HEPATIC ABSCESSES ULTRASOUND

Abscesses - Clinical features of an abscess
Patients present with fever, often accompanied by right upper quadrant (RUQ) pain and vomiting. Abnormal liver function tests (LFTs) and anaemia can also be present. The clinical history helps the sonographer to establish the nature of the focal lesion and aetiology of the abscess. Abscesses of any type may be solitary or multiple. Because the ultrasound appearances of abscesses can be similar to those of necrotic tumours or haematoma, the clinical picture is of particular importance to the sonographer.

Ultrasound appearances
Hepatic abscesses may display a variety of acoustic features. Their internal appearances vary considerably. In the very early stages there is a zone of infected, oedematous liver tissue which appears on ultrasound as a hypoechoic, solid focal lesion. As the infection develops, the liver tissue becomes necrotic and liquefaction takes place. The abscess may still appear full of homogeneous echoes from pus and can be mistaken for a solid lesion, but as it progresses, the fluid content may become apparent, usually with considerable debris within it. Because they are fluid-filled, abscesses demonstrate posterior enhancement. The margins of an abscess are irregular and often ill-defined and frequently thickened. The inflammatory capsule of the abscess may demonstrate vascularity on colour or power Doppler but this is not invariable and depends on equipment sensitivity and size of the lesion. Infection with gas-forming organisms may account for the presence of gas within some liver abscesses.

There are three main types of abscess:
● Pyogenic abscess. These form as a result of infection entering the liver through the portal venous system. Most commonly, appendiceal or diverticular abscesses are responsible, but intrahepatic abscesses are also seen in immunosuppressed patients and following postoperative infection. They are frequently multiple, and the patient must be closely monitored after diagnosis to prevent rapid spread. Pyogenic abscess is still considered a lethal condition, which has increased in recent years due to increasingly aggressive surgical approaches to many abdominal neoplasms.

● Amoebic abscess. This is a parasitic infection which is rare in the UK, but found frequently in parts of Africa, India and the southern parts of the USA. Suspicion should be raised when the patient has visited these countries. It is usually contracted by drinking contaminated water and infects the colon, ulcerating the wall and subsequently being transported to the liver via the portal venous system.

● Candidiasis abscess. This is a fungal infection which may be seen in immunosuppressed patients. It is a rare cause of abscess formation and is usually blood-borne. The resulting abscesses are likely to be small but multiple on presentation. About 25% of infected patients form hepatic abscesses and the infection may spread to other sites in the abdomen.

Management of hepatic abscesses
An ultrasound-guided aspiration to obtain pus for culture is useful for identifying the responsible organism. Aspiration combined with antibiotic therapy is usually highly successful for smaller abscesses and ultrasound is used to monitor the resolution of the abscesses in the liver. Ultrasound-guided drainage is used for large lesions, and surgical removal is rarely required. Further radiology may be indicated to establish the underlying cause and extent, for example barium enema or CT, particularly if amoebic infection is suspected.