Anorectal abscesses

Trouble starts when an abscess near a patient's anus bursts through to his skin. It probably originated in an anal gland, and may communicate through a tiny opening with his anal canal, at the pectinate line. A connection betweeen the skin and the anus (a fistula) is the reason why about half of these abscesses recur, or discharge persistently on to the perianal skin as chronic fistulae in ano. Abscesses (with no opening to the skin), sinuses (with an opening to the skin, but not to the anus), and fistulae (with openings to both) are thus part of the same disease process. Most abscesses settle by discharging spontaneously, or being drained, but a serious life-threatening infection can sometimes spread through a patient's perineum, or deeply into his pelvis. For an account of the anatomy of this region and the treatment of fistulae see Section 22.2.

The patient is usually a middle-aged man who says that a severe throbbing pain has kept him awake for several nights. When you examine him, you find a tense tender swelling near his anus. Sometimes, there may be little to see or feel, except mild tenderness at his anal margin, or, his whole perineum may feel tense and tender. If his abscess bursts to the surface, his pain goes. But he may now have a persistently discharging sinus or fistula opening on to the skin near his anus.

The anal glands are mostly posterior, so that most abscesses and most fistulae are posterior. These glands also extend into the sphincters, so that pus does too. It can track in various directions: (1) It usually tracks downwards to cause a perianal abscess. (2) It sometimes tracks laterally, through the sphincters, to cause an ischiorectal abscess. The ischiorectal spaces connect with one another behind the anus, so that infection on one side can spread to the other side (horseshoe abscess). (3) Rarely, pus tracks upwards: (a) under the mucosa of the anal canal to form a submucous abscess, or (b) between the sphincter muscles to form a high intermuscular abscess, or (c) above the levator ani muscles to form a supralevator abscess.

Fig. 5-11 ANORECTAL ABSCESSES form in the anal glands. The pus can track in any of the directions shown here. When an abscess bursts into the anal canal and on to the skin a fistula, may form. After Macleod JH, ''A Method of Proctology', Fig. 7.9. Harper and Row, with kind permission. Here are the classical types of anorectal abscess, but you may see combinations, and the diagnosis can be difficult. Only the first two are common.

A perianal abscess (common) presents as a red tender swelling close to the patient's anus. On rectal examination, there is little or no tenderness, induration, or bulging in his anal canal. There is usually no fistulous track, but if there is one, it goes straight through or above his subcutaneous external sphincter, and usually through the lowest part of his internal sphincter.

The abscess usually bursts spontaneously (unless it is treated surgically), and may persist as a fistula. Its external opening is surrounded by a button of granulation tissue within 5 cm of his anus. If the track is low, you can feel it through his skin as a cord passing from the external opening towards his anus. You may be able to feel its internal opening as a tender swelling, which is usually below his pectinate line.

An ischiorectal abscess (common) lies deeper than a perianal one, is larger and further from his anus; it forms a deep tender brawny swelling and is not fluctuant until late. He is likely to be toxic, febrile, and debilitated. On rectal examination you may feel a tender induration bulging into his anal canal on the same side. The infection may spread posteriorly and then to the other side as a horsehoe abscess, so that he now has signs on both sides. When an ischiorectal abscess discharges, it does so through an external opening, which is typically more than 5 cm from his anus. If a fistula forms, it almost always opens into his anus in the midline posteriorly below his anorectal line. From there it curves backwards and laterally into one or both of his ischiorectal fossae.

A submucous or high intermuscular abscess (rare) presents with pain in a patient's rectum and no external swelling, unless it is complicated by an ischiorectal or perianal abscess. On rectal examination you may be able to feel a soft, diffuse, tender swelling extending upwards from his pectinate line.

A pelvirectal abscess (rare) presents with fever, but no local anal or rectal signs. Later, it may extend downwards into his ischiorectal fossa. With your finger in his anus, you may be able to feel fluctuation above and lateral to his anorectal ring.

Don't delay treatment in the hope that an anorectal abscess will cure itself[md]always incise it. Pus will have formed by the time the patient presents, and antibiotics will not make it go away[md]they are only indicated if he has a high temperature and a spreading infection (rare). If his abscess is large, warn him that it is going to take weeks to heal. Unroof it and let it granulate. Don't try to curette it, and close it by curettage and primary suture. A large incision will not necessarily give a better result[md]recurrence depends on whether or not there is a tiny communication between the abscess and his anal canal[md]see Section 22.2.

ZBIG (50 years) complained of painful defaecation and passing pus and blood rectally. He was found to have an anorectal swelling, given a course of antibiotics, and sent home for readmission later for examination under anaesthesia. He returned after three days with severe pain, swollen crepitant buttocks, and a black gangrenous scrotum. His urine was tested and was found to contain sugar. He was referred, but died soon afterwards. LESSONS (1) Bacteria in anorectal abscesses come from the gut and are usually benign, but anaerobic infections can be dangerous. (2) Never treat an anorectal or perineal abscess with antibiotics without also draining it. (3) Spreading anaerobic infections originating in the gut need metronidazole. (4) Always test the urine. Serious infections are particularly common in diabetics. Fig. 5-12 AN ANORECTAL ABSCESS. A, a cruciate incision. B, insert your finger and break down loculi. C, the wound with its edges trimmed, being left to granulate.

ANORECTAL ABSCESSES [em]CAUTION ! (1) If a patient has an acute abscess don't probe around looking for fistulae[md]wait until his lesion has become chronic. If you probe unwisely, you may create an iatrogenic extrasphincteric fistula which will be very difficult to treat. (2) In the chronic phase, look carefully for the tracks in his skin and rectum that show its presence. If he has a fistula and you fail to diagnose it, he will not be cured. (3) If an abscess lies anteriorly, consider the possibility of a periurethral abscess in a man, and a Bartholin's abscess in a woman.

INDICATIONS FOR INCISION. Operate immediately you can feel a tender swelling. Don't wait for fluctuation. If pain has kept him awake, open his abscess.

ANTIBIOTICS are useless unless there are signs of spreading infection. If so, give him chloramphenicol and metronidazole.

EQUIPMENT. A scalpel and a bivalve speculum. A proctoscope and a sigmoidoscope are not essential; you are unlikely to see anything you cannot feel.

ANAESTHESIA. (1) For a large abscess, use ketamine, or general anaesthesia. (2) Local anaesthesia is unsatisfactory, although you can use it for a perianal abscess; but the patient will not be pain-free. It is even less satisfactory for other abscesses. (3) Intravenous thiopentone with pethidine is not ideal, because you may need more time than they allow you (A 8.8).

EXAMINATION UNDER ANAESTHESIA. Put him into the lithotomy position. Put a finger into his anus and feel its entire wall between two fingers, as in F, Fig. 22-2. Feel if there is an indurated upward extension of the abscess under the mucosa 3 cm or more above his internal sphincter. Feel the extent of the abscess, and for the point of maximum fluctuation.

Insert a bivalve speculum and look for pus coming out of an internal opening in the appropriate segment of his anal canal. You will only find one in about 10% of cases. You may feel the opening as a localized tender depression in his anal canal in the place suggested by Goodsall's rule in Fig. 22-6. Press on the abscess[md]you may see a bead of pus escape from the internal opening. If you do find a fistula, determine where it is in relation to his pectinate line.

If his abscess is acute, there is no defined wall, so you will not find a track. DON'T probe around, you may make one!

If his abscess is chronic with a well-defined wall, probe carefully to look for a fistula.

INCISION AND DRAINAGE. Support the mass with your finger in his rectum. Make a substantial cross-shaped incision at least twice the depth of the lesion over its most prominent or fluctuant part. This will be externally for a perianal or ischiorectal abscess, and inside his rectum above his anorectal line for a rare submucous or pelvirectal abscess. Make the incision large enough to admit one or two fingers, so that you can explore the abscess fully with your finger and break down all loculi by Hilton's method (5-3). Don't break down any natural barriers to the spread of infection. If possible, send a specimen of the pus for culture.

Now look again[md]but don't probe[md]to see if there is a fistulous opening.

If there is no fistula, cut off the corners of the flaps to prevent the edges of the wound coming together and adhering. A linear incision is never adequate. Wrap your finger in gauze and clean the walls of the abscess cavity.

If there is a fistulous opening, you can proceed immediately as follows, or better, wait 4 or 5 days.

If his fistula is low in his anal canal, at or below his pectinate line, lay it open and manage it as a low anal fistula (22.2).

If the opening of the fistula is above his pectinate line, leave it and either refer him, or deal with it later. Some surgeons thread a silk ligature through the fistula and tie it loosely round the sphincter, to mark its internal opening.

POSTOPERATIVELY, pack the cavity lightly with gauze[md]don't pack it too tight, or it won't drain. Tuck the edge of a gauze square into the wound to keep the edges of the skin apart, until the wound cavity has collapsed. Apply a T- bandage. Follow this with daily salt baths and packing, until the abscess cavity has healed from within outwards. It will heal slowly. Discharge him as soon as there is a flat granulating area, and review him regularly.

CAUTION ! (1) Be sure to push a piece of gauze down to the bottom of the cavity, so that it heals from the bottom up, without bridging of the edges. (2) Don't pack it so tightly that the pack interferes with granulation.

If you lack dressings, use salt baths (1.12) and ask a nurse to use her gloved hands to separate the walls of the abscess, which may be sticking together superficially.

DIFFICULTIES [s7]WITH ANORECTAL ABSCESSES If you find AN ABSCESS ON BOTH SIDES, open them both as described above, and incise both his ischiorectal fossae. There is sure to be a track between them, behind his anus; some surgeons would lay this open also at this stage.

If he has SIGNS OF SPREADING INFECTION, such as gross inflammatory swelling, areas of necrosis, or crepitation, he probably has an anaerobic infection, and needs urgent treatment, particularly metronidazole (2.9) and wide drainage.

If A FISTULA DEVELOPS later (common), treat it as in Section 22.2.

If he presents with a RECURRENT ABSCESS (common), there is almost certainly an underlying fistula. The opening may be very small, and you may have overlooked it when you drained his first abscess.

If you find an INTERNAL OPENING which communicates with his ischiorectal fossa above his anorectal ring, (rare) don't cut the muscle superficial to it, or he will become incontinent! Drain the abscess from below. A fistula will probably form.

If THE ABSCESS EXTENDS INTERNALLY under his submucosa, (rare) pass a director along the track and lay it open. It will bleed copiously. Try to tie the vessels. This may be difficult, so don't spend too long trying. If you fail, grasp them with haemostats, and leave these in place for 48 hours.

If he has a SUPRALEVATOR ABSCESS (very rare), refer him[md]treatment is difficult and controversial.