Diagnosis. When a patient complains of anal pain, and the examination does not reveal a fissure or a thrombosed hemorrhoid, the cause is most likely an anorectal abscess. The perianal area should be carefully inspected and palpated. A perianal abscess is usually obvious: a tender, indurated lump located at or just distal to the anal verge. Only advanced abscesses are fluctuant, and pain may precede the development of induration. If pressure over the skin surrounding the anus or the buttocks does not elicit pain or reveal induration, a gentle digital anal examination is required. Because virtually all anorectal abscesses are cryptoglandular in origin, palpation of the anal canal should reveal tenderness and (usually) induration caused by the infection harbored in the anal crypt.
In rare circumstances, the infectious process will extend upward toward the pelvis. This can be detected by tenderness and induration in the rectal wall overlying the "high" abscess.
If the suspected abscess cannot be confirmed by physical examination, including a careful digital rectal examination, a CT scan may be required. However, we obtain CT scans for this condition only rarely. The diagnosis can be accurately made by physical examination in more than 95% of patients with anorectal abscesses.2
Treatment. The only appropriate treatment of an anorectal abscess is incision and drainage. Cryptoglandular abscesses do not resolve with antibiotic treatment. In general, reserve antibiotics for immunocompromised patients and for those who have significant cellulitis associated with the abscess.
Although it is possible to accomplish incision and drainage in the office, the procedure is uncomfortable for the patient and adequate exposure is difficult to achieve in this setting. In addition, if the crypt containing the gland from which the infection arose ("the offending crypt") can be detected, the crypt and gland can be eradicated at the same time that the abscess is drained; this significantly reduces the likelihood of fistula formation. For these reasons, we treat anorectal abscesses in the controlled environment of the operating room.
Some surgeons use a local anesthetic, but we prefer either a general or spinal anesthetic. Injecting the tender, inflamed tissue associated with the abscess is extremely uncomfortable for the patient. In addition, it is very difficult to achieve sufficient relaxation with a local anesthetic to permit an adequate examination. In fact, infiltrating the anal tissues with a local anesthetic causes edema that makes it more difficult to find the source of the abscess.
After adequate anesthesia has been achieved, the patient is placed in the prone flexed position and careful examination with an anoscope is performed. Pressure placed over the abscess may produce pus from the crypt containing the infected gland. A crypt hook is inserted in the abscess, and an incision with electrocautery over the crypt hook results in division of skin and a portion of internal sphincter and allows unroofing of the abscess. The opening over the abscess is further enlarged by excising a 1-cm disk of skin to allow adequate drainage of the pus. We do not pack the cavity with gauze, nor do we use drains. If the crypt of origin is detected and the abscess drained as described (this is actually a fistulotomy), the risk of recurrent infection is less than 5%.3
If the offending crypt cannot be detected, the abscess is drained by making a cruciate incision over the abscess as close to the anal verge as possible. The edges of the incision are then excised to create an opening of about 1 cm in diameter. This procedure effects a cure in about 50% of patients.3
In half of the patients treated only by incision and drainage, a chronic fistula forms. The internal opening to the fistula is the crypt containing the chronically infected anal gland, and the external opening is the site where the incision was made to drain the abscess. For this reason, we place the incision as close to the anal verge as possible so that a fistula that may later form will be as short as possible.
While fissures, thrombosed hemorrhoids, and anorectal abscesses account for the vast majority of cases of anal pain, keep in mind that other, less common causes may be responsible, particularly in immunocompromised patients.
Herpes. Anorectal herpes simplex lesions can be quite painful. The diagnosis can be difficult initially because severe pain may precede the appearance of the typical clustered vesicles surrounded by a red areola. The lesions can occur on the rectal mucosa, anoderm, and perianal skin. The diagnosis is confirmed by viral culture of fluid from a vesicle. Remind your patient that these lesions are highly infectious. Oral acyclovir or valacyclovir shortens the duration of symptoms and reduces the frequency of episodes.4 Recurrence is, of course, the rule.
Syphilis. Multiple fissures or soft, symmetrical lateral fissures point to a diagnosis of syphilis. These lesions, which can be quite painful, often resemble poured wax after it has cooled. The characteristic appearance coupled with a positive rapid plasma reagin test are sufficient to make the diagnosis. If the diagnosis is still in question, obtain serum from the base of the lesion and order a fluorescent treponemal antibody-absorption test. The mainstay of treatment for syphilis continues to be long-acting penicillin preparations.
Infectious proctitis. An intense proctitis may result from infection with Chlamydia trachomatis or Neisseria gonorrhoeae, which can lead to anorectal pain and tenesmus. Send swab samples for gonococcal culture; negative results suggest chla- mydial infection. Rising titers of antibody to C trachomatis may help pin down the diagnosis. Doxycycline(Drug information on doxycycline) can be used to treat chlamydial infections; however, gonococcal infections require consultation with local health officials because of widespread antibiotic resistance.
• In men and most women, anal fissures occur very close to the posterior midline of the anal canal. Fissures that are not close to the midline suggest other processes that could result in anal or perianal ulceration, such as Crohn disease, syphilis, herpes, and carcinoma.
• Most fissures heal with conservative treatment, including stool softeners, warm sitz baths, and topical smooth muscle relaxants. If the fissure does not heal or if the pain does not diminish substantially over 2 to 3 weeks, a more aggressive approach is justified; internal anal sphincterotomy is nearly always curative.
• The pain of a thrombosed hemorrhoid is usually most severe during the first 24 to 48 hours after the clot forms, and then it resolves rapidly. If the patient continues to have severe pain—despite conservative treatment with topical corticosteroids, warm soaks, and stool softeners—excision is recommended.
• A perianal abscess is usually obvious: a tender, indurated lump located at or just distal to the anal verge. Only advanced abscesses are fluctuant, and pain may precede the development of induration.
• The only appropriate treatment of an anorectal abscess is incision and drainage. Reserve antibiotics for immunocompromised patients and for those who have significant cellulitis associated with the abscess.