low track, and not a high fistula. Ultrasonography is a useful tool for demonstrating the path of the fistula, but the expertise of anal ultrasonography is not easily available. Recently magnetic resonance imaging (MRI) pictures for anal fistulas have been described. These imaging modalities may have a role in cases of recurrent fistulas.
The usual treatment of a fistula in ano is
surgery. At an operation called fistulectomy the entire
fistula track is cut away. This often leaves a generous
wound in the buttock, which can take several weeks of
regular dressings to heal. The surgeon also makes a
thorough search for branches, to minimize the risks of
recurrence. Unfortunately despite all efforts the
recurrence rates for anal fistulas are over 10%.
A treatment first described by the ancient Indian surgeon, Sushruta (c 500 BC), involves the passage of a medicated thread ("ksharasootra") through the fistula track, with regular tightening. The thread cuts through the fistula and tissues and finally comes out. Excellent cure rates have been reported with this method. This technique may not be suitable for patients with multiple tracks. A side effect is severe inflammation of the skin where the thread is touching it. The inflammation may not resolve unless the thread is removed.
It is difficult to say if a fistula can be prevented. A healthy high fiber diet and avoidance of constipation may minimize the risks of fistula formation.
Fistula patients may take a normal diet
Pain near the rectum will always cause a patient to visit a doctor. The cycle of pain-discharge-decrease in pain should alert a patient to the possibility of a fistula. Since fistulas are associated with infection, one should avoid unnecessary delay in seeing a doctor.
Sood, MBBS (AIIMS), MS (AIIMS), MAMS, is a
practising surgeon attached to Dharamshila Cancer
Hospital, Sir Ganga Ram Hospital and to Noida Medicare
Center. Formerly Professor of Surgery, Himalayan
Institute of Medical Sciences, Dehradun, Dr Sood has a
special interest in gastrointestinal surgery. He has had
an active academic career, has published several papers
in national and international journals, and is the Editor
(with Dr Anurag Krishna) of a widely acclaimed book
titled Surgical Diseases in Tropical Countries.
Last revised: May 11, 2000