These abscesses are uncommon, but may be single or multiple. The commonest cause used to be a portal pyaemia from intra-abdominal sepsis, e.g. appendicitis or perforations, but now in many cases the aetiology is not known. Biliary sepsis, particularly in the elderly, is a common cause. Other causes include trauma, bacteraemia and direct extension from, for example, a perinephric abscess.