Acute appendicitis is a common paediatric surgical disease requiring urgent attention. Appendectomy is the most common surgical procedure performed for acute abdominal pain in children (15.1)¹. The diagnosis of acute appendicitis in childhood can sometimes be difficult.

The incidence of acute appendicitis has been estimated at about 1 case per 1,000 children per year, with slightly higher incidence among boys. The lifetime risk of appendicitis is estimated to be 8.67% for boys and 6.7% for girls. Incidence among preschool children is unusual, but in this age group delayed diagnosis and complications are more frequent. Around one-third of children with acute appendicitis are found to be perforated at surgery.

Children who have appendicitis are twice as likely to have a positive family history as are those with right lower quadrant pain, but no appendicitis². Early diagnosis continues to be the most important factor for prognosis. The rate of negative appendectomy is considered acceptable for up to 10% of laparotomies for suspected acute appendicitis. Paediatric surgeons performed significantly fewer negative appendectomies than general surgeons³.

The development of the caecum and appendix begins in the caecal diverticulum on the anti-mesenteric side of the caudal end of the medial intestine, around the fifth week of gestation. The appendix does not elongate as rapidly as the rest of the colon. After rotation and descent, the base of the appendix is located at the posteromedial wall of the caecum about 2.5 cm below the ileocaecal valve, but this descent finishes after childhood. The variability of its descent and rotation leads to multiple possible final positions of the appendix4. The infant caecum is located in the right iliac fossa in about 55% of individuals (15.2). The blood supply of the caecum and appendix is the appendiceal branch of the ileocolic artery, which passes behind the terminal ileum. The arterial supply is terminal, so that thrombosis leads to rapid necrosis (15.3). The malpositioned appendix may give rise to signs of inflammation in unusual locations, that make diagnosis difficult.

Obstruction is a fundamental factor in the development of acute appendicitis. Obstruction increases intraluminal pressure leading to ischaemia, bacterial invasion, bacterial overgrowth, necrosis, and perforation.

In the early phases, activation of receptors in the intestinal wall leads to perception of pain in the periumbilical region. In later phases, when the purulent secretion from the appendiceal wall contacts the parietal peritoneum, somatic pain fibres are triggered and the pain localizes near the appendiceal site, McBurney’s point. The characteristic organisms responsible of appendiceal inflammation are predominantly anaerobic, including Escherichia coli, Enterococcus, Bacterioides fragilis, Pseudomonas, Klebsiella, and Clostridium⁵.

Many terms have been used to describe the pathologic stages of appendicitis, from the normal state to perforation. Only the clinically relevant distinctions of simple appendicitis (15.4) and complicated appendicitis should be made.

The diagnosis of appendicitis should be based on a careful history and physical examination. The paediatric surgeon may expect to make the accurate diagnosis in 80-90% of cases. White blood count (WBC) and imaging rarely add significant information.

Acute appendicitis typically occurs in older children. The incidence of appendicitis gradually increases from age 1 year onwards, peaking at around age 11-12 years. Although appendicitis is uncommon in infants, this age group has a high rate of complications because of delayed diagnosis. Difficulties of diagnosis may arise with patients younger than 2 years, and with preadolescent obese girls. In these two patient categories, analytical and imaging studies can provide additional information.