Core Topics in General & Emergency Surgery: Companion to Specialist Surgical Practice (54 page)
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Authors: Simon Paterson-Brown MBBS MPhil MS FRCS
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Felicity J. Creamer and
B. James Mander
The emergency presentation of anorectal pathology constitutes a significant proportion of the general surgeon's workload. The problems encountered range from the acute pain of thrombosed haemorrhoids and perianal sepsis to the management of massive bleeding, trauma and foreign bodies. The management of many of these conditions is frequently straightforward; however, the close proximity of pathology to the structures involved in continence does require a degree of care and reflection. It is therefore imperative to ensure that any surgical intervention is appropriate, timely and minimally disruptive.
Understanding the pathophysiology and rationale for treatment in anorectal disease is impossible without sound knowledge of the anatomy of the anal canal. This is a 3- to 4-cm-long tube running downwards and backwards from the anorectal angle to the anus. It is divided in half by the dentate line, above which the canal is lined with hindgut-derived columnar epithelium and innervated by the autonomic hypogastric nerves, sensitive only to stretch. The section of the canal below the dentate line is lined with stratified squamous epithelium that merges at the anus with the perianal skin, and its nerve supply is derived from the somatic inferior rectal nerve making it sensitive to pain, pressure and temperature.
The canal is surrounded by a funnel of muscle essential in maintaining faecal continence. The inner muscle layer is the involuntary internal sphincter muscle, derived from the circular muscle of the rectum. Beyond this is the voluntary external sphincter, formed from striated muscle, continuous at its superior edge with the levator plate. Between these two muscle layers is the intersphincteric space, which contains mucous-secreting anal glands. Ducts from these glands open into the anal valves at the dentate line.
Three submucosal anal cushions are found, usually at the 3, 7 and 11 o'clock positions within the anal canal and contain fibroelastic tissue and arteriovenous anastamoses. In health they appose to form a tight seal within the canal, which helps to maintain continence, but in some people these can enlarge to form troublesome symptomatic haemorrhoids.
Perianal abscesses are defined as any collection of pus in the perianal tissues and are very common, with operative treatment being required in about 1 in 5000 people in Scotland annually.
1
They occur predominantly in adults, with a peak incidence in the third and fourth decades of life, men being affected two to three times more frequently than women. Patients present with signs and symptoms of acute inflammation, with pain being the most common symptom. In approximately one-third of patients they are associated with a persistent fistula-in-ano that, if left untreated, can result in recurrent infections.
2
Primary perianal abscesses are most commonly caused by infection within the anal glands (the cryptoglandular theory) with the common causative organisms being gut-derived enterococci.
3
,
4
The resulting suppuration can spread in several directions, resulting in infection in a variety of anatomical spaces (
Fig. 11.1
). The relative frequency with which abscesses occur in the various anatomical locations is shown in
Table 11.1
.
5
Primary abscesses can also be caused by suppurating skin infections, including carbuncles, furuncles and infected apocrine glands. The responsible bacteria in these cases is almost invariably staphylococcus and as these abscesses do not communicate with the anal canal they are not associated with fistula formation.
6
Studies have shown that taking a swab for culture at the time of abscess drainage can predict whether a fistula is likely to be present and thus guide decision-making regarding future management.
6
,
7
Table 11.1
Location of anorectal sepsis by anatomical site
| Anatomical site | Number | Percentage |
| Perianal abscess | 437 | 42.7 |
| Ischiorectal | 233 | 22.8 |
| Intersphincteric | 219 | 21.4 |
| Supralevator | 75 | 7.3 |
| Submucosal | 59 | 5.8 |
Data from Ramunjam PS, Prasad MI, Abcarian H et al. Perianal abscesses and fistulae: a study of 1023 patients. Dis Colon Rectum 1984; 27:593–7. With kind permission from Wolters Kluwer Health.
Figure 11.1
The spread of anal gland infection and common sites of anorectal sepsis. Infection of the anal gland within the intersphincteric space can spread in a variety of directions (see left side of diagram), resulting in abscess in a number of classical sites: 1, supralevator; 2, intersphincteric; 3, submucosal; 4, perianal; 5, ischiorectal. Note also the possibility of circumferential extension of sepsis (‘horseshoeing’) in the intersphincteric, ischiorectal and supralevator planes.
It is recommended that a swab from the abscess cavity is sent for culture to determine the likelihood of a subsequent fistula.
6
,
7
Secondary abscesses are much less common, accounting for just 10% of presentations.
8
They are the manifestation of distinct underlying disease, with inflammatory bowel disease (Crohn's disease in particular), colorectal neoplasia, diabetes mellitus, AIDS and tuberculosis all being potential causes. They can also occur as a complication of haemorrhoid surgery or as a consequence of trauma from foreign bodies.
On examination the abscess can usually be seen as a red, tender, fluctuant swelling near the anal verge; however, ischiorectal abscesses often present as a less distinct brawny swelling on one side of the anus and intersphincteric abscesses cannot usually be seen externally at all. Although this last type of abscess can be felt through the anal wall as a smooth, tender collection, digital rectal examination is usually excruciatingly painful without anaesthesia. This diagnosis should therefore be suspected in patients with severe anal pain and fever. In a few patients (particularly those who are immune-compromised or with diabetes mellitus) the abscess can be associated with cellulitis, which can progress to life-threatening necrotising infection if not treated promptly.
9
All patients presenting with anorectal sepsis or pain should have an examination of the anorectum, including proctosigmoidoscopy. It is our opinion that this can usually only be performed satisfactorily under general anaesthesia. As the diagnosis is usually obvious, few people would routinely recommend preoperative imaging (although some advocate its use, arguing that by identifying cavities and fistulas there is a reduction in the incidence of recurrence
10
). However, if the diagnosis is unclear (such as in intersphincteric or supralevator abscesses) or in cases of recurrent sepsis, imaging is very useful.
Magnetic resonance imaging (MRI) is an accurate method of identifying collections of pus and fistula tracts.
11
,
12
It is commonly used in investigating complex fistula disease in Crohn's disease but is rarely needed in the acute situation. Endoanal ultrasound is another sensitive method of identifying collections of fluid close to the anal canal and can also be used to identify fistula tracts (
Fig. 11.2
). It remains a technique practised by only a few specialist surgeons and so is rarely available in the emergency situation. However, it has been shown that in experienced hands it is at least as accurate as MRI and its use is likely to increase.
13
,
14
Figure 11.2
Endoanal ultrasound examination carried out on a patient under general anaesthesia. This patient presented with severe anal pain and perianal induration but without any specific area of fluctuation. The ultrasound demonstrates an extensive ischiorectal abscess cavity
(c
,
d)
extending around the anal canal (
a
, internal sphincter;
b
, external sphincter).
With thanks to Mr Mike Hulme-Moir, previous Clinical Fellow in Colorectal Surgery, Royal Infirmary, Edinburgh.
Treatment must be aimed at draining the abscess, thereby removing the source of sepsis. This should be done whilst minimising damage to the sphincters, preventing recurrence and minimising hospital stay. In most patients this involves making a linear incision over the cavity, gently breaking down any loculi and then dressing appropriately. There is no role for treatment with antibiotics unless the patient is immune-compromised or there is evidence of florid cellulitis or suspicion of necrotising infection. Although in North America this drainage is commonly undertaken under local anaesthesia, the more thorough examination, drainage and treatment that can be performed under general anaesthesia is, in the opinion of the authors, preferable – and probably prevents a significant proportion of re-operations. A large retrospective case study of 500 patients treated for perianal abscess at the Mayo Clinic was reported in 2001 and revealed a 7.6% re-operation rate.
15
The reasons for re-operation included incomplete drainage of the abscess cavity at the first operation, missed abscesses (most often posterior collections) and postoperative bleeding. There was no association reported between patient variables (such as age, immune suppression or diabetes) and so it must be concluded that surgical error was the only reason for these findings, emphasising the need for a thorough primary examination.
Historically, it was suggested that thoroughly ‘deroofing’ the abscess cavity with a wide cruciate incision was beneficial but this does little other than giving the patient a larger wound that will take longer to heal.
16
Similarly, a short-lived enthusiasm for primary wound closure after incision has been abandoned by most surgeons as studies have shown that it offers little immediate benefit in terms of time to wound healing and probably increases the chance of recurrent sepsis.
17
If the abscess cavity is very large, an alternative to making a huge incision is to insert a de Pezze or Malecott catheter via a smaller skin incision. This was looked at in one study, which showed that of the 91 patients who underwent this treatment compared to the 54 who underwent conventional treatment, hospital stay was shorter (1.4 vs. 4.5 days) and the need for community dressing shorter, with no disadvantages seen at long-term follow-up.
18
The management of specific abscesses is shown diagrammatically in
Fig. 11.3
. Simple perianal abscesses should be drained and the cavity gently curetted (
Fig. 11.3a
). With ischiorectal abscesses, the cavity is often huge (
Fig. 11.3b
). The cavity should be incised as near to the anal verge as possible to bring the external opening of any subsequent fistula close to the anal verge and thus minimise the trauma of subsequent fistulotomy should it be required. A large horseshoe abscess in the ischiorectal space is better drained through multiple short incisions than one large circumferential incision. As mentioned earlier, the size of the drainage wound can be minimised if a drainage catheter is used. Intersphincteric abscesses require drainage into the anorectum, with excision of part of the internal sphincter (
Fig. 11.3c
). Submucosal abscesses, although rare, are drained into the anal canal. Supralevator or pelvic abscesses must be drained with care and ideally not through the perineum or a high fistula-in-ano will be created. In true pelvic abscesses unrelated to spread from the anal glands, drainage can be achieved into the rectum or vagina. If the abscess is related to pelvic pathology, the primary disease process will need to be excised along with drainage of the pus.
Figure 11.3
Management of specific abscesses.
(a)
Perianal abscess is treated by excision of a small disc of skin and curettage of the cavity.
(b)
Ischiorectal abscess may require excision of a substantial amount of tissue to facilitate drainage. The alternative is to introduce a drainage catheter through a small stab incision.
(c)
Intersphincteric abscess is treated by excision of the mucosa and internal sphincter overlying the abscess. Such an abscess should not be drained through the perineal skin or a high fistula will result.
After the abscess has been opened and drained it is common to ‘pack’ the resulting cavity with absorbent dressing material, which must then be removed and replaced by community nurses. However, there is no good clinical evidence that this practice is beneficial to the patient and indeed, in our opinion, serves only to cause discomfort and inconvenience.
19
Studies have shown that perianal abscesses are associated with fistulas in about 60% of patients;
7
,
20
however, only 29–37% of these persist after the acute inflammation has resolved.
2
,
21
,
22
A persisting fistula tract increases the chance of a recurrent abscess and can cause perianal discharge, itch and pain even in the absence of an acute infection. However, identifying a fistula when acute inflammation is present can be tricky, especially for the less experienced surgeon. As noted previously, a swab from an abscess cavity that grows gut- rather than skin-derived bacteria would suggest a communication to the bowel.
6
,
7
These patients can then be reviewed in the clinic after the acute sepsis has resolved and a second-look examination under anaesthesia (EUA) booked if indicated.
However, the cryptoglandular theory of anorectal sepsis would suggest that the presence of intersphincteric pus would definitively predict an underlying fistula tract. This was tested in a 1994 prospective study of 22 patients. A radial drainage incision was made and extended into the intersphincteric space. Careful examination was then made to determine whether there was a fistula tract. It was found that intersphincteric sepsis predicted a fistula with 100% sensitivity and specificity. Patients were followed up for 38 weeks with no adverse outcomes reported. This has the advantage over microbiological analysis of the abscess (which is very sensitive but just 80% specific) in that no second procedure is needed.
23
However, it must be noted that this study was performed by two highly experienced colorectal surgeons and there is no evidence that similar results would be safely obtained by non-specialists. The probing and opening of tracts within friable, oedematous tissue, with the possibility of creating false passages, may do disproportionate damage to the sphincters and thus continence.
The majority of anorectal abscesses are adequately treated with incision and drainage alone and if a fistula tract is not obvious it should not be sought.
20
,
21
So should synchronous fistulotomy ever be performed? A recent Cochrane review of six randomised control studies from five different centres from 1987 to 2003 looked at concomitant fistula surgery at the time of abscess drainage in terms of recurrence, need for further surgery and postoperative incontinence.
24
However, as would be expected, the eligibility criteria and treatments offered varied considerably between the trials, making definitive recommendations difficult. Three studies also report fistula rates of 83–90%,
20
,
25
,
26
which is higher than would be expected, raising questions about whether iatrogenic tracks may have been created.
The majority of the studies included in the review dealt only with the surgical treatment of low fistulas. Of these, one randomised patients
after
the initial abscess drainage, with fistulotomy performed as a second procedure on day 3 of the acute admission.
25
Most studies excluded those with recurrent anorectal sepsis, previous surgery and inflammatory bowel disease (IBD).
24
All the studies showed that recurrence was less likely after fistula surgery (risk ratio 0.07–0.24), although follow-up times varied. Only two studies looked at short-term incontinence, with one (which included only low fistulas,
n
= 52) reporting no clinical incontinence in either group despite anal manometry revealing a transient reduction in the anal resting pressure in the fistulotomy group (76.3 mmHg vs. 91.1 mmHg), which had disappeared by week 12. Squeeze pressures were unaffected.
26
The other group (who had included high trans-sphincteric and suprasphincteric fistulas, which had been treated with cutting setons) reported transient incontinence of flatus in 3/100 of the control and 15/100 of the intervention group. For those who underwent drainage alone this had entirely resolved by 6 months; however, in the fistula surgery group, 6% were still having problems after 1 year.
20
Long-term continence rates were documented in five studies and were normal in four of them following simple drainage alone at 1 year or later. Of the studies performing low fistulotomy, incontinence of flatus was 0/24,
27
8/20
25
and 0/24.
26
The study that included high fistulas reported 2/100 incidence of incontinence for flatus and 4/100 for liquid incontinence with urgency.
20
The final study had performed fistulectomy and partial internal sphincterectomy, and they reported flatus/liquid incontinence in 6/32 of the control and 13/34 of the intervention groups, with four and one patients from each group, respectively, lost to follow-up.
28
All these data combine to give a risk ratio of 2.64 for long-term incontinence following synchronous fistulotomy.
24
The overall conclusions of the Cochrane meta-analysis were that synchronous fistulotomy is appropriate for low, uncomplicated fistula tracts. It should not be performed for high fistulas or anterior fistulas in women. It should also be avoided for groups where the risk of incontinence is high (e.g. those who have undergone previous anorectal surgery or have IBD).
24
Synchronous fistulotomy can be performed with care for low, uncomplicated fistula tracts to reduce the risk of abscess recurrence and further operations.
24
