Anorectal abscesses are classified according to the location of the abscess cavity. In order of decreasing frequency they are perianal, ischiorectal, intersphincteric (also called submucosal), and supralevator (Nelson 2002). One or more spaces can be involved by a given suppurative process at a time. For example, an intersphincteric abscess can extend to involve the supralevator space. From intersphincteric, supralevator, or ischiorectal space, pus can extend circumferentially to the opposite side via the deep postanal space resulting in what is called a horseshoe abscess. These abscesses can also extend to the scrotum and may cause Fournier’s gangrene; extend to the labia and can get diagnosed as Bartholin’s abscess; can extend to the thigh, calf, and abdominal wall; and lead to necrotizing fasciitis (Fig. 5.2).

Many different classifications were given for fistula-in-ano; however, the most useful classification is the one described by Parks et al. in 1976 (Fig. 5.3). Parks classified fistula-in-ano on the basis of course taken by main tract in relation to the anal sphincters, i.e., intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric. These groups can be further subclassified on the basis of secondary tracts and other finer anatomical details (Parks et al. 1976). The Park’s classification is not complete and in fact may not be accurate in some instances, e.g., the suprasphincteric classification as described by Park’s does not represent the natural spread of the disease. All supralevator extensions are actually upward extensions of an intersphincteric, tract, and the only other way the supralevator space can be reached is via an iatrogenic route.

Fistulas can also be classified as simple or complex. Complex fistula includes recurrent fistula, fistula with multiple tracts, anterior fistula in females, high fistulas, and fistula with extension to adjacent organs (Fig. 5.4a–c).

Patients with anorectal abscess can present in two ways, either as a draining sepsis or as contained infection. Patients with contained infection present with indolent onset of increasing pain around the anus, rectum, or buttocks. Later on, there can be severe, non-relieving, constant, throbbing pain with pressure sensation. Pain is commonly associated with systemic symptoms like fever and sweating. Patients with draining anorectal abscess also present with complaints of offensive discharge on their undergarments or on toilet paper, along with the history described above. Onset of discharge is associated with relief of pain.

On examination, findings vary according to anatomic location of anorectal abscess. Examination under anesthesia may be required in some cases. Perianal and ischiorectal abscess will have erythema, swelling, tenderness, and fluctuation over their respective sites. Intersphincteric or submucous abscess may not have any visible external manifestation despite patient’s complaint of severe excruciating anal pain. Digital rectal examination may not be possible because of severe tenderness. However, digital examination, if possible, will demonstrate tender fluctuant mass in these cases. Evaluation under anesthesia or MRI maybe required in cases where digital rectal examination is not possible or the diagnosis is in doubt. Supralevator abscess represents upward extension of intersphincteric abscess.

A fistula-in-ano represents the chronic phase of ongoing anorectal sepsis. A previous history of anorectal abscess drained either spontaneously or surgically can usually be elicited. Patients often report a cyclical pattern of pain, swelling, and drainage. Moisture can cause skin irritation, excoriation, and pruritus. Crohn’s disease should be excluded in patients with history of chronic diarrhea or abdominal pain.

Physical examination usually identifies one or more external openings with or without granulation tissue and a surrounding scar. Occasionally, the external opening may be subtle and appreciated only after closer inspection of an indurated area. Uncommonly, the patient may present during the phase where the external opening has temporarily closed. Palpation may elicit tenderness, expression of pus, and a fibrotic cord extending toward the anus. The external tracts are usually not felt during its entire course, unless it is a very low fistula. Several external openings may be present because of branching complex fistulous tracts, a condition called as watering-can perineum. It is generally not recommended to do probing of the fistula track in the office setting, but digital anorectal examination, anoscopy, and proctoscopy may help discover the internal opening (Fig. 5.4b) and the presence of any other rectal disease. The internal opening is often seen at the dentate line which is consistent with cryptoglandular theory of anorectal sepsis. An enlarged papilla is often present at the site of the internal opening. Most common site for internal opening is posterior midline as most anal glands are located posteriorly. The intersphincteric tract may be felt as a submucosal induration on digital rectal examination.

In 1900, Goodsall described a simple rule that uses the location of the external fistula opening to predict the location of the internal opening. Fistulas with external openings anterior to the anterior half of the anus, usually track in a radial fashion directly into the anal canal (Fig. 5.5). Fistulas with an external opening in the posterior half of the anus usually track in a curvilinear fashion to originate from the posterior midline. Exception to this rule includes multiple external openings, and external opening which is present anteriorly, more than 3 cm. from the anal verge. In most of these cases, the internal opening will be in the midline posteriorly.

Ciroco and Reilly found that Goodsall’s rule was inaccurate in patients with anterior external opening because almost 71 % of these fistulas have internal opening in midline anteriorly (Cirocco 1992). The Goodsall’s rule also fails in cases of fistula with associated carcinoma or Crohn’s disease (Fazio 1987). The Goodsall’s rule is not accurate in a fair number of patients and cannot be relied upon in all the cases.

Perianal abscess is a surgical emergency and should be treated by urgent incision and drainage (Whiteford 2005). Depending on the condition of the patient and location of the abscess, drainage can be done either as an outpatient procedure or may be done under anesthesia in an operating room. Conditions such as cellulitis without fluctuation, failed drainage in the office, abscesses with symptoms and signs of sepsis, or extensive abscesses with supralevator extension are more appropriately treated in the operating room, where a thorough examination under anesthesia can ensure optimal diagnostic evaluation and drainage. Although incision and drainage is effective in resolving the acute abscess, the patient is at risk for developing chronic anal fistula or recurrent perianal sepsis or both. These conditions occur in 35–50 % of patients after a first-time perianal abscess (Hamadani et al. 2009). Gender, smoking history, perioperative administration of antibiotics, and HIV status are not risk factors for fistula formation or recurrence of perianal sepsis (Hamadani et al. 2009). The drainage should be done as close to the anus as possible in order to shorten the length of any subsequent fistulous tract. Mechanical disruption of loculi around abscess cavity may cause injury to sphincter complex or the pudendal nerve and hence should be done carefully in order to ensure adequate drainage of all pus. Routine addition of antibiotics has not been shown to improve healing time or reduce recurrence rate (Llera and Levy 1985; Stewart et al. 1985; Macfie and Harvey 1977). Antibiotics should be considered for patients with high-risk conditions such as diabetes, immunosuppression, extensive cellulitis, prosthetic devices, and valvular heart diseases (Whiteford 2005; Dajani et al. 1997). After successful drainage, pain relief is usually immediate. Postoperatively, patients are advised to use sitz bath, laxatives, and analgesics. Bleeding and drainage usually subside within a few days. The wound heals over a matter of few weeks. Follow-up is encouraged because acute abscesses occur in 10 % and of chronic fistula-in-ano occurs in up to 50 % of patients (Vasilevsky and Gordon 1984).

The patient is placed in the prone jackknife, left lateral, or in lithotomy position, and the area surrounding the abscess cavity is adequately painted and draped. Patient may be given general anesthesia or perianal field block as per location of abscess. A stab incision is made with an 11 or 15 number blade at the point of maximum fluctuation in closest proximity to the anal verge. Larger cavities may require digital or hemostat-assisted exploration to break up any undrained abscesses. In addition to adequate drainage, one should endeavor to prevent acute recurrence of an abscess by either excising the overlying skin or by inserting drainage catheter. Either of these techniques will allow any undrained pus to be expelled and decrease the chance of acute recurrences (Isbister 1987; Read and Abcarian 1979). The patient is advised pain medications and a follow-up appointment in 1–2 weeks at which point the drainage catheter is removed. Antibiotics are prescribed if indicated.

Intersphincteric, supralevator, and deep postanal abscesses are best treated in the operating room where a thorough exam can be performed. For intersphincteric abscesses, the internal sphincter is divided from its lower end to the dentate line and hemostasis is achieved. If a supralevator abscess is a result of upward extension of an intersphincteric abscess, the abscess should be drained directly into the rectum (Fig. 5.11). However, if it is a result of an ischioanal abscess, it should be drained via the ischioanal fossa (Figs. 5.12 and 5.13). Supralevator abscesses that are caused from extrapelvic diseases such as Crohn’s, diverticulitis, or appendicular abscesses may be initially drained via the rectum or the ischioanal fossa. However, pathology of the offending organ must be addressed (Gordon and Nivatvongs 1999).

The horseshoe abscess is caused by an infected anal gland located in the posterior midline of the anal canal. The presence of the dense overlying anococcygeal ligament prevents the direct downward expression of an abscess. As a result, the suppuration follows the path of least resistance laterally into ischiorectal fossa, hence the term “horseshoe” (Fig. 5.14). Treatment requires unroofing of the abscess cavity through the overlying anococcygeal ligament along with counter drainage of the lateral extensions. Placement of a draining (loose) seton may prevent premature skin closure, avoid an acute abscess recurrence by providing a route of egress for the infection, and facilitate fibrosis of the fistula tract.

Fistulotomy performed at the same sitting as incision and drainage of a perirectal abscess is termed a “primary” or “synchronous” fistulotomy. Doing a primary fistula surgery along with drainage of the anorectal abscess has been a matter of much debate. The fear of causing incontinence and the fact that more than half of all drained abscesses may develop a fistula have resulted in condemning a primary surgery for an anorectal abscess. However, a recent systematic review comparing outcome after primary fistula surgery done along with drainage of perianal abscess, compared with drainage alone, showed that fistula surgery with abscess drainage significantly reduced recurrence or persistence of abscess/fistula or the need for repeat surgery (Malik et al. 2010). Statistically, there was no significant evidence of incontinence following fistula surgery with abscess drainage. This intervention may be recommended in carefully selected patients. Another meta-analysis comparing the two procedures concluded that there was no conclusive evidence if simple drainage or sphincter-cutting procedure is better in the treatment of anorectal abscess–fistula (Quah et al. 2006). A long-term follow-up seems not to influence the results of fistulotomy group and confirms that fistulotomy is an efficient and safe treatment of anal abscess with good long-term results (Benjelloum et al. 2013). An exception is a high fistula, where fistulotomy may be associated with a risk of recurrence and incontinence.

Surgery is the preferred modality of treatment for patients with in ano. With delay in treatment, a simple fistula can progress to chronic abscess or to a complex fistula and hence the need for timely intervention. There has been no consensus on surgical options for treating it. The existing options have not yielded satisfying results, hence the need to discover new options. Recurrence and incontinence are the two major paradoxical factors which a surgeon fears and drives him/her to tilt on one side or the other. Surgery for fistula can be performed under general, regional, or local anesthesia with sedation. Patient is placed either in lithotomy or prone jackknife position, depending on patient characteristic, location and extent of fistula, and the surgeon’s preference.