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Should we seek a fistula‐in‐ano when draining a perianal abscess?

2010; Wiley; Volume: 46; Issue: 5 Linguagem: Inglês

10.1111/j.1440-1754.2009.01694.x

1440-1754

Sebastian K. King,

Streptococcal Infections and Treatments

Perianal abscess formation is common in children, especially in the first year of life. It is generally considered a complication of infection of an anal gland, and typically produces a fistula-in-ano. Despite their frequency, both perianal abscess and fistula-in-ano are often inadequately managed, leading to high recurrence rates. The experience of Ezer et al.1 highlights the need for a clearer algorithm for the management of these related conditions. A perianal abscess develops initially as an infection within one of the glands that opens into the crypts of the anal valves. Despite an internal opening at the level of the anal valves, the abscess almost invariably 'points' superficially through the skin 1–2 cm from the anal verge.2 Technically, if the abscess spontaneously discharges through the skin and maintains its communication with the anal valves, there is a fistula-in-ano. However, a fistula-in-ano is not invariably demonstrated with a perianal abscess (20–85%).1, 3-7 This may be because of a number of factors, including blockage of the anal gland duct (which, in part, may be the reason the perianal abscess developed in the first place, and may contribute to difficulty cannulating it during surgery) or failure to look for a fistula-in-ano. Rosen et al.8 have described a non-operative approach to perianal abscesses, but found it produced a subsequent rate of fistula-in-ano formation of 77%. This result is not surprising, given what is known about the pathology of the condition. With a non-operative approach, the pus eventually discharges either externally through the skin or internally into the anal canal. The original cause remains, and in due course the abscess is likely to re-develop. Where drainage is external and persists, a fistula-in-ano exists. Similarly, incision and drainage alone, with the aim of relieving discomfort and preventing abscess extension, have a high recurrence rate. Incision and drainage of perianal abscesses have even been shown to increase the apparent rate of fistula-in-ano formation. Christison-Lagay et al.9 described a fistula-in-ano rate of 60% (50/83) following incision and drainage (further decreased by the use of synchronous antibiotics during initial drainage), while only 9/57 (16%) abscesses not drained developed a subsequent fistula-in-ano. A recurrence rate of 85%, as reported by Ezer et al., would suggest that the fistula-in-ano was either not looked for at the initial procedure, or not observed, meaning that the tract was not laid open1. Many clinicians will search for an associated fistula-in-ano while incising and draining the perianal abscess, on the basis that drainage alone is inadequate treatment.2 Fistulae-in-ano in infants are usually intersphincteric, which means that laying them open does not cause faecal incontinence.10 If identified, the entire fistulous tract may be laid open, and this will markedly decrease the risk of recurrence. For example, a recurrence rate of 12% in our experience (unpublished data) is considerably lower than the 85% recurrence rate for drainage alone reported in this issue by Ezer et al.1 The first step is to identify the internal (anal) opening. Skin compression over the abscess will often cause pus to extrude from the internal opening, thus revealing its exact location and facilitating cannulation with a fine lacrimal probe. If the probe is not introduced gently, it is possible to create a false passage, particularly when the probe is very fine. Incomplete laying open of the fistula-in-ano is more likely to lead to recurrence. If the fistula-in-ano cannot be probed via the anal opening, then it may be located through the abscess cavity. Once identified, with the lacrimal probe passed along the fistulous tract (Fig. 1), the fistula-in-ano is laid open by diathermy dissection down onto the probe. Once laid open, no dressing is required. The fistulous tract can be identified by introducing a fine lacrimal probe from its anal opening. The paper by Ezer et al. is important in that it confirms that incision and drainage of the perianal abscess, without identification of the fistula-in-ano, are often inadequate on their own and have a high recurrence rate. Until the fistulous tract is dealt with adequately, by laying it open, further infection is likely.