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Anorectal Abscess
Introduction
Anorectal abscess is an acute suppurative infection of the soft tissues around the anal canal and rectum that can cause significant discomfort in patients. These abscesses most commonly result from obstruction and infection of the glands in the anal crypt, a condition termed cryptoglandular etiology. The condition is more common in males who present with perianal pain and swelling, along with other symptoms depending on the location of the abscess.[1][2] Although anorectal abscess is used as an umbrella term to describe all the suppurative infections around the anal canal and the rectum, there are more specific terminologies to describe them.[3]
Anal glands are primarily located in the intersphincteric space; consequently, infection initially results in an intersphincteric abscess. This may either drain spontaneously through an internal opening in the anal canal or extend inferiorly into the perianal soft tissue, leading to a perianal abscess. When ruptured through the external sphincter into the ischiorectal or ischioanal fossa, it forms an ischiorectal or ischioanal abscess.
The cephalad extension of the interpshincteric abscess can result in a perirectal abscess or a supralevator abscess if it extends above the levator muscles. The posterior extension can cause a horseshoe abscess.[3][4] See Image. Perirectal Abscess. The diagnosis is often obvious on a thorough clinical examination, except for perirectal or supralevator abscesses that require imaging to establish an accurate diagnosis. Treatment almost always consists of surgical drainage of the abscess, and the approach varies based on the location and extent. Antibiotics are reserved for specific clinical scenarios only and are discussed below, along with the etiopathogenesis, evaluation, and treatment of anorectal abscess.[1]
Etiology
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Etiology
The cryptoglandular hypothesis is the most common etiology of anorectal abscess. The risk factors for developing cryptoglandular anorectal abscess include smoking, obesity, and immunocompromised states, such as diabetes mellitus.[5] The pathogens commonly involved are Escherichia coli and Bacteroides species.[6] Patients with Crohn disease develop anorectal abscess secondary to a penetrating inflammation rather than infection.
Gram-positive bacteria, such as staphylococci and streptococci, are predominant in Crohn disease-associated perianal infections.[7][8] Locally advanced anorectal cancers, including anal canal and perianal squamous cell carcinoma, Buschke-Lowenstein tumor, basal cell carcinoma, anal melanoma, perianal Paget disease, mycosis fungoides, and anorectal adenocarcinoma, can lead to anorectal abscess.[9][10] See Image. Anal Carcinoma.
Similarly, perforation of the anorectum due to impacted chicken or fish bones, foreign bodies, or trauma can cause suppuration and abscess formation.[11] The other etiologies include perineal tuberculosis, perineal actinomycosis, and sexually transmitted infections such as lymphogranuloma venerum, and HIV.[12][13][14][15] Conditions causing pelvic sepsis, such as appendicitis, diverticulitis, and gynecological sepsis, can cause a supralevator abscess, which can extend inferiorly through the levators into the ischiorectal fossa.[11] Among patients presenting with an anorectal abscess, 30% to 70% have a concomitant fistula-in-ano, and those without an initial fistula will develop 1 in approximately 30% to 50% of cases within months to years.[2]
Epidemiology
The incidence of anorectal abscesses ranges from 68,000 to 96,000 cases per year in the United States.[11] However, the true incidence is likely higher due to multiple subclinical infections and spontaneous drainage. The common age of presentation is 20 to 60, with a mean age of 40 in both sexes. Men are affected twice as often as women.[11]
Pathophysiology
Cryptoglandular Abscess
Anal glands are located circumferentially within the internal sphincter, intersphincteric space, and the external sphincter, which drain into the crypts of Morgagni at the level of the dentate line. The cryptoglandular theory states that anorectal abscesses result from blockage of these glands, which increases pressure within them and allows bacterial translocation into the intersphincteric space (see Image. Anal Canal). Therefore, anorectal abscesses initially begin as intersphincteric abscesses, and the route of extension results in various types. The most common manifestation is a perianal abscess that occurs due to a downward extension of the abscess into the subcutaneous tissue around the anal verge. The second most common type is an ischiorectal abscess, which results from infection spreading into the ischiorectal fossa through the external sphincter. A submucosal abscess can occur due to the abscess penetrating the internal sphincter into the submucosal space of the anal canal. Rarely, the infection can extend upwards into the intersphincteric space, causing either a perirectal abscess or a supralevator abscess.[16][17]
Crohn Disease
The pathophysiology of anorectal abscesses secondary to Crohn disease depends on the host, microbial, and environmental factors. The luminal bacteria trigger an aberrant immune response, leading to persistent mucosal inflammation that promotes epithelial-mesenchymal transition and cell invasion, eventually causing abscess formation or fistulization.[18]
Tuberculosis
Mycobacteria reach the anorectal region either by direct inoculation or by hematogenous or lymphatic dissemination. The affected anoperineal region can present with suppuration and abscess formation, along with other presentations such as ulceration, verrucous, lupoid, and miliary lesions.[19]
Anorectal Malignancies
They lead to anorectal abscesses either by tumor obstruction of the anal glands, resulting in infection, or by direct infiltration into the perianal skin and soft tissue, causing necrosis and suppuration.[10]
Histopathology
Cryptoglandular anorectal abscess shows features such as inflammatory infiltrates, abundant neutrophils, and necrotic debris. However, those due to Crohn disease, tuberculosis, and malignancies demonstrate disease-specific features, including non-necrotizing granulomatous inflammation with giant cells (Crohn disease), tuberculoid granulomas with caseation necrosis and acid-fast bacilli (tuberculosis), and neoplastic cells (malignancies) (see Image. Histopathology of Cutaneous Crohn Disease). Therefore, histopathological examination is crucial in evaluating anorectal abscesses, especially those with recurrent infections, atypical presentations, or other high-risk features.
History and Physical
A disease-specific history and a complete physical examination, including perineal and digital rectal examination, should be performed in patients with suspected anorectal abscess. The clinical manifestations depend on the abscess location and any associated complications. Most patients present with perianal throbbing pain and swelling, which is generally not related to defecation. This is a hallmark symptom of a perianal abscess.[20]
Patients with intersphincteric and perirectal abscesses can, however, present with pain that is exacerbated during defecation. The pain may be referred to the perineum, lower back, or gluteal region.[21] There may be a history of spontaneous discharge of pus from the perianal region or from the anal canal.[22] Ischiorectal abscesses are usually large and can be associated with systemic features of sepsis.
Supralevator abscesses generally present with deep-seated pelvic pain along with fever and urinary symptoms such as increased frequency, dysuria, or urinary retention. Acute urinary retention can also occur due to mechanical obstruction or surrounding inflammation from a perianal and ischiorectal abscess.[23] History should also focus on determining baseline anal sphincter function, past anorectal operations, obstetric history, high-risk behavior, use of blood thinners, urinary and gynecological pathologies, and personal and family history of inflammatory bowel diseases and cancers.[2]
Physical examination should assess for systemic features of sepsis, such as fever, tachycardia, and malaise. The perineal examination will reveal erythema, warmth, induration, tenderness, and a fluctuant swelling in the perianal and ischiorectal fossa in respective abscesses. Previous surgical scars, external openings of a fistula, signs of perianal Crohn disease, and spontaneous discharge of pus or blood from the anal canal should also be checked.[24]
A gentle digital rectal examination (DRE) should be performed unless the patient is in severe pain; when indicated, consider performing anoscopy or proctoscopy, as deeper abscesses may have relatively unrevealing external findings. Severe tenderness with bogginess, typically at the 6 o'clock position on a DRE, is characteristic of an intersphincteric abscess.[25] Similarly, a tender fluctuant swelling at or above the level of the anorectal ring can be a subtle sign of a supralevator abscess.[26] Physical examination should also aid in ruling out the common causes of anal and perianal pain, such as anal fissure, hemorrhoids, hidradenitis, pilonidal sinus and abscess, sexually transmitted infections, and benign and malignant anorectal neoplasms.[2]
Evaluation
The evaluation of patients with anorectal abscesses includes laboratory investigations (including microbiology and histopathology when indicated) to determine the severity of infection, underlying risk factors, and etiology, as well as imaging studies for clinically occult abscesses. Laboratory studies should consist of a complete blood count, serum creatinine, inflammatory markers such as C-reactive protein, blood glucose levels, and HbA1c, even in patients with undetected diabetes mellitus.[27]
Routine diagnostic imaging is not recommended for all patients with an anorectal abscess. However, patients with occult abscesses, the presence of concomitant fistula, recurrent infections, immunocompromised states, and perineal Crohn disease should undergo imaging.[2] The modalities include perineal and anal endoscopic ultrasound (EUS), computed tomography (CT), and magnetic resonance imaging (MRI). The American College of Radiology appropriateness criteria recommends the use of MRI pelvis and CT pelvis as 'usually appropriate', EUS as 'may be appropriate', and radiography and fluoroscopy as 'usually not appropriate'.[3]
Ultrasound
Transperineal ultrasound is a noninvasive, readily available, and cost-effective diagnostic tool with high accuracy for diagnosing perianal, ischiorectal, and intersphincteric abscesses.[28] However, it does not provide any additional information beyond a good clinical examination and is not useful for deeper locations, such as supralevator or deep postanal abscesses. EUS has the advantage of identifying intersphincteric, perirectal, and supralevator abscesses with localization of the internal opening in the presence of a fistula. Still, it can be very painful for patients.[29] Both transperineal and EUS are operator-dependent and lack high-quality data to support their widespread use in anorectal abscesses.[30]
CT
A CT scan is useful for patients presenting with clinical symptoms of an anorectal abscess but without characteristic findings on examination. They are also useful for evaluating suspected supralevator, deep postanal, horseshoe, and perirectal abscesses and can guide the appropriate route for abscess drainage. The sensitivity of a CT scan in diagnosing anorectal abscess is approximately 77% and is even lower in immunocompromised individuals.[31] CT is inferior to MRI in the identification of an internal opening or the fistula tract. Despite these drawbacks, CT is an essential investigation that can be performed quickly, cost-effectively, and is readily available in emergencies.
MRI
MRI is the gold-standard imaging modality for most anorectal pathologies. This modality can help identify concealed tracts and abscesses and provide excellent anatomical orientation of the anal sphincter complex. Although its use in emergencies is not feasible due to cost, time, and availability constraints, it can assist in evaluating complex and recurrent abscesses, especially supralevator abscesses. Certain patient groups, such as those with Crohn disease, anorectal malignancies, and radiation proctitis, specifically benefit from MRI before surgical management (see Image. Anorectal Abscess on Magnetic Resonance Imaging).[32]
Treatment / Management
Patients with acute anorectal abscesses should be treated promptly with incision and drainage. The timing should be based on the presence and severity of sepsis, ideally within 24 hours.[27] Although this can be performed in the clinic setting as an outpatient or in the emergency department with local anesthetic infiltration (for small, superficial abscesses), all efforts should be made to perform an examination under anesthesia (EUA) before abscess drainage.[33] Extensive infections, deep-seated abscesses, and patient risk factors such as the use of blood thinners and multiple comorbid illnesses should be managed under anesthesia. Study results have shown reduced rates of recurrence and fistula formation when anorectal abscesses are managed in the operating room.[34] Needle aspiration of anorectal abscesses is not recommended due to the high rate of recurrence.[35](A1)
Operative Technique
For perianal and ischiorectal abscesses being managed in the outpatient setting, the patient is either placed in the lateral decubitus or knee-elbow position. For larger and deeper abscesses, and for those requiring EUA, lithotomy, Lloyd-Davies, or prone jackknife positions are preferred. In general, an incision should be made as close as possible to the anal verge to minimize potential fistula tract length, must be large enough to provide adequate drainage, and must avoid anal sphincter injury.[2] (A1)
Radial incisions from the anus are preferred, and the loculi must be broken either with a hemostat or a blunt probe.[36] To prevent premature closure of the skin, the incision can be made cruciate for an ischiorectal abscess, and an ellipse of skin can be excised for a perianal abscess. The cavity should be irrigated with saline, with or without hydrogen peroxide and povidone iodine, and hemostasis should be achieved using direct pressure, cautery, or lignocaine with adrenaline.[1] Following the drainage, the cavity can either be left open or a drain can be placed.[37] Study results show increased rates of postoperative pain with perianal packing after abscess drainage without any benefit in healing or fistula formation.[38] Therefore, routine postoperative packing, unless for hemostasis, is not recommended.(A1)
An intersphincteric abscess should be drained under sedation. This type of abscess can be felt as a posterior bulge in the anal canal, and the overlying mucosa should be incised to expose the internal sphincter. A right-angled or a Kelly forceps is used to gently spread the fibers of the internal sphincter to drain the abscess. This can be accompanied by dividing the internal sphincter muscle up to the dentate line to maintain the patency of the abscess cavity. The cavity can then be irrigated, and the wound left open.[39]
The surgical management of a supralevator abscess depends on its etiology and anatomical extent. Those occurring via the extension of the intersphincteric abscess superiorly can be drained internally into the anal canal. Supralevator abscesses that are formed due to the spread of ischiorectal abscess through the levators should be drained externally with a transperineal incision.[40] Rarely, supralevator abscesses can occur due to the spread of pelvic etiologies such as appendicitis, diverticulitis, and gynecological disorders. This may require ultrasound- or CT-guided transabdominal drain placement or, sometimes, laparotomy or a laparoscopic lavage.[1]
Horseshoe abscesses require specialized techniques as they most often involve the deep postanal space and extend laterally into the ischiorectal spaces. The modified Hanley procedure involves division of the anococcygeal ligament and placement of counter-incisions over the ischiorectal fossae, with multiple setons from the midline to the counter-incisions to aid drainage. If an internal opening is identified, another seton is placed from the midline to the internal opening.[41] Deep postanal abscesses without horseshoe extension can be managed like an intersphincteric abscess, accessing the cavity from the posterior anal canal.[42]
In general, it is not recommended to probe the abscess cavity with an attempt to identify a fistula tract.[2] However, when a fistula is evident during the drainage of anorectal abscess, the role of primary fistulotomy is controversial. Although fistulotomy can result in effectively managing the primary pathology, inflammatory edema and induration can cause false tracts while probing, and a risk of sphincter injury.[43] While simple fistulas may benefit from primary fistulotomy and have a negligible recurrence rate, complex and recurrent fistulas with abscesses carry a higher risk of postoperative fecal incontinence.[44](A1)
Therefore, primary fistulotomy with anorectal abscess drainage should be selected carefully based on the location and severity of the abscess and surgical expertise.[44] Partial fistulotomy and placement of a draining seton can be considered in patients with complex fistulas with abscesses. The procedure carries a low risk of sphincter injury, but needs to be followed by a staged fistulotomy subsequently.[45] Similarly, the role of ligation of the intersphincteric fistula tract (LIFT) during the index procedure has been studied in a small series, with results showing lower rates of nonhealing in patients undergoing LIFT.[46](A1)
Routine antibiotic use after adequate drainage of an anorectal abscess in a healthy patient is not recommended, as it does not improve healing rates or prevent recurrence. Antibiotics are reserved for patients with complications such as cellulitis, systemic sepsis, or immunocompromised states.[27] Prophylactic antibiotics before abscess drainage are recommended for patients with prosthetic valves, congenital heart disease, and previous bacterial endocarditis.[47] Most anorectal abscesses are polymicrobial, and culture results do not predict abscess recurrence, fistula formation, or change clinical management.[48] However, in immunocompromised patients and those with severe infections or nonhealing wounds, cultures may be obtained to guide antibiotic therapy, especially for methicillin-resistant Staphylococcus aureus, which is seen in up to 34.8% of patients.[49](B2)
Differential Diagnosis
The following conditions should be included in the differential diagnosis for anorectal abscesses:
- Perianal skin and soft tissue infections
- These include cellulitis, simple subcutaneous abscesses, carbuncles, folliculitis, Bartholin abscess, and infected sebaceous cysts. The clinical presentation is similar to that of an anorectal abscess, with acute pain, erythema, and fever. Local examination usually does not reveal any tender, fluctuant swelling in the perianal or ischorectal region, and DRE is often unremarkable.[50]
- Pilonidal abscess
- A pilonidal abscess can be misdiagnosed as a posterior or deep anal abscess. However, a pilonidal abscess is characteristically located in the midline at the natal cleft; the induration does not extend up to the anal verge, and DRE will be unremarkable.[51]
- Hidradenitis suppurativa
- This can be differentiated from an anorectal abscess by its features of deep-seated nodules, draining tracts, and indurated fibrotic scars.[52]
- Thrombosed external hemorrhoid
- This condition appears as a purplish swelling associated with enlarged external or internal hemorrhoids at the anal verge. The patient will have a long-standing history of a mass descending per rectum and bleeding during defecation. Pain may be an acute symptom exacerbated by straining or constipation.[53]
- Acute anal fissure
- This causes a sudden, sharp pain during defecation associated with the passage of fresh blood, with a throbbing pain lasting minutes to hours after defecation. Local examination reveals a longitudinal tear in the anoderm, usually at the 6 o'clock position of the anal verge, with a spasm of the anal sphincter.[54]
- Perianal Crohn disease
- The lesions appear as erosions over the perianal skin, inflammatory skin tags, or multiple external openings. DRE reveals indurated anal mucosa with an internal opening.[55]
- Anorectal malignancies
- Squamous cell carcinoma of the anal canal and the perianal skin, and anorectal adenocarcinoma present with ulceroproliferative growth at the anal verge associated with pain, bleeding, discharge, and anal incontinence. Clinical examination, imaging, and histopathological examination confirm the diagnosis.[9]
- Sexually transmitted infections
- They include gonorrhea, chlamydia, syphilis, herpes, and HIV infections. The clinical features include anorectal pain, tenesmus, pruritus ani, perianal vesicles and other skin lesions, and inguinal lymphadenopathy.[56]
Prognosis
With early and appropriate management, anorectal abscesses have a good prognosis. However, in immunocompromised individuals, those with Crohn disease, or those where the abscess is detected late and has progressed to a potentially life-threatening complication such as Fournier gangrene, morbidity and mortality can be significant.[57][58] Of patients presenting with an anorectal abscess, 30% to 70% have concomitant fistula-in-ano, and among those without an initial fistula, approximately 30% to 50% will develop 1 within subsequent months to years.[2]
Complications
The complications of anorectal abscess include sepsis, perineal cellulitis, necrotizing soft tissue infection, and Fournier gangrene, formation of fistula in ano, and fecal incontinence. Recurrence of anorectal abscesses and fistula formation could be as high as 50%.[59] The causes include inadequate drainage of the primary abscess, premature closure of the skin edges, missed abscesses, horseshoe abscesses, and obesity.[60][61][62] Surgical and postoperative complications include reactionary or secondary hemorrhage, acute urinary retention, surgical site infection, incontinence to feces or flatus, pudendal nerve injury, and anal stricture.[63]
Postoperative and Rehabilitation Care
Following the drainage of anorectal abscess, the patients need adequate analgesics, laxatives or fiber supplements to avoid constipation, and instructions regarding wound care. If intraoperative cultures or biopsies are taken, they must be followed up and discussed with the patients. Those managing their own wounds postoperatively should be advised to use absorbent dressings to cover the area, maintain proper hygiene, and use sitz baths to promote healing.[64]
Patients with transient dysfunction of the anal sphincter should be taught Keigle exercises and referred for physiotherapy. Use of a doughnut pillow should be encouraged while sitting to avoid direct pressure on the wound and associated pain. Because of a high recurrence rate, all patients should be followed postoperatively until the wound has completely healed, which may take up to 8 weeks. If there is a recurrent abscess or fistula formation, further evaluation is needed to identify underlying factors that may be contributing to poor healing, including Crohn disease, HIV, neoplasm, or other etiology.
Consultations
Anorectal abscesses often require surgical intervention, even if they drain spontaneously. Therefore, a general or colorectal surgeon should be consulted to evaluate the patient. Alternatively, an emergency medicine clinician may perform the drainage procedure themselves for small and superficial abscesses. If the abscess is recurrent or complex, a workup for underlying causes, such as Crohn disease, anorectal malignancies, and HIV, should be performed, with appropriate consultations to gastroenterology, oncology, or the infectious diseases unit as needed.
Deterrence and Patient Education
There are a few effective strategies to prevent anorectal abscess in an otherwise healthy patient. A high-fiber diet promotes regular bowel movements, helps prevent constipation, straining, and anal gland obstruction. Similarly, maintaining good perineal hygiene and preventing skin breakdown or moisture can help prevent anorectal abscess. Patients with diabetes should maintain strict glycemic control since it is a significant risk factor for developing cryptoglandular abscess.
If a patient has an underlying etiology such as Crohn disease, treatment with anti-tumor necrosis factor agents, especially infliximab, is associated with improved healing rates of perianal fistulas and reduced recurrence of abscesses when combined with surgical drainage and seton placement. Patients with sexually transmitted infections should be promptly evaluated and managed, including their partners.[55][65] Since anorectal abscess is an acute surgical emergency, patients with risk factors should be warned regarding the high-risk symptoms and counseled to seek immediate medical care.
Enhancing Healthcare Team Outcomes
Patients with anorectal abscesses experience significant pain and distress due to the sudden onset, rapid progression, and debilitating effects. When managed in the emergency room, a quick but effective history and a focused, thorough examination are crucial for making an accurate diagnosis. Although most types of anorectal abscesses, such as perianal, ischiorectal, and intersphincteric abscesses, are clinically evident, the more complex ones, like supralevator or deep postanal with horseshoe abscesses, need the reliance on imaging for their diagnosis.[1]
Emergency medicine physicians, general surgeons, advanced practitioners, nurses, pharmacists, and other health professionals involved in managing these patients should possess the essential knowledge and clinical skills to adequately diagnose and manage anorectal abscesses. Early recognition and treatment of patients are crucial in reducing morbidity. Patient education about the risk factors, preventive measures, symptoms, and complications is imperative.
When necessary, appropriate referral pathways must be initiated, such as a gastroenterology consultation for suspected inflammatory bowel disease, colorectal surgery for recurrent or complex abscesses, an infectious disease specialty for sexually transmitted infections, and oncology for primary malignancies causing anorectal abscesses. Effective interprofessional communication fosters a collaborative environment where information is shared, questions are encouraged, and concerns are addressed promptly. Care coordination is pivotal in ensuring seamless and efficient patient care. The involved specialties, including the surgeons, physicians, advanced practitioners, nurses, pharmacists, and other healthcare professionals, must work together to streamline the patient's journey, from diagnosis through treatment and follow-up. This coordination minimizes errors, reduces delays, and enhances patient safety, ultimately leading to improved outcomes and patient-centered care that prioritizes the well-being and satisfaction of those diagnosed with anorectal abscess.
Media
(Click Image to Enlarge)
Perirectal Abscess.
Contributed by O Chaigasame, MD
(Click Image to Enlarge)
Anal Canal. This illustration shows a coronal view of the terminal rectum and anal canal. Prominent longitudinal muscle fibers of the rectum are visible. Other structures shown include the levator ani muscle, the internal sphincter, the anal canal, and the anal valves. The columns of Morgagni and the rugæ of the mucous membrane are also clearly depicted.
Henry Vandyke Carter, Public Domain, via Wikimedia Commons
(Click Image to Enlarge)
(Click Image to Enlarge)
Anorectal Abscess on Magnetic Resonance Imaging. The MRI pelvis shows circumferential irregular thickening of the mucosa of the rectum with preserved stratification. The surrounding areas show increased inflammatory signs, including perirectal enhancement, fatty stranding, and edema.
Contributed by S El-Nakeep, MD
(Click Image to Enlarge)
Histopathology of Cutaneous Crohn Disease. The image shows a histopathological biopsy of cutaneous lesions in Crohn disease, highlighting noncaseating granulomas.
Contributed by K Wanat, MD
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