Liver Abscesses and Hydatid Cysts


Pyogenic Abscesses

  1. Pathogenesis
    1. Biliary Tract Obstruction and Cholangitis
      • most common mechanism
      • after obstruction of the bile ducts, bacteria multiply and ascend into the intrahepatic biliary radicals
      • choledocholithiasis, benign and malignant strictures, and long-term palliative stents are the most common etiologies

    2. Portal Vein Bacteremia
      • formerly was the most common mechanism
      • results from an intestinal infection such as appendicitis or diverticulitis

    3. Hepatic Artery Bacteremia
      • results from systemic infections such as sepsis or endocarditis

    4. Direct Extension
      • etiologies include gangrenous cholecystitis and subphrenic abscess

    5. Trauma
      • bile leakage, hepatic necrosis, hematoma formation, and direct introduction of bacteria all contribute to abscess formation after traumatic injury to the liver

    6. Necrosis of Hepatic Tumors
      • associated with chemoembolization, alcohol injection, cryoablation or radiofrequency ablation of tumors

    7. Cryptogenic
      • no cause is identified in ~ 20% of cases
      • possible association with an occult colorectal cancer

  2. Pathology and Microbiology
    • nearly equal distribution between solitary and multiple abscesses
    • majority of abscesses are located in the right lobe only (60% - 75%), 20% are bilobar, < 10% are in the left lobe only
    • E. coli, Klebsiella, Staph Aureus, Streptococcus viridans, and Enterococcus are the most common aerobes isolated
    • Bacteroides is the most common anaerobe isolated
    • Candida is associated with immunosuppression, often from chemotherapy

  3. Clinical Manifestations
    1. Symptoms
      • patients have a variable clinical presentation
      • fever, chills, right upper quadrant pain are classic symptoms
      • many patients will have only nonspecific symptoms: malaise, anorexia, nausea, vomiting, weight loss
      • fever of unknown origin is also a common presentation

    2. Signs
      • right upper quadrant tenderness, fever, hepatomegaly, and jaundice are possible physical findings

  4. Diagnosis
    1. Laboratory Studies
      • leukocytosis is the most consistent lab abnormality
      • elevated alkaline phosphatase and transaminases are nonspecific but frequent abnormalities
      • elevated bilirubin implicates biliary obstruction as the etiology of the abscess
      • blood cultures are positive in 40% - 50% of patients
      • serologic testing will rule out an amebic abscess

    2. Imaging Studies
      1. Plain Films
        • chest and abdominal x-rays may show nonspecific findings: right lower lobe atelectasis or infiltrate, pleural effusion, elevated right hemidiaphragm
        • occasionally a subdiaphragmatic air-fluid level may be seen

        Pyogenic Liver Abscess with Subdiaphragmatic Air-Fluid Level
      2. Ultrasound
        • useful screening test
        • images the biliary tree more accurately than CT scan

        Ultrasound of Pyogenic Liver Abscess
      3. CT Scan
        • most sensitive and specific imaging procedure
        • should be done with IV contrast, if possible
        • peripheral rim enhancement or surrounding edema are specific for liver abscess
        • may also reveal the underlying condition causing the abscess
        • diagnostic or therapeutic procedures may be performed

        CT Scan of Pyogenic Liver Abscess
      4. MRI
        • as sensitive as CT for detecting liver abscesses
        • in combination with MRCP, provides detailed information about the relationship of the abscess with the biliary system

  5. Treatment
    • most patients are treated with a combination of antibiotics and percutaneous drainage
    • must also treat the underlying source

    1. Antibiotics
      • empiric therapy should be started with IV antibiotics active against gram-negative rods, streptococcus, and anaerobes
      • antibiotic coverage is modified once culture results are ready
      • IV therapy is given for 10 – 14 days, and oral antibiotics are continued for an additional month
      • patients with multiple small abscesses not amenable to drainage may be treated with antibiotics alone

    2. Drainage
      1. Percutaneous Drainage
        • mainstay of treatment, highly effective
        • involves placement of an 8- to 14-French drainage catheter into the abscess cavity under ultrasound or CT guidance
        • may be used for both single and multiple abscesses
        • care must be taken to avoid the pleural space
        • aspiration without drain placement is often effective for abscesses < 5 cm in diameter

      2. Surgical Drainage
        • most common indication is in patients who have an underlying condition requiring an operation (appendicitis, diverticulitis, biliary disease)
        • other indications include patients in whom percutaneous drainage is not advisable (coagulopathy, ascites), multiple or multiloculated abscesses, or failure of percutaneous drainage
        • most common approach is transabdominal; may also consider an anterior or posterior extraperitoneal approach
        • recently, laparoscopic drainage has been reported to have several advantages over percutaneous drainage:
          • the use of larger drainage catheters
          • avoidance of transpleural drainage
          • ability to search for and treat the underlying etiology

  6. Outcome
    • pyogenic liver abscesses are 100% fatal without treatment
    • with treatment, solitary abscesses have a 10% mortality and multiple abscesses a 40% mortality

Amebic Abscesses

  1. Epidemiology
    • associated with tropical and subtropical environments and areas of poor sanitation (India, Africa, Mexico, Central and South America)
    • immigration from and travel to endemic areas make amebiasis a problem in the United States (1% to 2% of the population)
    • only 3% of 10% of patients with amebic infection will develop a liver abscess
    • also associated with chronic immunosuppression (HIV, malnutrition, steroids)
    • much higher incidence in males (10:1 ratio)

  2. Pathogenesis
    • responsible pathogen is the protozoa Entamoeba histolytica
    • this parasite exists in two forms, an immobile cyst and an invasive trophozoite
    • humans are the principal host
    • human infestation occurs by the fecal-oral route from ingesting cysts from contaminated food or water or by direct contact
    • the cystic form is ingested and is resistant to the acidity in the stomach
    • the cyst wall is broken down by pancreatic enzymes in the small intestine, freeing the invasive trophozoite
    • the trophozoite lives and multiplies in the large intestine
    • in the majority of patients, no tissue invasion occurs
    • when tissue invasion does occur, the trophozoites enter mesenteric venules and reach the liver through the portal circulation
    • if sufficient numbers of trophozoites accumulate in the liver, necrosis and liquefaction of hepatic parenchyma occurs, giving rise to a single abscess cavity, usually in the right lobe
    • antiamebic antibodies develop rapidly, but do not halt the progression of the disease
    • the abscess cavity is sterile and odorless and composed of liquefied hepatic debris and blood (‘anchovy paste’)
    • trophozoites are isolated only from the outer rim of the abscess cavity

  3. Diagnosis
    1. History
      • patients will usually be males, age 20 – 40, who have recently travelled to or from an endemic area
      • there may be an antecedent attack of intestinal amebiasis
      • patients may present with an acute illness or a chronic indolent illness

    2. Symptoms
      • right upper quadrant pain, fever and chills are the most common symptoms
      • malaise, nausea, vomiting, anorexia, and weight loss also occur
      • some patients may have pulmonary symptoms: cough, pleuritic pain, shortness of breath
      • ~ 50% will have diarrhea

    3. Signs
      • fever
      • tender hepatomegaly is almost always present
      • jaundice is rare

    4. Laboratory Studies
      • diagnosis is made by an immunoassay which detects antibodies against the parasite
      • stool studies for amoebas are positive in only a minority of patients
      • leukocytosis and elevated liver function tests are common but nonspecific findings

    5. Imaging Studies
      • ultrasound and CT scan are both appropriate studies
      • lack of rim enhancement helps to distinguish between pyogenic and amebic abscesses
      • aspiration is indicated primarily if the diagnosis between pyogenic and amebic abscess is uncertain or if there is concern for a secondary bacterial infection

      Amebic Liver Abscess
  4. Complications
    • most dangerous complication is rupture into the pleural, peritoneal, or pericardial cavities
    • secondary bacterial infection in 10% of cases

  5. Management
    1. Antibiotics
      • most patients are successfully treated with amebicidal agents alone
      • metronidazole is the most widely used agent and is successful in treating both intestinal and extraintestinal amebiasis
      • should begin empiric treatment while awaiting the result of serologic tests
      • metronidazole should be given for 5 – 10 days, with a 95% success rate
      • if the patient fails metronidazole, emetine or dehydroemetine may be tried
      • intestinal colonization should be treated with a luminal agent such as iodoquinol

    2. Drainage
      • percutaneous drainage is indicated in the following instances:
        • diagnostic uncertainty
        • concern for secondary infection
        • persistent symptoms after 3 to 5 days of amebicidal therapy
        • left lobe abscesses at risk for perforation into the pleural or pericardial spaces

Hydatid Cysts

Hydatid Cysts
  1. Epidemiology
    • parasitic disease caused by the dog tapeworm, Echinococcus granulosis
    • intermediate hosts include sheep and cattle; humans are an incidental intermediate host
    • endemic areas include the Middle East, Iceland, Australia, New Zealand, southern Africa, and the southern half of South America
    • most reported cases in the United States have occurred in immigrants, especially from Greece and Italy

  2. Parasite Life Cycle
    • tapeworm resides in the jejunum of dogs and produces eggs that are passed in the feces
    • intermediate hosts then ingest the eggs by the fecal-oral route
    • ingested eggs hatch in the gut of the intermediate host and the embryo passes through the mucosa and enters the portal circulation
    • most embryos lodge in the liver, but occasionally they may pass through the liver into the lungs
    • once lodged in the liver, the cyst tends to grow progressively

  3. Pathology
    • 70% of hydatid cysts are located in the liver
    • 75% are located in the right lobe
    • grossly, the cyst has 2 layers: 1) the ectocyst, or pericyst, which is a fibrous adventitial layer contributed by the host, 2) the parasite-derived endocyst, which has an outer laminated membrane and an inner germinal layer
    • the germinal layer generates brood capsules containing scolices and daughter cysts, which float freely in the cyst fluid
    • when brood capsules settle to the most dependent portion of the cyst, they are called hydatid sand
    • a much less common form of the disease is caused by Echinococcus multilocularis, which causes an invasive tumor-like replacement of liver tissue

    Hydatid Cyst Structure
  4. Complications
    • intrabiliary rupture is the most common complication and occurs in 5% to 10% of cases
    • abscess formation, the second most common complication, occurs secondary to contamination from bacteria from the biliary tract
    • intraperitoneal rupture may occur, leading to formation of new cysts in the peritoneal cavity and, rarely, an anaphylactic reaction
    • cysts may also grow craniad into the pleural cavity and rupture

  5. Clinical Manifestations
    • most cysts are usually asymptomatic; many are found incidentally on routine imaging studies
    • when they become symptomatic, the most common symptoms include right upper quadrant pain, tenderness, and an abdominal mass
    • with biliary rupture, the classic triad of biliary colic, jaundice, and urticaria may be seen

  6. Diagnosis
    • diagnosis is made by a combination of clinical evaluation and imaging studies
    • CT scanning is the imaging study of choice and will usually show a septated, calcified cystic mass with daughter cysts and hydatid sand

      • CT Scan of Hydatid Cyst
    • serologic tests may be performed in equivocal cases
    • eosinophilia occurs in less than 25% of patients
    • ERCP is an important study if rupture into the biliary tree has occurred

  7. Management of Uncomplicated Hydatid Cysts
    • a small, densely calcified lesion can be assumed to be a dead hydatid and requires no therapy
    • all live hydatids require treatment because of the likelihood of developing complications over time

    1. Surgery
      • indications include biliary communication, cysts > 10 cm, multiple daughter cysts, or percutaneous treatment is not available
      • albendazole is usually started one week before surgery and continued for at least four weeks postoperatively

      1. Simple Cystectomy
        • involves removal of the cyst contents and lining wall and leaves only the patient’s adventitial lining
        • the cyst must be carefully packed off and isolated from the rest of the peritoneal cavity to protect against spillage
        • some surgeons inject scolicidal solutions (20% hypertonic saline) into the cyst prior to removing the cyst contents
        • bile leaks must be looked for and oversewn
        • residual cyst cavity should be packed with omentum

      2. Pericystectomy
        • entails dissection in the plane between the host adventitial layer and the underlying liver tissue
        • major operation associated with considerable blood loss
        • does not have better results than simple cystectomy

    2. PAIR Procedure
      • percutaneous procedure consisting of cyst puncture, aspiration of cyst contents, injection of a scolicidal agent, reaspiration after 15 minutes
      • done under US or CT guidance
      • aim is to destroy the germinal layer with scolicidal agents
      • contraindications include daughter cysts, biliary communication, and superficial cysts at risk of rupture into the peritoneal cavity
      • cure rate is > 95% in correctly chosen patients
      • complications include cyst spillage into the abdominal cavity, biliary fistula, chemical sclerosing cholangitis, bleeding and infection, local recurrence, and anaphylaxis
      • albendazole should be given 4 hours before the procedure and for 1 month after

  8. Management of Complicated Hydatid Cysts
    1. Intrabiliary Rupture
      • may cause biliary colic, obstructive jaundice, cholangitis, or pancreatitis
      • cyst contents in the biliary tree can usually be managed by ERCP with sphincterotomy
      • surgical common bile exploration may occasionally be required
      • simple cystectomy is sufficient to manage the cyst
      • the communication between the cyst and the bile duct must be carefully closed

    2. Intraperitoneal Rupture
      • surgical emergency
      • cyst is treated by simple cystectomy
      • peritoneal cavity must be cleaned manually and by irrigation with 20% hypertonic saline
      • long-term albendazole treatment is required (3 - 6 months)
      • further surgery may be necessary if peritoneal cysts develop







References

  1. Schwartz, 10th ed., pgs 1284 - 1287
  2. Cameron, 11th ed., pgs 307-317, 341 - 346
  3. Sabiston, 20th ed., pgs 1445 – 1454
  4. UpToDate. Pyogenic Liver Abscess. Joshua Davis, PhD, MBBS, FRACP, Malcolm McDonald, PhD, FRACP, FRCPA. Aug 17, 2018. Pgs 1 – 20
  5. UpToDate. Treatment of Echinococcosis. Pedro L. Moro, MD, MPH. Feb 20, 2020. Pgs 1 – 22