The vermiform appendix

The vermiform appendix is a vestigial organ The vermiform appendix is a vestigial organ. Its importance in surgery results only from its propensity for inflammation. AA is the most common cause of ‘acute abdomen’ Appendicectomy ( ‘appendectomy’) is the most frequent urgent abdominal operation. The diagnosis of appendicitis is clinical.

ANATOMY

It is a blind muscular tube with: mucosal, submucosal, muscular & serosal layers. At birth: the appendix is short & broad at its junction with the caecum, but growth of the caecum produces the typical tubular structure by the age of two years . During childhood: growth of the caecum rotates the appendix into a retrocaecal but intraperitoneal position .

In 25% of cases, rotation of the appendix does not occur, resulting in : pelvic, subcaecal or paracaecal position. Occasionally, the tip of the appendix becomes extraperitoneal, lying behind the caecum or ascending colon.

The various positions of the appendix

Rarely, the caecum does not migrate during development to the right lower quadrant, in these circumstances, the appendix can be found: - Near the gall bladder. - In case of intestinal malrotation, in the LIF. causing diagnostic difficulty if appendicitis develops .

The position of the base of the appendix is constant: found at the confluence of the three taeniae coli which fuse to form the outer longitudinal muscle coat of the appendix.  

The mesentery of the appendix (mesoappendix) arises from the lower surface of the mesentery or the terminal ileum. The appendicular artery, a branch of the lower division of the ileocolic artery, passes behind the terminal ileum to enter the mesoappendix a short distance from the base of the appendix.

Appendicular artery is ‘end-artery‘, thrombosis of which results in necrosis of the appendix (gangrenous appendicitis). Lymphatic channels traverse the mesoappendix to the ileocaecal lymph nodes

Microscopic anatomy:

The length is 7.5 -10 cm. The lumen is irregular, by multiple longitudinal folds of mucous membrane lined by columnar cell. Crypts are present, but are not numerous. In the base of the crypts lie argentaffin cells (Kulchitsky cells), give rise to carcinoid tumours . The appendix is the most frequent site for carcinoid tumours, which may present with appendicitis due to occlusion of the appendiceal lumen.

Submucosa contains numerous lymphatic aggregations Submucosa contains numerous lymphatic aggregations. The prominence of lymphatic tissue in the appendix of young adults seems to be important in the aetiology of appendicitis but no discernible change in immune function results from appendicectomy.

The incidence of appendicitis risen greatly in the first half of the twentieth century, particularly in Europe, America and Australia. In the past 30 years, the incidence fallen dramatically. Acute appendicitis is rare in infants, and becomes increasingly common in childhood and early adult life, reaching a peak incidence in the teens and early 20s. After middle age, risk of developing appendicitis is small.

Incidence of appendicitis is equal among males & females before puberty In teenagers and young adults, the male–female ratio increases to 3:2 but at age 25; thereafter, the greater incidence in males declines.

Aetiology

There is no single hypothesis for the aetiology of acute appendicitis There is no single hypothesis for the aetiology of acute appendicitis. Decreased dietary fibre and increased consumption of refined carbohydrates may be important. As with colonic diverticulitis, the incidence of appendicitis is lowest in societies with a high dietary fibre intake.

While appendicitis is clearly associated with bacterial proliferation within the appendix, no single organism is responsible. A mixed growth of aerobic & anaerobic organisms is usual.

Obstruction of the appendix lumen is important, and some form of luminal obstruction is found in the majority of cases & the Obstruction by: 1- A faecolith ( ‘appendicolith’): Composed of: inspissated faecal material, calcium phosphates, bacteria and epithelial debris . Rarely, a FB is incorporated into the mass.

2- A fibrotic stricture: indicates previous appendicitis that resolved 2- A fibrotic stricture: indicates previous appendicitis that resolved. 3- Tumour: ca-caecum obstruct the appendiceal orifice, & cause of AA in middle-aged & elderly. 4- Intestinal parasites: Oxyuris vermicularis (pinworm), proliferate in the appendix and occlude the lumen.

Pathology:

Obstruction of the lumen is essential for the development of appendiceal gangrene & perforation. Yet, in many cases of early appendicitis, the appendix lumen is patent despite the presence of mucosal inflammation and lymphoid hyperplasia. Some suggests an infective agent, possibly viral, which initiates an inflammatory response. Seasonal variation in the incidence is observed, more cases occurring between May and August

Lymphoid hyperplasia narrows the lumen of the appendix, leading to luminal obstruction. Once obstruction occurs, continued mucus secretion and inflammatory exudation increase intraluminal pressure, obstructing lymphatic drainage. Oedema and mucosal ulceration develop with bacterial translocation to the submucosa.

Resolution may occur at this point either: spontaneously or in response to antibiotic therapy but If the condition progresses, further distension of the appendix may cause venous obstruction and ischaemia of the appendix wall. With ischaemia, bacterial invasion occurs through the muscularis propria and submucosa, producing AA.

Finally, ischaemic necrosis of the appendix wall produces gangrenous appendicitis, with free bacterial contamination of the peritoneal cavity. Alternatively, the greater omentum and loops of small bowel become adherent to the inflamed appendix, walling off the spread of peritoneal contamination, & resulting in phlegmonous mass or paracaecal abscess. Rarely, appendiceal inflammation resolves, leaving a distended mucus-filled organ termed a ‘mucocoele’ of the appendix .

Risk factors for perforation of the appendix: 1- Extremes of age. 2- Immunosuppression. 3- Diabetes mellitus. 4- Faecolith obstruction. 5- Pelvic appendix. 6- Previous abdominal surgery

Clinical diagnosis:

 History: Classical features of AA begin with poorly localised colicky abdominal pain. This is due to midgut visceral discomfort in response to appendiceal inflammation and obstruction. The pain is first noticed in the periumbilical region & associated with anorexia, nausea and one or two episodes of vomiting that follow the onset of pain . Anorexia is a useful and constant clinical feature, particularly in children.

The patient often gives a history of similar discomfort that settled spontaneously. A family history is also useful as up to one-third of children with appendicitis have a first-degree relative with a similar history. With progressive inflammation of the appendix, the parietal peritoneum in the RIF becomes irritated, producing intense, constant & localised somatic pain. Patients report this as an abdominal pain that has shifted and changed in character. Typically, coughing or sudden movement exacerbates the RIF pain.

So Symptoms of appendicitis are: 1- Periumbilical colic. 2- Pain shifting to the RIF. 3- Anorexia. 4- Nausea.

The classic visceral–somatic sequence of pain is present in only half of those patients with AA. Atypical presentations include: pain that is predominantly somatic or visceral and poorly localised. Atypical pain is more common in the elderly, in whom localisation to the RIF is unusual. An inflamed appendix in the pelvis may never produce somatic pain involving the anterior abdominal wall, but may cause suprapubic discomfort & tenesmus. In this circumstance, tenderness may be elicited only on rectal examination .

During the first 6 hours, there is rarely any alteration in temperature or pulse rate. After that time, slight pyrexia (37.2 − 37.7°C) with a corresponding increase in the pulse rate to 80 or 90 is usual. However, in 20 % of patients, there is no pyrexia or tachycardia in the early stages. In children, a temperature greater than 38.5°C suggests other causes, e.g. mesenteric adenitis .

Two clinical syndromes of acute appendicitis can be seen: 1- Acute catarrhal (nonobstructive) appendicitis. 2- Acute obstructive appendicitis.

Signs: Diagnosis of AA depend on thorough abdominal examination more than history or lab.investigation. Clinical signs in appendicitis: 1- unwell patient with low-grade pyrexia. 2- Localised tenderness in the RIF. 3- Muscle guarding. 4- Rebound tenderness.

Inspection: limitation of respiratory movement in the lower abdomen Inspection: limitation of respiratory movement in the lower abdomen. superficial palpation: muscle guarding over the point of maximum tenderness, classically McBurney's point. Asking patient to cough or percussion over the site of maximum tenderness will elicit rebound tenderness.

Signs to elicit in appendicitis

1- Pointing sign: The patient is asked to point to where the pain began and where it moved . 2- Rovsing's sign: Deep palpation of LIF may cause pain in RIF.

3- Psoas sign:

4- Obturator sign: The hip is flexed and internally rotated 4- Obturator sign: The hip is flexed and internally rotated. If an inflamed appendix is in contact with the obturator internus, this cause pain in the hypogastrium (the obturator test; Zachary Cope).

Special features, according to position of the appendix

Retrocaecal: Rigidity is often absent, and even deep pressure may fail to elicit tenderness (silent appendix), this is because of the caecum is distended with gas & prevents the pressure exerted by the hand from reaching the inflamed appendix. However, deep tenderness is often present in the loin, and rigidity of the quadratus lumborum may be in evidence. Psoas spasm, due to the inflamed appendix being in contact with it & may cause flexion of the hip joint. Hyperextension of the hip joint may induce abdominal pain.

Pelvic: Occasionally, early diarrhoea results from an inflamed appendix being in contact with the rectum. When the appendix lies entirely within the pelvis, there is usually complete absence of abdominal rigidity. rectal examination reveals tenderness in the rectovesical pouch or the pouch of Douglas, Spasm of the psoas and obturator internus muscles may be present . An inflamed appendix in contact with the bladder may cause frequency of micturition.

Postileal: the inflamed appendix lies behind the terminal ileum. It presents the greatest difficulty in diagnosis because the pain may not shift, diarrhoea is a feature and marked retching may occur. Tenderness is ill defined, although it may be present immediately to the right of the umbilicus.

Special features, according to age

Infants: Appendicitis is relatively rare in infants under 36 months of age and, diagnosis is often delayed, thus the incidence of perforation & postop morbidity is considerably higher than in older children. Diffuse peritonitis can develop rapidly because of the underdeveloped greater omentum, which is unable in localising the infection.

Children: It is rare to find a child with appendicitis who has not vomited. Children with appendicitis usually have complete aversion to food.

The elderly: Gangrene & perforation occur much more frequently in elderly patients. Elderly patients with lax abdominal walls or obesity may harbour a gangrenous appendix with little evidence of it, and the clinical picture may simulate subacute intestinal obstruction. These features & with coincident medical conditions, produce a higher mortality for AA in the elderly

The obese: Obesity obscure & diminish all the local signs of AA. Delay in diagnosis & with the technical difficulty of operating in the obese, it better to operate through a midline abdominal incision. Laparoscopy is particularly useful in the obese.

Pregnancy: Appendicitis is the most common extrauterine acute abdominal condition in pregnancy. Diagnosis is complicated by delay in presentation as early non-specific symptoms are often attributed to the pregnancy. The caecum and appendix are progressively pushed to the right upper quadrant as pregnancy develops during the 2nd & 3rd trimesters.

Differential diagnosis

Children: 1- Acute gastroenteritis. 2- Mesenteric lymphadenitis: the pain is colicky in nature and cervical lymph nodes may be enlarged. 3- Meckel's diverticulitis: It may be impossible to clinically distinguish it from AA. 4- Intussusceptions: Appendicitis is uncommon before the age of two years, whereas the median age for intussusception is 18 months.

5- Henoch–Schönlein purpura: There is an ecchymotic rash, typically affecting the extensor surfaces of the limbs & on the buttocks. 6- Lobar pneumonia and pleurisy: especially at the right base. Abdominal tenderness is minimal, pyrexia is marked, & chest exam is important & CXR is diagnostic.

Adults: 1- Terminal ileitis history of abdominal cramping, weight loss & diarrhoea suggests regional ileitis rather than appendicitis. 2- Perforated peptic ulcer: the duodenal contents pass along the paracolic gutter to the RIF. (history of dyspepsia & a very sudden onset of pain in the epigastrium & passes to RIF. Erect CXR show gas under the diaphragm in 70 %.

3-Ureteric colic : Character & radiation of pain differs from AA 3-Ureteric colic : Character & radiation of pain differs from AA. Urinalysis & US or IVU is diagnostic. 4- Right-sided acute pyelonephritis : tenderness in the loin, fever (temperature 39°C) & possibly rigors and pyuria. 5- Testicular torsion: in a teenage or young adult. Pain can be referred to the RIF.

6- Acute pancreatitis: serum or urinary amylase level 6- Acute pancreatitis: serum or urinary amylase level. 7- Rectus sheath haematoma: Is rare but easily missed DD. often after an episode of strenuous physical exercise. Localised pain without GIT upset is the rule.

Adult female: In women of childbearing age the pelvic disease most often mimics AA. A careful gynaecological history should be taken in all women with suspected AA, concentrating on: menstrual cycle, vaginal discharge possible pregnancy .

1- Mittelschmerz: Midcycle rupture of a follicular cyst with bleeding produces lower abdominal & pelvic pain, typically midcycle. Systemic upset is rare, a pregnancy test is negative, and symptoms usually subside within hours. Occasionally, diagnostic laparoscopy is required.

2- Pelvic inflammatory disease: PID is a spectrum of diseases that include|: salpingitis, endometritis & tubo-ovarian sepsis Incidence of these conditions is increasing & diagnosis should be considered in every young adult female. Typically, the pain is lower than in AA & is bilateral. A history of vaginal discharge, dysmenorrhoea and burning pain on micturition is a helpful DD point.

The physical findings include adnexal and cervical tenderness on vaginal examination, Transvaginal ultrasound can be particularly helpful in establishing the diagnosis. Sometimes, diagnostic laparoscopy is indicated.

3- Ectopic pregnancy: Either: ruptured ectopic pregnancy (haemoperitoneum) right-sided tubal abortion, right-sided unruptured tubal pregnancy. There is history of a missed menstrual period, & pregnancy test may be positive. Severe pain is felt when the cervix is moved on vaginal examination. Signs of intraperitoneal bleeding usually become apparent, Pelvic ultrasonography should be carried .

4- Torsion/haemorrhage/rupture of an ovarian cyst: When suspected, pelvic ultrasound and a gynaecological opinion should be sought. 5- Endometriosis. 6- Right-sided acute pyelonephritis.

Elderly: 1- Diverticulitis: with a long sigmoid loop, the colon lies to the right of the midline. Abdominal CT & some time laparoscopy or exploratory laparotomy is indicated . 2- Intestinal obstruction: The diagnosis of intestinal obstruction is usually clear.

3- Carcinoma of the caecum: may mimic or cause obstructive appendicitis in adults. 4- Torsion appendix epiploicae. 5- Mesenteric infarction. 6- Leaking aortic aneurysm.