Inspection is the initial step of the abdominal examination and consists first of a general assessment of the patient’s overall state followed by focus on the abdomen. Patients with peritonitis tend to lie still with their knees flexed as doing so provides some alleviation of their pain. Upon closer inspection of the abdomen, one should note the presence of prior surgical scars, abdominal distension or visible peristalsis, any obvious masses suggestive of an incarcerated hernia or tumor, or erythema or ecchymoses secondary to traumatic injury or hemorrhagic complications of acute pancreatitis. Caput medusa may indicate liver disease.

Auscultation of the abdomen should be performed next and involves listening for the presence or the absence of bowel sounds, for the characteristics of those sounds, and for the presence of bruits. Although this step may be the least valuable overall, as bowel sounds may be completely normal in patients with severe intra-abdominal pathology, it may nonetheless provide some information that assists the physician in making a diagnosis. For example, the absence of bowel sounds may point towards a paralytic ileus, while ones that are high pitched in nature or rushed may indicate the presence of a mechanical bowel obstruction. Finally, bruits that are detected on the abdominal exam suggest the presence of turbulent flow, which is often the case for arterial stenoses.

Next, percussion is utilized to assess for any dull masses, pneumoperitoneum, peritonitis, and ascites. A largely tympanic abdomen may indicate the presence of underlying loops of gas-filled bowel typical of intestinal obstructions or a paralytic ileus. If findings of tympany extend to include the right upper quadrant (RUQ) however, it may be suggestive of free intraperitoneal air. Lastly, percussion can be used to detect ascites by the presence of shifting dullness or by the generation of a fluid wave. Percussion may be all that is necessary to elicit pain in the patient who has peritonitis, for whom further palpation should be deferred.

Palpation is the final, critical step as it enables the physician to better define the location and severity of pain and confirm any findings made on other aspects of the physical exam. Palpation should always commence away from the area of greatest pain to prevent any voluntary guarding, which should be distinguished from the involuntary guarding that accompanies peritonitis. Palpation can produce various signs commonly associated with specific disease processes. These include Murphy’s sign, characterized by an arrest in inspiration upon deep palpation of the RUQ in patients with acute cholecystitis, and Rovsing’s sign, observed many times in patients with acute appendicitis in which pain is elicited at McBurney’s point upon palpation of the left lower quadrant. Additionally, pain felt with hyperextension of the right hip, or iliopsoas sign, may indicate the presence of a retrocecal appendix, while a pelvic location of the appendix may be suspected in patients exhibiting Obturator sign, or pain created with internal rotation of a flexed right hip.

It is essential that all patients presenting with acute abdominal pain undergo a digital rectal exam as it may reveal the presence of a mass, the focal tenderness of a periappendiceal or peridiverticular abscess, and the presence of gross or occult blood. Finally, a pelvic examination should be performed in female patients presenting with lower quadrant pain to discern whether their pain has a gynecologic or obstetric source like pelvic inflammatory disease or a ruptured ectopic pregnancy. On exam, one should take note of any vaginal bleeding or discharge and any adnexal or cervical motion tenderness [4, 5].

Various laboratory studies can be used as adjuncts to help narrow down the differential, or to confirm or rule out a diagnosis. A complete blood count (CBC) with differential, for example, may help detect or confirm the presence of an infectious or inflammatory process by the demonstration of leukocytosis and/or a left shift. The accompanying hematocrit is also of value as it can provide information about one’s plasma volume, altered in cases of dehydration and hemorrhage. In addition, serum electrolytes, blood urea nitrogen (BUN), and serum creatinine may provide clues to the extent of any fluid losses resulting from emesis, diarrhea, and third-spacing as can lactic acid levels and arterial blood gases. The latter two tests may also help to confirm the presence of any intestinal ischemia or infarction as well.

Liver function tests (LFTs) can help in determining whether conditions of the hepatobiliary tract are the source of the patient’s symptoms, while measurements of serum amylase and lipase may implicate acute pancreatitis or its complications as the cause. Physicians should be mindful of the fact, however, that serum amylase levels may also be elevated in a variety of other acute abdominal conditions including intestinal obstruction, mesenteric thrombosis, ruptured ectopic pregnancy, and perforated PUD to name a few [7].

Urinary tests, namely, urinalysis, should be obtained in patients presenting with hematuria, dysuria, or flank pain to determine if their symptoms are genitourinary in origin. Urine samples can also be used to perform toxicology screens in those whose abdominal pain is thought to be the result of long-standing illegal drug use, as seen in the case of mesenteric ischemia that occurs with chronic cocaine abuse. Finally, human chorionic gonadotropin (Hcg) levels can help in determining whether complications of pregnancy, such as a ruptured ectopic pregnancy, are to blame. Regardless of whether or not it is the source of the patient’s symptoms, Hcg levels should be obtained in all women of childbearing age as it may affect decision making, especially if additional studies or surgical intervention are deemed necessary [4]. Finally, depending on the clinical situation, blood may be obtained for typing and crossmatching.

Radiologic imaging plays a key role in the evaluation and management of the acute abdomen (Table 2.1). Plain films, ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) are the most common imaging modalities employed in the diagnostic workup of these patients.

While plain films are less sensitive and specific compared to CT scanning, it is often the initial imaging study performed in patients presenting with acute abdominal pain. The advantages of their use include their rapidity and universal availability. Although patients are subject to ionizing radiation exposure, the dose is significantly lower than that of CT scans [8]. Plain films can be of greatest utility in patients suspected of a perforated viscus by the detection of a pneumoperitoneum, or the presence of free air beneath the right hemidiaphragm, as well as those with a suspected intestinal obstruction by the presence of dilated loops of bowel and air-fluid levels.

The advantages of abdominal US include the lower cost and the lack of ionizing radiation exposure [9], which is advantageous for the pediatric population and pregnant women. In addition, abdominal US is the imaging modality of choice for those patients presenting with suspected hepatobiliary pathology, with a sensitivity of 88% and specificity of 80% in the diagnosis of acute cholecystitis [10]. Features suggestive of acute cholecystitis on US include the presence of gallstones, gallbladder wall thickening, pericholecystic fluid, and an elicited Murphy’s sign (Fig. 2.2).

If an obstetrical or gynecologic condition is suspected as the source of a patient’s acute abdominal pain, pelvic and transvaginal US are the preferred imaging modalities to assess the uterus and adnexal structures. The presence of free fluid and an empty uterus on US in the setting of a positive pregnancy test is strongly suggestive of a ruptured ectopic pregnancy [11] while an enlarged and edematous ovary with an absence of blood flow is characteristic of a torsed ovary.

The CT scan has sensitivity of 96% overall for diagnosing most causes of the acute abdomen, compared to a 30% sensitivity for plain films [8]. As a result, the number of CT scans performed for patients presenting with acute abdominal pain has increased by 141% between 1996 and 2005 [12]. CT scanning has had a significant impact on the diagnosis of acute appendicitis as it has decreased the negative appendectomy rate from 24 to 3% [13]. Findings diagnostic of appendicitis on CT scan include an enlarged, nonopacified appendix, appendicoliths, and adjacent fat stranding while the presence of an abscess, phlegmon, and extraluminal gas points towards appendiceal perforation (see Fig. 2.2).

Although MRIs provide excellent visualization of the intrabdominal organs without the need for ionizing radiation, their cost and lack of universal availability make them less ideal for use in the evaluation of the acute abdomen [14]. In addition, some patients have contraindications to undergoing an MRI or are simply unable to tolerate the test because of claustrophobia. MRI, however, may be of utility for pregnant women in the setting of acute abdominal pain with equivocal US findings [15].

Diagnostic laparoscopy may be of utility in the evaluation of acute abdominal pain, especially in situations in which the underlying etiology remains unclear despite a thorough clinical evaluation and radiologic imaging. The advantages of diagnostic laparoscopy include its ability to make a definitive diagnosis in 90–98% of cases and determine whether further intervention is necessary [16, 17]. A resultant decrease in the negative laparotomy rate—and the fact that if further treatment is indicated that many acute abdominal conditions can be treated laparoscopically—equates to a decrease in morbidity and mortality, a shorter length of stay, and decreased hospital costs [16].

Abdominal pain is one of the most common complaints among elderly patients presenting to the emergency department [19]. As the presentation is often different than what is seen in younger patients, the ability to accurately diagnose the underlying cause of their abdominal complaints can be challenging. Elderly patients may lack the febrile response, leukocytosis, and severity of pain expected in those suffering from serious intra-abdominal pathology as a result of the age-dependent decline in immune function [20] along with a well-documented delay in pain perception [21].

The atypical presentation commonly seen in these patients may also be attributed to the effects of other, coexisting medical conditions and medications. For example, beta blockers may blunt the normal tachycardic response to acute abdominal processes while nonsteroidal agents and acetaminophen may prevent the development of a fever. Finally, diagnostic accuracy may be difficult to achieve because of the inability to obtain an adequate history from elderly patients with memory and hearing deficits. Combined, these factors contribute to the increased incidence of complications and increased morbidity and mortality observed in elderly patients presenting with acute abdominal pain. For example, although the incidence of acute appendicitis is lower in this population compared to their younger counterparts, the rate of perforation is significantly higher, reaching almost 70% in some series [22]. Furthermore, complications of acute cholecystitis occur in more than 50% of patients aged 65 or older [23].

Although on the opposite end of the age spectrum, the diagnosis of the acute abdomen in children can be equally as challenging, particularly in children who are preverbal or uncooperative. Further adding to the difficulty is the fact that the etiologies of abdominal pain in children can range from trivial (e.g., constipation) to potentially life-threatening (e.g., malrotation with midgut volvulus) with little to no difference in their presentation [24]. As a result, there are higher rates of misdiagnosis and complications in the pediatric population as well. In fact, the rate of perforation in childhood cases of acute appendicitis is 30–65%, which is significantly higher than what is reported for adults [25].

Overall, physicians should be mindful of the potential challenges posed to them in the evaluation of acute abdominal pain in these extremes of age and adjust their diagnostic approach accordingly.

The ability to make the diagnosis of an acute abdomen is often challenging for those patients who are immunocompromised as a result of conditions such as cancer requiring chemotherapy, transplantation, human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), renal failure, diabetes, and malnourishment to name a few. As a result of their body’s inability to launch a full inflammatory response, these patients may have a delayed onset of fever and other typical symptoms, experience less pain, and have an underwhelming leukocytosis [4]. As a result, a diagnosis may not be made until the development of overwhelming sepsis, multisystem organ failure, and death.