The appendix and Meckel's diverticulum

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Acute appendicitis

Acute appendicitis is common and affects one in seven persons. The diagnosis of appendicitis can be difficult. Delays in diagnosis complicate the illness.

Surgical pathology

With acute appendicitis, organisms invade the wall of the appendix and are lodged in the submucosa. Eventually, the full thickness of the wall is involved by acute inflammation and becomes swollen and reddened. With delay in diagnosis, the appendix becomes distended, especially if there is obstruction of the lumen. Venous stasis and then arterial occlusion result in gangrene at the tip of the appendix, where the blood supply is precarious, or at the site of obstruction in the appendix because of pressure necrosis.

Perforation may follow and can be localised by the greater omentum and loops of small bowel or may become generalised with diffuse contamination of the peritoneal cavity.

Clinical features

Symptoms

Abdominal pain

The nature of the pain may be highly variable. The most common initial presentation is a periumbilical, gnawing pain that migrates within a few hours to the right iliac fossa. There may be a preceding period of anorexia, nausea and vomiting that lasts 12–24 hours. Severe vomiting is uncommon. The usual sequence is anorexia, followed by central abdominal pain, then vomiting and finally pain in the right iliac fossa.

The initial periumbilical pain is due to obstruction and inflammation of the appendix and is mediated through the visceral pain fibres as a mid-gut pain. When appendicitis becomes transmural, the serosa of the appendix and the parietal peritoneum are involved, causing a localised pain mediated through the somatic pain fibres in the right iliac fossa.

Atypical presentations include a right upper quadrant pain from a long appendix or a right loin pain from a retrocaecal appendix. Patients presenting with peritonitis from perforated appendicitis have generalised abdominal pain.

Diarrhoea

Early in the course of the illness, patients may have one or two loose bowel movements as a response to visceral pain. Diarrhoea and tenesmus are most likely in the presence of an inflamed pelvic appendix irritating the rectal wall or a retroileal appendix irritating the terminal ileum. Severe and persistent diarrhoea is more likely to be due to gastroenteritis or inflammatory bowel disease.

Signs

General

With more advanced inflammation, the patient may look unwell. Moderate fever and tachycardia may be present and reflect the underlying infective process.

Local

Tenderness over the site of the appendix is the most important sign of appendicitis. The tenderness is localised and persistent and is classically at McBurney's point (one-third of the way from the anterior superior iliac spine to the umbilicus), although it may vary depending on the location of the appendix (The various positions of the appendix.). Tenderness may be minimal early in the course of the illness and hard to elicit in the obese or if the appendix is retrocaecal.

The various positions of the appendix.

Local muscular rigidity in the right iliac fossa is produced by inflammation of the parietal peritoneum overlying the appendix. Subtle rigidity can be detected by gently moving the palpating hand toward the area of maximal pain in the right iliac fossa while talking with the patient. This helps to differentiate true rigidity or guarding from voluntary spasm associated with nervousness. It is also helpful to ask the patient to cough or to sit up while watching the patient's facial expression; a grimace further suggests the presence of local peritonitis.

With local peritonitis, palpation in the left lower quadrant may cause pain in the right lower quadrant (Rovsing's sign). Signs of local peritonitis may be minimal in patients with a retrocaecal or pelvic appendicitis. The Psoas sign - pain caused by the extension of the right hip to stretch the psoas muscle - is generally present in retrocaecal appendicitis. Pelvic appendicitis is often difficult to differentiate from pelvic inflammatory disease but is usually associated with a right-sided tenderness on rectal examination.

Patients who present late with appendicitis may have generalised tenderness and rigidity, indicating perforation and peritonitis. Rebound tenderness indicates peritoneal inflammation and is best elicited by percussion. The delayed presentation of a tender, inflammatory appendiceal mass may occur in the right iliac fossa after 3 or more days.

Investigations

Investigations that are useful in the diagnosis of appendicitis are given in .

Differential diagnosis

Diagnosis of appendicitis is particularly difficult with a retrocaecal appendicitis. The pain is not as severe as that associated with abdominal or pelvic appendicitis and the pain rarely localises well to the right iliac fossa. The pain vaguely localises to the right side of the abdomen and rarely to the right flank or right upper quadrant. In neglected cases, a retrocaecal abscess develops as a result of perforation of the appendix.

Diagnosis in the elderly is often delayed because of late and less typical presentation. The incidence of perforation is therefore higher. Most elderly patients have fever and right-sided abdominal tenderness at presentation.

During pregnancy the appendix may be displaced, cephaled by the gravid uterus. In the second trimester of pregnancy, the appendix is displaced upwards to the right upper flank. Appendicitis may be confused with pyelonephritis, as pyuria is common during pregnancy. Owing to abdominal laxity, the abdominal findings are also less acute. Mild leucocytosis is also a normal physiological response in pregnancy.

Mesenteric adenitis

About 5% of patients undergoing an appendicectomy for ‘acute appendicitis’ are found to have mesenteric adenitis. The patient has clinical features similar to those of appendicitis; however, the appendix is normal and there are several enlarged lymph nodes in the mesentery of the terminal ileum.

The condition is most common in children. Some have a history of a recent sore throat together with a high fever. There is no muscle rigidity on presentation. The cause of the illness is obscure but is self-limiting, with spontaneous improvement over 24–36 hours.

At surgery, the appendix should be removed to avoid future confusion because a right iliac fossa incision is present.

Gynaecological conditions

Mittelschmerz pain occurs at mid-menstrual cycle from the rupture of a follicle at ovulation. Fever is uncommon and most patients have had previous painful ovulation.

In pelvic inflammatory disease, including salpingitis and tubo-ovarian abscess, there is a longer duration of symptoms, higher fever, greater leucocytosis and more pelvic pain. Gonococcal and chlamydial infection are the most common causes. Careful gynaecological history and examination are helpful.

Torsion of a fallopian tube and torsion or haemorrhage of an ovarian cyst tend to present with pain of sudden onset. Pelvic examination and ultrasound will help with the diagnosis.

Urological conditions

Urinary tract infection presents with urinary symptoms and rigors. Lack of abdominal rigidity and presence of pus and organisms in the urine indicate the diagnosis.

Right ureteric colic may cause confusion but the radiation of pain and haematuria should give the diagnosis.

Other conditions

Bacterial or viral gastroenteritis causes vomiting, profuse diarrhoea and diffuse abdominal pain without localised tenderness. Diarrhoea associated with appendicitis is rarely prolonged or severe. Non-specific ileitis may be secondary to Yersinia or Campylobacter infection.

Perforated caecal carcinoma with a pericolic abscess may mimic appendicitis, but the patients are usually elderly.

Acute cholecystitis may be confused with a high retrocaecal appendicitis.

Diverticulitis of a long redundant sigmoid colon lying on the right of midline may cause confusion. Rarely, a solitary caecal diverticulum becomes inflamed; this is usually seen in Asian patients.

Meckel's diverticulitis is rare and the diagnosis is usually made at surgery.

Management

If the diagnosis is clear, an appendicectomy is performed. If the diagnosis is suspected but not definite, a period of observation (usually in the hospital) is appropriate. Over the following 12–24 hours, the nature of the illness should clarify itself. The risk of perforation is low in the first 24 hours of symptomatic appendicitis.

Conventionally, open surgery is performed. A skin crease incision is made over the point of maximal tenderness in the right iliac fossa. Under anaesthesia, a mass may be palpable. The external and internal oblique muscles are split. The caecum is identified and the appendix is traced at its base on the posteromedial aspect. The mesoappendix is ligated and divided. The base of the appendix is ligated and transected. The appendix stump may be inverted using a purse-string in the caecum, although there is no firm evidence to suggest that this is necessary. All patients should receive prophylactic antibiotics administered preoperatively, usually in the form of a second- or third-generation cephalosporin and metronidazole. When there is severe sepsis, a full course of 5 days of therapy is recommended.

Alternatively, an appendicectomy can be performed laparoscopically. This approach has a lesser role if the diagnosis of appendicitis is firm because the conventional open approach involves only a small incision, is associated with a rapid recovery phase, and particularly incurs much less expense. Laparoscopy is helpful if the diagnosis is uncertain even after a period of observation and helps to diagnose pelvic inflammatory disease.

Patients presenting late may have a right iliac fossa mass. A computed tomography (CT) scan is performed to determine whether it is an abscess or a phlegmon. If an abscess is present, it is drained percutaneously under CT guidance. This obviates the need for surgery in most cases in patients with active sepsis. An appendiceal phlegmon is treated with bowel rest and intravenous antibiotics. Non-operative therapy is successful in 85% of cases and most patients are sent home after 7–10 days.

Because the risk of recurrent sepsis is about 25%, interval appendicectomy is generally performed 6–8 weeks after resolution of the acute illness. In patients older than 35 years, this is preceded by a barium enema examination or colonoscopy.

Meckel's diverticulum

Meckel's diverticulum is a congenital condition that arises from failure of embryonic obliteration of the omphalomesenteric duct connecting the foetal gut to the yolk sac. As distinct from other small bowel diverticula, Meckel's diverticulum is antimesenteric, contains all coats of the bowel and has its own blood supply (Meckel's diverticulum.). It is present in 2% of the population and is commonly within 1 m of the ileocaecal valve. In 20% of cases, the mucosa contains heterotopic epithelium of gastric, colonic or pancreatic origin. Symptomatic cases are usually males.

Meckel's diverticulum.

Clinical syndromes

Bleeding peptic ulceration adjacent to ectopic gastric epithelium is found. This usually occurs in young patients.

Small bowel obstruction due to intussusception may occur. The apex of intussusception is usually the inflamed heterotopic tissue at the mouth of the diverticulum. Obstruction of the small bowel may also be caused by the presence of a band between the apex of the diverticulum and the umbilicus, causing kinking or volvulus.

Meckel's diverticulitis is usually due to lodgement of enteroliths or a sharp foreign body in the diverticulum, or narrowing of the mouth of the diverticulum. The clinical features are similar to appendicitis. Perforation may occur, causing generalised peritonitis.

Gastric heterotopia may cause peptic ulcer-like symptoms, with meal-related pain around the umbilicus because of its mid-gut location.

Diagnosis

Barium small bowel follow-through does not always demonstrate Meckel's diverticulum because the mouth of the diverticulum is often narrowed with oedema. A sodium technetium-99 m scan will localise heterotopic gastric mucosa in Meckel's diverticulum in 90% of cases.

Treatment

Complicated or symptomatic Meckel's diverticulum should be treated with resection of the diverticulum or of the involved small bowel. If diverticulectomy is performed, care is taken to remove any peptic ulcer in the adjacent ileum.

Incidental Meckel's diverticulum found at laparotomy is usually left alone because most remain asymptomatic. Any band to the umbilicus or other viscus is divided. Resection is considered in children younger than 2 years; with the presence of palpable heterotopia (especially in men); and with evidence of prior Meckel's diverticulitis, such as adhesions.

Further reading

Birnbaum BA, Wilson SR. Appendicitis at the millennium. Radiology 2000;215:337–348.

Schumpelick V, Dreuw B, Ophoff K, Prescher A. Appendix and caecum. Embryology, anatomy and surgical applications. Surg Clin North Am. 2000;80:295–318.

Sajja S, ScheinMLaparoscopic appendectomy: an advance or a gimmick? Curr Surg. 2004 Mar-Apr;61(2):136–41.

McKinlay R, Mastrangelo MJ, Jr. Current status of laparoscopic appendectomy. Curr Surg. 2003 Sep-Oct;60(5): 506–12.

Martin JP, Connor PD, Charles K. Meckel's diverticulum. Am Fam Physician. 2000;61:1037–1042.
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