Abdominal pain is common and often inconsequential. Acute and severe abdominal pain, however, is almost always a symptom of intra-abdominal disease. It may be the sole indicator of the need for surgery and must be attended to swiftly: Gangrene and perforation of the gut can occur < 6 hours from onset of symptoms in certain conditions (eg, interruption of the intestinal blood supply due to a strangulating obstruction or an arterial embolus). Abdominal pain is of particular concern in patients who are very young or very old and those who have HIV infection or are taking immunosuppressants (including corticosteroids).
Textbook descriptions of abdominal pain have limitations because people react to pain differently. Some, particularly older people, are stoic, whereas others exaggerate their symptoms. Infants, young children, and some older people may have difficulty localizing the pain.
The term acute abdomen refers to abdominal symptoms and signs of such severity or concern that disorders requiring surgery should be considered.
Pathophysiology of Acute Abdominal Pain
Visceral pain comes from the abdominal viscera, which are innervated by autonomic nerve fibers and respond mainly to the sensations of distention and muscular contraction—not to cutting, tearing, or local irritation. Visceral pain is typically vague, dull, and nauseating. It is poorly localized and tends to be referred to areas corresponding to the embryonic origin of the affected structure. Foregut structures (stomach, duodenum, liver, and pancreas) cause upper abdominal pain. Midgut structures (small bowel, proximal colon, and appendix) cause periumbilical pain. Hindgut structures (distal colon and genitourinary tract) cause lower abdominal pain.
Somatic pain comes from the parietal peritoneum, which is innervated by somatic nerves, which respond to irritation from infectious, chemical, or other inflammatory processes. Somatic pain is sharp and well localized.
Referred pain is pain perceived distant from its source and results from convergence of nerve fibers at the spinal cord. Common examples of referred pain are scapular pain due to biliary colic, groin pain due to renal colic, and shoulder pain due to blood or infection irritating the diaphragm.
Peritonitis
Peritonitis is inflammation of the peritoneal cavity.
The most serious cause is perforation of the gastrointestinal tract, which causes immediate chemical inflammation followed shortly by infection from intestinal organisms. Peritonitis can also result from any abdominal condition that causes marked inflammation (eg, appendicitis, diverticulitis, strangulating intestinal obstruction, pancreatitis, pelvic inflammatory disease, mesenteric ischemia).
Intraperitoneal blood from any source (eg, ruptured aneurysm, trauma, surgery, ectopic pregnancy) is irritating and results in peritonitis.
Barium causes severe peritonitis and should never be given to a patient with suspected gastrointestinal tract perforation. However, water-soluble contrast agents can be safely used.
Peritoneosystemic shunts, drains, and dialysis catheters in the peritoneal cavity predispose a patient to infectious peritonitis, as does ascitic fluid.
Rarely, spontaneous bacterial peritonitis occurs, in which the peritoneal cavity is infected by bloodborne bacteria. Spontaneous bacterial peritonitis occurs primarily in patients with cirrhosis and ascites.
Peritonitis causes fluid to shift into the peritoneal cavity and bowel, leading to severe dehydration and electrolyte disturbances. Acute respiratory distress syndrome can develop rapidly. Kidney failure, liver failure, and disseminated intravascular coagulation follow. Without treatment, death occurs within days.
Etiology of Acute Abdominal Pain
Many intra-abdominal disorders cause abdominal pain (see figure Location of abdominal pain and possible causes); some are trivial, but some are immediately life threatening, requiring rapid diagnosis and surgery. These include ruptured abdominal aortic aneurysm (AAA), perforated viscus, mesenteric ischemia, and ruptured ectopic pregnancy. Others (eg, intestinal obstruction, appendicitis, severe acute pancreatitis) are also serious and nearly as urgent. Several extra-abdominal disorders also cause abdominal pain (see table Extra-Abdominal Causes of Abdominal Pain).
Location of abdominal pain and possible causes
Abdominal pain in neonates, infants, and young children has numerous causes not encountered in adults. These causes include
Meconium peritonitis
Volvulus of a gut with intestinal malrotation
Intestinal obstruction caused by atresia
Evaluation of Acute Abdominal Pain
Evaluation of mild and severe pain follows the same process, although with severe abdominal pain, therapy sometimes proceeds simultaneously and involves early consultation with a surgeon. History and physical examination usually exclude all but a few possible causes, with final diagnosis confirmed by judicious use of laboratory and imaging tests. Life-threatening causes should always be ruled out before focusing on less serious diagnoses.
In seriously ill patients with severe abdominal pain, the most important diagnostic measure may be expeditious surgical exploration.
In mildly ill patients, watchful waiting and a diagnostic evaluation may be best.
History
A thorough history usually suggests the diagnosis (see table History in Patients with Acute Abdominal Pain). Of particular importance are pain location (see figure Location of abdominal pain and possible causes) and characteristics, history of similar symptoms, and associated symptoms. Concomitant symptoms such as heartburn, nausea, vomiting, diarrhea, constipation, jaundice, melena, hematuria, hematemesis, weight loss, and mucus or blood in the stool help direct subsequent evaluation.
Known medical conditions and previous abdominal surgeries are important to ascertain.
Women should be asked whether they are or might be pregnant.
Physical examination
The general appearance is important. A happy, comfortable-appearing patient rarely has a serious problem, unlike one who is anxious, pale, diaphoretic, or in obvious pain. Blood pressure, pulse, state of consciousness, and other signs of peripheral perfusion must be evaluated. However, the focus of the examination is the abdomen, beginning with inspection and auscultation, followed by palpation and percussion. Rectal examination and pelvic examination (for women) to locate tenderness, masses, and blood are essential.
Palpation begins gently, away from the area of greatest pain, detecting areas of particular tenderness, as well as the presence of guarding, rigidity, and rebound (all suggesting peritoneal irritation) and any masses. Guarding is an involuntary contraction of the abdominal muscles that is slightly slower and more sustained than the rapid, voluntary flinch exhibited by sensitive or anxious patients. Rebound is a distinct flinch upon brisk withdrawal of the examiner’s hand. The inguinal area and all surgical scars should be palpated for hernias.
Red flags
Certain findings raise suspicion of a more serious etiology:
Severe pain
Signs of shock (eg, tachycardia, hypotension, diaphoresis, confusion)
Signs of peritonitis
Abdominal distention
Interpretation of findings
Distention, especially when surgical scars, tympany to percussion, and high-pitched peristalsis or borborygmi in rushes are present, strongly suggests bowel obstruction.
Severe pain in a patient with a silent abdomen who is lying as still as possible suggests peritonitis; location of tenderness suggests etiology (eg, right upper quadrant suggests cholecystitis, right lower quadrant suggests appendicitis) but may not be diagnostic.
Back pain with shock suggests ruptured abdominal aortic aneurysm, particularly if there is a tender, pulsatile mass.
Shock and vaginal bleeding in a pregnant woman suggest ruptured ectopic pregnancy.
Ecchymoses of the costovertebral angles (Grey Turner sign) or around the umbilicus (Cullen sign) suggest hemorrhagic pancreatitis but are not very sensitive for this disorder.
History is often suggestive (see table History in Patients with Acute Abdominal Pain). Mild to moderate pain in the presence of active peristalsis of normal pitch suggests a nonsurgical disease (eg, gastroenteritis) but may also be the early manifestations of a more serious disorder. A patient who is writhing around trying to get comfortable is more likely to have an obstructive mechanism (eg, renal or biliary colic).
Previous abdominal surgery makes obstruction caused by adhesions more likely.
Generalized atherosclerosis increases the possibility of myocardial infarction, abdominal aortic aneurysm, and mesenteric ischemia.
HIV infection makes infectious causes more likely.
Testing
Tests are selected based on clinical suspicion:
Urine pregnancy test for all women of childbearing age
Selected imaging tests based on suspected diagnosis
Standard tests (eg, complete blood count, chemistries, urinalysis) are often done but are of little value due to poor specificity; patients with significant disease may have normal results. Abnormal results do not provide a specific diagnosis (the urinalysis in particular may show pyuria or hematuria in a wide variety of conditions), and they can also occur in the absence of significant disease. An exception is serum lipase, which strongly suggests a diagnosis of acute pancreatitis.
A bedside urine pregnancy test should be done for all women of childbearing age because a negative result effectively excludes ruptured ectopic pregnancy.
An abdominal series, consisting of flat and upright abdominal x-rays and upright chest x-rays (left lateral recumbent abdomen and anteroposterior chest x-ray for patients unable to stand), should be done when perforation or obstruction is suspected. However, these plain x-rays are seldom diagnostic for other conditions and do not need to be otherwise automatically done.
Ultrasonography should be done for suspected biliary tract disease or ectopic pregnancy (transvaginal probe) and for suspected appendicitis in children. Ultrasonography can also detect abdominal aortic aneurysm but cannot reliably identify rupture.
Noncontrast helical CT is the modality of choice for suspected renal stones. CT with oral and IV contrast is diagnostic in about 95% of patients with significant abdominal pain and has markedly lowered the negative laparotomy rate. However, advanced imaging must not be allowed to delay surgery in patients with definitive symptoms and signs.
Treatment of Acute Abdominal Pain
Key Points
Look for life-threatening causes first.
Rule out pregnancy in women of childbearing age.
Seek signs of peritonitis, shock, and obstruction.
Blood tests are of minimal value.
