Applied Evidence
For patients who are critically ill, meet the criteria for systemic inflammatory response syndrome (SIRS), have severe clinical scores on either the Acute Physiology and Chronic Health Evaluation (APACHE) II (available at clincalc.com/icumortality/apacheii.aspx) or Bedside Index for Severity in Acute Appendicitis (BISAP; mdcalc.com/bisap-score-for-pancreatitis-mortality/), or who present >48 to 72 hours after onset of symptoms, abdominal CT with contrast is recommended (score=8).
Urolithiasis. Patients with abdominal pain from a presumed renal source should undergo a non-contrast CT of the abdomen and pelvis for initial imaging, according to the ACR (score=8). The sensitivity is 95% to 96% and specificity is 98%.8 To limit radiation exposure, low-dose protocols and limiting scan range are preferred.
Radiography can be useful in patients with known kidney stone disease and previous films; however, the sensitivity in other patients is poor (58%-62%).8 Because pelviectasis and ureterectasis can take hours to develop, US will miss more than 30% of acute obstructions in patients who are not fully hydrated and is therefore not recommended as a first-line imaging modality.8 The sensitivity of US increases to 71% when it is combined with kidney, ureter, and bladder radiography, but is still lower than that of CT or IV urography.8
Left lower quadrant pain: Suspect sigmoid diverticulitis
The differential for left lower quadrant (LLQ) pain includes colonic, gynecologic, and renal etiologies.12 The most common cause in adults is acute sigmoid diverticulitis. Patients often present with the clinical triad of fever, LLQ pain, and leukocytosis.14 A decision to obtain imaging should be based on both the clinical presentation and examination. It may not be required for patients who have mild symptoms or have had previous episodes of diverticulitis.
Clinical scoring systems have been studied for LLQ pain. However, none has been validated in all settings and therefore no such system is routinely used.15 CT of the abdomen and pelvis with contrast media is the ACR’s recommendation for the initial imaging study (score=9). CT has a reported overall accuracy of 99%.9
CT can also assess the severity of disease and help determine medical vs surgical treatment.14 US using graded compression has a sensitivity of 77% to 98% and a specificity of 80% to 99%, but is limited by body habitus, technical expertise, and patient comfort. Therefore, US has not gained widespread use (score=4) for patients with LLQ pain.9,14 MRI is emerging as a potential option; however, longer scan times, cost, and availability continue to limit its use.14
Right lower quadrant pain: Is it appendicitis?
The differential for right lower quadrant (RLQ) pain, like that of LLQ pain, includes colonic, gynecologic, and renal etiologies.12 The most common cause of acute RLQ pain requiring surgery is appendicitis. History and physical exam achieve a diagnostic accuracy of 80%.16
If the diagnosis is clear, no imaging is warranted. In patients with equivocal clinical presentations, however, imaging is cost-effective and may reduce the rate of perforation, morbidity, mortality, and postoperative hospital stays.16 In addition, the accuracy of clinical diagnosis for elderly patients and women of childbearing age with RLQ pain tends to be lower than that of adult men. Therefore, some experts call for a lower imaging threshold for these populations.
CT of the abdomen and pelvis with contrast is the recommended initial imaging study in nonpregnant adults (score=8). CT has a sensitivity and specificity of 91% and 90%, respectively.10
CT without contrast is indicated for patients with RLQ pain who have a contraindication to contrast media, although the relative radiation level remains the same.
If limiting radiation exposure is especially important, consider US, followed by CT with contrast if US is inconclusive.10
Low-dose CT has been investigated as an alternative, but is not routinely used. A limited abdominal CT scan from the bottom of the body of the T10 vertebra to the top of the symphysis pubis allows for adequate evaluation and alternate diagnoses of concern when compared with full CT scans of the abdomen and pelvis.17 This limited CT scan has been found to result in a total body effective radiation dose reduction of 23% and, in women, a breast equivalent dose reduction of 85%, without missing a single case of acute appendicitis or pertinent alternative diagnoses.17
Diffuse abdominal pain: Suspect a blockage
Finally, some patients may present with diffuse or non-localizable pain with fever. The etiologies that often present with diffuse or nonspecific pain include small bowel obstruction and mesenteric ischemia.