Chapter 51 – The Appendix

1279 CHAPTER 51 Approximately 8% of those in Western countries have appendi- citis at some time during their life, with a peak incidence between 10 and 30 years of age.1 Acute appendicitis is the most common general surgical emergency, and early surgical interven- tion improves outcomes. The diagnosis of appendicitis can be elusive, and a high index of suspicion is important in preventing serious complications from this disease. Worldwide, perforated appendicitis is the leading general surgical cause of death. EMBRYOLOGY AND ANATOMY The appendix, ileum, and ascending colon are all derived from the midgut. The appendix first appears at the eighth week of gestation as an outpouching of the cecum and gradually rotates to a more medial location as the gut rotates and the cecum becomes fixed in the right lower quadrant. The appendiceal artery, a branch of the ileocolic artery, supplies the appendix. Histologic examination of the appendix indicates that goblet cells, which produce mucus, are scattered throughout the mucosa. The submucosa contains lymphoid fol- licles, leading to speculation that the appendix might have an important, as yet undefined, immune function early in develop- ment. The lymphatics drain into the anterior ileocolic lymph nodes. In adults, the appendix has no known function. The length of the appendix varies from 2 to 20 cm, and the average length is 9 cm in adults. The base of the appendix is located at the convergence of the taeniae along the inferior aspect of the cecum and this anatomic relationship facilitates identification of the appendix at operation. The tip of the appen- dix may lie in various locations. The most common location is retrocecal but within the peritoneal cavity. It is pelvic in 30% and retroperitoneal in 7% of the population.2 The varying loca- tion of the tip of the appendix likely explains the myriad of symptoms that are attributable to the inflamed appendix. APPENDICITIS Historical Perspective In 1886, Reginald Fitz of Boston correctly identified the appendix as the primary cause of right lower quadrant inflam- mation. He coined the term appendicitis and recommended early surgical treatment of the disease. Richard Hall reported the first survival of a patient after removal of a perforated appendix, which focused attention on the surgical treatment of acute appendicitis. In 1889, Chester McBurney described characteristic migratory pain and localization of the pain along an oblique line from the anterior superior iliac spine to the umbilicus. McBurney described a right lower quadrant muscle-splitting incision for removal of the appendix in 1894. The mortality rate from appendicitis improved with the wide- spread use of broad-spectrum antibiotics in the 1940s. Advances have included improved preoperative diagnostic studies, interventional radiologic procedures to drain estab- lished periappendiceal abscesses, and the use of laparoscopy to confirm the diagnosis and exclude other causes of abdominal pain. Laparoscopic appendectomy was first reported by the gynecologist Kurt Semm in 1982 but has only gained wide- spread acceptance during the past decade. Other minimally invasive approaches to appendectomy have been reported, including transvaginal3 and single-incision laparoscopic surgery (SILS)4; however, these have not as yet been widely adopted. Pathophysiology Obstruction of the lumen is believed to be the major cause of acute appendicitis.2 This may be caused by inspissated stool (fecalith or appendicolith), lymphoid hyperplasia, vegetable matter or seeds, parasites, or a neoplasm. The lumen of the appendix is small in relation to its length and this configuration may predispose to closed-loop obstruction. Obstruction of the appendiceal lumen contributes to bacterial overgrowth and continued secretion of mucus leads to intraluminal distention and increased wall pressure. Luminal distention produces the visceral pain sensation experienced by the patient as periumbili- cal pain. Subsequent impairment of lymphatic and venous drainage leads to mucosal ischemia. These findings in combina- tion promote a localized inflammatory process that may prog- ress to gangrene and perforation. Inflammation of the adjacent peritoneum gives rise to localized pain in the right lower quad- rant. Although there is considerable variability, perforation typically occurs after at least 48 hours from the onset of symp- toms and is accompanied by an abscess cavity walled off by the small intestine and omentum. Rarely, free perforation of the appendix into the peritoneal cavity occurs, which may be accompanied by peritonitis and septic shock and can be com- plicated by the subsequent formation of multiple intraperito- neal abscesses. embryology and anatomy appendicitis neoplasms THE APPENDIX John Maa and Kimberly S. Kirkwood 1280  SECTION X  ABDOMEN should not necessarily be a deterrent to surgical intervention. Occasional patients have urinary symptoms or microscopic hematuria, perhaps because of inflammation of periappendiceal tissues adjacent to the ureter or bladder, and this may be mis- leading. Although most patients with appendicitis develop an adynamic ileus and absent bowel movements on the day of presentation, occasional patients may have diarrhea. Others may present with small bowel obstruction related to contiguous regional inflammation. Therefore, appendicitis needs to be con- sidered as a possible cause of small bowel obstruction, especially in patients without prior abdominal surgery. Physical Examination Patients with acute appendicitis typically look ill and are lying still in bed. Low-grade fever is common (≈38° C). Examination of the abdomen usually reveals diminished bowel sounds and focal tenderness, with voluntary guarding. The exact location of the tenderness is directly over the appendix. Usually, this occurs at McBurney’s point, located one third of the distance along a line drawn from the anterior superior iliac spine to the umbili- cus; however, the normal appendix is mobile, so it may become inflamed at any point on a 360-degree circle around the base of the cecum. Thus, the site of maximal pain and tenderness can vary. Peritoneal irritation can be elicited on physical examination by the findings of voluntary and involuntary guarding, percus- sion, or rebound tenderness. Any movement, including cough- ing (Dunphy’s sign), may cause increased pain. Other findings may include pain in the right lower quadrant during palpation of the left lower quadrant (Rovsing’s sign), pain on internal rotation of the hip (obturator sign, suggesting a pelvic appen- dix), and pain on extension of the right hip (iliopsoas sign, typical of a retrocecal appendix). Rectal and pelvic examinations are most likely to be nega- tive. However, if the appendix is located within the pelvis, ten- derness on abdominal examination may be minimal, whereas anterior tenderness may be elicited during rectal examination as the pelvic peritoneum is manipulated. Pelvic examination with cervical motion may also produce pain in this setting. If the appendix perforates, abdominal pain becomes intense and more diffuse and abdominal muscular spasm increases, pro- ducing rigidity. The heart rate rises, with an elevation of tem- perature above 39° C. The patient may appear ill and require a brief period of fluid resuscitation and antibiotics before the induction of anesthesia. Occasionally, pain may improve some- what after rupture of the appendix because of relief of visceral distension, although a true pain-free interval is uncommon. Laboratory Studies The white blood cell count is elevated, with more than 75% neu- trophils in most patients. A completely normal leukocyte count and differential is found in approximately 10% of patients with acute appendicitis. A high white blood cell count (>20,000/mL) suggests complicated appendicitis with gangrene or perforation. A urinalysis can also be helpful in excluding pyelonephritis or nephrolithiasis. Minimal pyuria, frequently seen in older women, does not exclude appendicitis from the differential diagnosis because the ureter may be irritated adjacent to the inflamed appen- dix. Although microscopic hematuria is common in appendicitis, gross hematuria is uncommon and may indicate the presence of a kidney stone. Other blood tests are generally not helpful and are not indicated for the typical patient with suspected appendicitis. Bacteriology The flora in the normal appendix is similar to that in the colon, with various facultative aerobic and anaerobic bacteria. The polymicrobial nature of perforated appendicitis is well estab- lished. Escherichia coli, Streptococcus viridans, and Bacteroides and Pseudomonas spp. are frequently isolated, and many other organ- isms may be cultured (Table 51-1). Among patients with an acute nonperforated appendicitis, cultures of peritoneal fluid are frequently negative and are of limited use. Among patients with perforated appendicitis, peritoneal fluid cultures are more likely to be positive, revealing colonic bacteria with predictable sensi- tivities. Because it is rare that the findings alter the selection or duration of antibiotic use, some have challenged the traditional practice of obtaining cultures.5 Diagnosis The differential diagnosis of appendicitis can include almost all causes of abdominal pain, as described in the classic treatise, Cope’s Early Diagnosis of the Acute Abdomen.6 A useful rule is never to place appendicitis lower than second in the differential diagnosis of acute abdominal pain in a previously healthy person. History Appendicitis needs to be considered in the differential diagnosis of almost every patient with acute abdominal pain. Early diag- nosis remains the most important clinical goal in patients with suspected appendicitis and can be made primarily on the basis of the history and physical examination in most cases. The typical presentation begins with periumbilical pain, caused by the activation of visceral afferent neurons, followed by anorexia and nausea. The pain then localizes to the right lower quadrant as the inflammatory process progresses to involve the parietal peritoneum overlying the appendix. This classic pattern of migratory pain is the most reliable symptom of acute appendi- citis.7 A bout of vomiting may occur, in contrast to the repeated bouts of vomiting that typically accompany viral gastroenteritis or small bowel obstruction. Fever ensues, followed by the devel- opment of leukocytosis. These clinical features may vary. For example, not all patients become anorexic. Consequently, the feeling of hunger in an adult patient with suspected appendicitis Table  51-1  Bacteria  Commonly  Isolated  in  Perforated  Appendicitis TYPE OF BACTERIA PATIENTS (%) Anaerobic Bacteroides fragilis 80 Bacteroides thetaiotaomicron 61 Bilophila wadsworthia 55 Peptostreptococcus spp. 46 Aerobic Escherichia coli 77 Streptococcus viridans 43 Group D streptococcus 27 Pseudomonas aeruginosa 18 Adapted from Bennion RS, Thompson JE: Appendicitis. In Fry DE (ed): Surgical infections, Boston, 1995, Little, Brown, pp 241–250. ThE AppENDix  ChAPTER 51  1281 SECTIO N X AB D O M EN small percentage of people without appendicitis. In patients with abdominal pain, the positive predictive value of the finding of an appendicolith on CT remains high (≈75%). Should CT be used routinely in the diagnostic evaluation of patients with suspected appendicitis? We do not recommend it, but one study has found that liberal use of CT scans is prob- ably warranted because this has been credited with a declining incidence of negative appendectomy (i.e., the fraction of patho- logically normal appendices that are removed).10 In the setting of typical right lower quadrant pain and tenderness with signs of inflammation in a young male patient, a CT scan is unneces- sary, wastes valuable time, may be misinterpreted, and exposes the patient to risks for allergic contrast reaction, nephropathy, aspiration pneumonitis, and ionizing radiation. The latter carries increased risk in children in whom the rate of radiation-induced cancer has been estimated at 0.18% following an abdominal CT scan.11 CT has proved most valuable for older patients in whom the differential diagnosis is lengthy, clinical findings may be confusing, and appendectomy carries increased risk.12,13 In Radiographic Studies Computed tomography (CT) is commonly used in the evalua- tion of adult patients with suspected acute appendicitis. Improved imaging techniques, including the use of 5-mm sec- tions, have resulted in increased accuracy of CT scanning,8 which has a sensitivity of approximately 90% and a specificity of 80% to 90% for the diagnosis of acute appendicitis in patients with abdominal pain. Results of a recent randomized study have suggested that the use of high-resolution multidetector CT (64- MDCT) with or without oral or rectal contrast results in more than 95% accuracy in the diagnosis of acute appendicitis.9 In general, CT findings of appendicitis increase with the severity of the disease. Classic findings include a distended appendix more than 7 mm in diameter and circumferential wall thicken- ing and enhancement, which may give the appearance of a halo or target (Fig. 51-1). As inflammation progresses, one may see periappendiceal fat stranding, edema, peritoneal fluid, phleg- mon, or a periappendiceal abscess. CT detects appendicoliths in approximately 50% of patients with appendicitis and also in a FIGURE 51-1  A,  CT  scan  of  the  abdomen or  pelvis  in  a  patient  with acute appendicitis may reveal an appendicolith (arrow). B, CT  typically  shows  a  distended  appendix  (arrow)  with  diffuse  wall  thickening and periappendiceal fluid (arrowhead). C, The appendix  may  be  described  as  having mural  stratification,  referring  to  the  layers  of  enhancement  and  edema within  the wall  (arrow);  this  may  also  be  referred  to  as  a  target  sign. C,  Cecum; TI,  terminal  ileum.  A C B 1282  SECTION X  ABDOMEN operator-dependent accuracy and difficulty interpreting the images by those other than the operator. Because performance of the study may require hands-on participation by the radiolo- gist, ultrasonography may not be readily available at night or on weekends. Pelvic ultrasound can be especially useful in excluding pelvic pathology, such as tubo-ovarian abscess or ovarian torsion, which may mimic acute appendicitis. Although they are commonly obtained, the indiscriminate use of plain abdominal radiographs in the evaluation of patients with acute abdominal pain is unwarranted. In one study of 104 patients with acute onset of right lower quadrant pain, interpre- tation of plain x-rays changed the management of only six patients (6%) and, in one case, contributed to an unnecessary laparotomy.16 A calcified appendicolith is visible on plain films in only 10% to 15% of patients with acute appendicitis. Although its presence strongly supports the diagnosis in a patient with abdominal pain, the low sensitivity of this test renders it of little value in preoperative decision making. Plain abdominal films may be useful for the detection of ureteral calculi, small bowel obstruction, or perforated ulcer, but such conditions are rarely confused with appendicitis. Failure of the appendix to fill during a barium enema has been associated with appendicitis, but this finding lacks sensitivity and specificity because up to 20% of normal appendices do not fill. Diagnostic Laparoscopy Although most patients with appendicitis will be accurately diagnosed based on history, physical examination, laboratory studies and, if necessary, imaging studies, there are a small number in whom the diagnosis remains elusive. For these patients, diagnostic laparoscopy can provide a direct examina- tion of the appendix and a survey of the abdominal cavity for other possible causes of pain. We use this technique primarily for women of childbearing age in whom preoperative pelvic ultrasound or CT fails to provide a diagnosis. Concerns about the possible adverse effects of a missed perforation and perito- nitis on future fertility sometimes prompt earlier intervention in this patient population. Special Patient Populations The diagnosis of appendicitis is particularly difficult in the very young and in older adults. It is in these groups that diagnosis is most often delayed and perforation occurs most frequently. Imaging studies are strongly considered here. Because of increas- ing concerns about radiation-induced cancers in children,11 ultrasonography is the preferred initial imaging modality for this group. For older patients, CT offers the ability to detect the broader array of conditions, such as diverticulitis and malig- nancy, found in the differential diagnosis. In infants, nonfocal findings such as lethargy, irritability, and anorexia may be present in the early stages of appendicitis, with vomiting, fever, and pain apparent as the disease progresses. Ultrasound is useful for the evaluation of appendicitis and other acute abdominal emergencies, such as pyloric stenosis, in infants. In preschool-aged children, the differential diagnosis includes intussusception, Meckel’s diverticulitis, and acute gas- troenteritis. Intussusception may be distinguished by the colicky nature of the pain, with intervening pain-free periods, and the absence of peritonitis. Meckel’s diverticulitis is relatively uncom- mon, but its presentation is similar to that of appendicitis, except that the pain and tenderness typically localize in the patients with atypical symptoms, CT scan may reduce the nega- tive appendectomy rate. Liberal use of cross-sectional imaging seems most appropriate and, as always, the study needs to be performed only in settings in which it has a significant potential to alter management. Given the recent increased awareness of the risks of cumulative radiation exposure in young adults undergoing CT scanning,14 it remains to be seen whether mag- netic resonance imaging (MRI) will replace CT as the preferred modality for the evaluation of the appendix in younger patients. The morbidity rate of perforated appendicitis far exceeds that of a negative appendectomy. Thus, the strategy has been to set a low enough threshold for removal of the appendix to mini- mize the cases of missed appendicitis. With increased use of CT, the frequency of negative explorations has declined in recent years, without an accompanying rise in the number of perfora- tions. An analysis of more than 75,000 patients from 1999 to 2000 revealed a negative appendectomy rate of 6% in men and 13.4% in women.12 Among patients with abdominal pain, ultrasonography has a sensitivity of approximately 85% and a specificity of more than 90% for the diagnosis of acute appendicitis. Sonographic find- ings consistent with acute appendicitis include an appendix of 7 mm or more in anteroposterior diameter, a thick-walled, non- compressible luminal structure seen in cross section, referred to as a target lesion, or the presence of an appendicolith (Fig. 51-2). In more advanced cases, periappendiceal fluid or a mass may be found. Ultrasonography has the advantages of being a noninva- sive modality requiring no patient preparation that also avoids exposure to ionizing radiation. Thus, it is commonly used in children and in pregnant patients with equivocal clinical find- ings suggestive of acute appendicitis. Ultrasonography has been shown to change the disposition of 59% of children with abdominal pain who had already been evaluated by the surgical team.15 Disadvantages of ultrasonography include FIGURE 51-2  Ultrasound of a normal appendix (top) illust