What is a liver abscess?
A liver abscess, also known as a hepatic abscess, is an accumulation of pus within the liver as a result of an infection. Overall liver abscesses are fairly rare and more frequently seen in developing nations. Most liver abscesses are caused by bacteria and amebic parasites (protozoa). However, other protozoa, fungi and helminths (parasitic worms) may also be responsible for hepatic abscesses.
A liver abscess may occur as a single abscess (solitary) or multiple lesions varying in size from a few millimeters to several centimeters in a larger abscesses. The term liver or hepatic abscess is also used to refer to a biliary abscess (gallbladder) which are usually multiple. A liver abscess is one type of intra-abdominal abscess and may be associated with other abscesses in the abdomen.
Types and Causes of Hepatic Abscesses
There are several types of liver abscesses based on the causative organism :
- Pyogenic abscess – bacteria, one or more species
- Amebic abscess – amebas which are single-celled parasites (protozoa), most common is Entameba histolytica
- Fungal abscess – due to fungi, particularly yeasts like the Candida species
- Parasitic abscess – rare, associated with helminths
A pyogenic abscess accounts for majority of the liver abscesses and are more frequently associated with the following bacteria :
Pathophysiology of Liver Abscess
How does a liver abscess form?
Since a pyogenic abscess is the most common form, it is worth considering its pathogenesis. However, the development of other types of abscesses may have a similar pathogenesis. Bacteria may reach the liver through a number of routes :
- Blood stream (hematogenous spread) – portal vein or artery.
- Direct infiltration from a neighboring organ/site – intra-abdominal infections like appendicitis, diverticulitis or infectious colitis.
- Ascending infection up the bile duct (ascending cholangitis).
- Penetrating injury through the abdominal wall.
Bacteria that reach the liver via the blood stream or biliary tract usually causes small multiple abscesses. Direct infiltration and penetrating injuries tend to cause a solitary large abscess. Once the bacteria reach the liver tissue, the body attempts to isolate the microorganisms by walling it off and promoting immune activity within this localized infection. Pus containing immune cells, bacteria, cellular debris, tissue fluid and blood then accumulates at the site where it is referred to as an abscess.
Signs and Symptoms of a Liver Abscess
In the past, direct invasion often associated with complications of appendicitis and other intra-abdominal infections were the leading causes of liver abscesses. However better treatment and management these days has reduced the incidence and subsequently ascending infections associated with cholangitis (bile duct infection) has become the most common cause particularly in the elderly. The signs and symptoms of these conditions may appear at first and therefore should be considered in the early clinical presentation of a liver abscess.
Signs and symptoms of a liver abscess includes :
- Right upper quadrant abdominal pain, but may extend to the left side as well or present with referred pain to the right shoulder.
- Fever and chills.
- Tenderness in the liver area with an enlargement of the liver (hepatomegaly) palpable .
- Anorexia – loss of appetite.
- Cough and/or hiccups due to irritation of the diaphragm
- Jaundice sometimes
Some patients may present with no abdominal pain.
Although rare, a subdiaphragmatic liver abscess may spread into the thoracic cavity to cause empyema (pus around the lungs) or a lung abscess. The clinical features of these conditions may therefore also be present and needs to be investigated. Sepsis or peritonitis are other severe complications that need to be considered.
Diagnosis of a Liver Abscess
The diagnosis of a liver abscess depends on the medical history (history of intra-abdominal infections or signs/symptoms indicating so) and the current clinical presentation. Some patients may only report a fever of unknown origin as diagnosis could be missed on prior clinical assessment.
Laboratory studies may include a CBC (complete blood count), liver function test (LFT), blood culture and culture of abscess fluid. A CT scan and ultrasound are usually sufficient to confirm diagnosis.
Treatment of a Liver Abscess
Antibiotics are usually sufficient for treating small multiple abscesses. Surgical drainage may be required for larger abscesses, especially the solitary massive abscess. Percutaneous (through the skin) drainage may sometimes be considered if suitable. Certain antibiotics like metronidazole may also be used for an amebic abscess and antifungal drugs may be commenced after drainage of a fungal abscess. Without prompt treatment, there is a risk of the infection spreading and the rupture of an abscess has a poor outlook and is often fatal.