2020年10月27日星期二

what does a hemorrhoids look like,Medical illustration︱The "four lines and three areas" of the anal canal: draw it out for everyone to see, so intuitive!

    Today, a more complicated ultra-low rectal cancer operation was performed. During the operation, it was also found that the patient’s left liver had a lesion with suspected metastatic nodules. Finally, our team and the hepatobiliary surgery team jointly performed a radical operation for rectal cancer and liver lesions. Of resection.

    I didn't want to write anything tonight, but after taking a shower and looking at my computer, it seemed to be full of blood and resurrected in an instant. Today, I shared a tweet I wrote before, and edited it again to get new fans.

    The anal canal is the end of the digestive tract. The upper end of the anal canal ends at the dentate line and connects with the rectum, and it ends at the anal edge downwards.

    Before clarifying the "four lines" and "three zones" of the anal canal, we might as well clarify two important concepts, one is "anatomy anal canal" and the other is "surgery anal canal":

    1. Anatomy The anal canal refers to the part from the dentate line to the edge of the anus. It is also called the skin anal canal or the proper anal canal. The front wall is shorter than the back wall. Adults are 3-4cm long, without peritoneal covering, around the anal canal. Surrounded by external sphincter and levator ani muscle. As shown in the figure below (1).

    2. Surgery Anal canal refers to the part from the edge of the anus to the plane of the anal canal and rectum ring, also known as the muscular anal canal or clinical anal canal. The adult is about 4.2cm long. As shown in the figure below (2).

    Figure (1): The red area shows the anal canal

    Picture (2): The red area shows the surgical anal canal

    Anatomy anal canal discusses the anal canal from the perspective of embryogenesis, and surgical anal canal discusses the anal canal from the aspect of morphology and function. The two are not only different, but also related to each other. Next, let's learn about the four important linear signs of the anal canal, and the resulting three surgical anal canal divisions.

    One

    Anal margin line

    Anal margin line, also known as anal orifice, anal margin, is the lowest boundary of the digestive tract. As shown in the following figure (3) and figure (4).

    Picture (3): The yellow line shows the anal margin line

    Picture (4): The yellow line shows the anal margin line (this picture is a specimen from Miles operation, the same below)

    two

    White line

    White Line (White Line), also known as anal white line, Hilton line, is the junction line between the middle and lower parts of the anal canal, directly facing the junction between the lower edge of the internal sphincter and the lower part of the skin of the external sphincter. Finger examination can clearly touch an obvious circular groove, which is called the intersphincter groove (also known as the white line), which is not easy to identify with the naked eye, as shown in Figures (5) and (6) below.

    Figure (5): The green line shows the white line

    Figure (6): The green line shows the white line

    Clinically, this groove is often used to locate the boundary between the internal and external sphincter. When internal sphincter lysis is performed during the operation, this groove is an anatomical sign: cut the anal canal to migrate the skin, pick out the internal sphincter and cut it under clear vision, as shown in the following figure (7).

    Picture (7): The white line is the dividing line between the internal and external sphincter of the anus

    three

    Dentate line

    Above the white line, 2-3cm from the edge of the anus. The jagged circular line connecting the lower end of each anal column and the edge of each anal flap is called the Dentate Line or the Anocutaneous Line. The following figure (8) and figure (9).

    Figure (8): The blue line shows the dentate line

    Figure (9): The blue line shows the dentate line

    This line is the transition zone of the endoderm. The epithelium, blood vessels, lymphatics and nerves of the upper and lower sides are of completely different sources. They are important anatomical landmarks, as shown in the figure below (10).

    Figure (10): Comparison of the anatomical structure of the dentate line

    More than 85% of anorectal diseases occur near the dentate line, which is of clinical significance. In addition, the dentate line is where the endoderm and ectoderm meet. Almost all anus and rectal congenital malformations such as anal atresia occur at the dentate line.

    The dentate line is also the inducing area of ​​defecation reflex. The dentate line area is distributed with highly specialized sensory nerve terminal tissues. When the stool reaches the anal canal from the rectum, the nerve endings in the dentate line area are stimulated, which will cause the internal and external sphincter to relax and the levator ani muscle to contract. , So that the anal canal is dilated and the stool is discharged. If the dentate line is cut during the operation, the bowel reflex will be weakened and constipation or sensory incontinence will occur.

    four

    Anal straight line

    The Anorectal Line is the horizontal line of the upper end of the rectal column, the dividing line between the inner mouth of the rectum neck and the ampulla of the rectum. On the plane of the anorectal ring, it is the attachment of the levator ani muscle. As shown in Figure (11) and Figure (12) below.

    Picture (11): The red line shows the rectal straight line

    Figure (12): The red line shows the straight line of the anus

    The anal straight line is the starting mark of the anal canal in surgery. It extends the upper boundary of the surgical anal canal to 1.5cm above the dentate line. This level is exactly the level of the anorectal ring, which is an important anatomical mark for high anal fistula surgery. significance!

    Fives

    Division of the anal canal

    There are four important marking lines (or linear markings) on the lumen surface of the anal canal in surgery. From the anal side to the oral side, they are the anal marginal line, the white line, the dentate line and the anal straight line. The anal canal can be divided into three areas by these four marking lines: 1. Anal skin area (also called belt) is located between the white line and anal margin line; anal comb area (also called hemorrhoid belt) is located between the dentate line and the white line. Between the lines; the anal column area is located between the anal straight line and the dentate line (also known as the column belt). See Figures (13) to (15) respectively.

    Picture (13): The yellow area shows the anal skin area

    Picture (14): The green area shows the anal comb area

    Picture (15): The blue area shows the anal column area

    1. Four linear signs of anal canal in surgery:

    Anal straight line---the dividing line between rectum and anal canal;

    Dentate line --- the starting line of the anal canal in anatomy;

    White line---the dividing line between the internal anal sphincter and the external anal sphincter;

    Anal margin line---the marking line of the anal opening.

    2. Division of the anal canal in surgery (zoning):

    Confirm the anal column area by the anal straight line and the dentate line;

    The dentate line and the white line---together confirm the anal comb area;

    Confirm the anal skin area by the white line and the anal margin line.

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