Amoebic hepatic abscess
Amoebic hepatic abscesses are a form of hepatic abscess resulting from Entamoeba histolytica infection.
Patients may experience general malaise or present with frank sepsis and right upper quadrant pain. Although the causative pathogen is found worldwide, it is endemic to the Middle East and Eastern Asia and a travel history should always be sought in suspected cases.
They can sometimes be difficult to differentiate from other liver abscesses. They tend to be round or oval and be variable in size although most are around 2-6 cm in diameter. An enhancing wall is present in most cases.
Other described features include:
- an incomplete rim of oedema
- margin of the abscess tends to be smooth in around 60% of cases and nodular in around 40%
- internal septations: may be present in around 30% of cases
- focal intrahepatic biliary dilatation peripheral to an abscess may be uncommonly present
Extrahepatic abnormalities can be present in a considerable amount of patients which include:
- pleural effusion
- perihepatic fluid collection
- gastric or colonic involvement
- retroperitoneal extension
May appear as a hypoechoic lesion with low-level internal echoes and absence of significant wall echoes.
Usually appear as rounded, well-defined lesions with attenuation values that indicate the presence of complex fluid (e.g. 10–20 HU). An enhancing wall and a peripheral zone of oedema may be seen with the wall thickness around 3-15 mm. The central abscess cavity can show septations and/or fluid-debris levels.
Described signal characteristics include:
- T1: generally homogeneous low signal intensity(signal homogeneity within the abscess can be present more often on T1- than on T2-weighted images 5)
- T2: generally homogeneous high signal intensity; perilesional oedema may be seen in half of the cases
Treatment and prognosis
Management centres on initiating anti-parasitic agents, most commonly metronidazole which also treats amoebic dysentry. Traditionally, amoebic abscesses are treated with medical therapy as the first line as opposed to percutaneous or surgical drainage, which is the first line of treatment in pyogenic liver abscesses.
In practice, percutaneous drainage may frequently be required, particularly in larger abscesses which are at risk of spontaneous rupture into the peritoneal, pleural, or pericardial spaces.
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