The anatomy of the anal region is shown in figure 1. Abscesses around the anal canal arise from infection of the anal crypt of Morgagni (figure 2) and can be either superficial perianal abscesses (80%) or deeper ischiorectal abscesses (20%) (figure 3). A perianal abscess is found adjacent to the anal canal, either on the right or left side, anterior or posterior. The patient usually complains of pain that may be, but not always, associated with a fever. The diagnosis is made by inspection of the perianal area, which will reveal a red, angry, and often fluctuant abscess. A digital examination should not be done due to the painful nature of the problem. Figure 3 shows the location of perianal and perirectal abscesses. Abscesses are classified according to the spaces they invade. Most superficial perianal abscesses can be drained safely in the office and do not require operative drainage. The most difficult to treat are those that track proximally or circumferentially within the intersphincteric plane or within the ischiorectal fossa or postanal space. Examination under anesthesia may be required to determine the location and extent of the abscess. An ischiorectal abscess, however, is large, involves either the right or the left ischiorectal space or the deep postanal space, and requires operative drainage.
For office drainage, the patient should be placed in the standard kneeling position on a Ritter table. For operative drainage, a prone, jackknife position is best. If done in the operating room, a general or spinal anesthetic is desirable.
For a perianal abscess, the skin over the abscess is numbed with ethylene chloride. Injection of the site with Xylocaine is excessively painful and unnecessary. Once the area is sufficiently numbed, a stab incision is made over the abscess to drain pus. This should be sufficiently large to allow adequate drainage. There is no need to excessively probe this abscess. The incision should be made as close to the anal canal as possible so that if a fistula-in-ano does develop, the fistula tract will be as short as possible.
A. OPERATIVE DRAINAGE OF ISCHIORECTAL ABSCESS
Ischiorectal abscesses are drained immediately. Careful palpation often shows evidence of fluctuation not seen in the perianal tissue. Operation is not delayed until fluctuation is obvious, because a perirectal abscess may rupture through the levator muscle into the retroperitoneal tissue.
No special preoperative preparation is required. Antibiotic therapy is given.
General anesthesia with endotracheal intubation may be used; however, regional anesthesia, either spinal or epidural, is satisfactory.
The prone or jackknife position is preferred for drainage.