Acute appendicitis is the most common surgical emergency abdomen. According to statistics, it is the most common acute abdomen in general hospitals, accounting for 10-15% of surgical admissions. The reason why appendicitis is common and requires surgical treatment is closely related to the anatomical features of the appendix.
Location and shape of the appendix
The appendix is an elongated blind tube attached to the inner posterior wall of the cecum, about 5-8 cm long and 0.5-0.8 cm in diameter, with its base on the inner posterior side of the cecum, about 2.5 cm below the ileocecal valve. The base of the appendix is relatively fixed, while the body and tip are relatively free (sometimes the body and tip of the appendix can be partially fixed behind the peritoneum) and can point in all directions.
Structure of the appendix, blood supply and nerves
The structure of the appendix is similar to that of the colon, with a mucosal layer, a submucosal layer, a circular muscle layer, a longitudinal muscle layer, a subplasma layer and a plasma membrane layer. The mucosa and submucosa are rich in lymphoid tissue and are distributed longitudinally (this is the reason why infection spreads easily along the submucosa).
The arteries of the appendix mostly originate from the ileal branch of the ileocolic artery, which travels to the appendix after the end of the ileum through the free edge of the appendiceal mesentery, sending 3-5 branches along the way to the appendiceal wall for blood supply. The appendiceal artery is mostly a single artery and has no anastomosis with other arteries, so it is the terminal artery. The appendiceal vein travels with the eponymous artery and joins the portal vein via the ileocolic and superior mesenteric veins.
Variations and malformations of the appendix
1.Variation of location
The appendix is more variable than any other organ in terms of its position in the abdominal cavity, depending on the position and morphology of the cecum.
The retroperitoneal position of the appendix includes three conditions.
(1) retroperitoneal intussusception of the cecum.
(2) retroperitoneal extraperitoneal position of the cecum.
(3) the cecum is intraperitoneal and the appendix is attached to the retroperitoneal plasma membrane of the cecum.
Whether the appendix is anterior or posterior to the cecum, the majority of appendices are intraperitoneal, very few are extraperitoneal, and inferior cecum plasma membrane is rare. However, a long appendix can reach behind the ascending colon and approach the right kidney or the descending duodenum, in which case the distal end of the appendix can be located outside the peritoneum.
The clinical term “appendiceal ectopic” includes eight conditions.
(1) Left-sided appendix, where the appendix is anywhere to the left of the midline of the abdomen.
(2) High appendix, in which the appendix is located above the umbilical level.
(3) low appendix, where the appendix is in the pelvis below the level of the anterior superior iliac spine
(4) intra-hernial appendix, where the appendix is located within the extra-abdominal hernia sac
(5) extraperitoneal appendix, where the appendix is located outside the peritoneal wall layer
(6) intramural appendix, where the appendix is located in the tissue within the wall of the ileocecal cecum
(7) intraluminal appendix, where the appendix is located within the intestinal lumen of the cecum
(8) misplaced appendix, where the appendix root is located in any intestinal collaterals beyond the convergence point of the lower pole of the cecum and the colonic band.
2.Abnormal appendiceal development
(1) segmental appendix, which is actually multiple appendiceal atresia.
(2) Appendiceal diverticulum.
(3) Excessive appendiceal length, >20 cm.
(4) Excessive appendiceal thickness, >2 cm in diameter, up to 5 cm.
(5) short appendix, <1 cm.
(6) Appendiceal agenesis, which is very rare, so it should not be rashly identified as appendiceal agenesis when the appendix is not found during surgery.
3.Appendiceal malformation
(1) Partial duplication of the appendix.
(2) Complete duplication of the appendix.
(3) collaterally shaped appendix.
(4) Appendiceal appendix duplication.
Appendiceal ectopic tissue
1, appendiceal endometriosis.
2, appendiceal ectopic pancreas.
3.appendiceal gastric mucosa ectopic.
4.Appendiceal esophageal mucosal ectopic.
Clinical points
1.Anatomical factors associated with easy inflammation of the appendix and rapid development of inflammation
(1) A large amount of lymphatic tissue in the appendiceal wall, which easily invites infection factors in the blood and intestine and induces inflammatory reactions.
(2) The appendiceal lumen is narrow and susceptible to infection due to poor drainage, and the inflamed appendiceal wall is swollen and the lumen is even narrower, causing obstruction of the appendiceal lumen.
(3) The appendiceal mucosa can absorb water and easily form fecal stones to obstruct the appendiceal lumen.
(4) The appendix is a blind duct, and the slender lumen is easily blocked by foreign bodies such as parasites and food residues.
(5) The appendix is free at the end and is highly mobile, which can easily cause injury and invite foci of infection in the surrounding tissues.
(6) The appendix itself is curved and variable, and when the gastrointestinal tract is dysfunctional, it can cause reflex spasm of the appendiceal muscle, contributing to appendiceal torsion and overturning.
(7) The appendiceal artery is the terminal artery, and the blood flow of the appendix is impaired or even forms intravascular embolism during vasospasm, which can easily lead to appendiceal gangrene and perforation.
2.Intraoperative search for the appendix
For acute appendicitis surgery, the key step often lies in the search for the appendix, and the methods are.
(1) According to the preoperative examination, an incision is made centered on the most important point of pressure pain, which is often taken as a McDonald’s incision.
(2) Since all three colonic bands of the cecum converge at the root of the appendix, tracing by colonic band is a more reliable way.
(3) Search for the appendix according to the common part of the appendix, i.e., about 2.5 cm below the ileocecal valve, and search for the appendix represented by the index finger according to the “right hand rule” (Jinzhe Zhang: when the right hand is in the rotated anterior position, the end of the ileum is the thumb, the middle, ring and little fingers are clenched as the cecum, and the position of the index finger is the appendix), and its body and tip are mostly found in the anterior cecum, anterior ileum, posterior cecum and inferior cecum.
(4) Pursuing along the ileocecal mesentery or ileocecal fold.
(5) at the transposition of the greater omentum.
(6) Concentration of exudate and pus accumulation.
(7) The inflamed appendix is a hard strip, which can be probed by the fingers during surgery. This method is often preferred by surgeons, but formally, this technique is not advocated as the primary method of searching for the appendix because of the tendency to aggravate intestinal adhesions by disturbing the peritoneal cavity too much. On the other hand, care should be taken to identify the fallopian tubes in women when palpating by hand, so that they are not mistakenly incised as the appendix.
(8) Common variant sites, such as pelvic position and subhepatic position.
(9) There is no appendix in the ileocecal region, but the appendix may be located in a special position such as retroperitoneal position, within the subplasma wall of the cecum or even within the cecum lumen.
3.Special intraoperative precautions
(1) Intraoperative extrusion of the appendix is contraindicated. When the appendix is septic, bacterial emboli can flow with the blood into the portal vein and liver, causing dangerous septic portal phlebitis and liver abscess. Intraoperative squeezing can promote the occurrence and development of this condition.
(2) Extraction of the appendix should be gentle. The appendix has vagal nerve fiber distribution, which travels within the tract to distribute in the appendiceal wall. Intraoperative stretching of the appendiceal tract can cause hyperreflexia of the vagus nerve, neurogenic shock, and lead to cardiac and respiratory poly arrest.