Acute suppurative infection occurring in or around the soft tissues surrounding 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 frequent development of an anal fistula after surgical incision and drainage. This is a common anorectal condition and represents the acute phase of the inflammatory pathological process in 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 involving anaerobic bacteria and Mycobacterium tuberculosis, often presenting as mixed infections. Perianal subcutaneous abscesses are the most common, typically resulting from infection of the anal glands spreading outward through the subcutaneous portion of the external sphincter or directly outward.

bubble_chart Clinical Manifestations

Perianal subcutaneous abscess is the most common type, usually caused by infection of the anal glands spreading outward through the subcutaneous portion of the external sphincter or directly outward. It is often located in the subcutaneous area around the anus and is generally small. The main symptoms include persistent severe pain around the anus, aggravated by pressure or coughing, difficulty walking, restlessness, and no obvious systemic infection symptoms. Local examination reveals obvious redness and swelling of the perianal skin, accompanied by induration and tenderness, with possible fluctuation. If necessary, puncture can be performed for confirmation. If not treated in time, it often ruptures spontaneously, forming a low anal fistula. The infection may also penetrate upward through the perianal fascia, spreading to the ischiorectal fossa. In the early stages, it is sometimes misdiagnosed as thrombosed external hemorrhoids, but the latter has clear boundaries and no inflammatory reaction in the surrounding skin.

A few perianal abscesses can resolve with antibiotics, sitz baths, and local physical therapy, but most require surgical treatment, which involves two methods.

(1) Treatment of simple abscesses

In the lithotomy or lateral position, under local or spinal anesthesia, a radial incision is made at the abscess site. After draining the pus, the index finger is inserted to explore the size of the abscess cavity and separate any septa. If necessary, the edges of the incision may be slightly extended to facilitate drainage. Finally, a Vaseline gauze strip is placed into the abscess cavity for drainage.

(2) Abscesses communicating with anal fistulas

After incising the abscess, a probe is used to carefully examine the internal opening. The fistula tract is then incised, with appropriate excision of the skin and subcutaneous tissue, and slight removal of the tissue around the internal opening to ensure smooth drainage. If the internal opening is deep and the fistula tract passes through the anal sphincter, a seton technique may be employed. The advantage of these procedures is that the abscess is cured at the initial stage [first stage], preventing the formation of an anal fistula. However, during acute inflammation, if locating the internal opening proves difficult, blind exploration should be avoided to prevent the spread of infection or the creation of false tracts. In such cases, only incision and pus drainage are performed, and anal fistula surgery is deferred until the fistula forms. The intermediate stage [second stage] surgery has the advantage of precise results and a high cure rate.

It is worth noting that some literature reports indicate that simple incision and drainage of perianal abscesses may not recur. For example, Hanley (1978) reported a 35–40% non-recurrence rate, while Scoma (1974) reported 34%. Vasilevsky (1984) followed 103 cases of anorectal abscesses treated with incision and drainage for 1 month to 9 years, finding no recurrence in intersphincteric abscesses. Among 83 perianal abscesses and 9 ischiorectal fossa abscesses, 11% experienced recurrent abscesses, and 37% developed anal fistulas. Therefore, initial stage [first stage] surgery should not be considered routine to avoid compromising anal function.