First imaging study in acute abdomen

What should be the first imaging study obtained ? 

An acute abdominal series consists of an upright, supine, and lateral decubitus abdominal film. It is quick and inexpensive, yet can provide vital information. Upright chest radiograph may reveal free air under the diaphragm or suggest a pulmonary process. Free air may also be seen over the liver in a left lateral decubitus abdominal film. Air-fluid levels on the upright film may suggest bowel obstruction, whereas lack of air in the rectum may indicate a complete obstruction. Only 10% of gallstones are radiopaque, but 90% of ureteral calculi are visualized. Appendiceal fecalith may suggest appendicitis in the setting of right lower quadrant pain. Air in the biliary tree may be seen with biliary-enteric fistula or pelvic pyelophlebitis.

How is ultrasound (US) used? 

US helps to evaluate the gallbladder and biliary tree, to assess for free peritoneal fluid, and can visualize the female adnexa (in the setting of possible ectopic pregnancy or ovarian cyst or mass). Unfortunately, abdominal US examination is limited in the setting of obesity as well as bowel distention.

What additional imaging studies may help in the diagnosis? 

Computed tomography (CT) scan of the abdomen and pelvis with oral and intravenous contrast is useful in the setting of intraabdominal abscess, pancreatitis, aortic aneurysm or dissection, arterial and venous occlusive disease, hepatic, splenic, retroperitoneal, and renal disorders. Upper and lower gastrointestinal (GI) series may pinpoint the level of bowel obstruction or establish the diagnosis if CT is inconclusive. Angiography or US (less sensitive) can be used to assess mesenteric arterial flow.

If the diagnosis is in doubt, what other procedure should be done? 

Surgical exploration of the abdomen is the next step if diagnostic studies are equivocal, and it is mandatory if the patient’s condition worsens despite aggressive resuscitation. In many centers laparoscopy has widely supplanted laparotomy for exploration, even with suspected pathologic conditions such as perforated peptic ulcer, diverticulitis, and appendicitis.

Is exploratory laparotomy justified, even if it produces no significant findings? 

Yes. Despite the risk of general anesthesia, postoperative pain, risk of wound infection, and a small lifetime risk of bowel obstruction from adhesions (less than 5%), it is still safer to undergo a surgical exploration than to miss the diagnosis of appendicitis or bowel infarction.

In blunt trauma, CT scan of the abdomen and pelvis reveals free peritoneal fluid collections. When is observation appropriate instead of immediate surgical exploration? 

In the setting of trauma, any free fluid seen on CT should be concerning for possible bowel injury, for which CT is notoriously insensitive. Any patient must be hemodynamically stable for observation to be appropriate. Small lacerations to the liver or spleen are readily identifiable and should be treated with aggressive resuscitation. Escalating pain, fluid requirements, or need for blood transfusion should prompt an immediate exploration.


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