Perirectal Abscess 

Perirectal and perianal abscess are commonly encountered emergency department (ED) problems. Timely and appropriate treatment is needed to prevent serious morbidity and mortality.

This article focuses on perirectal abscess and provides some discussion of perianal abscess. These entities are distinct, with potentially different ED evaluation and different treatment and disposition. Differentiation of the more complex perirectal abscess from the simpler perianal abscess is crucial.

The majority of perirectal abscesses are caused by obstruction of the anal glands, with obstructing debris leading to infection. Most individual have about 6-8 of these glands lying at the level of the dentate line, which divides the squamous epithelium distally and the columnar epithelium proximally. These obstructed anal glands lead to stasis, bacterial overgrowth, and abscess formation that extends into the intersphincteric groove between the internal and external anal sphincter.^[1]

Anorectal abscesses are classified according to their location. Perianal abscesses are the most common, extending superficially to the anal verge, where they may be easily incised and drained.^{[1, 2, 3, 4]}

Intersphincteric or submucosal abscesses may collect between the internal and external anal sphincters and lie completely within the anal canal, leading to severe pain, and may only be found by digital rectal examination or anoscopy.

Ischiorectal abscesses may form from the purulent drainage tracking across the external anal sphincter into the deep ischiorectal fossa. These abscesses may traverse the deep postanal space into the contralateral side, forming a “horseshoe abscess.”

Supralevator abscesses are less common and may form from cephalad extension of the intersphincteric abscess above the levator ani muscle or from caudal extension of a suppurative abdominal process into the supralevator space. These abscesses may be diagnosed based on CT scan findings, and they cause pelvic and rectal pain.

Approximately 10% of perirectal abscesses may be caused by reasons other than anal gland infection. These abscesses may be sequelae of Crohn disease, trauma, human immunodeficiency virus (HIV) infection, sexually transmitted diseases, radiation therapy, or foreign bodies.^[1]

Both aerobic and anaerobic bacteria are responsible for abscess formation. The predominant anaerobic species are most commonly Bacteroides fragilis, Peptostreptococcus, Prevotella, Fusobacterium, Porphyromonas, and Clostridium. The predominant aerobic bacteria include Staphylococcus aureus, Streptococcus, and Escherichia coli.^[5] More recent studies have noted community-acquired methicillin-resistant S aureus (MRSA) as a pathogen leading to abscess formation.^{[6, 7]}

Mortality/Morbidity

The overall mortality from perirectal abscesses is quite low.^[2]

According to previous data, recurrent abscess formation occurs in approximately 10% of patients, with chronic fistula-in-ano occurring in up to 50% of patients.^{[2, 8]} In more recent literature,^[9] 37% of patients develop chronic anal fistula or recurrent sepsis. In this study, risk factors were age younger than 40 years and nondiabetic status; no difference in these complications was noted with regard to HIV status, sex, antibiotic usage, or smoking status.

After anal fistula formation, multiple complications may develop after surgical treatment. Up to 43% of patients have reported fecal incontinence after surgical fistula repair for complex fistula-in-ano.^[10] Other postoperative complications from surgical repair include temporary postejaculation urethral irritation and postoperative urinary retention.^[11] Constipation may also occur as a result of pain on defecation.

Race

No racial predilection has been found.

Sex

The incidence of perirectal abscess in men is 2- to 3-fold that of women.^[12]

Age

Anorectal abscesses most often present in the third to fourth decade.^[12]