1. Four vulnerabilities of bacterial invasion
Flies do not bite seamless eggs. The shell of the egg looks hard, but it still has gaps in it by flies and mosquitoes. The anus is the same, it is often attacked by bacteria, but where are the loopholes in the anus?
(1) Anal sinus
The innermost tissue of the anus in contact with the intestinal contents. The upper 1/3 is rectal mucosa and the lower 2/3 is the anal skin. However, neither the intestinal mucosa nor the anal skin will be easily broken by bacteria. The problem is mainly in the intestinal mucosa. The junction with the skin of the anal canal-the tooth line. The tooth line is located about 3cm inside the anus and can be seen with an anoscope. Its shape is like a tooth, so it is called the tooth line, or tooth line for short. On the one hand, the tooth line is a very important marking line inside the anus, and at the same time, it is also a breakthrough for bacteria to penetrate the anus. The shape of the rectum looks like a waist drum, with a large middle, small ends and an anal canal. When the rectum transitions from the wide midsection (ampullary) to the closed anal canal, the mucosa of the rectal wall forms 6-10 mucosal bulges that protrude into the intestinal cavity, which is medically called "rectal column". A half-moon valve is connected between the lower ends of every two rectal columns. The rectal column and this valve together form a small recess, this small recess is the anal sinus, or anal recess. The opening of the anal sinus is upward, usually open, and closed during defecation. The openings of the anal glands are distributed in the anal sinuses, which secrete anal gland fluid to lubricate and protect the anal canal. If certain factors prevent the anal sinus from closing during defecation, or if dry stool scratches the anal sinus, feces and bacteria will enter the sinus and block the opening of the anal gland. The secretion is blocked, anal gland infection occurs, and then it spreads out along the lymphatic vessels outside the anal gland, causing diseases such as abscess and anal fistula. Perianal abscess and anal fistula are all infected through this way, so the internal mouth of this part of the disease is at the dental line. Therefore, the biggest weakness of the anus is the anal sinus.
Of course, the significance of the existence of the dental line is definitely not to provide a population for the bacteria to invade the anus. It is the most important marking line in the anus: it is the dividing line between mucous membrane and skin, internal and external hemorrhoids, autonomic nerves and body nerves. The direction of the veins and lymphatic drainage are different on the upper and lower teeth. The rectal venous plexus on the dentate first returns to the liver, so rectal cancer first metastasizes to the liver. The anal venous plexus under the tooth line first returns to the lungs, so anal cancer usually metastasizes to the lungs first. In addition, the tooth line is also one of the anal sensation centers and cannot be overly damaged during surgery.
(2) Anal margin skin
There are more than three skins on the anal margin, with many hairs, folds, and glands, so it is particularly easy to hide dirt and dirt. If you do not pay attention to hygiene, it is easy to cause subcutaneous infections and lead to subcutaneous abscesses. Bacteria invade the anus through this entrance, generally not too deep or too wide.
(3) Anal skin
As mentioned earlier, the skin of the anal canal has a strong firmness. If there is no laceration or damage, it will generally not be invaded by germs. Bacteria invade the anus through this route mostly in patients with anal fissures, mainly subcutaneous anal fistulas, which are more common in anteroposterior and lateral positions.
(4) Blood circulation
A purulent infection occurs in adjacent tissues and organs. When the body's resistance is reduced, the bacteria will enter the anus through the bloodstream and cause infection. This approach is relatively rare in clinical practice, and is characterized by the absence of an internal mouth in the lesion.
Second, the eight gaps of purulent fistula
After the bacteria enter the anus through the above four ways, it is necessary to find a place to stay, looking for "good bully" targets, these targets are the spaces around the anus and rectum. The so-called gaps are spaces and crevices. These places are filled with fat, which will quickly become pus after being infected by bacteria, and will form a fistula over time. There are mainly eight such gaps around the anus and rectum. The characteristics, outcome, prognosis and treatment of each gap after the onset of the disease are different. We need to understand.
(1) Perianal subcutaneous space
The perianal subcutaneous space is distributed under the skin of the anal margin, both front and rear, left and right, but it is the most superficial space after the onset of the disease. The route of infection is the anal sinus and the skin of the anal margin. The lesions are mostly limited and rarely spread to the surrounding area. The inner mouth is at the position of the tooth line corresponding to the lesion. The operation is relatively simple.
(2) Subfascial space of perineum
The subfascial space of the perineum is located on the front side of the anus. It is small in women and wide in men, extending to the root of the scrotum. The gap in this part is divided into two levels. The superficial layer and the perianal subcutaneous space are connected. The route of infection is the anal sinus at the anterior tooth line of the anus and the lacerated anal canal skin, so the internal mouth is generally located here. If the disease is not treated in time, it will spread to the scrotum.
(3) Posterior anal space
The posterior space of the anal canal is located on the back of the anus, divided into two layers, the superficial layer and the perianal subcutaneous space are connected. The deep layer leads to the space between the ischial and rectal fossa on both sides. The route of infection is the posterior anal sinus at the dental line and the posterior anus fissure. The inner mouth is mostly at the back midline position. It is easy to spread to both sides after the onset.
(4) Space between ischiorectal fossa
The ischiorectal fossa gap is the largest perianal gap, one on the left and one on the left, and communicates with the deep gap after passing through the anal canal. The path of infection is basically the anal sinus. There are two possibilities for the position of the internal mouth: one is the position corresponding to the lesion, and the other is the posterior median position. How to judge it will be introduced in the relevant chapters later. The symptoms of these two spaces are very serious after infection, and they will spread to the opposite side, forming a horseshoe or half horseshoe abscess. Most complex anal fistulas originate from abscesses in this area.
(5) Intersphincter space
The intersphincteric space refers to the internal and external sphincter muscles. Strictly speaking, there is no obvious gap in this part, but it is the primary site of many perianal infections. As mentioned earlier, the anal sinus is the main entrance for bacteria to invade the anus, but the real access to the anus depends on the anal glands, and most of the anal glands are located between the sphincter muscles. Bacteria often infect here first, and then spread to other gaps. There is no definite location of the inner mouth, but there will be more mid-tooth lines in the future, and the direction of spread is uncertain.
(6) Submucosal space of rectum
Rectal submucosal space The lower rectal mucosa, both front and back, left and right, belong to the high space. The bacterial invasion is through the anal sinus. The lesions are mostly limited and rarely spread to the surrounding area. The inner mouth and the lesion are at the same location.
(7) Posterior rectal space
The posterior rectal interstitial space is located on the back of the rectum and is the highest of all the spaces. The route of bacterial infection is the anal sinus, and the internal mouth is at the posterior midline. After the onset, it may spread to the pelvic and rectal spaces on both sides, forming high horseshoe abscesses and anal fistulas. Clinical treatment is difficult.
(Eight) pelvic rectal fossa space
The pelvic rectal fossa space is located on both sides of the lower end of the rectum, one on the left and one on the left, above the pelvic floor, below the peritoneum, and the corresponding ischiorectal space below, which is a high space. The route of infection is empty, and the internal mouth is mostly located at the posterior midline. After the onset, it may use the posterior rectal space to move to the opposite side, or it may spread down to the ischiorectal space.