Diagnostic pitfalls in abdominal CT.

Many factors result in suboptimal performance of abdominal computed tomography (CT) or inaccurate interpretation of the images. Improper technique, observers' errors, and lack of clinical information are major contributors to misdiagnoses. Because of inadequate oral administration of contrast material, normal structures (eg, bowel) may remain unopacified and simulate tumors. Repeat scanning with additional contrast material and sodium bicarbonate, at selected levels, and perhaps with changes in patient position often reveals the true nature of pseudotumors in the gastrointestinal tract. Dynamic CT of the liver, performed during contrast material injection, yields the best results. Occasionally, reconstruction of axial images in coronal or sagittal planes helps delineate normal sectional anatomic variations of the diaphragm and liver and avoid misdiagnosis of pseudomasses. Volume averaging can cause problems when the section thicknesses are larger than the lesions (eg, small hepatic cysts) or structures are very close (eg, kidney and spleen); repeat CT with thinner sections is needed to obtain accurate attenuation values or delineate normal anatomic relationships. The gallbladder, spleen, and pancreas can change position due to prior surgery and raise suspicion of a mass unless clinical history is known. Familiarity with these and other pitfalls described herein should lead to accurate interpretation of CT scans.