An anal abscess is an infection in the one the glands located within the muscles of the anal canal. The glands exist to secrete mucus into the anal canal. The duct of the glands can become occluded leading to stasis of the mucus and sometimes infection.
The infection causes swelling and severe localised pain to the anus. There maybe associated fever and constipation or occasionally diarrhoea. The infection is more common in those patients with diarrhoea, immunosuppression and inflammatory bowel disease.
The treatment of anal abscess infection, also known as perianal sepsis is for an examination of the anus to be performed under general anaesthetic in an operating room. An incision is made into the abscess and the pus drained. The cavity is then irrigated with saline to ensure that the pus is completely drained. Swabs are sent for microbiological assessment to ensure that the causative organism is identified.
About half of patient who develop anal abscesses will go on to develop a fistula. This is an abnormal tunnel leading from the anal canal to the skin close to the anus. It is really a remnant of the infected gland, duct and tract through which the pus drained. If a fistula has occurred, most patients recognise mild pain and a chronic intermittent discharge of pus from the skin close to the anus.
The treatment of an anal fistula is to perform an examination of the anus under general anaesthetic. The examination maybe guided by a pre-operative magnetic resonance imaging MRI sequence or ultrasound of the anus to check the anatomy. During the examination of the anus under general anaesthetic, probes are passed into the fistula tract. If the fistula is low and incorporates little anal muscle then a fistulotomy can be performed. This converts the “tunnel” of the fistula into a “gutter” which then heals from the deep to superficial. In doing so, the fistula is resolved. When however, the fistula incorporates a significant amount of anal muscle then a drain or seton is inserted into the tract. This provides continuous passive drainage of pus from the fistula tract so that inflammation and infection can resolve.
Subsequent examinations under general anaesthetic are then required over a period of weeks to months later either to adjust the seton in such a way that the fistula is healed and anal continence is maintained or to allow for curative surgical procedures to be performed. These procedures involve various methods to suture the tract closed or to plug it with collagen plugs.