Acute Abdomen

              The causes of an acute abdomen are legion, including infection, bowel perforation, inflammation, obstruction, ischemia, volvulus of various structures, gynecologic abnormalities, and tumor infiltration; these conditions are discussed in their respective chapters.At times the first evidence of a serious underlying disease is an acute abdomen, such as Crohn’s disease manifesting as bowel perforation. Colonic epiploic appendagitis, a condition diagnosable by imaging, is an example of an acute abdomen not requiring surgical intervention. Less common etiologies for an acute abdomen include lymphoma infiltrating the bowel and resulting in perforation, a perforating primary small bowel neoplasm, and a perforated bowel duplication cyst with spill of the contents into the peritoneal cavity.
              In pediatrics, perforation is more common in neonates than in older children. Among neonates with gastrointestinal perforation, most common etiologies are necrotizing enterocolitis, isolated ileal perforations, a combination and sequella of malrotation/volvulus. Etiologic factors in children are trauma, Meckel’s diverticula complications, intussusception, pseudomembranous colitis, and post-operative complications. In children, screening US detects an abdominal abnormality in about half of those with acute or subacute abdominal pain.
             Past teaching has been to study an acute abdomen with conventional radiographs, an approach supplanted by CT, generally without IV contrast. At times images with and without IV contrast are useful. Computed tomography has had a major impact in the diagnosis and subsequent management of patients presenting with an acute abdomen. Some studies suggest that CT is superior to clinical evaluation in diagnosing a cause for an acute abdomen. Such an approach appears to hold up regardless of the duration of signs and symptoms and in patients with no prior disease. Nevertheless, rather than use CT in a shotgun approach for all patients presenting with an acute abdomen, a more selective choice of imaging studies often establishes a diagnosis more quickly. For instance, with suspected cholecystitis, US should be the initial imaging modality; suspected acute uncomplicated pancreatitis generally requires little or no imaging, except possibly endoscopic retrograde cholangiopancreatography (ERCP), while pancreatic necrosis calls for contrast-enhanced CT or MR. Ultrasonography is more commonly employed in pediatric patients. CT is especially useful in obese patients, nondiagnostic US, or with suspected bowel obstruction.
               In some centers US is used liberally for the initial study of patients with an acute abdomen. It is readily performed and detects a number of acute conditions. One limitation is the presence of dilated bowel. Also, while in experienced hands such diagnoses as appendicitis are readily made, a normal US examination does not exclude appendicitis, pyelonephritis, and other isorders.Likewise, early pancreatitis and bowel ischemia do not have specific US findings. Laparoscopy is still preferred by some as a diagnostic and therapeutic modality in patients presenting with an acute abdomen. Even if conversion to an open laparotomy is necessary, laparoscopic findings are useful as a guide for the subsequent incision.

This is radiology images of the Acute abdomen secondary to jejunal perforation. Oral and intravenous (IV) contrast-enhanced CT reveals ascites and pneumoperitoneum. Higher density material is present within this fluid adjacent the liver (arrow) and also in the left upper quadroon (curved arrow). Although angiography revealed patent vessels, surgery suggested emboli and ischemia for the patient’s perforation.
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