Perianal abscesses make up 34.5–58.4 % percent of anorectal abscesses in several series [6, 7, 11, 12, 15].

Their symptoms are along the spectrum of fever, perianal pain, fluctuance, or spontaneous drainage of abscess [3, 10, 13, 16, 17].

Physical examination may reveal tenderness, erythema, induration, and/or fluctuance. Typically no further tests are needed for diagnosis. However, for patients where physical examination does not reveal an obvious abscess, endoanal ultrasound (EUS) can be used as an adjunct in the office setting.

The treatment of perianal abscesses is incision and drainage. The area of maximal pain or fluctuance is identified, local anesthesia is injected (1 % lidocaine with epinephrine 1:200,000 or 0.25 % Marcaine with epinephrine 1:200,000), a cruciate incision is made, and purulence is expressed. Figure 4.2 demonstrates the location and appropriate drainage technique of a perianal abscess. Tonkin et al. demonstrated that it was safe and effective to not pack wounds after incision and drainage by showing similar rates (p >0.2) of recurrence, fistulas, healing times, and pain scores at the first dressing change [2]. These results were verified by Perera et al. who showed that the non-packing group had a faster healing time with less pain while having similar recurrence rates [5]. Therefore, no packing is required unless necessary for hemostasis.

Incidence of ischiorectal abscesses has been reported as 22–33.9 % in several studies [6, 7, 11, 12].

Their symptoms are similar to those for perianal abscess and fall along the same spectrum of fever, perianal pain, fluctuance, or spontaneous purulent drainage [3, 8, 10, 13].

Physical examination may reveal tenderness, erythema, induration, and/or fluctuance. Typically no further tests are needed for diagnosis.

Ischiorectal abscesses can be drained in a similar fashion to perianal abscesses. However, it is important to note that the incision should be made as close as possible to the anal verge to shorten the potential fistula tract. Large ischiorectal or horseshoe abscesses are best drained under spinal or general anesthesia [15, 16]. In addition, if the abscess cavity is large, it is necessary to break up loculations to achieve adequate drainage [16, 17]. However, one is cautioned to avoid causing sphincter injury with aggressive disruption of loculations [18]. Figure 4.3 demonstrates the location and proper drainage technique for ischiorectal abscesses.

Alternatively, catheter drainage can be used instead of incision and drainage in stable patients without signs of sepsis. Local anesthetic of choice is injected at the area of maximal fluctuance and the surrounding skin. A stab incision is made as close as possible to the anal verge to minimize potential fistula length and complexity. The pus is evacuated and a 10–16 French mushroom catheter is placed in the incision. If the incision and mushroom catheter are sized appropriately, no sutures are needed. The mushroom catheter is trimmed to 2–3 cm from the skin to avoid making the external portion too short so it will not fall into the wound. The catheter is left in place until the drainage decreases to an acceptable level [8].

Intersphincteric abscesses represent 23–47 % of anorectal abscesses in several large series [1, 6, 7, 10].

Patients typically present with pain without external signs of infection [3, 8].

In a patient with no external signs of infection but with pain, an intersphincteric abscess should be suspected and an examination under anesthesia undertaken. Because of increased patient pain and lack of diagnostic information at the bedside, it would be inappropriate to proceed with further invasive testing in this setting [3, 8].

Exam under anesthesia is mandated for intersphincteric abscesses secondary to the lack of physical examination findings and the pain out of proportion to examination when evaluating the patient at the bedside. Under anesthesia, a digital rectal examination frequently reveals an area of fullness. The area of fluctuance in the intersphincteric plane should be opened with a knife. The internal sphincter muscle must be opened enough to express the pus in the intersphincteric space. The wound can then be marsupialized for better healing and to keep the tract open. A low intersphincteric abscess can typically be treated with drainage, division of the internal sphincter, and marsupialization. High intersphincteric abscesses, although uncommon, typically require placement of a mushroom catheter for adequate drainage [19]. Figure 4.4 demonstrates the anatomic location and proper drainage technique of an intersphincteric abscess.

Supralevator abscesses have been estimated to represent 9–42 % of abscesses in the literature [6, 12].

Patients typically present with perianal pain, pelvic pain, rectal bleeding, ileus, and/or urinary retention [3, 8, 12].

Supralevator abscesses can arise from ischiorectal or intersphincteric abscesses extending upward or from pelvic abscesses secondary to diverticulitis, appendicitis, or tubo-ovarian abscess draining downward. Because of the varied treatment based on origin of infection, supralevator abscesses are often evaluated with imaging (CT or MRI) [8, 20].

If the abscess is arising from an ischiorectal abscess, it can be drained through the perianal skin. However, if it is arising from an intersphincteric abscess, it should be drained through the internal sphincter and into the rectum to avoid the creation of a suprasphincteric fistula. If the abscess arises in the pelvis, it can be drained through the rectum, through the perianal skin, or percutaneously under imaging guidance depending on the size and position of the abscess [8]. In addition, if the abscess is associated with perforated viscus or inflammatory condition, the abscess should be treated according to treatment principles for these conditions and may require operative intervention [21]. Figure 4.5 demonstrates the location and proper drainage technique for supralevator abscesses arising from either an ischiorectal abscess or an intra-abdominal process.

The deep postanal space is the potential space between the external sphincter complex anteriorly, the coccyx and anococcygeal ligament inferiorly and posteriorly, and the levator plates superiorly. Purulent material can track to this space, and when it extends laterally into the ischioanal fossa, the abscess is termed a horseshoe abscess [22].

Patients typically present with perianal pain, pelvic pain, rectal bleeding, and/or urinary retention [3, 8, 12].

Physical examination typically reveals tenderness, erythema, induration, and/or fluctuance. In addition, patients will typically have pain and/or fullness palpated on digital rectal examination. Tan et al. showed that preoperative MRI is sensitive in detecting fistula tracts and horseshoe fistulas (100 % sensitivity and specificity). Additionally, ultrasound has been shown to aid in identifying fistulas causing horseshoe abscesses [23]. Ratto et al. showed that hydrogen peroxide-enhanced ultrasound increased the accuracy of detecting horseshoe fistulas from 81 to 92 % [24].

Multiple approaches have been described to treat the complicated deep postanal space abscess (Fig. 4.6). The most invasive procedure is the Hanley procedure in which a midline incision is made between the anus and the coccyx and the external sphincter is spread. The lower half of the internal sphincter muscle is divided to facilitate drainage. Counter incisions are then made over each ischioanal fossa [25, 26]. Inceoglu and Gencosmanoglu showed complete healing in 12 ± 3 weeks, no recurrence in a median follow-up period of 35 months, and no morbidity of mortality [25]. A modified Hanley procedure has been described using setons and drains to avoid cutting the sphincter muscle [15, 16]. Leventoglu et al. showed complete healing in 8 weeks in all of their 21 patients with one recurrence noted after a mean follow-up of 20 months. In addition, they reported no change from the preoperative Cleveland Clinic incontinence score [16]. Tan et al. showed that patients whose internal opening was identified at the initial operation and who had a seton successfully placed had fewer operations and shorter interval to final operation (median 5 vs. 14 months) [22]. Alternatively, Tan et al. describe a one-stage intersphincteric approach, which involves draining the abscess, removing the septic source, and ligating the intersphincteric fistula tract without division of the sphincter muscles. They showed an overall success rate of 70.6 % at 8 months, and the failures were treated with advancement flaps [27].