Anatomy of Appendix and AppendicitisJuly 9, 2011 | 2:11 pm | Anatomy | No Comment
Also called as vermix, vermiform appendix is a narrow vermin (worm shaped) tube arising from the posteromedial aspect of the cecum (a large blind sac forming the commencement of the large intestine) about 1 inch below the iliocecal valve. Small lumen of appendix opens into the cecum and the orifice is guarded by a fold of mucous membrane known as ‘valve of Gerlach’. The 3 taenia coli (taenia libera, taenia mesocoli and taenia omental) of the ascending colon and caecum converge on the base of the appendix.
Although the appendix serves no digestive function, it is thought to be a vestigial remnant of an organ that was functional in human ancestors.
The length varies from 2 to 20 cm with an average of 9 cm with diameter of about 5mm. It is longer in children compared to adults. In the fetus it is a direct outpouching of the caecum, but differential overgrowth of the lateral caecal wall results in its medial displacement.
The appendix is suspended by a small traignular fold of peritoneum, called the mesoappendix.
- Inflammation of the appendix is known as the appendicitis. Acute appendicitis is a common cause of abdominal pain requiring surgery, particularly in the West where there is low roughage diet. Appendicitis usually follows obstruction of the lumen with distal infection and ulceration. The usual causes are: fecolith, calculi, foreign body, tumor, worms (Oxyuriasis vermicularis), diffuse lymphoid hyperplasia, vascular occlusion, inadequate dietary fiber intake, etc.
- The lumen of the appendix is relatively wide in the infant and is frequently completely obliterated in the elderly. Since obstruction of the lumen is the usual precipitating cause of acute appendicitis it is not unnatural,therefore, that appendicitis should be uncommon at the two extremes of life. It is seen more commonly in older children and young adults.
- Right lower quadrant of abdomen and more specifically right iliac fossa.
- McBurney’s point lying at the junction of lateral one-third and the medial two-thirds of the line joining the umbilicus to the right anterior superior iliac spine roughly corresponds to the position of the base of the appendix.
- McBurney’s point is the site of maximum tenderness in appendicits.
- Examination of a case of acute appendicitis reveals following physical signs:
- Hyperaesthesia in the right iliac fossa
- Tenderness at McBurney’s point
- Muscle guard and rebound tenderness over the appendix
- Appendicectomy is usually performed through a muscle-splitting incision in the right iliac fossa. The caecum is delivered into the wound and, if the appendix is not immediately visible, it is located by tracing the taeniae coli along the caecum—they fuse at the base of the appendix. When the caecum is extraperitoneal it may be difficult to bring the appendix up into the incision; this is facilitated by first mobilizing the caecum by incising the almost avascular peritoneum along its lateral and inferior borders.
Variations in Appendix position:
Although the base of the appendix is fixed, the tip can point in any direction. Hence, the position of the appendix is extremely variable. The appendix is the only organ in the body which is said to have no anatomy. When compared to the hour hand of a clock, the positions would be:
- 12 o clock: Retrocolic or retrocecal (behind the cecum or colon)
- 2 o clock: Splenic (upwards and to the left – Preileal and Postileal)
- 3 o clock: Promonteric (horizontally to the left pointing the sacral promontory)
- 4 o clock: Pelvic (descend into the pelvis)
- 6 o clock: Subcecal (below the cecum pointing towards inguinal canal)
- 11 o clcok: Paracolic (upwards and to the right)
Most common position of appendix (75% of cases): Retrocecal
Second most common position of appendix (20% of cases): Subcecal
If the appendix is very long, it may actually extend behind the ascending colon and abut against the right kidney or the duodenum; in these cases its distal portion lies extraperitoneally.
The location of the tip of the appendix determines early signs and symptoms of appendicitis.
- Retrocecal: Extension of the hip joint may cause pain because the appendix is disturbed by stretching of the psoas major muscle. Pain usually localizes in the right flank.
- Pelvic: Pain may be felt when the thigh is flexed and medially rotated, because the obturator internus is stretched. Pelvic appendix may irritate the bladder or rectum causing suprapubic pain, pain with urination, or feeling the need to defecate.
- Retroileal: In some males, it can irritate the ureter and cause testicular pain.
- Pregnancy: the appendix can be shifted and patients can present with RUQ (Right upper quadrant) pain.
- Appendicular artery: The mesoappendix, containing the appendicular branch of the ileocolic artery (branch of superior mesenteric artery), descends behind the ileum.
- Accessory appendicular artery: An accessory appendicular artery can branch from the posterior cecal artery which is also a branch of ileocolic artery.
- Acute infection of the appendix may result in thrombosis of the appendicular artery with rapid development of gangrene and subsequent perforation.
- The accessory appendicular artery can lead to significant intraoperative and postoperative hemorrhage and should be searched for carefully and ligated once the main appendicular artery is controlled.
Appendicular vein –> Ileocolic vein –> Superior mesenteric vein –> Portal vein
- There is abundant lymphoid tissue in its walls.
- From the body and apex of the appendix 8-15 vessels ascend in the mesoappendix and are ocasionally interrupted by one or more nodes –> unite to form 3 or 4 larger vessels –> inferior and superior ileocolic nodes
- A few of them pass indirectly through the appendicular nodes situated in the mesoappendix.
Appendicular dyspepsia: Chronic appendicits produces dyspepsia resembling disease of stomach, duodenum or gall bladder. It is due to passage of infected lymph to the subpyloric lymph nodes which causes irritation of pylorus.
- Sympathetic nerves: T9 and T10 spinal segments through the celiac plexus
- Parasympathetic nerves: Vagus
Both the appendix and the umbilicus are innervated by segment T10 of the spinal cord and hence the pain caused by appendicitis is first felt in the region of umbilicus (referred pain). With increasing inflammation pain is felt in the right iliac fossa due to involvement of the parietal peritoneum of the region which is sensitive to pain in contrast to pain insensitive visceral peritoneum.
Histology: Inside to outside
- No villi
- Epithelium invaginates to form crypts of Liberkuhn but the crypts do not occur as frequently as in the colon
- Muscularis mucosae is ill defined
- Large accumulations of lymphoid tissue in the lamina propria and submucosa. Hence appendix is also called abdominal tonsil.
- There is often fatty tissue in the submucosa.
3. Muscularis externa:
- Thinner than in the remainder of the large intestine
- Comprises 2 layers: Inner circular muscle layer and Outer longitudinal muscle layer
- Outer longitudinal smooth muscle layer does not aggregate into taenia coli
4. Serosa and peritoneum
The submucosal lymphoid follicles enlarge, peak from 12-20 years, and then decrease. This correlates with the incidence of appendicitis. Enlarged or hyperplastic lymhoid follicles contribute to the obstruction of small lumen of appendix.
In acute appendicitis, the microscopy of cross section of appendix reveals:
- Fibrin on peritoneal surface
- Neutrophil exudate in lumen
- Neutrohpil exudate spreads in submucosa and soon affects all layers
Tags: Appendicitis, Appendix
Last updated: July 9, 2011