Definition and Epidemiology

Abdominal pain is a common reason patients seek care in primary care offices, urgent care centers, and emergency rooms. Gastrointestinal discomfort is also a challenging condition to diagnose because the pain can be related to abdominal gas or a more serious condition requiring emergency care.¹ There are many causes of abdominal pain, and the patient’s description of the discomfort may be vague, but for any patient reporting abdominal discomfort, the health care provider’s first priority is to determine whether the patient’s pain is the result of an acute abdomen, indicating an emergency referral.¹

Pathophysiology and Clinical Presentation

There are several major mechanisms of abdominal pain, including pain from obstruction of a hollow viscus, capsular distention, peritoneal irritation, mucosal ulceration, vascular insufficiency, altered body motility, nerve injury, abdominal wall injury, and pain referred from an extra-abdominal site. Determination of the specific type of pain gives a provider valuable information about the possible cause of the pain. Abdominal wall pain is often described as a constant achy feeling. Visceral pain, the pain arising from a hollow viscus, is usually the result of distention or spasm of a hollow organ, as in early intestinal obstruction; it is commonly described as dull and crampy and is poorly localized. Parietal pain is a sharp, well-localized pain arising from irritation of the parietal peritoneum, such as the pain of acute appendicitis with inflammation spread to the peritoneum. Referred pain is an aching type of pain experienced away from the disease process and is perceived to be near the surface of the body. The pain referral phenomenon is a result of the shared central pathways for afferent neurons from different locations (e.g., pain from an inflamed gallbladder may be felt in the right scapula¹).

Location of the abdominal pain is another factor that can aid in identifying the cause of the patient’s discomfort. Pain localized to the right upper abdominal quadrant generally emanates from the chest cavity, liver, gallbladder, stomach, bowel, or right kidney or ureter. Left upper quadrant pain is usually associated with the heart or chest cavity, spleen, stomach, pancreas (especially acute pancreatitis), or left kidney or ureter. The source of left lower abdominal pain can include the bowel, left ureter, or pelvis and is most commonly associated with diverticulitis, particularly when the pain is protracted and severe.² Right lower quadrant pain is associated with the appendix, bowel, right ureter, or pelvis, with the most common diagnosis being appendicitis. Cholecystitis or peptic ulcer perforation also must be considered. Pain that migrates across several quadrants is typically associated with the bowel, whereas abdominal wall pain from trauma or inflammation can occur in any quadrant.

In some patients, abdominal pain can be subtle and the diagnosis obscure. This is particularly true in older adults, who are less likely than younger ones to have a fever or pain and more likely to be hypotensive, lethargic, or confused.³

Lower abdominal or pelvic discomfort in females can suggest a gynecologic problem (e.g., an ovarian cyst). In women of childbearing age, even those with a history of tubal ligation, abdominal pain, or abnormal vaginal bleeding, it is imperative to perform a pregnancy test to exclude the possibility of ectopic pregnancy.⁴

An accurate diagnosis in patients complaining of acute abdominal pain is highly dependent on history, physical examination, and appropriate laboratory and radiologic procedures. Previous abdominal surgery, medication history (including over-the-counter drugs, vitamins, and supplements), allergies, social and sexual history, last menstrual period, dietary history, last food or fluid ingested, and family history of abdominal pain are important considerations that should be elicited. Causes of acute abdominal pain include appendicitis, cholecystitis, diverticulitis, small bowel obstruction, perforated peptic ulcer, peritonitis, ruptured ectopic pregnancy, pelvic inflammatory disease, ruptured abdominal aortic aneurysm (AAA), hypercalcemia, superior mesenteric artery syndrome, and acute intermittent porphyria.^5–7 In female patients, it is important to obtain a sexual history and to consider pelvic inflammatory disease. It is also essential to remember that acute diseases of the chest, including myocardial infarction, congestive heart failure, pulmonary infarction, and pneumonia, may mimic primary diseases of the abdomen.

Specialist referral is indicated for suspected gastrointestinal bleeding, bowel obstruction, orthostatic vital sign changes, abnormal findings, jaundice, positive pregnancy test result, severe localized or unilateral lower abdominal pain, or a history of trauma and any indication of peritoneal irritation.

Pathophysiology

Appendicitis is primarily thought to be caused by the blockage of the appendiceal lumen, leading to distention of the appendix as a result of accumulated intramural fluid with secondary bacterial infection. Acute appendicitis is described as simple, gangrenous, or perforated on the basis of operative findings. In simple appendicitis, the appendix is viable and intact. Gangrenous appendicitis is characterized by necrosis of the appendiceal wall. Perforated appendicitis refers to disruption of the appendix. Acute appendicitis is thought to be secondary to obstruction of its orifice, with secondary bacterial infection.⁹

When the appendiceal lumen becomes obstructed, the mucosa continues to secrete fluid until the intraluminal pressure exceeds venous pressure. At this point, the appendix becomes hypoxic, the mucosa ulcerates, and bacteria invade the wall. Infection causes additional swelling and ischemia as a result of thrombosis of small intramural vessels.⁹ Gangrene and perforation usually develop in 24 to 36 hours. Perforation leads to a release of the luminal contents into the peritoneal cavity.

Clinical Presentation

The most reliable historical feature in the diagnosis of acute appendicitis is the sequence of symptoms. The three signs and symptoms most predictive of acute appendicitis include pain that starts in the epigastrium or periumbilical area, migration of the pain to the right lower quadrant, and abdominal rigidity.^6,9 The pain can be diffuse or occur at other sites in the abdomen, including the left lower quadrant.⁶ Another predictor is the duration of the pain; patients with appendicitis have been shown to have pain of a shorter duration than that of patients with other disorders.¹⁰

Anorexia, nausea or vomiting, constipation, or rarely diarrhea accompanied by low-grade fever follows the onset of pain. Not all patients will have every symptom; however, when the symptoms occur in any other order, the diagnosis of appendicitis should be questioned.^6,10

Physical Examination

The diagnosis of acute appendicitis requires a careful history and a thorough physical examination (including a pelvic examination for female patients). Often the symptoms are subacute and nonspecific; crampy abdominal discomfort that comes and goes, some malaise, and possibly a change in bowel habits occur initially.¹ Anorexia and nausea are quite common, with the latter occurring after the pain onset; vomiting is possible.¹ A fever is usually present. In some patients diarrhea and urinary symptoms are possible.¹ Abdominal tenderness is elicited by asking the patient to cough. Localized tenderness is a valuable physical finding, and the patient can often specify the painful spot with one finger. By systematically performing a thorough abdominal examination starting in the upper abdomen in an area without pain and ending in the area of pain, localized tenderness can be determined, usually in the right lower quadrant between the umbilicus and the anterosuperior iliac spine (McBurney point). The Rovsing sign (right lower quadrant pain) is elicited by palpating the left lower quadrant.¹ There may be signs of peritoneal irritation, including guarding, rebound tenderness, and obturator sign (elicited by passive rotation of the right leg with the patient supine and the right hip and knee flexed) and psoas sign (the supine patient raises the straightened right leg against resistance by the practitioner). A rectal examination is necessary and may reveal tenderness or a mass.

Diagnostics

Acute appendicitis is suggested by the history and physical examination findings. An elevated white blood cell count is present in 70% to 90% of patients with acute appendicitis. The health care provider should immediately refer a patient with suspected appendicitis for surgical consultation. Elevated white blood cell count is present in 70% of patients with acute appendicitis; a left shift is present 95% of the time.¹ A serum beta-human chorionic gonadotropin (β-hCG) level should be obtained in women of childbearing age because appendicitis is common in pregnancy and it is necessary to exclude a ruptured ectopic pregnancy. Serum amylase and lipase levels are necessary. Sickle cell disease should be excluded in patients of African, Indian, Mediterranean, or Spanish descent.¹ A C-reactive protein level is also necessary, as is a urinalysis.

Imaging studies are not required in most cases of suspected appendicitis. However, imaging modalities may be necessary if the presentation is atypical or in patients at the extremes of age. Plain abdominal radiographs show nonspecific signs and are not recommended. Ultrasonographic evidence of appendicitis includes appendiceal wall thickening, luminal distention, and lack of compressibility. Ultrasound is useful in children and in pregnant women and if the cause of the discomfort seems gynecologic, although, in general, ultrasound can be limited by operator skill and interpretation. A computed tomography (CT) scan is most useful for diagnosis if the cause of the abdominal pain is unclear.¹

Differential Diagnosis

Conditions that mimic acute appendicitis include gastroenteritis, mesenteric lymphadenitis, acute salpingitis, mittelschmerz, ruptured ectopic pregnancy, ruptured corpus luteum cyst, ureteral colic, Meckel diverticulitis, sigmoid diverticulitis, perforated peptic ulcer, cholecystitis, intestinal obstruction, cecal diverticulitis, intestinal ischemia, and perforated colonic carcinoma. Basilar pneumonia may also be confused with appendicitis.

Abdominal discomfort in older patients should always be evaluated and appropriate treatment initiated. Treatment of appendicitis is usually a prompt appendectomy, preferably within 24 hours of symptom onset to prevent perforation and peritonitis. In patients with uncomplicated appendicitis, antibiotic therapy is a possible option, though controversial because appendicitis can recur.¹¹

If surgery is required, patients should have nothing by mouth and intravenous fluid and electrolyte repletion initiated as necessary. Perioperative systemic antibiotics, such as metronidazole and ceftizoxime, have been shown to prevent wound infection in simple appendicitis. If the appendix is perforated, antibiotic therapy to cover anaerobic as well as aerobic pathogens is initially indicated until culture results are available. Antibiotics are also indicated for patients with suspected septicemia and patients scheduled for laparoscopic surgery. Surgery for an appendiceal abscess may spread a localized infection to other parts of the peritoneal cavity; therefore, percutaneous CT-guided drainage of an abscess is used to allow the acute inflammation to resolve before elective appendectomy is performed.¹²

Complications

Complications of appendicitis include gangrene, perforation with peritonitis, and abscess formation. Pylephlebitis, which is septic thrombophlebitis of the portal venous system, should be suspected in any patient with appendicitis who has shaking chills. Septicemia, urinary retention and infection, small bowel obstruction, and mesenteric thrombophlebitis may also occur. Common complications associated with appendectomy include wound infection, pneumonia, intraperitoneal abscesses, enterocutaneous fistulas, wound or inguinal hernias, and possibly minor bleeding.

Indications for Referral or Hospitalization

Immediate surgical referral or a transfer to the emergency department is indicated for suspected appendicitis or other acute abdominal pain. Hospitalization is indicated for monitoring and surgical care, if necessary.

Patient and Family Education

Patients must understand that abdominal pain may be a sign of serious illness or may be related to a chronic disorder. Localized abdominal pain or pain that increases in severity warrants discussion with the health care provider. Patients must also understand that abdominal pain accompanied by fever, chills, severe vomiting or diarrhea, significant rectal bleeding, black and tarry stools, weakness, or dizziness requires a visit to the health care provider.

Families of older patients should understand that pain perception may be diminished; the associated delay in presentation results in more than 30% of older adults with appendicitis having perforation at presentation.¹³ In older adults, any of the previously listed symptoms, even if unaccompanied by abdominal pain, should be evaluated by a medical professional.¹⁴

Pathophysiology

In a bowel obstruction, distention results in decreased absorption and increased secretions that cause further distention and fluid and electrolyte imbalances. Bacterial proliferation may occur as a result of stasis. Distention increases the risk of bowel perforation and diffuse peritonitis. Mechanical obstruction of the bowel lumen may occur from lesions (e.g., adhesions; congenital, inflammatory, or neoplastic lesions), femoral or indirect inguinal hernia, polypoid tumors, intussusception, volvulus, gallstone ileus, impacted feces, or bezoar formation.¹⁷ Intussusception, often recognized as an abdominal mass on examination with a history of acute symptom onset, occurs when a bowel segment telescopes into the adjacent bowel, resulting in symptoms of intermittent bowel obstruction. Volvulus results from abnormal twisting of a bowel segment along its mesenteric axis.

Clinical Presentation

Bowel obstruction manifests with intermittent and crampy abdominal pain, vomiting, obstipation, abdominal distention, hyperactive bowel sound, and fever. The pain is usually relieved by vomiting, intestinal tube decompression, or the passage of intestinal contents through a partial obstruction. Pain that progresses in severity, localizes, or becomes constant demonstrates progression to a strangulated obstruction; this condition requires urgent surgery. The presentation of a patient with ileus differs slightly in that bowel sounds are more frequently decreased or absent.¹⁶

A careful history of the chronicle of the illness, the patient’s medication history, the last bowel movement, and the presence of flatus is necessary. A prior history of bowel obstructions, abdominal irradiation, abdominal inflammation or cancer, or abdominal or pelvic operations should be identified because these conditions are all associated with bowel obstructions.