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KembaraXtra – Emergency & Acute Medicine – Perirectal Abscess
Perirectal abscess is a localized infection with accumulation of purulent material adjacent to the anus or rectum. It most commonly results from infection of the anal crypt glands with spread into adjacent potential spaces separated by muscle and fascia. Perianal abscesses are the most common and typically present with a visible, tender red bulge near the anus. Ischiorectal abscesses occur in a large potential space and may grow significantly before diagnosis; they can communicate posteriorly to form a horseshoe abscess. Intersphincteric abscesses remain confined between the internal and external sphincters. Supralevator abscesses are deep, located above the levator ani, often present with systemic symptoms, and usually require operative drainage under general anesthesia. Infections are typically polymicrobial with mixed enteric organisms. Associated conditions include diabetes, inflammatory bowel disease, malignancy, and immunocompromised states.
Patients commonly present with constant perianal, rectal, or pelvic pain. Pain is often worsened by defecation, sitting, or coughing. Deeper abscesses such as ischiorectal or supralevator may produce dull pelvic or rectal pain and may be less painful if located above the dentate line. Fever, chills, constipation, and drainage may occur. On examination, findings include perianal swelling, erythema, induration, fluctuance, and marked tenderness. An abscess in the inner buttock cleft is a red flag, as rectal abscesses can track outward. Digital rectal examination is essential and may reveal rectal wall swelling or focal tenderness. A fistulous tract may be palpable as a cord-like structure or identified with gentle probing.
Diagnosis is primarily clinical and based on careful history and thorough rectal examination. A high index of suspicion is required in patients with persistent perirectal pain. Routine laboratory testing and imaging are not required for simple perianal abscesses. Leukocytosis with left shift may be present. Blood cultures are reserved for patients with signs of sepsis. CT scan with IV contrast or MRI is helpful when a deeper abscess is suspected or when the diagnosis is unclear. MRI is particularly useful for identifying fistulous tracts. Endoanal ultrasound may also assist in selected cases.
The differential diagnosis includes anal fissure, thrombosed or inflamed hemorrhoids, sentinel pile, anal ulcer, proctitis, and anorectal carcinoma.
Prompt incision and drainage are the definitive treatments. Delay in drainage may worsen outcomes. Bedside drainage is appropriate only for localized perianal abscesses. A radial incision should be made close to the anal verge, the cavity explored to break loculations, and copious irrigation performed. Loose packing may be placed and removed after 48 hours. Operative drainage under general anesthesia is indicated for deeper abscesses or when adequate drainage cannot be achieved with local anesthesia.
Antibiotics are not routinely required after adequate drainage but are indicated in patients with extensive cellulitis, systemic infection, immunosuppression, valvular heart disease, prosthetic devices, or diabetes. Oral options include amoxicillin-clavulanate or a fluoroquinolone with consideration for MRSA coverage when indicated. Intravenous regimens may include cefoxitin, ampicillin-sulbactam, or combination therapy with ampicillin, gentamicin, and either clindamycin or metronidazole.
Postprocedural care includes sitz baths three times daily beginning 24 hours after drainage, high-fiber diet or bulking agents, and adequate analgesia.
Patients requiring operative drainage or those with systemic toxicity or sepsis should be admitted. Patients with adequate bedside drainage and no systemic illness may be discharged with close follow-up. All patients should be referred to a surgeon within 24–48 hours to evaluate for fistula formation, which occurs in approximately 25–50% of anorectal abscesses.
Careful assessment of the extent of infection is critical. Thorough rectal examination and probing are mandatory, and imaging should be obtained when deeper extension is suspected. Deep abscesses above the dentate line may present with minimal pain and isolated fever, increasing the risk of delayed diagnosis.
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