Classification of the abscess is based on the location in relation to the levator and sphincteric muscles of the pelvic floor.
Classification by decreasing frequency: perianal, ischioanal, intersphincteric, and supralevator
Epidemiology
May occur at any age
More common in males 2:1
In children, more common in those less than 2 years
Pathophysiology and Etiology
Most often originates from an occluded anal gland with subsequent bacterial overgrowth and abscess formation
Infection from within the anal glands, penetrates through the internal sphincter, and ends in the intersphincteric space
Chronic infection and inflammation may result in the formation of fistula-in-ano. This occurs in up to 50% as a result of persistent anal sepsis or an epithelialized tract.
Constant anal or perianal pain that often precedes local findings
Localized swelling, erythema, and fluctuance
Painful defecation or ambulation
Constitutional symptoms (e.g., fever or malaise)
Perianal abscess
Result of distal vertical spread of the infection to the anal margin
Presents as tender, fluctuant mass
Most common type of perianal abscess
Ischiorectal abscess
Secondary to horizontal spread of infection across the external anal sphincter into the ischiorectal fossa
Infection may track across the internal anal sphincter into the anal canal.
Presents as diffuse, tender, indurated, fluctuant area
Patients may have pain and fever prior to visible swelling.
Intersphincteric abscess
Limited to the intersphincteric space between the internal and external sphincters; therefore, often does not cause perianal skin changes
Associated with painful defecation
Accounts for only 2 " 5% of all anorectal abscesses
Supralevator abscess
May arise from two different sources
Proximal vertical spread from the gland through the intersphincteric space to the supralevator space
Pelvic inflammation or infection (e.g., Crohn disease)
Presents with pelvic or anorectal pain, fever, and, at times, urinary retention
Rectal exam usually reveals an indurated swelling above the anorectal ring.
Imaging may be necessary to establish the diagnosis.
Horseshoe abscess
Secondary to abscessed anal gland located in the posterior midline of the anal canal
Due to presence of anococcygeal ligament, the infection is forced laterally into the ischiorectal fossae and is therefore known as "horseshoe. "
May be unilateral or bilateral
Presents with pain
Diagnostic Tests & Interpretation
Lab
CBC
Abscess culture
Imaging
Magnetic resonance imaging (MRI)
Preferred modality, as it provides excellent spatial and contrast resolution
Enables comprehensive evaluation of the entire peritoneum and lower pelvis
Computed tomography (CT) scan
Has limited soft tissue contrast resolution which makes distinguishing perineal musculature and fistula tracts difficult, although organized fluid collections larger than 1 cm are generally seen
This modality also uses ionizing radiation, which is less desirable in the pediatric population.
Ultrasound (US)
Endoscopic and transperineal US have been used, but do not always show the full extent of inflammation.
Deeper structures may not be visualized, owing to the lack of sound wave penetration.
Endoscopic US may be used to diagnose, characterize, and monitor rectal abscesses.
Differential Diagnosis
Pilonidal infection
Bartholin abscess
Presacral epidermal inclusion cyst
Hidradenitis suppurativa
Rectal duplication cyst
Treatment
General Measures
Lack of fluctuation should not delay treatment.
Abscess should be drained with placement of a seton or drainage catheter.
Abscess should be cultured at time of drainage to direct therapy in the case antibiotics are needed.
Antibiotics are reserved for situations in which infection does not appropriately respond to drainage or with adjacent cellulitis, an immunocompromised patient, a patient with abnormal cardiac valves, enteric organism on culture, or in Crohn disease.
Sitz baths may be helpful with drainage.
Surgery/Other Procedures
Drainage may be performed either with conservative incision and drainage or with judicious probing for fistulae.
It is a matter of debate as to whether a fistulotomy or fistulectomy should be performed at the time of drainage for an accompanying fistula.
Ongoing Care
If abscess recurs, consider other associated conditions (e.g., neutropenia, HIV, diabetes mellitus, Crohn disease, rectal duplication cyst).
Exploration for fistula-in-ano is recommended to prevent recurrence.
Prognosis
Prognosis is good if there is early detection and drainage of abscesses.
Patients typically recover well after surgical drainage without the need for antibiotics.
Complications
Sepsis
Fistula formation
Special Considerations
Crohn disease should be considered in patients with perirectal abscess with or without fistula-in-ano.
Signs and symptoms that increase suspicion for Crohn disease include weight loss or poor growth, chronic diarrhea, or abdominal pain.
Additional Reading
Caliste X, Nazir S, Goode T, et al. Sensitivity of computed tomography in detection of perirectal abscess. Am Surg. 2011;77(2):166 " 168. [View Abstract]
Chang HK, Ryu JG, Oh JT. Clinical characteristics and treatment of perianal abscess and fistula-in-ano in infants. J Pediatr Surg. 2010;45(9):1832 " 1836. [View Abstract]
Hammer MR, Dillman JR, Smith EA, et al. Magnetic resonance imaging of perianal and perineal Crohn disease in children and adolescents. Magn Reson Imaging Clin N Am. 2013;21(4):813 " 828. [View Abstract]
Lejkowski M, Maheshwari A, Calhoun DA, et al. Persistent perianal abscess in early infancy as a presentation of autoimmune neutropenia. J Perinatol. 2003;23(5):428 " 430. [View Abstract]
Malik AI, Nelson RL, Tou S. Incision and drainage of perianal abscess with or without treatment of anal fistula. Cochrane Database Syst Rev. 2010;(7):CD006827. [View Abstract]
Marcus RH, Stine RJ, Cohen MA. Perirectal abscess. Ann Emerg Med. 1995;25(5):597 " 603. [View Abstract]
Niyogi A, Agarwal T, Broadhurst J, et al. Management of perianal abscess and fistula-in-ano in children. Eur J Pediatr Surg. 2010;20(1):35 " 39. [View Abstract]
Rosen NG, Gibbs DL, Soffer SZ, et al. The nonoperative treatment of fistula-in-ano. J Pediatr Surg. 2000;35(6):938 " 939. [View Abstract]
Whiteford MH, Kilkenny J III, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48(7):1337 " 1342. [View Abstract]
Codes
ICD09
566 Abscess of anal and rectal regions
565.1 Anal fistula
ICD10
K61.1 Rectal abscess
K60.3 Anal fistula
K61.3 Ischiorectal abscess
K61.4 Intrasphincteric abscess
SNOMED
91669008 Perirectal abscess (disorder)
197150008 anal fissure and fistula (disorder)
36046008 Ischiorectal abscess (disorder)
197163002 Supralevator abscess (disorder)
FAQ
Q: What are complications of this problem?
A: Fistula formation is seen in up to 50% of patients, with a predilection for males.
Q: What are the most common organisms of the abscess?
A: Staphylococcus species
Q: What other disease may perirectal abscess be associated with?
A: Crohn disease. If there has been exposure, tuberculosis should also be excluded.
Q: What treatments can be done other than surgery?
A: Sitz baths and warm compresses may be able to help with smaller more superficial abscess.