F. Radiologic evaluation
Radiologic evaluation of the patient with abdominal pain is a key element in the workup. However, its use should be very selective to avoid unnecessary cost and possible morbidity associated with some modalities.
Plain abdominal x-rays often serve as the initial radiologic evaluation.
X-rays should be obtained in the supine and erect positions.
Free intraperitoneal air is best visualized on an upright chest x-ray with both hemidiaphragms exposed.
If the patient is unable to assume an upright position, a left lateral decubitus x-ray should be obtained.
Free air may not be detectable in up to 20% of cases of perforated viscus.
The bowel gas pattern is assessed for dilation, air-fluid levels, and the presence of gas throughout the small and large intestine.
In small-bowel obstruction, one sees small-bowel dilation (valvulae conniventes) and air-fluid levels in the bowel proximal to the obstruction. There is a paucity of gas in the segment of bowel distal to the obstruction. The absence of air in the rectum suggests complete obstruction (beware of the presence of colonic gas following rectal examination).
A sentinel loop (i.e., a single, dilated loop of bowel) may be seen adjacent to an inflamed organ (as in pancreatitis) and is due to localized ileus.
Calcifications should be noted.
The vast majority of urinary stones (90%) contain calcium and are visible on plain x-rays, whereas only 15% of gallstones are calcified.
Calcifications in the region of the pancreas may indicate chronic pancreatitis.
Fecalith in the RLQ may suggest appendicitis.
Calcification in the wall of the aorta may suggest an AAA.
The most common calcifications seen in the abdomen are “phleboliths” (benign calcifications of the pelvic veins). Phleboliths can be distinguished from renal stones by their central lucency, which represents the lumen.
The presence of gas in the portal or mesenteric venous systems, intramural gas in the GI tract, or gas in the biliary tree (in the absence of a surgical enteric anastomosis) is an ominous finding.
Ultrasonography (US) may provide diagnostic information in some conditions. Ultrasound is portable, relatively inexpensive, and free of radiation exposure. US visibility is limited in settings of obesity, bowel gas, and subcutaneous air.
RUQ US is particularly useful in biliary tract disease.
Gallstones can be detected in up to 95% of patients.
Findings suggestive of acute cholecystitis include gallbladder wall thickening of greater than 3 mm, pericholecystic fluid, a stone impacted at the neck of the gallbladder, or Murphy’s sign.
Dilation of the CBD (>8 mm, or larger in elderly patients) indicates biliary obstruction. Gallstones in the CBD may also be seen.
US can be used in the evaluation of RLQ pain.
It may be helpful in the diagnosis of appendicitis, particularly in the pediatric population or in nonobese adults.
Its utility and accuracy are operator dependent.
Pelvic or transvaginal US is particularly useful in women in whom ovarian pathology or an ectopic pregnancy is suspected.
Testicular US is adjunctive to physical exam in diagnosing testicular pathology (e.g., testicular torsion, epididymitis, orchitis).
Contrast studies, although rarely indicated in the acute setting, may be helpful in some situations.
In most instances, a water-soluble contrast agent (e.g., Hypaque) should be used to avoid possible barium peritonitis in the event of bowel perforation.
Contrast enema is particularly useful in differentiating adynamic ileus from distal colonic obstruction.
Computed tomographic (CT) scanning may provide a thorough evaluation of the patient’s abdomen and pelvis relatively quickly. Oral and intravenous contrast should be administered if not specifically contraindicated by allergy, renal insufficiency, or patient hemodynamic instability. CT scanning is the best radiographic study in the patient with unexplained abdominal pain. It is of particular benefit in certain situations, including the following:
When an accurate history cannot be obtained (e.g., the patient is demented or obtunded or has an atypical history).
When a patient has abdominal pain and leukocytosis and examination findings are worrisome but not definitive for peritoneal irritation.
When a patient with a chronic illness (e.g., Crohn disease) experiences acute abdominal pain.
When evaluating retroperitoneal structures (e.g., in a stable patient with a suspected leaking AAA).
When evaluating patients with a history of intra-abdominal malignancy.
Magnetic resonance imaging (MRI)
MRI provides cross-sectional imaging while avoiding ionizing radiation.
Image acquisition takes longer than for CT scan; patients must be able to lie on their backs for a prolonged period of time and cannot be claustrophobic.
MRI has its greatest application in pregnant women with acute abdominal and pelvic pain (AJR 2005;184:452).
Radionuclide imaging studies have few indications in the acute setting.
Biliary radiopharmaceuticals, such as hepatic 2,6-dimethylimino-diacetic acid or di-diisopropyliminodiacetic acid, evaluate filling and emptying of the gallbladder. Nonfilling implies cystic duct obstruction and may indicate acute cholecystitis. This test is
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TABLE 11-1 Differential Diagnosis for Acute Abdominal Pain
Upper abdominal Perforated peptic ulcer Acute cholecystitis Acute pancreatitis Mid and lower abdominal Acute appendicitis Acute diverticulitis Intestinal obstruction Mesenteric ischemia Ruptured AAA Other OB/GYN PID Ectopic pregnancy Ruptured ovarian cyst Urological Nephrolithiasis Pyelonephritis/cystitis Nonsurgical Acute MI Gastroenteritis Pneumonia DKA
especially valuable in the diagnosis of acalculous cholecystitis and biliary dyskinesia.
Radioisotope-labeled red blood cell (RBC) or WBC scans are sometimes helpful in localizing sites of bleeding or inflammation, respectively.
Technetium-99m pertechnetate may be used to detect a Meckel diverticulum because this isotope is concentrated in the ectopic gastric mucosa that frequently lines the diverticulum.
Invasive radiologic techniques may have a role in some situations, including angiographic diagnosis and therapeutic intervention for mesenteric arterial occlusion and acute GI bleeding.