28
Appendix
Elliot C. Pennington, MD
Peter A. Burke, MD
ANATOMY & PHYSIOLOGY
In infants, the appendix is a conical diverticulum at the apex of the cecum, but with differential growth and distention of the cecum, the appendix ultimately arises on the left and dorsally approximately 2.5 cm below the ileocecal valve. The taeniae of the colon converge at the base of the appendix, an arrangement that helps in locating this structure at operation. The appendix is freely mobile in the majority and is fixed retrocecally in 16% of adults.
The appendix in children is characterized by a large concentration of lymphoid follicles that appear 2 weeks after birth and number about 200 or more at age 15 years. Thereafter, progressive atrophy of lymphoid tissue proceeds with fibrosis of the wall and partial or total obliteration of the lumen. If the appendix has a physiologic function, it is probably related to the presence of lymphoid follicles.
ACUTE APPENDICITIS
General Considerations
Approximately 7% of people in Western countries have appendicitis at some time during their lives. With more than 250,000 appendectomies for acute appendicitis performed annually in the United States, it is the most common surgical emergency encountered by the general surgeon and accounts for about 1% of all surgical operations.
Obstruction of the proximal lumen by fibrous bands, lymphoid hyperplasia, fecaliths, calculi, or parasites has long been considered to be the major cause of acute appendicitis. A fecalith or calculus is found in only 10% of acutely inflamed appendices. Though evidence of temporal and geographic clustering of cases has suggested a primary infectious etiology this remains to be proven.
As appendicitis progresses, the blood supply is impaired by bacterial infection in the wall and distention of the lumen; gangrene and perforation occur at about 24 hours, though the timing is highly variable. Gangrene implies microscopic perforation, bacterial contamination of the peritoneum, and peritonitis. This process may be effectively localized by adhesions from nearby viscera.
Clinical Findings
Acute appendicitis may simulate almost any other acute abdominal illness, and in turn may be mimicked by a variety of conditions. Progression of symptoms and signs is the rule—in contrast to the fluctuating course of some other diseases.
Typically, the illness begins with vague midabdominal or periumbilical discomfort followed by nausea, anorexia, and indigestion. The pain is continuous but not severe, with occasional mild cramping. The patient may feel constipated or may vomit. Importantly, within several hours of the onset of symptoms the pain shifts to the right-lower quadrant, becoming localized and causing discomfort on moving, walking, or coughing.
Physical examination shows localized tenderness to palpation and perhaps slight muscular guarding. Rebound or percussion tenderness (the latter provides the same information more humanely) may be elicited in the right-lower quadrant. Rectal and pelvic examinations are likely to be negative; if positive, these more often point to another etiology. The temperature is only slightly elevated in the absence of perforation. Administration of narcotic pain medications does not affect the accuracy of the physical examination.
A common misconception is that inflammation of a retrocecal appendix produces an atypical syndrome. This is incorrect; the clinical findings in this situation are the same as for ordinary (antececal) appendicitis. Acute appendicitis may mimic other surgical diseases if the appendix is located outside the right-lower quadrant (ie, sigmoid diverticulitis, acute cholecystisis, or a perforated ulcer). Even when the cecum is normally situated, however, a long appendix may reach to other parts of the abdomen.
Three general points are worth remembering: (1) people with early (nonperforated) appendicitis often do not appear ill. Finding localized tenderness over the McBurney point is the cornerstone of diagnosis. (2) A rule that will help considerably with atypical cases is never to place appendicitis lower than second in the differential diagnosis of acute abdominal pain in a previously healthy person. (3) Patients with appendicitis most commonly have a history of generalized abdominal that over time becomes focused in the right-lower quadrant.
The average leukocyte count is 15,000/μL, and 90% of patients have counts over 10,000/μL. In three-fourths of patients, the differential white count shows more than 75% neutrophils. It must be emphasized, however, that 1 patient in 10 with acute appendicitis has a normal leukocyte count, and many have normal differential cell counts. Appendicitis in HIV-positive patients, while up to three times more common, produces the same syndrome as in healthy adults but the white blood cell count is usually normal.
Urinalysis is typically normal, but a few leukocytes and erythrocytes and occasionally even gross hematuria may be noted, particularly in retrocecal or pelvic appendicitis.
On plain radiographs localized air-fluid levels, localized ileus, or increased soft tissue density in the right-lower quadrant is present in 50% of patients with early acute appendicitis. Less common findings are a calculus, an altered right psoas shadow, an abnormal right flank stripe, or free peritoneal air (from perforated appendicitis). In general, the findings on plain films rarely aid in diagnosis.
A CT examination of the abdomen may be of help in diagnosis. An enlarged appendix with wall thickening, enhancement, or periappendiceal fat stranding is the most useful CT findings of acute appendicitis. Other findings may be present, including focal cecal thickening, appendicoliths, extraluminal or intramural air, and pericecal phlegmon, but are less reliable. Oral contrast administration is not. CT scans are of greatest value in patients with less than typical clinical and laboratory findings, where a positive study would be an indication for appendectomy. In young adults, low-dose CT is noninferior to standard-dose CT. In the face of typical time course of disease, right-lower quadrant pain and tenderness plus signs of inflammation (eg, fever, leukocytosis), a CT scan would be superfluous and, if negative, even misleading. Ultrasound imaging is generally less reliable than CT, though may become more reliable when done using a combined transabdominal and transvaginal approach. When appendicitis is accompanied by a right-lower quadrant mass, an ultrasound or CT scan should be obtained to differentiate between a periappendiceal phlegmon and an abscess or tumor.
Appendicitis is the most common nonobstetric surgical disease of the abdomen during pregnancy affecting between 1 in 1400 and 1 in 6600 live births, with cases equally distributed through all three trimesters. By far the most common presentation is right-lower quadrant pain, tenderness, and leukocytosis—the classic syndrome—but the enlarged uterus occasionally will have pushed the appendix into the right-upper quadrant, which gives rise to pain in this location. Some symptoms, such as nausea and vomiting, occur in normal pregnancy, which may obscure accurate diagnosis. Fever is less common than with appendicitis in the absence of pregnancy. The main problem is to recognize appendicitis and perform appendectomy promptly. Both CT and MRI are highly sensitive and specific for the diagnosis of acute appendicitis during pregnancy. Delay in operation runs a higher than usual risk of perforation and diffuse peritonitis, because the omentum is less available to wall off the infection. The mother is in greater jeopardy of serious abdominal infection, and the fetus is more vulnerable to premature labor with complications. Laparoscopic appendectomy is well tolerated by the mother and fetus, but the frequency of technical complications is higher than with the open approach. Appendectomy during pregnancy is often followed by preterm labor but rarely by preterm delivery. Early appendectomy in pregnancy has decreased the maternal death rate to under 0.5% and the fetal death rate to less than 10%. Appendectomy in general does not increase a woman’s risk for infertility later in life.
Diagnosis & Differential Diagnosis
The clinical diagnosis of appendicitis rests on a combination of localized pain and tenderness accompanied by signs of inflammation, such as fever, leukocytosis, and elevated C-reactive protein levels. Migration of pain from the periumbilical area to the right-lower quadrant is also diagnostically significant. In the absence of signs of inflammation the diagnosis is less certain, and in this situation a CT scan may be of value. The best strategy in equivocal cases is to observe the patient for a period of 6 hours or more. During this time, patients with appendicitis experience increasing pain and signs of inflammation, while those without appendicitis generally improve. False-positive diagnoses often involve cases where the surgeon has accorded more significance to the patient’s pain than to the presence or absence of inflammatory signs. Over the past 20 years, the overall false-positive rate for the diagnosis of appendicitis has dropped from 15% to 10% without an accompanying rise in the number of perforations. Thus, diagnostic accuracy appears to be improving. Some patients experience chronic appendicitis, which involves pain lasting 3 weeks or more, and typically includes an acute illness in the recent past compatible with acute appendicitis that was managed nonoperatively.
The diagnosis of acute appendicitis may be difficult in patients at the extremities of age, and it is in these groups that diagnosis is most often delayed. Infants display only lethargy, irritability, and anorexia in the early stages, but may develop vomiting, fever, and pain as the disease progresses. The elderly may not display any classic symptoms, even though the course of appendicitis is more virulent in this age group.
The highest incidence of false-positive diagnosis (20%) is in women between ages 20 and 40 and is attributable to gynecologic conditions such as pelvic inflammatory disease. Compared with appendicitis, pelvic inflammatory disease is more often associated with bilateral lower quadrant tenderness, left adnexal tenderness, onset of illness within 5 days of the last menstrual period, and a history that does not include nausea and vomiting.
Clinical scoring systems can be effective in the diagnosis of acute appendicitis. For example, the Alvarado Score, which uses both physical examination (anorexia, migration of pain, nausea, right-lower quadrant tenderness, rebound pain, and elevated temperature) and laboratory findings (leukocytosis, shift of WBC count to the left) has excellent negative predictive value, with a sensitivity of 99%.
Complications
The complications of acute appendicitis include perforation, peritonitis, abscess, and pylephlebitis.
Perforation follows the natural history of acute appendicitis, and most likely appears because of delay in seeking treatment. Perforation is accompanied by more severe pain and higher fever (average, 38.3°C) than in simple appendicitis. It is unusual for the acutely inflamed appendix to perforate within the first 12 hours. Appendicitis has progressed to perforation by the time of appendectomy in about 50% of patients under age 10 or over age 50. Perforation in young women increases the subsequent risk of tubal infertility about fourfold.
Localized peritonitis results from microscopic perforation of a gangrenous appendix, while spreading or generalized peritonitis usually implies gross perforation into the free peritoneal cavity. Increasing tenderness and rigidity, abdominal distention, and adynamic ileus are obvious in these patients. High fever and severe toxicity mark progression of this catastrophic illness.
Localized perforation occurs when the periappendiceal infection becomes walled off by omentum and adjacent viscera. Clinical presentation consists of the usual findings in appendicitis, and may include a right-lower quadrant mass. An ultrasound or CT scan should be performed; if an abscess is found, it is best treated by percutaneous imaging-guided aspiration. Opinion differs about how small abscesses and phlegmons should be handled. Some surgeons prefer a regimen consisting of antibiotics and expectant management followed by elective appendectomy 6 weeks later, so as to avoid spreading the localized infection and the need for a more extensive operation. This strategy is associated with lower rates of overall complications, abscess formation, bowel obstruction, and reoperation. Other surgeons recommend immediate appendectomy, which some believe shortens the duration of illness.
When an unsuspected abscess is encountered during appendectomy, it is usually best to proceed and remove the appendix. If the abscess is large and further dissection would be hazardous, drainage alone is appropriate.
Appendicitis recurs in only 10% of patients whose initial treatment consisted of antibiotics with or without drainage of an abscess. Therefore, when the presence of ancillary conditions increases the risks of surgery, interval appendectomy may be postponed unless symptoms recur.
Pylephlebitis is suppurative thrombophlebitis of the portal venous system. Chills, high fever, low-grade jaundice, and, later, hepatic abscesses are the hallmarks of this grave but fortunately rare condition, which affects less than 1% of patients. Prompt surgery and antibiotic therapy is indicated.
Prevention
There is no effective prevention strategy for appendicitis. In the past it was common to perform an incidental appendectomy in young people during the course of an abdominal operation for another illness—as long as the exposure was adequate and there were no specific contraindications. The declining lifetime risk of appendicitis now calls this practice into question. A related question concerns the appropriate course when a laparoscopy is performed for presumptive appendicitis and the appendix looks normal. There is no consensus on these cases, with some surgeons preferring to remove the appendix and some electing to leave it in place. In children, it is not necessary to remove the appendix after an incidentally diagnosed appendicolith.
Treatment
With few exceptions, the treatment of appendicitis is surgical (ie, appendectomy). The operation can be done open (Figure 28–1) or laparoscopically. A laparoscopic approach is desirable when the preoperative diagnosis is uncertain. In select patients, outpatient laparoscopic appendectomy may be possible.
Figure 28–1. Technique of open appendectomy. A: Incision. B: After delivery of the tip of the cecum, the mesoappendix is divided. C: The base is clamped and ligated with a simple throw of the knot. The next step—inversion of the stump—is optional. D: A clamp is placed to hold the knot during inversion with a purse-string suture of fine silk. E: The loosely tied inner knot on the stump assures that there is no closed space for the development of a stump abscess.
Prophylactic antibiotics are indicated preoperatively with a single-drug regimen, usually a cephalosporin. Culturing abdominal fluid is not indicated even when the appendix has perforated, as the organisms obtained are the typical fecal flora. Abdominal drains are called for only to treat established abscesses.
If a patient with appendicitis cannot be taken to a modern surgical facility for care, treatment should consist of antibiotics alone. The complication-free success rate of this approach is above 93%, though acute appendicitis may recur in this population. Success rates of greater than 60% have been reported at 1 year.
The laparoscopic approach to appendectomy was first described by Kurt Semm in 1983. There has been much debate over the appropriate role of laparoscopy in the treatment of appendicitis since that initial report, with an increasing majority of cases in this country performed laparoscopically. In one large study, patients treated laparoscopically had lower overall morbidity (except organ space surgical site infections in patients with complicated appendicitis), but similar serious morbidity, mortality, and length of stay. Generally, patients undergoing laparoscopic appendectomy have less postoperative pain and a shorter length of stay by 1 day. However, laparoscopic appendectomy may be associated with increased overall hospital costs and longer operative times. Conversion rates from laparoscopic to open approach range from 0% to 27%, and should be based on surgeon experience, judgment, and ability to safely perform the procedure. Currently most patients in the United States undergo laparoscopic treatment, and this approach is safe for both uncomplicated and complicated appendicitis. In select patients, the appendix can be removed using a single-port technique.
Although a death rate of zero is theoretically attainable in acute appendicitis, deaths still occur, some of which are avoidable. The mortality rate in simple acute appendicitis is approximately 0.1% and has not changed significantly since 1930. Progress in preoperative and postoperative care has reduced mortality from perforation to about 5%. Nonetheless, postoperative infections still occur in 30% of cases of gangrenous or perforated appendicitis. While the cases may be more technically challenging, obese patients have similar rates of complication, length of stay, and readmission. The substantial increase in tubal infertility that follows perforation in young women is avoidable by early appendectomy. If the entirety of the appendix is not removed, stump appendicitis can occur in the residual appendix.
Many controversies exist regarding the treatment of acute appendicitis. Some surgeons routinely irrigate all four quadrants in all appendectomies, while others do not. Irrigation has been shown to reduce postoperative abscess rates in perforated appendicitis only. There is emerging evidence that antibiotics alone may be a preferable initial treatment of uncomplicated acute appendicitis. While it is clear that postoperative antibiotics are not beneficial for nonperforated appendicitis after appendectomy, no consensus exists on the drug regimen or duration of antibiotics for perforated disease.
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TUMORS OF THE APPENDIX
Benign tumors, including carcinoids, were found in 4.6% of 71,000 human appendix specimens examined microscopically, typically as incidental findings.
Malignant Tumors
Primary malignant tumors were found in 1.4% of appendices in the same large series. Carcinoid and neuroendocrine tumors comprise the majority of appendiceal cancers, and the appendix is the commonest location of carcinoid tumors of the gastrointestinal tract. Carcinoid tumors of the appendix are most commonly found at the tip and are usually benign, but tumors over 2 cm in diameter may exhibit malignant behavior. About half of these tumors are discovered during an appendectomy for acute appendicitis, with the remainder identified incidentally. Lesions less than 2 cm in diameter invade the appendiceal wall in 25% of cases, but only 3% metastasize to lymph nodes. Hepatic metastases and the carcinoid syndrome are truly rare. Appendectomy alone is adequate treatment unless the lymph nodes are visibly involved, the tumor is more than 2 cm in diameter, mucinous elements are present in the tumor (adenocarcinoid), or the mesoappendix or base of the cecum is invaded; in these cases, right hemicolectomy is recommended. The recurrence rate after surgical treatment is near zero.
Colonic adenocarcinoma can arise in the appendix and spread rapidly to regional lymph nodes or implant on other peritoneal surfaces. Most patients present with advanced disease. Adenocarcinoma is virtually never diagnosed preoperatively, and about half of cases present as acute appendicitis. Right hemicolectomy should be performed if disease is localized to the appendix and/or regional lymph nodes. The 5-year survival rate is 60% after right hemicolectomy and only 20% after appendectomy alone, but the latter group includes patients with distant metastases at diagnosis.
Mucocele and Pseudomyxoma Peritonei
An appendiceal mucocele is a cystic, dilated appendix filled with mucin. Simple mucocele is not a neoplasm and results from chronic obstruction of the proximal lumen, usually by fibrous tissue. Rarely, mucocele is caused by a neoplasm—cystadenoma, or adenocarcinoma grade 1 in the older terminology, now often called a mucinous appendix neoplasm (MAN). This lesion may arise de novo or (perhaps) in a preceding simple mucocele. Appendectomy is adequate treatment in either case. If a MAN ruptures, it can lead to a condition known as pseudomyxoma peritonei, characterized by diffuse mucin production throughout the peritoneal cavity, with variable amounts of tumor cellularity. Patients can be treated with either simple appendectomy or right hemicolectomy.
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MULTIPLE CHOICE QUESTIONS