About 7% of all people will develop appendicitis over the course of their lifetime.¹ Each year in the United States, about 60,000 to 80,000 children develop appendicitis. It is particularly common in the preteen and teen years, with the average age of onset being about 10 years. Before puberty, boys and girls are affected equally; after puberty, there is a slight male predominance.

PATHOPHYSIOLOGY

The appendix, whose function remains unknown, arises from the cecum. Roughly 5% to 15% of people have retrocecal appendixes. In children, the appendix is relatively longer and thinner than in adults, which makes it more susceptible to perforation early in the course of the disease. The greater omentum remains thin, short, and fragile until about 10 years of age. It is therefore less likely to wall off a perforated appendix in a younger child, making generalized peritonitis more common in children than in adults.²

The pathogenesis of appendicitis begins with obstruction of the appendiceal lumen. The most common cause of obstruction is enlargement of the lymphoid tissue (Peyer patches) in the wall of the appendix. The lymphoid follicles enlarge probably in response to ingested microorganisms, most likely viruses associated with upper respiratory infections. Fecal material, undigested food, other foreign material, or pinworms may also lead to obstruction. Regardless of the initial trigger, the resultant obstruction causes dilation of the lumen of the appendix and thickening of its wall. Bacterial overgrowth results within the structure, with subsequent bacterial invasion of the appendiceal wall, inflammation, and ischemia. If unchecked, gangrene and eventual appendiceal perforation will occur. As the transmural appendiceal inflammation progresses, so does the local peritoneal inflammation. With perforation, the peritonitis can become widespread.

The responsible bacteria are usual fecal flora, most commonly Escherichia coli, Peptostreptococcus, Bacteroides fragilis, and Pseudomonas species, and the process is usually polymicrobial.

The classic presentation of appendicitis is not difficult to recognize and occurs in approximately two thirds of cases. Many preschool-age children, however, present with atypical and challenging clinical pictures.

Typically, a previously healthy child awakes with vague periumbilical pain that is uncomfortable but not debilitating. Shortly after the onset of pain, infrequent nonbilious emesis often develops. Over the next few hours, the poorly localized pain gradually increases in intensity before moving to the right lower quadrant. There is associated anorexia and low-grade fever. A child with appendicitis prefers to remain still, so the jarring and shaking movements during a car ride are painful. Diarrhea, if it occurs, is infrequent and consists of small stools caused by irritation of the sigmoid colon by the inflamed appendix (as opposed to large stools typical of gastroenteritis). Likewise, bladder irritation may produce dysuria or urgency.

In atypical cases, the pain pattern may be quite different. Young children in particular may not recognize or may be unable to verbalize the change in location of the pain, or they may not develop localized pain. In some, such as those with a retrocecal appendix, the pain may never shift in location, or it may originate in or migrate to the right upper quadrant or flank.

Some children with appendicitis never develop vomiting. Also, although most patients with appendicitis have a low-grade fever, some are afebrile, and an occasional child has a temperature above 39°C. Finally, although anorexia is common, some children report being hungry; if they are actually offered food, however, most but not all patients with appendicitis will decline.

If appendicitis remains unrecognized, perforation will ultimately occur. About one third to one half of children with perforated appendixes have been seen by physicians before the diagnosis of perforation is made.^3,4 With perforation, there is usually temporary relief of the pain, but within hours it classically becomes generalized and progressively more severe as the child develops diffuse peritonitis. However, if the contamination is well localized (walled off) by the omentum, the child develops a discrete abscess and may have localized tenderness without severe pain.

Before examining the child, having him or her ambulate and climb up or down from the parent’s lap or examining table can yield helpful clues. A hunched-over posture, tentative gait, limp, and difficulty mounting or dismounting or pain with climbing up or down are suggestive of peritoneal irritation. For non-ambulatory patients, jarring the examining table may produce evidence of pain.

On physical examination, a patient with appendicitis (non-perforated) usually has a temperature of 38°C to 38.3°C, tachycardia, and a normal respiratory rate and blood pressure. Reliable examination of the abdomen may require accommodations that ease the child’s anxiety (e.g. examination on a caregiver’s lap). Asking the child to point to the spot that hurts and examining that area last may also facilitate the process. Classically, the abdomen appears flat with normal or hypoactive bowel sounds. Localized and reproducible tenderness at McBurney point (one third of the way along a line that would join the umbilicus to the right anterior superior iliac spine) is virtually diagnostic, a useful finding, especially with a normally positioned appendix.

Many techniques are used to elicit signs of peritoneal irritation. For rebound tenderness, the examiner presses down on the tender area slowly, maintains pressure for a few seconds, and then abruptly removes his or her hand. The child experiences pain if there is peritoneal inflammation, but this maneuver may also be uncomfortable for anxious children without peritonitis. Additionally, many experts believe that this test is unduly distressing and recommend finger percussion throughout the abdomen, leaving the right lower quadrant for last. Pain limited to percussion of the right lower quadrant, or referred pain to the right lower quadrant with percussion of other quadrants, is suggestive of peritonitis (Rovsing sign). In older children, having them stand, lift up onto their toes, and then drop down onto their heels can elicit localized abdominal pain. A prone supine patient may report right lower quadrant tenderness when the examiner percusses the plantar surface of the heel or the lateral aspect of the pelvis. Any of these maneuvers can produce pain if there is peritoneal irritation.

Voluntary muscle guarding is nonspecific and can be seen with abdominal pain from myriad causes and in ticklish or anxious patients. Involuntary muscle guarding, in contrast, is a powerful finding in a patient with appendicitis but can be subtle and difficult to appreciate.

The previously described signs are common when a normally positioned appendix is inflamed; however, with retrocecal appendicitis, these physical findings may be absent. When the inflamed appendix lies on the psoas muscle, use of this muscle causes pain. The examiner places his or her hand above the knee of the prone supine patient and asks him or her to raise the thigh against the resistance provided by the examiner. Alternatively, the child lies on his or her left side and the examiner extends the patient’s right thigh at the hip. Pain with these maneuvers yields a positive psoas sign.

If the inflamed retrocecal appendix is adjacent to the internal obturator muscle, pain is elicited when it is stretched. With the patient prone supine, the examiner flexes the right lower extremity at the knee and hip and internally rotates it. If right lower quadrant pain is produced, the obturator sign is positive.

A rectal examination may sometimes be helpful. Suggestive findings include tenderness greater on the right side, fullness on the right, and heme-negative stools. Patient cooperation is needed for reliable rectal palpation. Grossly bloody stools are not found with appendicitis, and even occult blood should prompt a consideration of other diagnoses.

COURSE OF ILLNESS

By 24 hours after pain onset, about 15% of children have perforation. By 48 hours after the initial symptoms, roughly 75% have perforation. A child with pain of 4 days duration has an approximately 90% risk of perforation. If perforation occurs, the mortality rate increases to as high as 5%, compared with less than 0.1% for non-perforated appendicitis.¹ Those who die are predominantly very young children or those with perforated appendixes and peritonitis who undergo surgery before adequate fluid resuscitation. The morbidity rate also rises appreciably in those with perforation.

The condition most commonly confused with appendicitis is gastroenteritis. Many other diseases can simulate appendicitis, including constipation, urinary tract infection, right lower lobe pneumonia, ovarian torsion or cyst, incarcerated inguinal hernia, testicular torsion, intussusception, hemolytic uremic syndrome, diabetic ketoacidosis, and abdominal trauma (Table 155-1). In sexually active female patients, pelvic inflammatory disease and ectopic pregnancy are also considerations.