Perianal abscesses are the most common type of anorectal abscesses. These abscesses can cause quite a bit of discomfort for patients. They are located at the anal verge and if left untreated can extend into the ischioanal space or intersphincteric space since these areas are continuous with the perianal space. They can also cause systemic infection if left untreated.
Ninety percent of all anorectal abscesses are caused by non-specific obstruction and subsequent infection of the glandular crypts of the rectum or anus. A perianal abscess is a type of anorectal abscess that is confined to the perianal space. Other causes can include inflammatory bowel diseases such as Crohn disease, as well as trauma, or cancerous origins. Patients with recurrent or complex abscesses should be evaluated for Crohn disease.
The prevalence of perianal abscesses and anorectal abscesses, in general, are underestimated, since most patients do not seek medical attention, or are dismissed as symptomatic hemorrhoids. It is estimated that there are approximately 100,000 cases of the benign anorectal disease in general. The mean age at presentation is 40 years old, and adult males are twice as likely to develop with abscess than females.
On presentation, patients will most commonly complain of severe pain in the anal area. This is due to an infection of the anal glands which are not adequately draining through the anal crypts. The anal glands empty into ducts that traverse the internal sphincter and empty into the anal crypts at the level of the dentate line. Infection of these glands if not adequately draining will form an abscess which can spread along several planes along the perianal or perirectal spaces. The perianal space surrounds the anus and is continuous with the fat of the buttock.
Aerobic and anaerobic organisms have been found to be responsible for these abscesses including Bacteroides fragilis, Peptostreptococcus, Prevotella, Fusobacterium, Porphyromonas, Clostridium species, Staphylococcus aureus, Streptococcus, and Escherichia coli. Once the collection forms, it can spread along the path of least resistance, which is typically into the intersphincteric space and other potential spaces.
A detailed history and physical examination are pertinent to every patient and may be the only requirement for diagnosis. Patients will complain of anal pain which may be dull, sharp, aching, or throbbing. This may be accompanied by fever, chills, constipation, or diarrhea. Patients with perianal abscess typically present with pain around the anus, which may or may not be associated with bowel movements, but is usually constant. Purulent discharge may be reported if the abscess is spontaneously draining, and blood per rectum may be reported in a spontaneously draining abscess.
A physical exam can typically rule out other causes of anal pain, such as hemorrhoids, and will yield an area of fluctuance or an area of erythema and induration in the skin around the perianal area. Cellulitis should be noted and marked if extending beyond the fluctuant area. For follow-up purposes, it should be noted whether the patient has diabetes, and their average blood sugar on routine fingerstick should also be noted.
A physical exam is typically the only requirement for diagnosis. The digital rectal exam should be performed and may yield a fluctuant mass. Cellulitis may extend beyond the fluctuant area and should be marked. Computed tomography or MRI may be used in the setting of clinical suspicion without signs discussed above, especially in the setting of unexplained significant anorectal pain, and in the immunocompromised patient who may not mount an immune response. MRI is the preferred method of imaging as CT scan may miss small abscesses in the immunocompromised patients. Anorectal ultrasound may be used however it is not tolerated well secondary to pain.
Laboratory testing will usually reveal an elevated white blood cell count. However, an absence of a leukocytosis should not deter the physician from appropriate treatment of an abscess.
Perianal abscesses are an indication for timely incision and drainage. Antibiotic administration alone is inadequate and inappropriate. Once incision and drainage are performed, there is no need for antibiotic administration unless certain medical issues necessitate the use. Such conditions include valvular heart disease, immunocompromised patients, diabetic patients, or in the setting of sepsis. Antibiotics are also considered in these patients or cases with signs of systemic infection or significant surrounding cellulitis.
Incision and drainage are typically performed in an office setting, or immediately in the emergency department. Local anesthesia with 1% lidocaine may be administered to the surrounding tissues. A cruciate incision is made as close to the anal verge as possible to shorten any potential fistula formation. Blunt palpation is used to ensure no other septation or abscess pocket is missed. It is useful before completion of procedure to excise a skin flap of the cruciate incision or the tips of the four skin flaps to ensure adequate drainage and prevent premature healing of the skin over the abscess pocket. Packing may be placed initially for hemostasis. Continual packing may be further utilized for healing by secondary intention. Patients are encouraged to keep the incision and drainage site clean. Sitz baths may assist in pain relief.
More extensive abscesses may require the operating room for the adequate exam under anesthesia to ensure adequate drainage, as well as inspect for other diseases such as fistula in ano.
Horseshoe perianal abscesses are uncommon. They are abscesses which surround the entire anus. These abscesses are typically drained through an incision and drainage posterior to the anus. It is helpful to place counter incisions at the anterior extent of the abscess to ensure adequate drainage. Penrose drains may be placed through these incisions to aid in continued drainage. These drains are left in place for 2 to 3 weeks and then removed in the post-operative office visit.
Prompt follow-up with surgical services is advisable to monitor wound healing. Inadequate drainage may result in the reformation of an abscess, which may require repeat incision and drainage. If not promptly diagnosed and treated, perianal abscesses may lead to several other sequelae including fistula in ano, perianal sepsis, or necrotizing soft tissue infection of the anus and surrounding buttock. If fistula in ano is detected, patients will need operative drainage, fistulotomy or seton placement, which may have a risk of incontinence. Necrotizing soft tissue infection treatment goals are debridement of all non-viable tissue and may require colostomy for diversion of stool during healing. If not adequately treated, necrotizing soft tissue infection may have mortality as high as 50%.
Dealing with Perianal Complications in Crohn Disease: A Need for an Interprofessional Approach
Lack of Medical Evidence
Perianal abscess in patients with Crohn disease causes significant morbidity. Even though there are several treatments for perianal abscess, very few are based on evidence. Some of the treatments include drainage of the abscess, assessment of the Crohn disease status, determining sinus tracts, medical treatment and surgery. With the availability of new biological therapies, the outcomes are even more conflicting. Once the abscess has been drained, attempts may be made to eradicate the fistula and control Crohn disease. Definitive treatment for perianal complications of Crohn disease is very challenging and rarely lead to complete healing. No matter what treatment is selected one must weight the risk of ana sphincter injury which can be devasting. Given these facts, expert opinion suggests that an interprofessional approach to management of perianal disease in these patients is crucial to improving outcomes. Because Crohn disease is a systemic disorder, the health care team should consist of the following:
The outcomes of perianal abscess treatment depend on the timing of the surgery. Patients with early diagnosis and treatment tend to have good outcomes, but those who have a delay in treatment usually have prolonged hospital course, need for repeated surgical treatments at higher risk of recurrence. The key to improving outcomes is to follow the patient and monitor for any perianal symptoms closely. (Level V)