An acute suppurative infection occurring in or around the soft tissues of the anal canal and rectum, leading to the formation of an abscess, is referred to as a perianal or perirectal abscess. It is characterized by spontaneous rupture or the formation of an anal fistula following surgical incision and drainage. This condition is a common anorectal disease and represents the acute phase of the inflammatory pathological process of the anal canal and rectum, with anal fistula being the chronic phase. Common causative bacteria include Escherichia coli, Staphylococcus aureus, Streptococcus, and Pseudomonas aeruginosa, occasionally accompanied by anaerobic bacteria and Mycobacterium tuberculosis, often resulting in mixed infections. The ischiorectal fossa is a common site, typically resulting from the spread of infection from the anal glands through the external sphincter to the ischiorectal space.

bubble_chart Diagnosis

The ischiorectal fossa is relatively common and is often caused by the spread of infection from the anal glands through the external sphincter to the ischiorectal space. The abscess is deeper and more extensive than perianal abscesses, with a volume of approximately 60-90 ml. At the onset, the patient experiences persistent pain on the affected side, which gradually worsens, causing restlessness. Systemic infection symptoms may also occur, such as lack of strength, fever, loss of appetite, and even shivering and nausea. Sometimes, there may be reflexive difficulty in urination. Due to the deep location of the infection, local signs are not obvious in the initial stage. Later, redness and swelling appear on the affected side, sometimes with deep tenderness. During a rectal examination, a tender mass can be felt on the affected side, and there may even be a sense of fluctuation. If not treated promptly, the abscess may penetrate downward into the perianal space and then break through the skin, forming a high anal fistula.

Ischiorectal fossa abscesses are prone to spreading and should be surgically treated early. Sacral anesthesia is generally used, with the patient in a lateral or lithotomy position. A thick needle is first used to puncture the area where tenderness is most pronounced, and after aspirating pus, an incision is made in the anterior-posterior direction at that site. The incision should generally be more than 2.5 cm away from the anus to avoid injury to the anal sphincter. The abscess cavity is incised, and the index finger is inserted to separate the fibrous septa within the cavity, draining all the pus. Then, a small amount of marginal skin and subcutaneous tissue is excised to facilitate drainage (Figure 1). The abscess cavity is packed with Vaseline gauze for drainage. During the incision and drainage, attention should be paid to the amount of pus drained. If it exceeds 90 ml, it often indicates that the abscess may have spread to the contralateral ischiorectal fossa or to the pelvic rectal space above the levator ani muscle, and careful exploration is required.

Figure 1 Incision and drainage of ischiorectal fossa abscess.