Amoebic Hepatic Abscess

Imaging Studies Ultrasonography is the preferable initial diagnostic test. It is rapid, inexpensive, and is only slightly less sensitive than CT scan (75-80% sensitivity vs 88-95% for CT scan). Ultrasonography simultaneously evaluates the gallbladder and avoids radiation exposure. As opposed to scanning with technetium-99m, sonography often can distinguish an abscess from a tumor or other solid focal lesion. The lesions tend to be round or oval, with well-defined margins, and hypoechoic. CT scan is sensitive but the findings are not specific. The abscess typically appears low density with smooth margins and a contrast-enhancing peripheral rim. The use of injected contrast may differentiate hepatic abscesses from vascular tumors. MRI is sensitive, but the findings are not specific. This test provides information comparable with less expensive imaging procedures. Technetium-99m liver scanning is useful for differentiating an amebic liver abscess from a pyogenic abscess; however, it is not used as a first-line test. Because amebic liver abscesses do not contain leukocytes, they appear as cold lesions on hepatic nuclear scanning, with a typical hot halo or a rim of radioactivity surrounding the abscess. In contrast, pyogenic liver abscesses contain leukocytes and, therefore, typically appear as hot lesions on nuclear scanning. Gallium scanning is helpful in differentiating pyogenic abscess (similar to technetium-99m nuclear hepatic scanning) but requires delayed images, which makes the test less helpful. Hepatic angiography is only useful to differentiate liver abscesses from vascular lesions. Plain chest or abdominal films may show elevation and limitation of motion of the right diaphragm, basilar atelectasis, and right pleural effusion or gas within the abscess cavity. None of the imaging tests can definitely differentiate a pyogenic liver abscess, an amebic abscess, or malignant disease. Clinical, epidemiological, and serological correlation is needed for diagnosis.