Description of the condition
A perianal abscess is a collection of pus under the skin around the anus. Most perianal abscesses result from an infection in the anal glands (cryptoglandular infection), which can then spread via several different routes. The most common spread of infection is a downward extension to the perianal skin forming a perianal abscess (Parks 1961). Alternatively infection may spread alongside the rectum (ischiorectal), upwards above the muscles of the pelvic floor (supralevator), or between the muscles of the anal canal (intersphincteric) (Parks 1976). Extension across the midline of the body results in a horseshoe abscess. The cause of cryptoglandular infection is unique to perianal abscesses and therefore makes this condition pathologically distinct from abscesses in other locations. Approximately 10% of perianal abscesses are not caused by infected anal glands and result from conditions such as: skin appendage infection; Crohn’s disease; tuberculosis; trauma; chronic inflammation and infection of sweat glands (hidradenitis suppuritiva); human immunodeficiency virus (HIV) infection; sexually transmitted diseases; radiation therapy; malignancy or foreign bodies (Eisenhammer 1978; Goligher 1975; Hamadani 2009; Nelson 1985; Phillips 1997; Sangwan 1996; Whiteford 2007).
In the UK, the annual incidence of perianal abscess is 40 per 100,000 of the adult population, and acute perianal abscess is the seventh most common emergency condition in general surgery (www.hesonline.gov.uk). During 2012 to 2013, perianal abscesses resulted in 20,451 hospital episodes in England (diagnosis codes; anal abscess, anorectal abscess, ischiorectal abscess, intersphincteric abscess) (www.hesonline.gov.uk). This represents 3.4% (20,451 out of 605,107) of all general surgery emergency hospital episodes, and equates to 1.1% (20,451 out of 1,823,749) of total general surgery hospital episodes. The acute and on-going management of perianal abscess cavities accounts for significant hospital and community resource utilisation in England and probably elsewhere, although we have been unable to locate equivalent non-UK data to support this.
Depending on the exact anatomical location, perianal abscesses usually result in pain, swelling and redness of the anal area. Other symptoms may include fever and malaise. Over time, abscesses increase in size and, if untreated, will usually burst, which may or may not result in adequate drainage of the pus. It is thought that if the pus is not adequately drained, the skin may close prematurely and the abscess could recur. More rarely, untreated abscesses can also result in severe whole body (systemic) infection or devastating, rapidly spreading tissue infection and gangrene (necrotising fasciitis), therefore, early surgical drainage of the abscess is recommended. In the UK, standard surgical drainage involves incising the skin over the abscess in order to drain all the pus and allow wound irrigation. Following drainage, an internal dressing is applied ('packed') to the resulting cavity for haemostasis. Common practice in the UK is to continue packing until the abscess cavity has healed without being sewn shut (by secondary intention). The pack is changed every day or every few days by community nursing teams.
Alternative strategies for managing the abscess cavity have been tried. In the USA and Australia, one variation in the technique for incision and drainage is to use a small stab incision and place a latex catheter (e.g. a 10-14F de Pezzer catheter) into the cavity (Beck 1988; Isbister 1987; Kyle 1990). This is done under local anaesthetic, unlike practice in the UK where a general anaesthetic is routinely used. The catheter is cut short and drains into an external dressing. It is removed when it stops draining. Even when a catheter is not used, in the USA simple drainage is often performed in an outpatient setting under local anaesthetic (Whiteford 2007).
Sewing up (curettage) of the abscess cavity with primary sutured closure was first described in 1960 (Ellis 1960). Primary closure with antibiotic treatment may result in reduced healing times, but the increased incidence of recurrent sepsis negates any benefit (Mortensen 1995). This technique of primary closure is no longer used.
Sitz baths (immersing the area in warm water) have been used for treating perianal abscess cavities following incision and drainage. These have been employed both with packing (Read 1979), and without packing (Tang 1996; Vasilevsky 1984). Although a review of the literature found no benefit for this practice, it makes logical sense to irrigate an infected wound (Tejirian 2005).
Perianal fistulae (fistulae-in-ano) are a complication of perianal abscesses. A fistula may occur if a perianal abscess drains spontaneously through the perianal skin and if the infection becomes chronic (Parks 1961). The fistula becomes a tract between the anal canal and the perianal skin that is lined with granulation tissue (present in healing wounds) or skin cells (epithelium). It intermittently discharges pus and may result in recurrent abscesses. Fistulae usually require surgical intervention. This can be at the initial draining of the abscess (Malik 2010), but usually is performed later. Up to a third of patients with a perianal abscess will develop a fistula (Hamadani 2009; Lohsiriwat 2010; Ramanujam 1984; Vasilevsky 1984).
Following incision and drainage, management of the remaining wound cavity becomes the primary clinical focus to ensure optimal wound closure and prevent recurrence. In the UK, anecdotally, it is common for the cavity to be dressed with an internal dressing (packed) and covered with an external dressing or pad. However, in some other countries use of an internal dressing (packing) is not routinely recommended (Ommer 2012). We propose a review that focuses on the impact of internal dressings (packing) in the healing of cavities resulting from the surgical drainage of perianal abscesses.
Description of the intervention
Several dressing types are available to manage perianal abscess cavities; we have summarised the key categories below. There are limited audit-type data available on the types of dressings that are used for packing cavities resulting from the drainage of perianal abscesses. Where packing is not used, the wound may just be covered with an external dressing that is not in contact with the cavity itself.
Basic wound contact dressings
Low-adherence dressings and wound contact materials: usually cotton pads that are placed directly in contact with the wound. These can be non-medicated (e.g. paraffin gauze dressing) or medicated (e.g. containing povidone iodine or chlorhexidine).
Absorbent dressings: applied directly to the wound or used as secondary absorbent layers in the management of heavily-exuding wounds.
Advanced wound dressings
Alginate dressings: highly absorbent dressings made of calcium alginate, or calcium sodium alginate, that may be combined with collagen. The alginate forms a gel when in contact with moisture; this gel can be lifted off when the dressing is removed or rinsed away with sterile saline. Bonding the alginate to a secondary viscose pad increases absorbency.
Foam dressings: normally these contain hydrophilic polyurethane foam and are designed to absorb wound exudate and maintain a moist wound environment. There are various versions, and some include additional absorbent materials, such as viscose and acrylate fibres or particles of superabsorbent polyacrylate, which are silicone-coated for non-traumatic removal.
Hydrocolloid dressings: these are occlusive dressings usually composed of a hydrocolloid matrix bonded onto a vapour-permeable film or foam backing. When in contact with the moisture at the wound surface this matrix forms a gel to provide a moist environment. Fibrous alternatives have been developed that resemble alginates and are not occlusive, but which are more absorbant than standard hydrocolloid dressings.
Capillary-action dressings: these consist of an absorbent core of hydrophilic fibres held between two low-adherent contact layers.
Odour-absorbent dressings: these dressings contain charcoal and are used to absorb wound odour. Often these types of wound dressings are used in conjunction with a secondary dressing to improve absorbency.
How the intervention might work
It is thought that use of an internal dressing (packing) aids haemostasis, that is control of bleeding from the small blood vessels that line the abscess cavity, as well promoting healing by secondary intention by preventing the wound edges from closing. It is thought that healing in this way prevents the recurrence of the abscess.
Why it is important to do this review
It is unclear whether packing (compared with not packing) of the cavity following drainage of a perianal abscess is advantageous in promoting healing and preventing adverse events including fistula, abscess recurrence and pain. Anedoctally, the use of packing as a treatment approach in this context varies internationally and there is limited guidance for practice (Ommer 2012; Steele 2011; Williams 2007). A German guideline that reported on the diagnosis and treatment of anal abscess stated that regular packing is not required (Ommer 2012), and cited one small trial to support this (Tonkin 2004).
Packing has implications for patients and healthcare services: regular changing of internal dressings (change of packing) requires a considerable amount of community nurse time and, anecdotally, is painful for patients. Additionally the associated healthcare appointments may require patients to take time off work. We believe a transparent and robust review is required to the benefits, harms and costs of packing (compared with not packing) post-operative perianal abscess cavities in order to identify, synthesise and report the current evidence base.