Acute appendicitis

While there are isolated reports of perityphlitis (fatal inflammation of the caecal region) from the late 1500s, recognition of acute appendicitis as a clinical entity is attributed to Reginald Fitz who presented a paper to the first meeting of the Association of American Physicians in 1886 entitled ‘Perforating inflammation of the vermiform appendix’. Soon afterwards Charles McBurney described the clinical manifestations of acute appendicitis including the point of maximum tenderness in the right iliac fossa that since bears his name. The incidence of appendicitis seems to have risen greatly in the first half of the twentieth century, particularly in Europe, America and Australasia, with up to 16 per cent of the population undergoing appendicectomy. In the past 30 years the incidence has fallen dramatically in these countries, with the number of operations in England and Wales declining from 113 000 in 1966 to 48 000 in 1990. In developing countries, which are adopting a more refined Western-type diet, the incidence continues to rise. No reason has been established for these changes in the incidence of acute appendicitis.

Acute appendicitis is relatively 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 the risk of developing appendicitis in the future is quite small. The incidence of appendicitis is equal amongst males and females before puberty. In teenagers and young adults the male:female ratio increases to 3:2 at the age of 25 years, thereafter the greater incidence in males declines.

  Aetiology

There is no unifying hypothesis regarding the aetiology of acute appendicitis. While appendicitis is clearly associated with bacterial proliferation within the appendix, no single organism is responsible, indeed a mixed growth of aerobic and anaerobic organisms is usual. The initiating event causing bacterial proliferation is controversial. Obstruction of the appendix lumen has been widely held to be important, and indeed some form of luminal obstruction by either a faecolith or stricture is found in the majority of cases.

A faecolith is composed of inspissated faecal material, calcium phosphates, bacteria and epithelial debris. Rarely a foreign body is incorporated into the mass. The incidental finding of a faecolith is a relative indication for prophylactic appendicectomy (Fig. 59.5). A fibrotic stricture of the appendix usually indicates previous appendicitis which resolved without surgical intervention (Fig. 59.6). Obstruction of the appendiceal orifice by tumour, particularly carcinoma of the caecum, is an occasional cause of acute appendicitis in middle age and the elderly. Intestinal parasites, particularly Oxyuris vermicularis (syn. pinworm), can proliferate in the appendix and occlude the lumen.

Pathology

Obstruction of the appendiceal lumen seems to be essential for development of appendiceal gangrene and perforation. Yet, in many cases of early appendicitis the appendix lumen is patent despite the presence of mucosal inflammation and lymphoid hyperplasia. Occasional clustering of cases amongst children and young adults suggests an infective agent, possibly viral, which initiates an inflammatory response, which within the narrow lumen of the appendix leads 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. Where 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 acute appendicitis (Fig. 59.7). 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 a phlegmonous mass or paracaecal abscess (Fig. 59.8). Rarely, appendiceal inflammation resolves leaving a distended mucus-filled organ termed a mucocele of the appendix (Fig. 59.9).

It is the potential for peritonitis that is the great threat of acute appendicitis. Peritonitis occurs as a result of free migration of bacteria through an ischaemic appendicular wall, through frank perforation of a gangrenous appendix or delayed perforation of an appendix abscess. Factors which promote this process include extremes of age, immunosuppression, diabetes mellitus, faecolith obstruction of the appendix lumen, a free-lying pelvic appendix and previous abdominal surgery which limits the ability of the greater omentum to wall off the spread of peritoneal contamination (Table 59.1). In these situations a rapidly deteriorating clinical course is accompanied by signs of diffuse peritonitis and systemic sepsis syndrome.

Clinical diagnosis history

The classical features of acute appendicitis begin with poorly localised colicky abdominal pain (Table 59.2). This is due to midgut visceral discomfort in response to appendiceal inflammation and obstruction. The pain is frequently first noticed in the periumbilical region and is similar to, but less intense than, the colic of small bowel obstruction. Central abdominal pain is associated with anorexia, nausea and usually one or two episodes of vomiting which follow the onset of pain (Murphy). Anorexia is a useful and constant clinical feature, particularly in children. The patient often gives a history of similar discomfort which settled spontaneously.

With progressive inflammation of the appendix, the parietal peritoneum in the right iliac fossa becomes irritated producing more intense, constant and localised somatic pain which begins to predominate. This is often reported by the patient as an abdominal pain which has shifted and changed in character. Typically, coughing or sudden movement exacerbates the right iliac fossa pain.

The classical visceral—somatic sequence of pain is present in only about half those patients subsequently proven to have acute appendicitis. Atypical presentations include pain which is predominantly somatic or visceral and poorly localised. Atypical pain is more common in the elderly in whom localisation to the right iliac fossa is unusual. An inflamed appendix in the pelvis may never produce somatic pain involving the anterior abdominal wall, but may instead cause suprapubic discomfort and tenesmus. In this circumstance, tenderness may only be elicited on rectal examination and is the basis for the recommendation that a rectal examination should be performed on every case of lower abdominal pain.

During the first 6 hours there is rarely any alteration in temperature or pulse rate. After that time, slight pyrexia (37.2—37.70C) with corresponding increase in the pulse rate to 80 or 90 is usual. However, in 20 per cent of cases there is no pyrexia or tachycardia in the early stages. In children a temperature greater than 38.50C suggests other causes, for example mesenteric adenitis (vide in Ira).

Typically, two clinical syndromes of acute appendicitis can be discerned, acute catarrhal (nonobstructive) appendicitis and acute obstructive appendicitis. The latter is characterised by a much more acute course. The onset of symptoms is abrupt and there may be generalised abdominal pain from the start. The temperature may be normal and vomiting is common, so that the clinical picture may mimic acute intestinal obstruction. Once recognised, urgent surgical intervention is required because of the more rapid progression to perforation.

 

Clinical diagnosis signs (Tables 59.3 and 59.4)

The diagnosis of appendicitis rests more on thorough clinical examination of the abdomen than on any aspect of the history or laboratory investigation. The cardinal features are those of an unwell patient with low grade pyrexia, localised abdominal tenderness, muscle guarding and rebound tenderness. Inspection of the abdomen may show limitation of respiratory movement in the lower abdomen. The patient is then asked to point to where the pain began and to where it moved (the pointing sign). Gentle superficial palpation of the abdomen, beginning in the left iliac fossa moving anticlockwise to the right iliac fossa, will detect muscle guarding over the point of maximum tenderness, classically McBurney point. Asking the patient to cough or gentle percussion over the site of maximum tenderness will elicit rebound tenderness.

Deep palpation of the left iliac fossa may cause pain in the right iliac fossa (Rovsing’s sign), which is helpful in supporting a clinical diagnosis of appendicitis. Occasionally an inflamed appendix lies on the psoas muscle and the patient, often a young adult, will lie with the right hip flexed for pain relief (the psoas sign). Spasm of the obturator internus is sometimes demonstrable when the hip is flexed and internally rotated. If an inflamed appendix is in contact with the obturator internus, this manoeuvre will cause pain in the hypogastrium (the obturator test) (Zachary Cope). Cutaneous hyperaesthesia may be demonstrable in the right iliac fossa, hut is rarely of diagnostic value.

Special features, according to position of the appendix

Retrocaecal

Rigidity is often absent and even on deep pressure tenderness may he lacking (silent appendix), the reason being that the caecum, distended with gas, prevents the pressure exerted by the hand from reaching the inflamed structure. However, deep tenderness is often present in the loin, and rigidity of the quadratus lumborum may he in evidence. Psoas spasm, due to the inflamed appendix being in contact with that muscle, may he sufficient to cause flexion of the hip joint. Hyperextension of the hip joint may induce abdominal pain when the degree of psoas spasm is insufficient to cause flexion of the hip.

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, and often tenderness over McBurney’s point is lacking as well. In some instances deep tenderness can he made out just above and to the right of the symphysis pubis. In either event, a rectal examination reveals tenderness in the rectovesical pouch or the pouch of Douglas, especially on the right side. Spasm of the psoas and obturator internus muscles may he present when the appendix is in this position. An inflamed appendix in contact with the bladder may cause frequency of micturition.

Post ileal

Although this is rare, it accounts for some of the cases of missed appendix’. Here 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, if any, is ill-defined, although it may he 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 for obvious reasons the patient is unable to give a history. Because of this, diagnosis is often delayed and thus the incidence of perforation and postoperative morbidity is considerably higher than in older children. Diffuse peritonitis can develop rapidly due to the underdeveloped greater omentum, which is unable to give much assistance 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. In addition, they do not sleep during the attack and very often bowel sounds are completely absent in the early stages.

The elderly

Gangrene and 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 coupled with coincident medical conditions produce a much higher mortality for acute appendicitis in the elderly.

The obese

Obesity can obscure and diminish all the local signs of acute appendicitis. Delay in diagnosis coupled with the technical difficulty of operating in the obese make it wiser to consider operating through a midline abdominal incision

Pregnancy

Appendicitis is the most common extra uterine acute abdominal condition in pregnancy with a frequency of from one in 1500 to one in 2000 pregnancies. Diagnosis is complicated by delay in presentation; early nonspecific symptoms are often attributed to the pregnancy, and the changing location of the appendix during pregnancy. As pregnancy develops during the second and third trimesters, the caecum and appendix are progressively pushed to the right upper quadrant of the abdomen. This displacement can result in flank or back pain, and may be confused with pyelonephritis, while lower abdominal pain may be confused with torsion of an ovarian cyst. Foetal loss occurs in 3—5 per cent of cases, increasing to 20 per cent if perforation is found at operation.