CHAPTER 77

Acute Abdomen (Appendicitis)

Roxanne L. Massoumi, MD, and Steven L. Lee, MD, MBA, FACS, FAAP

Appendicitis is among the most common surgical emergencies in children. Pediatricians play a key role in the diagnosis and management of patients with abdominal pain and must be able to distinguish appendicitis from other causes of abdominal pain. When a patient presents with the classic signs and symptoms of appendicitis, the diagnosis is simple. Unfortunately, approximately 50% of patients present with atypical signs and symptoms of appendicitis, making the diagnosis difficult. Until recently, nearly every aspect of the diagnosis and management of children with appendicitis has been controversial. Thus, it is important for primary care physicians, emergency department physicians, and surgeons to communicate effectively to provide the highest level of care and cost efficiency.

Epidemiology

More than 70,000 children are affected by appendicitis each year in the United States. The lifetime risk of appendicitis is 9% in boys and 7% in girls.

Pathophysiology

The 2 main causes of abdominal pain are distention of the viscera, causing visceral pain, and irritation of the peritoneum, causing somatic pain. Distention of any hollow organ in the abdomen causes crampy and intermittent abdominal pain. Examples include distention of the biliary tree, small or large intestine, urinary structures (ie, bladder, ureters), or gynecologic structures (ie, uterus, fallopian tubes). This visceral pain is poorly localized and tends to be reported in the midline. Distention of any foregut structure localizes to the epigastric region. Foregut structures derive their blood supply from the celiac trunk and include the stomach, duodenum, and biliary tree. Distention of midgut structures localizes to the periumbilical region, and distention of hindgut structures localizes to the suprapubic region. Midgut structures are supplied by the superior mesenteric artery (ie, duodenum to transverse colon) and hindgut structures by the inferior mesenteric artery (ie, transverse colon to rectum). Unlike visceral pain, somatic pain is well localized. Irritation of the parietal peritoneum results in sharp pain and localized tenderness on examination. Anything that causes the irritated peritoneum to move or stretch worsens the pain and tenderness.

The classic example of these 2 types of pain occurs with appendicitis. The basic pathophysiology of appendicitis is obstruction of the lumen of the appendix followed by infection. Obstruction may be caused by fecal material (ie, appendicolith, fecalith), lymphoid hyperplasia, foreign body, tumor, or parasites. Following obstruction, the appendix becomes distended from accumulation of mucus and proliferation of bacteria. This distention results in a vague periumbilical pain. As intraluminal pressure increases, lymphatic and venous drainage are impaired, resulting in edema of the appendicular wall. As the overlying parietal peritoneum becomes progressively more irritated, the pain localizes to the right lower quadrant (RLQ). This stage is known as acute appendicitis. Further increase in pressure limits arterial inflow and ultimately results in tissue necrosis and perforation. Although the natural history of untreated appendicitis is usually perforation and abscess, not all patients progress to perforation.

Clinical Presentation

Abdominal pain is the most common symptom of and is present in nearly every patient with appendicitis. The classic presentation of a child with appendicitis includes a history of initial periumbilical pain migrating to the RLQ. The pain is gradual in onset and progressively worsens. Anorexia, nausea, and vomiting typically are associated with appendicitis. In most cases, these associated symptoms manifest after the onset of abdominal pain. Intermittent, crampy pain that manifests after the onset of vomiting or diarrhea is less commonly associated with appendicitis. The inflamed appendix irritates the overlying peritoneum by direct contact, which results in focal peritonitis and localized RLQ pain. The symptoms vary based on the location of the appendix, however. When the appendix is retrocecal, a dull ache is often described. When the tip of the appendix is located in the pelvis, atypical pain is described. A child may report dysuria and urinary frequency resulting from the inflamed appendix irritating the bladder. Diarrhea or tenesmus may occur if the appendix is adjacent to the rectum. Fever, tachycardia, and leukocytosis occur as a consequence of systemic inflammatory mediators released by ischemic tissues, white blood cells, and bacteria. Higher fevers are associated with perforated appendicitis.

Differential Diagnosis

Acute appendicitis can mimic nearly any intra-abdominal process and should be high on the differential in all children who report abdominal pain. Other causes of RLQ pain that are often indistinguishable from acute appendicitis include mesenteric adenitis, viral gastroenteritis, regional bacterial enteritis, tubo-ovarian pathologic processes, inflammatory bowel disease, Meckel diverticulum, cecal diverticulitis, and constipation. Other causes of lower abdominal pain include urinary tract infection, kidney stone, uterine pathologic process, bowel obstruction, and malignancy (eg, lymphoma). Vague abdominal pain can be caused by right lower lobe pneumonia, sigmoid diverticulitis, pancreatitis, hepatitis, and cholecystitis.

Evaluation

History

A careful history is required to distinguish acute appendicitis from other causes of abdominal pain (Box 77.1). In most patients with acute appendicitis, pain is often the first symptom. Associated symptoms, such as nausea, vomiting, and diarrhea, present after the onset of pain. It is important to distinguish intermittent crampy pain from constant and progressively worsening pain. If the patient has nausea, vomiting, or diarrhea followed by intermittent crampy pain, the diagnosis of gastroenteritis is more likely than appendicitis. A patient may develop a low-grade fever within 24 hours of the pain. Higher fevers manifest later and occur more frequently with perforated appendicitis. For the patient in whom fever is the first sign or symptom, appendicitis is less likely.

Physical Examination

A thorough physical examination is necessary to rule out other causes of abdominal pain. Upper respiratory infections may result in mesenteric adenitis, causing abdominal pain. The patient with acute appendicitis usually lies still, because movement worsens the pain. The most common finding is focal tenderness in the RLQ. Applying pressure to a stethoscope while listening to the abdomen is a subtle means of palpating the abdomen in the frightened child in whom it is difficult to obtain an accurate examination. Because of the level of discomfort, it may be difficult to elicit rebound tenderness and pal-pate for a mass. Asking the child to walk or jump is an easier and more accurate method of determining the degree of peritoneal irritation. Narcotic analgesics improve patient comfort but do not alter the inflammatory process; thus, tenderness persists. Localized tenderness is dependent on peritoneal irritation; thus, obesity, a retrocecal appendix, or walling off of the appendix by the omentum, mesentery, or small bowel may make the diagnosis of appendicitis more challenging.

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