A detailed history and physical examination are pertinent to every patient and may be all that is necessary to make a 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 also 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 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.[10][11][12]

Laboratory testing will usually reveal an elevated white blood cell count. However, the absence of a leukocytosis should not deter the physician from the appropriate treatment of an abscess, namely surgical drainage.

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.[1][13]

Incision and drainage are typically performed in the clinic 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 the 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.[1] 

The differential diagnosis for a perianal abscess includes anal trauma, anal fissure, anal fistula, thrombosed external hemorrhoid, pilonidal cyst, buttocks abscess, cellulitis, Crohn’s disease, ulcerative colitis, malignancy, proctitis, HIV/ AIDS, other sexually transmitted diseases, Bartholin’s abscess, and hidradenitis suppurativa.

With appropriate and prompt drainage mortality from a perirectal abscess is very low. However, in immunocompromised patients, those with Crohn's, or those where the abscess is detected late and has progressed to a potentially deadly condition such as Fournier's gangrene mortality and morbidity can be significant[14][15]. Additionally, the morbidity even in healthy patients can be significant with approximately one-third of patients developing a fistula secondary either to the disease process itself or the surgical drainage.[14]

• Sepsis
• Recurrent abscess
• Fistula formation (either secondary to the disease process itself or surgical intervention)
• Fecal incontinence (either secondary to the disease process itself or surgical intervention)

After treatment, the patient needs pain control, laxatives or fiber supplements to avoid constipation, and instructions on how to properly perform sitz baths.

Outpatient antibiotics are rarely indicated but should be considered if the patient demonstrates signs of systemic infection such as fevers or high leukocytosis. Cultures and sensitivities of the causative organism are rarely helpful.[16]

Because of a high recurrence rate, all patients need to be followed up until there is complete healing, which may take up to 8 weeks. Additionally up to one-third of patients may either already have a fistula in ano or develop one after their abscess which is another reason to have close follow-up. If there is a recurrent abscess further evaluation is needed for potential Crohn's HIV, neoplasm, or other underlying etiology.

Perirectal abscesses often require surgical drainage even if they have ruptured or are already training. Therefore a general or colorectal surgeon should be consulted to evaluate the patient. Alternatively, an ED physician may perform the drainage procedure themselves.

If the abscess is recurrent or complicated then a work-up for Crohn's disease or HIV should be performed with appropriate consultations to gastroenterology or an HIV management team as needed.

There are few effective strategies to prevent perianal abscess in an otherwise healthy patient. Keeping the perianal area clean and dry to avoid skin breakdown can be helpful. High fiber diets may theoretically reduce the chance of anal gland blockage but there is no real evidence to confirm that as an effective treatment. If the patient has an underlying etiology such as Crohn's or HIV then treatment of that condition can help reduce the risk of developing a perianal abscess.

Horseshoe perianal abscesses are uncommon. They are abscesses which surround the entire anus. These abscesses are typically drained through an incision and drainage performed 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 and prevent premature closure. 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's Disease: A Need for an Interprofessional Approach

Lack of Medical Evidence

Perianal abscess in patients with Crohn's disease causes significant morbidity. Even though there are several treatments for perianal abscess, very few are based on evidence.[1] Some treatments include drainage of the abscess, assessment of Crohn's 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's disease. Definitive treatment for perianal complications of Crohn's disease is very challenging and rarely lead to complete healing. No matter what treatment is selected one must weigh the risk of ana sphincter injury which can be devastating. Given these facts, expert opinion suggests that an interprofessional approach to the management of perianal disease in these patients is crucial to improving outcomes.[17] Because Crohn's disease is a systemic disorder, the health care team should consist of the following:

• Colorectal surgeon
• Dietitian to determine the need for nutrition
• Gastroenterologist to monitor for Crohn's disease
• Nurses to educate the patient on perianal complications
• Pharmacists to follow the prescribed drugs and ensure that the patient is not developing adverse drug reactions

Outcomes

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.[18](Level V)