Anorectal sinuses and fistulae

The anorectal abscesses in Section 5.13, and the sinuses and fistulae described here, are part of the same disease process. An abscess is the acute phase, and a sinus or fistula the chronic one. Both sinuses and fistulae are tracks lined by granulation tissue, which open on to the skin near the anus. The difference between them is that a sinus has no internal opening, whereas a fistula opens into the patient's anal canal, or occasionally into his rectum. Usually, there is only one internal opening, but he may have several external ones. These can either be insignificant little holes, or prominent little nodules of granulation tissue, which heal over temporarily. The treatment of sinuses and fistulae is similar.

Typically, a patient with a fistula starts by having an abscess, which either bursts and fails to heal, or is not drained properly (see Section 5.13), after which he complains of a chronic painless discharge which soils his clothes. His fistula is only painful when it becomes temporarily blocked, so that pus builds up inside it.

Fistulae can take any of the paths shown in Fig. 22-5; they can be subcutaneous (common), low anal, high anal, or intermuscular (rare).

A fistula seldom heals spontaneously, and almost always needs surgery. Cut down on it, deroof it, expose it, and let the wound you have made heal from the bottom by granulation during several weeks. A fistula nearly always goes through the anal sphincters, so that in cutting down on it, you have to cut them. Fortunately, a patient usually has some sphincter capacity to spare, and as his fistula usually goes through his sphincters quite superficially, you can cut the superficial part of them without making him incontinent. But if his fistula goes deep, and you cut too much of his sphincters, he will become incontinent. If, on the other hand, you make the opposite mistake of not cutting deeply enough, you may leave part of the track behind, with the result that his fistula recurs.

You have a 50% chance of finding the internal opening quite easily, by passing a probe from the external opening towards his anal canal. One of the worst mistakes is to create an internal opening, where there was none before, in the process of looking for it, by forcing a probe through into his anal canal. This makes a sinus into an iatrogenic fistula, opens up healthy tissue to infection, and makes cure more difficult.

The key landmarks are his pectinate line, and his anorectal ring. If necessary, you can cut both his sphincters below his pectinate line. In doing so, you preserve his anorectal ring (formed by his puborectalis muscle), and he remains continent, although he may have some incontinence of watery stools. Cutting his anorectal ring makes him completely incontinent. Fortunately, fistulae which go deep to the anorectal line are rare. If you find he has one, and cannot refer him, all you can do is to lay open the superficial tracks, curette the deep ones and hope for the best. This is difficult surgery, so examine him carefully and only operate if he has an easier fistula[md]incontinence is worse than the intermittent discharge from a fistula!

Fistulae which have external openings in front of a transverse line across the anus enter directly into it by the shortest path. Fistulae behind this line usually curve round, so that they enter the anus posteriorly at 6 o'clock (Goodsall's rule, Aa, 22-6). In doing so they follow a horseshoe path, and are often bilateral, one side communicating with the other. There are exceptions, and very superficial fistulae behind the line may occasionally track directly into the anus.

You will find that the track of a horseshoe fistula hugs the puborectalis part of the levator ani muscle, as it forms a sling round the sides and back of the anorectal junction, external to the external sphincter. Fortunately, the internal opening of such a horseshoe fistula is usually at the pectinate line, although the fistula itself may go much deeper.

Provided you trim the wound edges well, the common straight superficial fistulae heal with only minimal postoperative care, but this is critical for deep ones. The wound must be laid open widely, and it must granulate from the bottom up. If it heals leaving pockets, it will recur. So try to prevent the opposing granulating walls of the wound, or its skin edges, from touching one another, uniting, and leaving an unhealed pocket underneath them. Your main difficulty in treating these patients is likely to be to persuade them to stay long enough in hospital. If you are short of beds, a relative or the staff of a health centre will have to manage the wound.

PERIANAL ABSCESSES, SINUSES, AND FISTULAE ARE NOT HELPED BY ANTIBIOTICS! Fig. 22-5. PATTERNS OF FISTULAE. A, two subcutaneous fistulae, one opening at the pectinate line, and one just below it. B, two low anal fistulae. C, several high ones. D, some more high fistulae. Fistula (1) is the commonest high fistula; it goes high towards the levator ani, but does not penetrate it. The high extension is often missed, but it must be explored and laid open. Fistulae (2) and (3) penetrate the levator ani. E, high intermuscular fistulae (rare) may exist alone (4), or be an extension of a low anal fistula (5). After Goligher JC, ''Surgery of the Anus, Rectum and Colon', (4th edn 1980) Figs. 121 to 126. Bailli[gr]ere Tindall, with kind permission.

ANORECTAL FISTULAE X-RAY. X-ray the patient's chest: his fistula may be tuberculous (uncommon). If it is tuberculous, surgery is usually unnecessary. He may or may not have an obvious chest lesion.

EXAMINATION IN THE THEATRE. Prepare him for anaesthesia, if necessary. Before you start, warn him that you are going to examine him under anaesthesia to try to find where his fistula runs. Explain that if he has one of the easier fistulae, you are going to operate. Otherwise, you may have to leave it (unusual). Further indications are given below.

If the opening is less than 5 cm from his anus, his fistula is perianal, if it is more than 5 cm away, it is probably high. Multiple openings suggest a horseshoe fistula. Record the position of all external openings carefully on a copy of diagram A, in Fig. 22-4.

Feel for the thickened track which runs from the external opening(s) towards his anus. If a fistula is superficial, you can usually feel its firm, fibrous track quite easily. As you press it pus may exude from the external opening.

Put a finger into his anus and try to feel the internal opening: you may be able to feel an induration at its internal end. Feel the entire circumference of his rectum, as far as your finger can reach. Determine particularly where the fistula might be in relation to his anorectal ring and his pectinate line. Try to feel the track between your two fingers. Does it appear to come to an end low down, or high up in his anus? If you feel induration at the level of his puborectalis or above (rare), he has a complex high fistula.

PROCTOSCOPY. Examine his anal canal with a proctoscope. You may be able to see the internal opening of his fistula, usually at 6 o'clock on his pectineal line. Insert the proctoscope as far as it will go, withdraw the obturator, and then gradually withdraw the instrument itself. As soon as its end becomes obstructed and closed by his anorectal ring, stop. If you can still see the opening of the fistula, it is safely below the critical level of his anorectal ring.

You may be able to feel the track of a horseshoe fistula as a thick horizontal indurated rod, hugging his puborectalis sling.

In 50% of cases you will find the opening easily, in the other 50%, it will be present but tiny. A probe may show it, but if it does not, inject methylene blue (or boiled milk) into the external opening, and look for this flowing into his anus[md]finding the internal opening is the key to all fistula operations!

PROBING. Don't do this until you have finished your initial inspection. You may need to wait until he is anaesthetized. Decide where a track is probably going to go before you start probing. Pass the probe as far as possible towards his anal canal, and feel for its end in his anus. It may pass through into the lumen, or it may stop before getting there. If his fistula is superficial it will pass horizontally, if it is deep, the probe will pass almost vertically, parallel to his anus.

CAUTION ! (1) If the probe passes vertically, and not towards his mid anal canal (even though there is an opening there), he probably has a high complex fistula or a deep sinus. (2) Only pass a probe into the rectum through a fistulous track[md]don't force it through normal tissues.

DEROOFING [s7]AN ANAL FISTULA INDICATIONS. You should now know where the fistula runs. Only operate on the easier and more superficial fistulae. The main risk is incontinence. Refer him if: (1) His fistula has multiple openings, unless you have had some experience with the operation. (2) He has had previous unsuccessful operations. (3) The probe passes vertically upwards. (4) His fistula is palpable in his upper anal canal, or above his anorectal ring (rare).

Other factors which increase the risk of subsequent incontinence are: (1) The liability to attacks of diarrhoea, or a history of soiling, which might indicate reduction of his sphincter capability. (2) A female patient, particularly if she is old.

EQUIPMENT. This includes a medium-sized malleable silver probe, or a probe-pointed director.

ANAESTHESIA. (1) Ketamine. (2) Light general anaesthesia. Avoid relaxants and subarachnoid anaesthesia. You want to be able to feel the anorectal ring, so as not to cut it. Muscular relaxation makes feeling it more difficult, but does provide better exposure.

Fig. 22-6 A LOW ANAL FISTULA can have several tracks, as in A, and B, or only one, as in the remainder of these figures. Aa, Goodsall's rule. Fistulae above a horizontal line across the anus usually pass directly into it; fistulae behind the line usually curve round it to enter at 6 o'clock. C, passing a probe-pointed director along the track from the external to the internal opening, and out through the patient's anus. D, cutting down on the director. E, scraping away the granulation tissue with a sharp spoon. F, trimming the edges of the wound. G, the final pear-shaped guttered wound. If there is much fibrous tissue round the track, excise it. H, packing the wound with gauze soaked in hypochlorite. After Goligher JC, ''Surgery of the Anus, Rectum and Colon', (4th edn 1980). Figs. 139 and 140, Bailli[gr]ere Tindall, with kind permission.

A SUBCUTANEOUS OR LOW ANAL FISTULA. Carefully confirm the findings you obtained before you anaesthetized him. If you thought that his fistula was blind at the inner end (a sinus), confirm this. Pass a probe or director through the track, from the external opening towards his anal canal, either completely through to its lumen, or as far as it will go. It may enter his anal canal, or it may stop before doing so.

If the probe enters his anus superficial to his pectinate line, cut down on all structures superficial to it, and lay the track open. If you are using a director, cut down to the groove in it. Look at the velvety track of the opened fistula. If there is no such track, you have probably opened up a false passage. Look carefully for any side openings, and feel among the fatty tissue for nodules of induration, that might be offshoots of the fistula. As a general rule, all fistulous tracks communicate with one another. Using a sharp spoon, curette the tracks, so as to leave only healthy tissue, and trim away any overhanging skin.

Alternatively, make a narrow pear-shaped incision to include both the internal and external openings. Excise both of them, and the track of tissue that still clings to the probe.

If the probe enters his anus deep to his pectinate line, leave the fistula untreated, or refer him. Even experts find these fistulae difficult.

CAUTION ! (1) Don't cut deep to his pectinate line, or you will cut too much sphincter. (2) When you cut down on to a probe or director, do so by the most direct route.

If the probe does not enter his anal canal, he has a sinus. Lay it open in the same way, but without opening into his anus.

With all sinuses and fistulae, look, feel, and probe for other track openings and areas of induration. If you find any, open them and curette them. Curette the granulation tissue.

Control bleeding with diathermy, or tie off bleeding vessels with 2/0 plain catgut. Excise the skin edges and bevel them, so as to leave a conical or pear-shaped concave raw area. Be sure that there will be no pockets or overhanging edges, when muscle tone returns. If a fistula is complex, you will have to make a deep, wide wound.

Always send tissue for histology to exclude tuberculosis. Apply flat squares of gauze soaked in hypochlorite, or salt solution, pad it with plenty of gauze, and hold it in place with a T-bandage. Avoid vaseline gauze because it may cause a foreign body granuloma (''paraffinoma').

Fig. 22-7 A HIGH POSTERIOR HORSESHOE FISTULA[md]ONE. A, the fistula shown on a standard diagram of the anus. B, a coronal section. C, a sagittal section. This is the fistula that is being operated on in the next diagram. After Goligher JC, ''Surgery of the Anus, Rectum and Colon', (4th edn 1980). Fig. 128, Bailli[gr]ere Tindall, with kind permission.

ISCHIORECTAL (horseshoe) FISTULAE usually have two or more external openings. Pass a director into an opening, and lay open one side at a time.

Point the director forwards, make it project against his skin at the side of his anus, and cut down on it. The track will be deeply overhung by fat; trim this. Turn the director posteriorly, and see if you can follow the track across to the other side, and then forwards on that side.

Now see if you can find the opening into his anus posteriorly. If you have seen a definite opening below his anorectal ring, encourage the director to follow it there, and lay the fistula open.

CAUTION ! (1) Most of these fistulae have a posterior opening close to the pectinate line, and if you miss it and don't lay it open, the fistula will recur. If you don't find such an opening, make one. (2) Lay open all side tracks.

If oozing is a problem, apply pressure from adrenalin soaked gauze. Gutter, trim and dress the wound as above. If his fistula is complex and deep, feel it with your gloved finger each day, to keep the edge of the granulating wound smooth, and to make sure that no deep pockets are left, which would lead to recurrent infection. Lay a flat gauze square on it. If you are worried about the way it is healing, take him back to the theatre and further lay the wound open.

POSTOPERATIVE CARE is the same as for any granulating anal wound, with daily, or twice daily, salt baths (sitting in a bowl of saline), regular dressing changes, and measures to ensure soft stools. Warn him that a perianal fistula may take 2 weeks to heal, and an ischiorectal one 4 weeks. An extensive horseshoe fistula may take 12 weeks. If necessary, trim away any excess granulation tissue.

Fig. 22-8 A HIGH POSTERIOR HORSESHOE FISTULA[md]TWO. This is the fistula in Fig. 22-7. A, passing the director forwards. B, cutting down on the track on the left side. C, passing the director along the posterior part of the track towards the right. D, exposing the track on the right side. E, passing the director forwards through the posterior communication into the patient's anus. G, the final horseshoe-shaped wound, with part of his sphincter divided. After Goligher JC, ''Surgery of the Anus, Rectum and Colon', (4th end 1980). Fig. 147, Bailli[gr]ere Tindall, with kind permission.

DIFFICULTIES [s7]WITH ANAL FISTULAE If a FISTULA PASSES FORWARDS from his (or her) anus, it may be an URETHRAL FISTULA (23.8), or originate in Bartholin's glands (23.4).

If a FISTULA IS POSTERIOR, don't confuse it with a PILONIDAL SINUS (22.8). If it is low and immediately behind his anus, it may have arisen in an anal fissure.

If the EXTERNAL OPENING IS SOME DISTANCE FROM HIS ANUS, look out for a long curved fistula, or a high one. Its thickened track will usually show you its course and destination. Probe it, but don't expect it to enter his anus.

If his FISTULA EXTENDS UP THROUGH A HOLE IN HIS LEVATOR ANI, and you cannot refer him, pass a haemostat through the hole and stretch it. Enlarge the opening to provide free drainage. If necessary, cut backwards, laterally or forwards, but not medially. Enlarge the external wound by wide trimming, especially posteriorly, to provide a wide gutter, extending backwards towards the side of his coccyx. Provided there is no internal opening above his levator ani, or chronic pelvic disease, such as regional ileitis, his prognosis is good.

CAUTION ! Don't look for an opening in his rectum, there almost never is one, unless the cause of the fistula was a penetrating injury.

If you find a HIGH INTERMUSCULAR FISTULA (submucous fistula, unusual), leave it. If it really is submucous, it can be opened into his rectum, but if it happens to be outside his rectal wall, and you cut into it, this will be a disaster.

If he also has PILES, excise them, or they may thrombose and bleed postoperatively. Or, if they are first- degree, do Lord's procedure (22.5), and leave his anus packed.

If he has RECURRENT DISCHARGE FROM THE TRACK, his wound has healed over externally, without healing from below. Operate again. It will not heal with antibiotics. Also consider the possibility of tuberculosis.

If he has ULCERATIVE COLITIS, or CROHN'S DISEASE (both uncommon in the developing world), he is a special case, so refer him.

If there is GREAT NODULAR THICKENING of his subcutaneous tissue, purplish discoloration (in a white skin), numerous sinuses which seldom discharge much pus, and no real cavity or track, suspect SUPPURATIVE HIDRADENITIS (rare).

If he, or more likely she, has MULTIPLE FISTULAE with much scarring and skin bridges between them, suspect LYMPHOGRANULOMA VENEREUM (22.10) or colloid carcinoma of the anus.