356: Acute Appendicitis and Peritonitis

INCIDENCE AND EPIDEMIOLOGY

Appendicitis occurs more frequently in Westernized societies. Although its incidence is decreasing for uncertain reasons, acute appendicitis remains the most common emergency general surgical disease affecting the abdomen, with a rate of approximately 100 per 100,000 person-years in Europe and the Americas or about 11 cases per 10,000 people annually. Approximately 9% of men and 7% of women will experience an episode during their lifetime. Appendicitis occurs most commonly in 10- to 19-year-olds, although the average age at diagnosis appears to be gradually increasing, as is the frequency of the disease in African Americans, Asians, and Native Americans. Overall, 70% of patients are less than 30 years old and most are men; the male-to-female ratio is 1.4:1.

One of the more common complications and most important causes of excess morbidity and mortality is perforation, whether it is contained and localized or unconstrained within the peritoneal cavity. In contrast to the trend observed for appendicitis and appendectomy, the incidence of perforated appendicitis (~20 cases per 100,000 person-years) is increasing. The explanation for this phenomenon is unknown. Approximately 20% of all patients have evidence of perforation at presentation, but the percentage risk is much higher in patients under 5 or over 65 years of age.

PATHOGENESIS OF APPENDICITIS AND APPENDICEAL PERFORATION

Appendicitis was first described in 1886 by Reginald Fitz. Its etiology is still not completely understood. Fecaliths, incompletely digested food residue, lymphoid hyperplasia, intraluminal scarring, tumors, bacteria, viruses, and inflammatory bowel disease have all been associated with inflammation of the appendix and appendicitis.

Although not proven, obstruction of the appendiceal lumen is believed to be an important step in the development of appendicitis. In some cases, obstruction leads to bacterial overgrowth and luminal distension, with an increase in intraluminal pressure that can inhibit the flow of lymph and blood in some cases. Then, vascular thrombosis and ischemic necrosis with perforation of the distal appendix may occur. Any perforation that occurs near the base of the appendix should raise concerns about another disease process. Most patients who will perforate do so before they are evaluated by surgeons.

Appendiceal fecaliths (or appendicoliths) are found in approximately 50% of patients with gangrenous appendicitis who perforate but are rarely identified in those who have simple disease. As mentioned earlier, the incidence of perforated, but not simple, appendicitis is increasing. The rate of perforated and nonperforated appendicitis is correlated in men but not in women. Together these observations suggest that the underlying pathophysiologic processes are different and that simple appendicitis does not always progress to perforation. Furthermore, some cases of simple acute appendicitis may resolve spontaneously or with antibiotic therapy, and recurrent disease is remotely possible. The relative frequency of these events is unknown.

When perforation occurs, the resultant leak may be contained by the omentum or other surrounding tissues to form an abscess. Free perforation normally causes severe peritonitis. These patients may also develop infective suppurative thrombosis of the portal vein and its tributaries along with intrahepatic abscesses. The prognosis of the very unfortunate patients who develop this dreaded complication is very poor.

CLINICAL MANIFESTATIONS

More refined approaches to diagnosis, supportive care, and surgical intervention are likely responsible for the remarkable decrease in the risk of mortality from simple appendicitis to currently less than 1%. Nevertheless, it is still important to identify patients who might have appendicitis as early as possible to minimize their risk of developing complications. Patients who have had symptoms for more than 48 h are more likely to perforate.

Appendicitis should be included in the differential diagnosis of abdominal pain for every patient in any age group unless it is certain that the organ has been previously removed (Table 356-1).

The appendix’s anatomical location, which varies, directly influences how the patient presents for care. Where the appendix can be “found” ranges from local differences in how the appendiceal body and tip lie relative to its attachment to the cecum (Figs. 356-1 and 356-2), to where the appendix is actually situated in the peritoneal cavity—for example, from its typical location in the right lower quadrant, to the pelvis, right flank, right upper quadrant (as may be observed during pregnancy), or even the left side of the abdomen for patients with malrotation or who have severely redundant colons.

Because the differential diagnosis of appendicitis is so extensive, deciding if a patient has appendicitis can be difficult (Table 356-2). Soliciting an appropriate history requires detecting symptoms that might suggest alternative diagnoses. Patients with appendicitis may not have any abdominal discomfort early in the disease process. Furthermore, many patients may not present with the classically described history or physical findings.

What is the classic history? Nonspecific complaints occur first. Patients may notice changes in bowel habits or malaise and vague, perhaps intermittent, crampy, abdominal pain in the epigastric or periumbilical region. The pain subsequently migrates to the right lower quadrant over 12–24 h, where it is sharper and can be definitively localized as transmural inflammation when the appendix irritates the parietal peritoneum. Parietal peritoneal irritation may be associated with local muscle rigidity and stiffness. Patients with appendicitis will most often observe that their nausea, if present, followed the development of abdominal pain, which can help distinguish them from patients with gastroenteritis, for example, where nausea occurs first. Emesis, if present, also occurs after the onset of pain and is typically mild and scant. Thus, timing of the onset of symptoms and the characteristics of the patient’s pain and any associated findings must be rigorously assessed. Anorexia is so common that the diagnosis of appendicitis should be questioned in its absence.

Arriving at the correct diagnosis is even more challenging when the appendix is not located in the right lower quadrant, in women of childbearing age, and in the very young or elderly. Because the differential diagnosis of appendicitis is so broad, often the key question to answer expeditiously is whether the patient has appendicitis or some other condition that requires immediate operative intervention. A major concern is that the likelihood of a delay in diagnosis is greater if the appendix is unusually positioned. All patients should undergo a rectal examination. An inflamed appendix located behind the cecum or below the pelvic brim may prompt very little tenderness of the anterior abdominal wall.

Patients with pelvic appendicitis are more likely to present with dysuria, urinary frequency, diarrhea, or tenesmus. They may only experience pain in the suprapubic region on palpation or on rectal or pelvic examination. A pelvic examination in women is mandatory to rule out conditions affecting urogynecologic organs that can cause abdominal pain and mimic appendicitis such as pelvic inflammatory disease, ectopic pregnancy, and ovarian torsion. The relative frequencies of some presenting signs are displayed in Table 356-3.

Patients with simple appendicitis normally only appear mildly ill with a pulse and temperature that are usually only slightly above normal. The provider should be concerned about other disease processes beside appendicitis or the presence of complications such as perforation, phlegmon, or abscess formation if the temperature is >38.3°C (~101°F) and if there are rigors.

Patients with appendicitis will be found to lie quite still to avoid peritoneal irritation caused by movement, and some will report discomfort caused by a bumpy car ride on the way to the hospital or clinic, coughing, sneezing, or other actions that replicate a Valsalva maneuver. The entire abdomen should be examined systematically starting in an area where the patient does not report discomfort if possible. Classically, maximal tenderness is identified in the right lower quadrant at or near McBurney’s point, which is located approximately one-third of the way along a line originating at the anterior iliac spine and running to the umbilicus. Gentle pressure in the left lower quadrant may elicit pain in the right lower quadrant if the appendix is located there. This is Rovsing’s sign (Table 356-4). Evidence of parietal peritoneal irritation is often best elicited by gentle abdominal percussion, jiggling the patient’s gurney or bed, or mildly bumping the feet.

Atypical presentation and pain patterns are common, especially in the very old or the very young. Diagnosing appendicitis in children can be especially challenging because they tend to respond so dramatically to stimulation and obtaining an accurate history may be difficult. In addition, it is important to remember that the smaller omentum found in children may be less likely to wall off an appendiceal perforation. Observing the child in a quiet surrounding may be helpful.

Signs and symptoms of appendicitis can be subtle in the elderly who may not react as vigorously to appendicitis as younger people. Pain, if noticed, may be minimal and have originated in the right lower quadrant or, otherwise, where the appendix is located. It may never have been noticed to be intermittent, or there may only be significant discomfort with deep palpation. Nausea, anorexia, and emesis may be the predominant complaints. The rare patient may even present with signs and symptoms of distal bowel obstruction secondary to appendiceal inflammation and phlegmon or abscess formation.

LABORATORY TESTING

Laboratory testing does not identify patients with appendicitis but can help the clinician work through the differential diagnosis. The white blood cell count is only mildly to moderately elevated in approximately 70% of patients with simple appendicitis (with a leukocytosis of 10,000–18,000 cells/μL). A “left shift” toward immature polymorphonuclear leukocytes is present in >95% of cases. A sickle cell preparation may be prudent to obtain in those of African, Spanish, Mediterranean, or Indian ancestry. Serum amylase and lipase levels should be measured.

Urinalysis is indicated to help exclude genitourinary conditions that may mimic acute appendicitis, but a few red or white blood cells may be present as a nonspecific finding. However, an inflamed appendix that abuts the ureter or bladder may cause sterile pyuria or hematuria. Every woman of childbearing age should have a pregnancy test. Cervical cultures are indicated if pelvic inflammatory disease is suspected. Anemia and guaiac-positive stools should raise concern about the presence of other diseases or complications such as cancer.

IMAGING

Plain films of the abdomen are rarely helpful and so are not routinely obtained unless the clinician is worried about other conditions such as intestinal obstruction, perforated viscus, or ureterolithiasis. Less than 5% of patients will present with an opaque fecalith in the right lower quadrant. The presence of a fecalith is not diagnostic of appendicitis, although its presence in an appropriate location where the patient complains of pain is suggestive.

The effectiveness of ultrasonography as a tool to diagnosis appendicitis is highly operator dependent. Even in very skilled hands, the appendix may not be visualized. Its overall sensitivity is 0.86, with a specificity of 0.81. Ultrasonography, especially intravaginal techniques, appears to be most useful for identifying pelvic pathology in women. Ultrasonographic findings suggesting the presence of appendicitis include wall thickening, an increased appendiceal diameter, and the presence of free fluid.

The sensitivity and specificity of computed tomography (CT) are 0.94 and 0.95, respectively. Thus, CT imaging, given its high negative predictive value, may be helpful if the diagnosis is in doubt, although studies performed early in the course of disease may not have any typical radiographic findings. Suggestive findings on CT examination include dilatation >6 mm with wall thickening, a lumen that does not fill with enteric contrast, and fatty tissue stranding or air surrounding the appendix, which suggests inflammation (Figs. 356-3 and 356-4). The presence of luminal air or contrast is not consistent with a diagnosis of appendicitis. Furthermore, nonvisualization of the appendix is a nonspecific finding that should not be used to rule out the presence of appendiceal or periappendiceal inflammation.

SPECIAL PATIENT POPULATIONS

Appendicitis in the most common extrauterine general surgical emergency observed during pregnancy. Early symptoms of appendicitis such as nausea and anorexia may be overlooked. Diagnosing appendicitis in pregnant patients may be especially difficult because as the uterus enlarges the appendix may be pushed higher along the right flank even to the right upper quadrant or because the gravid uterus may obscure typical physical findings. Ultrasonography may facilitate early diagnosis. A high index of suspicion is required because of the effects of unrecognized and untreated appendicitis on the fetus. For example, the fetal mortality rate is four times greater (from 5 to 20%) in patients with perforation.

Immunocompromised patients may present with only mild tenderness and may have many other disease processes in their differential diagnosis, including atypical infections from mycobacteria, Cytomegalovirus, or other fungi. Enterocolitis is a concern and may be present in patients who present with abdominal pain, fever, and neutropenia due to chemotherapy. CT imaging may be very helpful, although it is important not to be overly cautious and delay operative intervention for those patients who are believed to have appendicitis.

TREATMENT

Acute peritonitis, or inflammation of the visceral and parietal peritoneum, is most often but not always infectious in origin, resulting from perforation of a hollow viscus. This is called secondary peritonitis, as opposed to primary or spontaneous peritonitis, when a specific intraabdominal source cannot be identified. In either instance, the inflammation can be localized or diffuse.

ETIOLOGY

Infective organisms may contaminate the peritoneal cavity after spillage from a hollow viscus, because of a penetrating wound of the abdominal wall, or because of the introduction of a foreign object like a peritoneal dialysis catheter or port that becomes infected. Secondary peritonitis most commonly results from perforation of the appendix, colonic diverticuli, or the stomach and duodenum. It may also occur as a complication of bowel infarction or incarceration, cancer, inflammatory bowel disease, and intestinal obstruction or volvulus. Conditions that may cause secondary bacterial peritonitis and their mechanisms are listed in Table 356-5. Over 90% of the cases of primary or spontaneous bacterial peritonitis occur in patients with ascites or hypoproteinemia (<1 g/L).

Aseptic peritonitis is most commonly caused by the abnormal presence of physiologic fluids like gastric juice, bile, pancreatic enzymes, blood, or urine. It can also be caused by the effects of normally sterile foreign bodies like surgical sponges or instruments. More rarely, it occurs as a complication of systemic diseases like lupus erythematosus, porphyria, and familial Mediterranean fever. The chemical irritation caused by stomach acid and activated pancreatic enzymes is extreme and secondary bacterial infection may occur.

CLINICAL FEATURES

The cardinal signs and symptoms of peritonitis are acute, typically severe, abdominal pain with tenderness and fever. How the patient’s complaints of pain are manifested depends on their overall physical health and whether the inflammation is diffuse or localized. Elderly and immunosuppressed patients may not respond as aggressively to the irritation. Diffuse, generalized peritonitis is most often recognized as diffuse abdominal tenderness with local guarding, rigidity, and other evidence of parietal peritoneal irritation. Physical findings may only be identified in a specific region of the abdomen if the intraperitoneal inflammatory process is limited or otherwise contained as may occur in patients with uncomplicated appendicitis or diverticulitis. Bowel sounds are usually absent to hypoactive.

Most patients present with tachycardia and signs of volume depletion with hypotension. Laboratory testing typically reveals a significant leukocytosis, and patients may be severely acidotic. Radiographic studies may show dilatation of the bowel and associated bowel wall edema. Free air, or other evidence of leakage, requires attention and could represent a surgical emergency. In stable patients in whom ascites is present, diagnostic paracentesis is indicated, where the fluid is tested for protein and lactate dehydrogenase and the cell count is measured.

THERAPY AND PROGNOSIS

Whereas mortality rates can be less than 10% for reasonably healthy patients with relatively uncomplicated, localized peritonitis, mortality rates >40% have been reported for the elderly or immunocompromised. Successful treatment depends on correcting any electrolyte abnormalities, restoration of fluid volume and stabilization of the cardiovascular system, appropriate antibiotic therapy, and surgical correction of any underlying abnormalities.

Acknowledgment

The wisdom and expertise of Dr. William Silen is gratefully acknowledged in this updated chapter on acute appendicitis and peritonitis.