Section 1: Epidemiology and aetiology
A perianal abscess (also known as an anorectal abscess or anal sepsis) represents an infection of the soft tissues surrounding the anal canal, with formation of a discrete abscess cavity. The severity and depth of the abscess is variable, and the abscess cavity is often associated with a fistula tract.
Perianal sepsis is a common condition that may occur at any age. There is an early peak in babies under 12 months old, and then a later peak in the third and fourth decades of life. This pattern can be mapped to the incidence of predisposing factors.
Men are affected more frequently than women, with a male-to-female ratio of 2-3:1.1 This male predominance is particularly marked in infancy. Approximately 30 per cent of patients with anorectal abscesses report a previous history of similar abscesses.2
Interestingly, the incidence of perianal abscess formation increases in the spring and summer. There is no evidence for a relationship between poor personal hygiene or diarrhoea and the development of perianal sepsis.
The anal canal has 4-10 anal glands that serve to lubricate the canal. These glands are drained by their respective crypts of Morgagni. The internal anal sphincter is believed to serve as a barrier to infection passing from the gut lumen to the deep perirectal tissues.
This barrier can be breached through the crypts of Morgagni, which can penetrate through the internal sphincter into the intersphincteric space. When the anal glands and crypts are blocked, the static glandular secretions become infected.
The clinical presentation of perianal sepsis will depend on the anatomical site of the infection.
Common organisms implicated in abscess formation include Escherichia coli and the Enterococcus and Bacteroides species. However, no specific bacterium has been identified as a unique cause of abscesses.
It must not be forgotten that anal malignancy may be misdiagnosed as perianal sepsis and perianal sepsis may complicate anal cancer.
Although perianal sepsis is common in healthy individuals, there are other conditions that are strongly associated.
The classic associations are Crohn's disease, diabetes mellitus (important for increased incidence of perianal sepsis and higher risk of developing extensive tissue destruction and uncontrolled sepsis), anal fistulae (providing a passage for infection to pass from gut lumen to perianal tissue), steroid use and immunodeficiency.
The history taking for patients presenting with symptoms of perianal sepsis should include screening questions for these conditions or their associated symptoms.
Perianal abscesses are classified according to the location of the abscess cavity and relationship to the internal sphincter.
The locations listed in order of decreasing frequency are: perianal 60 per cent, ischiorectal 20 per cent, intersphincteric 5 per cent, supralevator 4 per cent and submucosal 1 per cent.3
Section 2: Making the diagnosis
Patients presenting with perianal sepsis will fall into two groups; those with draining sepsis and those with contained infection.
Those that have contained infection will complain of increasing pain around the anus, rectum and buttock. Depending upon the exact location of the abscess, pain may be worse on sitting and prior to defecation.
The duration of symptoms is variable but at first presentation the history is usually no more than a few days.
Pain is commonly accompanied by systemic upset in the form of fevers and sweats. On examination, it is common to find an area of fluctuance near to the anal verge. Suprasphincteric abscesses may present with a similar history but examination of the perineum may be normal. In this situation an area of fluctuance and tenderness may be found on digital rectal examination.
Patients with draining sepsis may give the history described above, but in addition they will describe an offensive discharge found on their underwear or toilet paper. Patients note that the onset of this discharge was associated with moderate relief of the pain.
On examination, if the abscess cavity is discharging onto the perianal skin, a point of discharge may be identified. For intersphincteric abscesses the point of discharge is often in the anal canal.
In this situation, pus may be expressed from the anal verge by palpation of the surrounding skin or gentle digital rectal examination.
In the immunocompromised patient perianal abscesses may herald the beginning of a more widespread infection, which may be complicated by necrotizing fasciitis or sepsis.
These patients may have extensive skin changes and display signs of systemic illness.
At presentation or at the time of drainage a pus swab should be sent for culture. The presence of bowel flora in the pus is useful in suggesting an underlying fistula.
In the acute phase, most patients undergo incision and drainage of the abscess. This is usually done without prior imaging and the only blood tests performed are to assess for anaesthetic risk or signs of systemic infection.
In more chronic perianal sepsis imaging is the key to defining the anatomy of the abscess cavity and its relationship to the anal sphincters.
Due to the bony nature of the pelvis, MRI is the modality of choice4 and is used widely in this complex patient group.
Section 3: Managing the condition
All perianal abscesses require prompt referral to surgery for assessment and probable incision and drainage under general anaesthesia. This also provides the opportunity to perform a thorough rectal examination and in some cases a rigid sigmoidoscopy to assess for the presence of causative anal fistulae.
At this time, the abscess cavity is incised and commonly packed. If a fistula tract is found the surgeon may elect to site a loose seton stitch or perform a fistulotomy (laying open of the fistula). The follow-up management of this wound commonly falls to practice or community nurses.
There is little role for antibiotics in managing perianal sepsis as the penetration of the antibiotic into the abscess cavity is poor. Early surgical management reduces the risk of fistula formation,5 or for those with existing fistulae, the development of more complex fistulous tracts.
Inflammatory sinus tract
MRI scan: presacral collection
Chronic anal sepsis
Chronic anal sepsis is commonly managed under the joint care of the GP and a colorectal surgeon. The key to this is in defining local anatomy, allowing ongoing drainage of pus and, where possible, treating fistulae while preserving the integrity of the internal and external sphincters.
Where sphincters are at risk, fistulotomy may not be appropriate. In this situation a seton stitch is very useful. A seton is a surgical-grade cord that is passed through the fistula tract so that the cord creates a loop between the outside world and the fistula track. The cord provides a path for continuous draining of pus while it is healing, by preventing the exterior of the wound from closing over and trapping pus.
A seton is usually tied loosely for drainage, but may be applied with more tension and tightened periodically in an attempt to definitively remove low (internal opening is below the sphincter muscles) fistulae.
This is achieved by ischaemia in the tissue edges inside loops allowing the seton to slowly cut through and leave scarring behind the loop. This 'pulling out' of the fistula without surgery is a lengthy process (months) but may be very effective and is generally well tolerated by patients.
Setons must not be removed in the community without prior discussion with the responsible surgeon as this is likely to worsen the situation with regard to recurrent or ongoing sepsis.
For fistulae that are very high in the anal canal or for very extensive/complex sepsis, setons may not be effective. In these rare situations the only remaining option is the formation of a temporary defunctioning stoma.
During the treatment of both acute and chronic anal sepsis, tight control of diabetes mellitus and, where appropriate, the medical management of Crohn's disease is important.
Section 4: Prognosis
The follow-up regime is highly variable. Patients with uncomplicated presentations of perianal sepsis are likely to be seen once by a colorectal surgeon in the outpatient department.
This is an opportunity to review the microbiology results of the initial pus swabs and examine for a fistula.
For first presentations of uncomplicated perianal sepsis the outcome is good if the abscess is treated promptly.
However, approximately two thirds of patients with rectal abscesses treated by incision and drainage, or by spontaneous drainage, will develop a chronic anal fistula and sepsis.
There is a significant morbidity and socio-economic cost associated with the perianal wound left after incision and drainage and/or fistulotomy or seton treatment.
Patients who suffer chronic perianal sepsis are managed in the outpatient department wherever possible and treatments are generally well tolerated. Many of these patients are able to return to work and normal life alongside managing this chronic condition.
Predicting recurrence requires thorough assessment of the risk factors and strict management where possible.
Section 5: Case study
A 26-year-old man presented with a short history of perianal pain. He had also noticed a 'lump' at the anal verge. He reported yellowish, offensive fluid passing peranus immediately after defecation.
His GP had asked him about any personal or family history of diabetes mellitus or Crohn's disease, which the patient denied. He does not take any regular medication and has not used any illicit drugs, including anabolic steroids.
He divulged that his bowel habit has always been frequent, but is now up to 5-6 times per day. He denied any blood in his stool but admitted to some lower abdominal pain that was eased by opening his bowels.
He also mentioned that he had experienced similar symptoms a number of times over the past four years but never as severe as this. His BMI was 20 but the GP noted that the last time his BMI was recorded in the surgery it was 24.1.
On examination he had a fluctuant mass on the anal verge. This mass was exquisitely tender and pus was noted around the anus.
Referral to surgery
His GP referred him to the acute surgical service for an incision and drainage under general anaesthesia.
A 2cm incision was made over the area of maximum fluctuance and the resulting cavity was loosely filled with an alginate pack. While under anaesthetic, a rigid sigmoidoscopy was performed. The rectal mucosa was noted to be inflamed and biopsies were taken. A fistula opening in the anal canal was noted and a loose seton sited.
He was discharged on the same day with an appointment to see his practice nurse the following day and adequate analgesia. He was also given a follow-up outpatient appointment with a colorectal surgeon.
Six weeks later at the outpatient appointment, he reported that the abscess cavity had healed and that he was well.
He tolerated the seton well and the daily discharge that he initially suffered had ceased. The swabs taken at the time of his drainage procedure grew bowel organisms (a finding supportive of the presence of a fistula) and histology of rectal biopsies showed granulomatous change consistent with Crohn's disease.
The diagnosis of Crohn's disease was discussed at length. The association between Crohn's disease, anal fistulae and abscesses was also discussed.
It was decided to convert the seton to a cutting seton. A follow-up appointment was made with the surgeon and the patient was referred for a colonoscopy and to gastroenterology for discussion of management of Crohn's disease.
Section 6: Evidence base
- Guidi L, Ratto C, Semeraro S, et al. Combined therapy with infliximab and seton drainage for perianal fistulizing Crohn's disease with anal endosonographic monitoring: a single-centre experience. Tech Coloproctol 2008; 12(2): 111-7.
This methodologically sound, prospective study has provided strong evidence for the benefit of combined use of setons and infliximab in the management of perianal sepsis in Crohn's disease.
This avoids the previous problem of healing of skin prior to obliteration of fistulous tract.
- Joyce M, Veniero JC, Kiran RP. Magnetic resonance imaging in the management of anal fistula and anorectal sepsis. Clin Colon Rectal Surg 2008; 21(3): 213-9.
Expert opinion and literature review of the role of MRI in the management of perianal sepsis.
- Malik AI, Nelson RL. Surgical management of anal fistulae: a systematic review. Colorectal Dis 2008; 10(5): 420-30.
This systematic review has integrated the evidence on the newer approaches to fistula management that have yet to reach common practice in this country. Flap repair combined with fibrin glue treatment of fistulae may increase failure rates. Radiofrequency fistulotomy produces less pain and may allow for speedier healing.
- Malik AI, Nelson RL, Tou S. Incision and drainage of perianal abscess with or without treatment of anal fistula. Cochrane Database Syst Rev 2010; 7: CD006827.
This systematic review provides evidence that fistula surgery with abscess drainage significantly reduces recurrence or persistence of abscess/fistula or the need for repeat surgery.
- The British Society of Gastroenterology guidelines on the management of inflammatory bowel diseases includes guidance on the medical management of fistulating perianal Crohn's disease. www.bsg.org.uk/pdf_word_docs/ibd.pdf
- Phillips RKS. Colorectal surgery: a companion to specialist surgical practice 2009. Saunders WB.
The RCGP covers this topic in statement 15.2 of the RCGP curriculum, Digestive problems
- Patient UK. Anorectal abscess www.patient.co.uk/doctor/Ano-rectal-Abscess.htm Information and advice for doctors.
- NHS Clinical Knowledge Summaries www.cks.nhs.uk/patient_information_leaflet/anal_fistula A well-structured and understandable patient information leaflet. www.cks.nhs.uk/crohns_disease/management/scenario_suspected_crohns_disease/suspecting_crohns_disease Key reading to develop understanding of when to suspect Crohn's disease and how to make the diagnosis.
1. Isbister WH. A simple method for the management of anorectal abscess. Aust N Z J Surg 1987; 57(10): 771-4.
2. Ramanujam PS, Prasad ML, Abcarian H, et al. Perianal abscesses and fistulas. A study of 1023 patients. Dis Colon Rectum 1984; 27(9): 593-7.
3. Nelson R. Anorectal abscess fistula: what do we know? Surg Clin North Am 2002; 82(6): 1139-51, v-vi.
4. Joyce M, Veniero JC, Kiran RP. Magnetic resonance imaging in the management of anal fistula and anorectal sepsis. Clin Colon Rectal Surg 2008; 21(3): 213-9.
5. Hamadani A, Haigh PI, Liu IL, et al. Who is at risk for developing chronic anal fistula or recurrent anal sepsis after initial perianal abscess? Dis Colon Rectum 2009; 52(2): 217-21.
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