ORGANUM
The vermiform appendix is a normal true diverticulum of the cecum that is prone to acute and chronic inflammation - it typically presents acutely, within 24 hours of onset, but can also present as a more chronic condition. Acute appendicitis is most common in adolescents and young adults, with a lifetime risk of 7%.
It classically presents initially as generalised or periumbilical abdominal pain that later localises to the right lower quadrant. The vermiform appendix can be located at any point in the abdomen, depending on if there were any abnormal developmental issues, including midgut malrotation, or if there are any other physiological/pathological processes such as pregnancy or prior abdominal surgeries. If there has been perforation with a contained abscess, the presenting symptoms can be more indolent - causing little to no pain.
The cause of appendicitis is usually an obstruction of the appendiceal lumen. This can be from an appendicolith (a stone of the appendix) or some other mehcnial aetiologies. Appendiceal tumours such as carcinoid tumours, appendiceal adenocarcinoma, intestinal parasites, and hypertrophied lymphatic tissue are all known causes of obstruction and appendicitis.
The exact aetiology of acute appendicitis is often unknown; when the appendiceal lumen gets obstructed, bacteria build up in the appendix can cause acute inflammation with perforation and abscess formation. The appendix contains both aerobic and anaerobic bacteria such as E.coli and Bacteroides spp; however recent studies showed a high number of bacteria phyla in patients with complicated perforated appendicitis.
Appendicitis occurs more often between the ages of 5 and 45, with a mean age of 28. The incidence is approximately 233 per 100,000 people. Males have a slightly higher predisposition than females - 8.6%:6.7% lifetime incidence respectively.
The pathophysiology of acute appendicitis is not entirely known. It likely stems from obstruction of the appendiceal orifice. The background aetiology of obstruction might differ depending upon the age groups. Overt luminal obstruction is typically caused by a gallstone, tumour, mass or mass of worms (oxyuriasis vermicularis - pinworm).
Lymphoid hyperplasia is essential, which result in inflammation, localised ischemia, perforation and the development of a contained abscess or frank perforation with resultant peritonitis. The obstruction may be aused by lymphoid hyperplasia, infections (parasitic), fecaliths (stone made of feces), or benign/malignant tumours. When obstruction is the cause, it leads to an increase in intraluminal and intramural pressure, causing small vessel occlusion and lymphatic stasis. Once obstructed, the appendix fills with mucus and becomes distended, and as lymphatic and vascular compromise advances, the wall of the appendix becomes ischemic and necrotic.
Bacterial overgrowth then occurs in the obstructed appendix, with aerobic organisms predominating in early appendicitis and mixed aerobes/anaerobes later on in the course. Common organisms include:
E.coli
Pepto streptococcus
Bacteroides
Pseudomonas
Once significant inflammation and necrosis occur the appendix is at risk of perforation, leading to localised abscess and sometimes frank peritonitis. While the most common position of the appendix is retrocecal, the position of the tail can very - retrocecal, subcecal, pre-and post-ileal, and pelvic
Typically, early appendicitis produces periumbilical pain that ultimately localises to the right lower quadrant, followed by nausea, vomiting, low-grade fever, and a mildly elevated peripheral white cell count. The visceral afferent nerve fibres at T8 through T10 are stimulated, which leads to vague centralised pain. As the appendix becomes more inflamed, the adjacent parietal peritoneum is irritated, and the pain localises to the right.
A classic physical finding in the McBurney sign, deep tenderness located two thirds of the distance from the umbilicus to the right anterior superior iliac spine. Classic signs and symptoms of acute appendicitis are often absent - in some cases, a retrocecal appendix may generated right flank or pelvic pain. A malrotated colon may give rise to appendicitis in the left upper quadrant. Pain upon passive extension of the right leg with the patient in the left lateral decubitus position is known as the psoas sign; the maneuverer stretches the psoas major muscle, which can be irritated by an inflamed retrocecal hip. Patients often flex the hip to shorten the psoas major muscle and relieve pain.
Physical exam will find certain positive sign as the disease develops:
RLQ guarding and rebound tenderness over McBurney's point
Rovsing's sign - RLQ pain elicited by palpitation of the left lower quadrant
Dunphy's sign - Increased abdominal pain with coughing
As with other causes of acute inflammation, there is neutrophilic leukocytosis. In some cases, the peripheral leucocytosis may be minimal, or alternatively, so great that other causes are considered. Ketones may be found in urine and the CRP may be elevated. A combination of normal WBC and CRP has a 98% specificity for the exclusion of acute appendicitis.
Appendicitis can be a clinical diagnosis, but a CT scan can diagnose appendicitis and it is being used with increasing frequency - the CT criteria for appendicitis include:
Enlarged appendix >6mm in diameter
Appendiceal wall thickening >2mm
Periappendiceal fat stranding
Appendiceal wall enhancement
Presence of appendicoliths (25%)
A abdominal ultrasound can also be used to look for a specific index of compressibility along with a diameter of less than 5mm to exclude appendicitis.
The diagnosis is especially difficult in young children and the very old as other causes of abdominal pain are relevant in these communities.