Introduction
Acute appendicitis is one of the most common surgical conditions afflicting children and adults. Approximately 250,000 cases occur annually in the United States, with the highest incidence in patients 10 to 19 years of age. The lifetime risk of developing appendicitis has been estimated at 8.6% for males and 6.7% for females, with a lifetime risk of undergoing an appendectomy estimated at 12% for males and 23% for females. Appendiceal perforation in the pediatric population is more common than in adults, occurring in up to 50% of patients. In children younger than 5 years of age, the perforation rate is 65%, and 95% in children younger than 2 years of age.
A thorough understanding of this common surgical condition is important for all healthcare providers, who should be able to recognize and refer patients with possible appendicitis to be further evaluated promptly in order to avoid complications related to delayed diagnosis.
Embryology and Anatomy
The development of the appendix begins during the eighth week of gestation. The appendix initially projects from the apex of the cecum, but as the right terminal haustrum develops, the appendix is displaced medially toward the ileocecal valve. The colonic teniae arise from the base of the appendix, and are displaced by the growth of the right haustrum. Lymph nodes begin to develop by the seventh month of gestation and continue to proliferate until puberty, after which they start to regress.
The position of the appendix is variable, as first described by Melier, in 1827. In adults, the appendix varies in length, but averages about 8 cm; it is relatively longer and narrower in children. The appendix has its own mesentery, called the mesoappendix, which contains the appendicular artery, a branch of the ileocolic artery, which arises from the superior mesenteric artery. The ileocolic vein drains blood from the cecum and appendix, and enters the superior mesenteric vein to drain into the portal vein ( Figure 50-1 ).
Pathophysiology
The etiology of appendicitis was outlined in 1939 by Wangensteen and Dennis in their paper “Experimental Proof of the Obstructive Origin of Appendicitis in Man.” Appendicitis is initiated by obstruction of the appendiceal lumen. When the lumen of the appendix becomes obstructed, the flow of normal mucosal secretions is inhibited. This leads to increased intraluminal pressure and compromised venous drainage, which leads to ischemic breakdown of the mucosa. Simultaneously, luminal bacteria, typically Escherichia coli, Bacteroides fragilis, Pseudomonas aeruginosa , and Clostridium species, proliferate and traverse the appendiceal wall. This sequence of events results in an acute infection, gangrene, and ultimately perforation.
As the inflammatory process progresses, the omentum, as well as adjacent loops of bowel, may surround the inflamed area. If the disease progresses to perforation, these surrounding structures act as barriers that wall off the infection and frequently prevent free perforation and instead result in the formation of an inflammatory mass (phlegmon) or abscess. The formation of a phlegmon or abscess is central to the success of nonoperative management of complicated appendicitis, which will be discussed later.
Pathology
The appendix comprises the same four layers as the rest of the intestine (the mucosa, submucosa, muscularis propria, and serosa). The mucosa is made of a surface layer of epithelial cells, a loose connective tissue layer known as the lamina propria, as well as the muscularis mucosa that separates the mucosa from the submucosa. The epithelial surface contains a combination of columnar cells with basally located nuclei, goblet cells with apical mucin, and absorptive cells. Scattered Paneth cells containing secretory granules and neuroendocrine cells are present in this layer as well. These neuroendocrine cells are the origin of the carcinoid tumor, which is the most common appendiceal neoplasm. The lamina propria, just beneath the surface epithelial layer, contains the crypts of Lieberkühn as well as lymphoid follicles with germinal centers.
The submucosa contains a rich network of blood vessels, lymphatics, and nerves. The network of ganglion cells and Schwann cells found within this layer is known as Meissner’s plexus. The next layer is the muscularis propria, which consists of two layers of smooth muscle. The muscle fibers of the inner layer are arranged in a circular fashion, whereas the fibers of the outer layer are arranged longitudinally. Another neural network, known as Auerbach’s plexus, lies between these muscle layers. The outermost layer of the appendiceal wall, the serosa, is made up of a band of fibrous tissue with an overlying layer of cuboidal mesothelial cells.
Clinical Presentation
Early diagnosis is vital to improving outcome and avoiding the morbidity of appendiceal perforation. Although laboratory and radiologic studies are often useful aids in making the diagnosis, the key components are the history and physical examination.
In fact, the history and physical examination portion of the encounter is so important that several clinical scoring systems have been developed to aid in decision-making during evaluation of patients with possible appendicitis. The first of these clinical scoring systems developed was the Alvarado score described by Alvarado in 1986. Points are assigned for the presence of clinical findings such as rebound tenderness, fever, nausea/vomiting, or anorexia. Based on a potential score of 10, patients are given a likelihood of appendicitis based on their total score. Samuel applied this same concept in 2002 when developing the Pediatric Appendicitis Score (PAS). A retrospective analysis of 1170 children was used to develop a weighted clinical scoring system with eight clinical features ( Table 50-1 ). When analyzed prospectively, a cut-off value of 6 of 10 was found to have a sensitivity of 88% and specificity of 50%. Furthermore, Goldman et al. prospectively validated the PAS and noted that patients who had a score 2 or less and were discharged without further investigation (computed tomography scan, ultrasonography, or hospital observation) had only a 2.4% chance of having appendicitis, whereas those who had a PAS of 7 or greater and were taken to the operating room without further studies had only a 4% chance of having a normal appendix.
| Finding | Score |
|---|---|
| Symptoms | |
| Migration of pain | 1 |
| Anorexia | 1 |
| Nausea/emesis | 1 |
| Signs | |
| Tenderness in right lower quadrant | 2 |
| Cough/percussion/hopping tenderness | 2 |
| Fever >38°C | 1 |
| Laboratory Studies | |
| WBC count >10,000 cells/mL | 1 |
| Polymorphonuclear neutrophilia >7500 cells/mL | 1 |
Although there is less validity of the PAS in younger children and females, the greatest utility of the system may arise from using it in a clinical decision-making tree. For example, a two-point cut-off can be used to distinguish those patients who can be safely discharged from those who should proceed with further diagnostic imaging or go directly to the operating room.
The classically taught presentation of periumbilical pain that migrates to the right lower quadrant is a reflection of the progression of inflammation and pain from visceral to somatic pathways. The initial symptom is usually periumbilical abdominal pain. This vague pain, which results from distension of the appendix secondary to luminal obstruction, is transmitted by visceral afferent fibers entering the spine at T10, causing referred pain in the associated dermatome, namely the periumbilical area. As the inflammation becomes transmural and reaches the parietal peritoneum, the peritoneal somatic afferent pain fibers become involved. This causes pain that localizes to the vicinity of the appendix, which is usually at McBurney’s point, located in the right lower quadrant, two-thirds of the distance along a line extending from the umbilicus to the anterior-superior iliac spine. Localized pain may also occur in the right upper quadrant, the right flank, or the suprapubic area, depending on the location of the appendix. If the patient has malrotation or situs inversus, pain may occur in the epigastrium or left lower quadrant. If the appendix is close to the bladder, the inflammation may result in symptoms similar to those of a urinary tract infection.
Nausea and vomiting are common findings associated with appendicitis. The persistent obstruction of the lumen, which initially causes abdominal pain, ultimately results in dilation of the appendix and serosal stretching, which causes nausea and vomiting. Thus, nausea and vomiting that occur before the onset of pain are unlikely secondary to appendicitis. Anorexia is also a common symptom, although somewhat less frequent in the pediatric population. Diarrhea can also occur with appendicitis, especially in younger children. If perforation occurs, the resulting decompression of the appendiceal lumen may transiently relieve symptoms.
Clinicians should attempt to define the duration of illness by inquiring about vague symptoms that may precede pain. “When was the last time you felt perfectly fine” is a question that can help clarify the duration of symptoms. The “classic” migratory pain that begins in the periumbilical region and then localizes to the right lower quadrant is not present in all patients with appendicitis, particularly in the presence of a pelvic or retroperitoneal appendix.
Appendicitis in infants presents its own set of unique difficulties. The diagnosis is frequently delayed because of the inability to obtain an adequate history; this partly accounts for the increased incidence of appendiceal rupture, with subsequent increased morbidity and mortality. Common signs in infants with appendicitis include irritability, lethargy, fever, anorexia, and vomiting. In addition to the increased risk of perforation, infants are also at an increased risk of developing generalized peritonitis after perforation. This is thought to be due to the diminished ability of this patient population to contain the perforation.
Patient Evaluation
The goals of evaluation are prompt identification of patients with appendicitis while avoiding unnecessary delays and excessive use of imaging studies. Delayed diagnosis may result in appendiceal perforation, whereas the incorrect diagnosis of appendicitis results in unnecessary surgery and potential postoperative complications.
A thorough history and physical examination remain central to the diagnosis of appendicitis. Unfortunately, both may be less reliable in younger children, which renders imaging studies more frequent and necessary in this patient population. The onset, duration, and progression of abdominal pain are important factors to consider. Pain secondary to appendicitis is usually slow in onset and persistent, and it typically begins as generalized abdominal pain and progressively is localized to the right lower quadrant. Physical findings include right lower quadrant tenderness, right lower quadrant pain with palpation of the left lower quadrant (Rovsing’s sign), and right lower quadrant pain with right hip extension (psoas sign) or internal rotation of the flexed right thigh (obturator sign). Despite this relatively constant point of maximal tenderness, and depending on the location of the appendix, it is possible for tenderness to occur anywhere in the abdomen, including the left side in cases such as malrotation and situs inversus.
Diagnostic Tests
The importance of the early diagnosis of acute appendicitis has led to attempts at better defining the role of blood tests, specifically the white blood cell (WBC) count and C reactive protein (CRP), as well as imaging studies in making the correct and prompt diagnosis. This is of particular importance in the pediatric population, where patients are more likely to have an atypical presentation and physicians may need to rely on additional tests to help make the diagnosis.
The WBC count is usually elevated in patients with appendicitis, particularly in the presence of perforation. Unfortunately, up to 20% of these patients have a normal WBC count. The role of CRP, an acute-phase reactant with a short half-life, in the workup of appendicitis is similarly unclear, given that most conditions mimicking appendicitis involve inflammation and thus an elevation in CRP level. The literature is full of conflicting reports of the utility of CRP, when used alone or in conjunction with WBC counts, for the diagnosis of acute appendicitis. A recent study, looking at the role of WBC and CRP in the evaluation of abdominal pain noted that when both these values are normal for age, there is a less than 5% possibility that a patient has acute appendicitis.
A urinalysis may help clarify the cause of abdominal pain. Although the finding of abnormal WBC and red blood cell (RBC) counts in the urine may reflect an inflammatory process near the bladder or ureter, the presence of bacteria should raise the concern for the possibility of a urinary tract infection as the cause of abdominal pain.
Imaging Studies
The diagnosis of appendicitis may be straightforward in children who present with a classic history and physical examination findings; however, atypical presentations can result in diagnostic uncertainty, which may result in delayed treatment and increased morbidity. It is in these cases that imaging studies play a central role. The primary aim of imaging studies is to expedite the identification of the cause of abdominal pain, define the extent of the disease in perforated appendicitis, and reduce the rates of perforation and unnecessary operations.
Plain radiographs of the abdomen are generally unnecessary and contribute little to the evaluation of patients suspected of having appendicitis, unless small bowel obstruction is suspected. Some findings on abdominal radiographs that may suggest appendicitis include the presence of a fecalith, scoliosis, a focally dilated loop of bowel in the right lower quadrant (sentinel loop), focal loss of the right psoas shadow (psoas sign), and bowel obstruction.
Computerized tomography (CT) is an accurate imaging modality used for diagnosing appendicitis. The sensitivity of helical CT has been reported to be 90% to 100%, with a specificity of 91% to 99%. Typical appendiceal CT protocols include 5-mm sectioning with both intravenous and oral contrast agents. Intravenous contrast helps identify the inflamed appendix, which is especially helpful in patients with early appendicitis and a paucity of mesenteric fat. Oral contrast material, when present in the entire lumen of the appendix, rules out appendicitis. Oral contrast also helps differentiate loops of bowel from a fluid-filled abscess near the appendix when perforated appendicitis is suspected. That said, several studies have shown equivalent results in adults and children without oral contrast or with rectal-only contrast. A normal appendix should appear as a contrast or air-filled tubular structure. The wall should be less than 2 mm thick, and surrounding fat should appear homogenous with no stranding. The findings in appendicitis vary according to the severity of the disease. In early appendicitis, the appendix appears as a fluid-filled tubular structure with a thickened wall and adjacent fat stranding. The appendiceal diameter varies in size, but is usually between 7 and 15 mm ( Figure 50-2 ). An appendicolith is found on CT in 30% of cases. CT findings that may be seen in perforated appendicitis include abscess formation or an inflammatory mass (phlegmon), as well as extraluminal air in the area of the appendix. Appropriate application of CT scanning for the evaluation of appendicitis in children can dramatically improve the diagnostic capability of the evaluating practitioner. Raja et al. performed an 18-year retrospective analysis that showed that CT scanning resulted in a reduction of negative appendectomy from 23% to 1.7%.
Graded compression sonography, the ultrasound technique used to evaluate the appendix, is another radiologic technique available to the physician. With gradual compression sonography, sequential pressure is applied to the abdominal wall with the ultrasound probe. This displaces normal loops of bowel and identifies an abnormal appendix, which is seen as a fluid-filled, noncompressible structure larger than 6 mm in diameter ( Figure 50-3, A and B ). A fecalith, if present, appears as a bright, echogenic structure with posterior acoustic shadowing. Although the success of this modality is operator dependent, based on two meta-analyses, the sensitivity has been reported to be 78% to 83%, with a specificity of 83% to 93%.
The choice of ultrasound or CT varies between institutions, as the accuracy of ultrasound is somewhat operator dependent. Doria et al. noted that CT scans have a significantly higher sensitivity than ultrasound (94% vs. 88%, respectively), and thus may decrease the rate of missed appendicitis. Ultrasound offers the advantage of being fast, noninvasive, and inexpensive; it uses no ionizing radiation and can better delineate gynecologic pathology. It also has the advantage of not requiring any patient preparation or use of intravenous or oral contrast. On the other hand, CT scans are not operator dependent, have a higher sensitivity, and can better delineate the extent of disease in perforated appendicitis. However, concern about the long-term effects of CT scans ionizing radiation has resulted in a shift in practice trends toward increased ultrasound utilization (2005, 16.8% ultrasound and 27.7% CT; 2007, 20.4% ultrasound and 35.2% CT; and 2009, 24.5% ultrasound and 29.2% CT).
Moss et al. sought to identify factors associated with choice of imaging modality as recorded in the Kids’ Inpatient Database. Of the 9377 patients examined, 69.5% had CT scan alone, 22.1% had ultrasound alone, and 8.4% underwent both exams. Using logistic regression model analysis, they found that those patients who had an increased odds ratio of CT scan utilization included older patients, male patients, and patients seen at rural, non-children’s hospital centers and nonteaching hospitals.
Recently, with the increased debate regarding pediatric exposure to ionizing radiation, emergent magnetic resonance imaging (MRI) for evaluation of appendicitis has garnered some interest. With improvements in MRI technology, faster imaging protocols, and more ubiquitous availability, the use of MRI in diagnosis of appendicitis has become more feasible. In a recent series, one group went so far as to use MRI as the primary imaging modality on 208 children ages 5 to 17 for a 1-year period. The protocol examined did not use any oral or intravenous contrast. In addition, all scans were done without sedation using a breath-holding technique. The findings were then analyzed retrospectively for diagnostic accuracy and were found to have a sensitivity of 97.6% and specificity of 97.0%. Additionally, to address concern of clinical feasibility in terms of delays in care, the group found that the mean time from when the study was requested to when the MR sequences were obtained was about 78.7 ± 52.5 minutes, with a median of 65 minutes. Total scan times were 14.2 ± 8.8 minutes with a median of 12 minutes. Finally, the time from obtaining the last images to a generated report was 57.4 ± 35.2 minutes. The authors note that these time parameters were acceptable to consulting emergency physicians, pediatricians, and surgeons at their institution. At the time of chapter submission, this study represents the largest series of MRI as the primary imaging modality in evaluation of pediatric appendicitis. Overall, the group concluded that MRI without contrast is an effective and timely imaging technique for children with suspected appendicitis. However, further studies regarding cost analysis are necessary and, admittedly, MRI may not be readily available in an emergent setting at many institutions.
Differential Diagnosis
The clinical presentation of appendicitis can mimic many different conditions; conversely, many different conditions can present like appendicitis ( Box 50-1 ). This is particularly true in children, who frequently present with an atypical history and physical examination findings.
Infant
Abdominal trauma—child abuse
Gastroenteritis
Intussusception
Pneumonia
Urinary tract infection
Meckel’s diverticulitis
Child
Constipation
Gastroenteritis
Henoch-Schönlein purpura
Hemolytic-uremic syndrome
Meckel’s diverticulitis
Mesenteric adenitis
Omental torsion
Ovarian torsion
Pneumonia
Urinary tract infection
Crohn’s disease
Adolescent
Constipation
Crohn’s disease
Gastroenteritis
Meckel’s diverticulitis
Mesenteric adenitis
Mittelschmerz
Omental torsion
Ovarian cyst rupture
Urinary tract infection
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