(Referring to the original article published in Chinese Journal of General Surgery Luo Y. Diagnosis and treatment of posterior anorectal hiatus abscess: with 93 case reports.2012,21(4):443-446) There are several hiatuses around the human anorectum, which are anatomically divided into pelvic rectal hiatus; posterior rectal hiatus; sciatic rectal hiatus; posterior anal canal hiatus; and perianal hiatus. These interstices are filled with fatty connective tissue and are common sites of infection. Once infected, a perianal abscess can form. Abscesses can be located in different interstitial spaces, thus forming abscesses in different interstitial spaces. Luo Yong, Department of General Surgery, Affiliated Hospital of Inner Mongolia Medical University Infection of the posterior anal canal gland spreads to the posterior rectal space of the anal canal to form an abscess, which can also spread to both sides of the scirorectal space via the posterior anal canal space to form a posterior horseshoe-shaped abscess, which can be cured at once by giving appropriate surgical methods at this stage. If it is allowed to break down by itself or simply cut and drain, it will form a complicated posterior horseshoe-shaped anal fistula, which increases the difficulty of surgical cure and is prone to recurrence of anal fistula due to improper treatment. Due to the special anatomical structure, the presence of Mihor triangle in the posterior wall of the anal canal makes the posterior wall weaker, and the formation of the anal right angle makes the posterior wall of the anal canal protrude into the intestinal cavity, and the impact and abrasion forces on the posterior wall during defecation are greater, making it very easy for injury to occur. It also increases the chance of injury to the anal crypt of the posterior wall of the anal canal. At the same time, in this high-pressure area of the rectal ring, the posterior wall of the anal canal is under the greatest pressure. In addition, the opening of the anal saphenous fossa located at the dentate gland is open in the form of “cups”, which makes it easy for feces to accumulate in it, and the anal saphenous fossa of the posterior wall of the anal canal is more likely to accumulate fecal impurities, and once saphenous inflammation is formed, the anal glands are blocked and cannot be excreted, which also increases the pressure in the posterior part of the anal canal, followed by infection and formation of perianal abscess. In addition, the blood supply to the posterior anal canal union is insufficient, mainly from the blood supply of the inferior rectal artery in which 85% of the arterial branches are small or absent, and only 15% of the blood supply is normal, and the branches issued by the anal artery through the internal sphincter septum are perpendicular to the muscle fibers into the muscle tissue, and sphincter spasm may compress the blood vessels and thus aggravate the ischemia of the posterior anal union. As a result, 80% of perianal abscesses and fistulas are located in the posterior wall of the anal canal. Due to the presence of the caudal ligament, once the infection enters the deep posterior space of the anal canal, which is located deep in the caudal ligament, the abscess can spread to one or both sides of the sciatic-rectal space and become a semi-annular horseshoe around the anal canal, forming a horseshoe-shaped or semi-horseshoe-shaped abscess. It accounts for 15-20% of perianal abscesses. Clinical manifestations are large area of perianal skin redness, hardness and pressure pain, but fluctuating sensation may not be obvious. The treatment cannot achieve the radical cure simply by performing an incision and drainage of the sciorectal fossa. The primary pus cavity in the deep space behind the anal canal must be adequately drained, and the primary internal opening must be searched for and treated by hanging. It has been suggested that the reason why horseshoe-shaped perianal abscesses are difficult to cure and prone to fistula formation is not the failure to identify the internal orifice but the poor drainage. The authors’ surgical approach to 93 cases of retrorectal abscesses was to preserve the caudal ligament to reduce the risk of surgical trauma and anal incontinence. First, a small curved incision (≤2 cm in length) was made in one or both sides of the colorectal fossa to place a tube for drainage, and the pus cavity was explored toward the posterior anal canal space, then windows were opened on both sides of the caudal ligament (11:00 and 1:00 in the thoracic-knee position), and a line was hung to place a tube for drainage after searching for an internal opening from one side of the window, and it was also important to open a window on the other side so that no dead space was left in the posterior anal canal space and adequate drainage was achieved. For full horseshoe-shaped abscess, arc-shaped incisions are first made on both sides of the anus to drain the pus and place the tube, and then a radial window incision is made 2 cm away from the anal canal along the posterior side of the anal canal avoiding the caudal ligament (at 11 or 1 point of the thoracic knee), and the index finger is extended into the abscess cavity to probe the direction of the abscess cavity, at this time, a pore with a diameter of about 5-10 mm can be palpated along the posterior side of the deep surface of the caudal ligament to the opposite side, through which the abscess reaches the anal canal. The deep posterior gap develops to the opposite side and can be appropriately cut open to enlarge this gap to facilitate exploration to the opposite side. After finding the internal orifice with a probe, drainage is performed by hanging a tube. An additional window is opened next to the caudal ligament on the opposite side according to the extent of the abscess and a tube is placed for drainage. For fistulous posterior interstitial abscesses, the fistula is first removed close to the posterior midline of the anal canal, and then windows are opened on both sides of the caudal ligament to find the internal orifice, and then a line is hung and placed for drainage. For simple posterior interstitial abscess of the anal canal, a window is opened on both sides of the caudal ligament and a tube is placed to find the internal opening. For posterior rectal space abscess, the abscess is higher and deeper and mainly develops to the posterior rectal space, and the internal port is still found at the posterior dentate line of the anal canal, and if the internal port cannot be found, it is not necessary to hang a line and drain directly. Postoperatively, antibiotics were routinely applied in static drip, flushed with metronidazole solution through the drainage tube, and the local wound was changed daily. The whole group of 93 cases was followed up for 6-24 months after surgery, and 89 cases were cured in one operation (95.7%) without anal incontinence and normal defecation function. 21 cases of total horseshoe-shaped abscess were cured in one operation by first removing the posterior rectal space drains on both sides of the caudal ligament after 5-7 days, and then removing the drainage of the sciatic rectal fossa after 3-5 days, and changing the medication twice a day. In the treatment of 45 cases of hemi-horse-shoe abscess, the curved incision on one side of the sciorectal fossa was explored first, and then drainage tubes were placed in the windows on both sides of the caudal ligament, and the internal openings were found and hung. Nine cases of simple posterior anal canal abscesses were cured after surgical treatment with a window on both sides of the caudal ligament for drainage and suturing; five of the six cases of posterior rectal abscesses were cured in one stage, and one of them formed a fistulous posterior anal canal abscess 6 months after surgery, which was cured after eliminating the fistula located in the colorectal fossa, finding an internal port on the posterior side of the anal canal and suturing, and draining the abscess.