What should be noted about the choice of incision location for periorectal abscess?
I. Perirectal abscess of the anal canal
(I) Overview.
Perianal canal and perirectal abscess refers to an acute purulent infection in the soft tissue around the anal canal and rectum or in the interstitial space around it, and the formation of an abscess. It is an acute infectious process, usually a manifestation of an underlying anal fistula, and abscesses can be caused by specific and non-specific etiologies.
1. Specific etiologies include the following.
(1) Invasion of foreign bacteria.
(2) trauma.
(3) malignant tumors.
(4) radiation.
(5) Immunocompromised states.
(6) infectious dermatitis.
(7) tuberculosis.
(8) Actinomycosis.
(9) Crohn’s disease.
(10) Anal fistula.
(11) Surgery.
(2) Non-specific anal canal, anorectal abscess and anal fistula are thought to be caused by blockage of the anal sinus duct
(ii) Clinical manifestations.
1, perianal abscess
Characterized by superficial/tender masses outside the anus, mild systemic toxic symptoms, local swelling, redness, pressure pain, and fluctuating sensation. This is the most common type of anorectal abscess, accounting for about 40-48% of cases, and only a small percentage are associated with potential anal fistulas.
Treatment: Abscesses should be drained promptly, lack of swelling is not a reason to delay treatment, and puncture of the abscess site with a hypodermic needle is a simple diagnostic test. In exceptional cases antibiotics can be used as adjunctive therapy.
2. Abscesses of the sciatic rectal fossa
It may present as a large red/hard/tender lump on the buttock or may not actually be obvious, with the patient feeling only intense pain, which is aggravated by movement and defecation, and may have generalized symptoms of toxicity such as discomfort, fever and chills, and elevated body temperature. This type of abscess accounts for 20-25% of cases.
Treatment: Proper drainage of the sciorectal abscess, requiring an incision as close as possible to the medial side, 2.5 cm away from the anus and not at the point where the fluctuating sensation is most pronounced, can avoid the next step of fistulotomy, the pus cavity needs to be flushed, and once antibiotics are administered, they should last for 48 hours.
3. Pelvic rectal abscess
Rare but important, the patient’s self-conscious local symptoms are not obvious, while the systemic symptoms are significant, examination: rectal palpation can reveal infiltration, pressure, elevation, and even fluctuation outside the anterolateral wall of the upper rectum. Diagnosis mainly relies on puncture and pus extraction, and if necessary, anal canal ultrasonography to assist in diagnosis.
Treatment: incision is the same as for sciatic rectal fossa abscess, index finger is positioned, pus cavity and interval are fully dilated, and drainage is performed.
4.Post-rectal abscess
Symptoms are the same as pelvic rectal abscess, and treatment is the same as pelvic rectal abscess, but its incision is more posteriorly oriented.
5.High intermuscular abscess
It is located in the upper part of the sphincter space, between the rectal ring muscle and the longitudinal muscle, above the levator muscle, and is relatively rare, less than 2.5% in most reports, but 9.1% in some reports, and one of the symptoms is discharge of pus from the anal canal and occasional dull pain in the rectum.
Treatment: Effective treatment requires an understanding of the course of the infection and, more importantly, finding an internal opening at the level of the saphenous fossa under anesthesia to confirm that an external drainage should be performed if an internal opening is found, or an internal drainage if not possible. It is important to note that external drainage when the internal orifice is above the levator muscle can lead to a high extra-sphincter fistula, a consequence that can be quite complicated to manage. A perirectal abscess, an acute infectious process, is usually a sign of an underlying fistula.
Anal fistula
A perianal fistula is a granulomatous duct that connects to the skin of the perineum, with the inner opening located near the dentate line and the outer opening located at the perianal area and skin. The wall of the fistula consists of thickened fibrous tissue with a layer of granulation tissue that does not heal over time. The incidence is second only to that of hemorrhoids and is most often seen in young male adults, probably related to the high secretion of sebaceous glands, one of the sex hormone target organs in men.
(I) Etiology
Most anal fistulas are due to general purulent infections, and anal fistulas are the sequelae of perianorectal abscesses, so perianorectal abscesses are the underlying cause of anal fistulas. The abscess breaks down or fails to heal after incision and eventually forms a fistula. A few are specific infections, such as tuberculosis, clonorchiasis and, more rarely, ulcerative colitis. Fistulas can also be formed as a result of infection secondary to trauma to the rectum and anal canal, and malignant tumors of the rectum and anal canal can also ulcerate into fistulas, but they are rare and are clearly distinguishable from general purulent fistulas.
(II) Pathology
Anal fistulas have primary internal orifices, fistulas, branched canals, and secondary external orifices. The internal orifice, the entrance to the source of infection, is mostly in and near the anal sinus, and is more common on either side of the posterior median line, but can also be in the lower rectum or any part of the anal canal. The fistulae are straight or curved, and a few have branches. The external opening, where the abscess breaks down or is incised and drained, is mostly located outside the skin around the anal canal. Because the primary lesion constantly enters the canal through the internal opening, and because the canal is tortuous and travels near the internal and external sphincters, the wall of the canal is composed of fibrous tissue and there is granulation tissue inside the canal, it does not heal over time.
Generally, simple anal fistulas have only one internal and one external port, and these are the most common. If the external mouth is temporarily closed and the local drainage is poor, redness and swelling will gradually occur, and then an abscess will form, and the closed external mouth can be re-perforated or another external mouth can be formed elsewhere. This repeatedly expands the lesion or sometimes causes several external openings that are connected to the internal opening.
(iii) Classification
There are many ways to classify anal fistulas, but they are classified according to the location of the perianal rectal abscess and the relationship between the fistula and the anal sphincter. At present, anal fistulas are classified into four categories according to the relationship between the anal canal and the sphincter.
1. inter-sphincter fistula
Mostly low anal fistulas, the most common, accounting for about 70%, are the consequence of perianal abscesses. A few fistulas pass upward, forming a blind end between the rectal ring muscle and the longitudinal muscle or penetrating into the rectum to form a high intersphincteric fistula.
2.Transsphincter fistula
It can be a low or high anal fistula, accounting for about 25% of cases, as a consequence of an abscess in the colorectal fossa. The fistula passes between the internal sphincter, the superficial external sphincter and the deep part, and there are often several external openings with branches communicating with each other. The external opening is close to the anal verge, about 5 cm, and a few fistulas pass upward through the anal raphe to the rectal connective tissue, forming a pelvic rectal fistula.
3.Suprasphincter fistula
It is a high anal fistula, rare, accounting for 5%. The fistula passes upward through the levator muscle and then downward to the colorectal fossa where it penetrates the skin. Because the fistula often involves the anorectal ring, it is more difficult to treat and often requires staged surgery.
4. Extra-sphincter fistula
The least common, accounting for 1%, is a consequence of a pelvic rectal swelling combined with an abscess in the colorectal fossa. The fistula passes through the levator muscle and communicates directly with the rectum. This type of fistula is often due to clonorchiasis, intestinal cancer, or trauma, and treatment should pay attention to its primary lesion. The above classification is more detailed in terms of high and low levels, which facilitates the choice of surgical approach.
Marks and Ritchie (1977) tabulated and compared the characteristics of the above four major anal fistulas, indicating that intersphincteric fistulas have a simple clinical presentation; whereas the latter three have a long history, with many surgeries and abscesses draining, and horseshoe or spreading is common, as are lateral and multiple external openings.
(iv) Clinical manifestations and diagnosis
1, anal fistula often has a history of perianal abscesses that break down on their own or cut open to drain pus, the main symptom is repeatedly flowing a small amount of pus from the external mouth, contaminating the underwear; sometimes the pus stimulates the perianal skin and has an itchy feeling. If the fistula drains freely, there is no local pain and only slight swelling discomfort, which patients often do not mind. Most of them do not have systemic symptoms; when the fistula invades a larger and deeper area or has more branches, repeated inflammatory infections can lead to systemic symptoms such as wasting, anemia, constipation, and difficulty in defecation.
If the fistula is superficial, a hard strip can be felt under the skin, and if the fistula is deep, it is not easy to feel the fistula. The skin around the anus is often thickened and reddened due to the stimulation of secretions.
If there are external openings on the left and right sides of the anal canal, it should be considered a “hoof and iron” fistula. This is a special type of fistula through the sphincter, but also a high curved anal fistula, fistula around the anal canal, from one side of the sciatic rectal fossa to the opposite side, become a semi-ring type, such as hoof-shaped so named. There is an internal opening near the dentate line, while the number of external openings can be multiple, scattered on the left and right sides of the anus, with many branches that spread around. The hoof-shaped anal fistula is divided into two types: anterior hoof-shaped and posterior hoof-shaped. The latter is more common because the posterior part of the anal canal is looser in tissue than the anterior part and the infection spreads easily.
Rectal palpation: there is mild pressure pain at the internal opening and a few hard nodules can be palpated. X-rays, injected with 30% to 40% iodine oil from the external orifice, can be used for fistula distribution, mostly for high anal fistulas and hoof-and-iron fistulas.