Anorectal complaints are a frequent reason for a surgical consultation. The four most common benign anorectal disorders are: perianal abscess, fistula-in-ano, anal fissures, and hemorrhoids. A perianal abscess is an infection that occurs when an anal crypt gland becomes obstructed and cannot drain freely into the anal canal. The gland’s infected products build up, resulting in a collection of pus in the soft tissues around the anus or rectum (Fig. 17.1). Patients typically present with pain and tenderness at the site and are often febrile.

In most cases an erythematous, indurated, fluctuant site is readily apparent in the perianal area. In certain cases, however, the abscess cavity is located higher within the anal canal and no findings will be seen on external inspection. For example, an intersphincteric abscess forms in the plane between the internal and external sphincters, and may only be appreciated on digital rectal exam as a tender bulge into the anal canal. A supralevator abscess is located even more proximally above the levator ani muscle. In this situation, a CT scan may be the necessary to diagnose the presence of an abscess (Fig. 17.2).

Treatment of a simple perianal abscess involves incision over the indurated area and drainage of the purulent material. A drain is left within the cavity to prevent the skin from closing over prematurely, which would result in recurrence of the abscess. More complex maneuvers are required to effectively drain abscesses located proximally in the anal canal.

While drainage of the perianal abscess relieves the acute infection, it does not address the underlying cause of the process. Indeed, about half of all abscesses will result in an epithelialized fistula from the inciting anal gland to the skin overlying the drainage site, a condition known as a fistula-in-ano. Patients who develop a fistula will have a persistent sinus track with chronic purulent drainage. Treatment of an anorectal fistula requires eradication of the fistulous tract. A fistulotomy is performed by making an incision along the length of the fistula tract in order to fillet it open. This method is effective for most simple fistulas, however, the treatment of complex fistulas can involve a combination of techniques including setons and soft tissue advancement flaps.

In most cases, fistula-in-ano occurs as a consequence of a prior abscess, as described. However, in individuals with Crohn’s disease, perianal fistulas can develop spontaneously, are often multiple, may occur in unusual locations, and are resistant to therapy. Crohn’s disease is a type of inflammatory bowel disease that can affect any site along the gastrointestinal site from the oral cavity to the anus. The most commonly affected area is the small bowel, and the hallmark of Crohn’s disease is the development of strictures along the intestines causing bowel obstruction. Perianal involvement is also common among those with Crohn’s disease, and is often the clinical manifestation that leads a clinician to suspect the diagnosis.

Perianal fistulae associated with Crohn’s disease are notoriously refractory to treatment. In extreme cases, complete fecal diversion with a colostomy may be indicated to allow healing of the perineal area. The recent introduction of infliximab—a monoclonal antibody—provides a new treatment option for patients who do not respond to conventional therapy. The use of infliximab has been shown to result in significant clinical improvement in patients with fistulizing Crohn’s disease.

Another common benign anorectal process is the anal fissure. This condition begins when the anal mucosa is torn, and is then unable to heal due to spasm of the exposed internal sphincter muscle. This spasm counteracts the healing process by further pulling apart the edges of the fissure. The site is irritated with each bowel movement, leading to a chronic non-healing condition. Patients with anal fissures complain of severe perianal pain and may report some bleeding with bowel movements.