LIVER ABSCESS

DEFINITION

Hepatic abscess: pyogenic, amoebic or fungal.
For hydatid disease, see separate notes

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INCIDENCE

 Uncommon
1:5000 hospital admissions.

Risks
Poor hygiene
Malnutrition
Immunosuppression
Homosexuals
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AETIOLOGY

Pyogenic (~80% in West)
Amoebic (~10%)
Fungal (<10%)

Pyogenic
Anaerobes (bacteroides, fusobacterium), coliforms (E. coli, klebsiella), staph. aureus.
--> in cholangitis klebsiella, E. coli and Enterococcus
--> in pts with biliary malignancy and multiple antibiotic courses, Pseudomonas and multi-resistant aerobes, VRE and yeast occur.
--> in contiguous cholecystitis, clostridium perfringens and bacteroides in addition to the typical biliary bugs.
--> in divertics / appdx, gram -ves, Bacteroides
--> in systemic spread, staph, MRSA, enterococcal.
--> anaerobes in cryptogenic cases.
Hydatid (Echinococcus granulosis, Echinococcus multilocularis).

Amoeba - Entamoeba histolytica
- seen in Pacific Islands, Indian Subcontinent, South America, Mexico and tropical Africa.
- typically affects young to middle aged men.

Fungal - Candida albicans, next Aspergillus and Cryptococcus
- consider fungi in chronic ICU patients, prolonged antibiotics, immunocompromised, or if not responsive.

Rarely
TB, syphilis, Q-fever, schistosomiasis, actinomycosis, malaria, Leishmania (Kalaazar), flukes, Clonorchis sinensis.

Iatrogenic Abscess
Growing category due to ablative liver treatments.

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BIOLOGICAL BEHAVIOUR

Pathogenesis
Bacterial
1/3 related to biliary tract pathology
- often bilateral and numerous
- often following malignant obstruction
1/5 to portal spread (GI tract)
- tends to be R lobe, single or low numbers
- appendicitis or diverticulitis
Rest:
- contiguous spread, e.g. from adjacent severe cholecystitis
- bacteraemia (via hepatic artery; distant source)
- trauma (injury or liver-directed therapy)
- infective cysts
- necrotic tumours.
--> if systemic, often singly and small, either or both lobes

Note from Cameron:
Classically where a young man's disease from appendicitis etc; now times have changed.
= more likely biliary source in older people (40%; often with underlying malignancy)
= lately, subtle shift toward underlying hepatic malignancy association (due to aggressive approaches to deal with liver tumors)

Anatomical
R hepatic lobe predominates 2:1, and bilobar abscesses are relatively uncommon

Amoeba
Cyst stage is infective
- fecal-oral transmission; mainly by food and water
- resistant to gastric acid; SI trypsin breaks down wall
--> releases Trophozoites
Trophozoite stage causes invasive disease.
- colonize intestinal wall when cysts broken
- parasites invade mesenteric lymphatics and enter the liver, forming an abscess.

For some reason, M:F 10:1

Liver abscess is most common extraintestinal location of amebiasis,
but only occurs in 1% of amebiasis pts.

Presentation
Usually present acutely with fever and pain
- else sub-acute with weight loss, malaise.
Often 10-12 weeks post-travel
- 95% within 5 months of returning from endemic area
Hepatomegaly with tenderness is common
Usually single R lobe focus (~80%)

Complications
Rupture or direct extension into surrounding organs, eg pleural cavity, pericardium or peritoneum.

Negative prognostic features
BiliR>35
encephalopathy
abscess volume >500mL
albumin <20
multiple amoebic abscesses
complications above.

Fungal
Us. immunocompromised pts, e.g. HIV
Mixed bacterial and fungal can occur in long-term biliary stent malignancy pts.
Treat same as for pyogenic and with appropriate antimicrobials.
- i.e. IV amphotericin B (formerly; now micafungin and caspofungin more commonly.).
- then oral fluconazole after initial IV therapy.
High mortality rate but with modern antifungals, fungemia and death often are preventable

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MANIFESTATIONS

Symptoms

 Local
Painful abdomen / mass.
- can get R shoulder pain, pleuritic, cough and dyspnoea, hiccups if diaphragm irritated
May compress biliary tree, with jaundice, or even rupture into it, with biliary obstruction and secondary infection.
Systemic
Depending on the bug - fever (90% - most consistent feature)
- rigors (half), anorexia,
Severe sepsis without other signs possible
Vague features, e.g. diarrhoea, weight loss, nausea and vomiting may dominate

Pulmonary
Present in 1/4
Can cough anchovy-paste (amoebic)

Signs
Observe
If biliary obstruction
Palpate
Hepatomegaly, localised tenderness.
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INVESTIGATIONS

Haematology
WCC, CRP.

Biochemistry
Elevated enzymes is variable.
Hypoalbuminaemia and elevated alk phos are most common.

Microbiology
Blood cultures +ve in half or so.
Amoebic:
- Trophozoites may be identified in pus or
- serum amoebic serology.

Imaging
CXR positive features in 50%
- e.g. R hemidiaphragm elevation, pleural effusions, RLL atelectasis, RUQ abN extraluminal gas, even PV gas.

USS: 80-90% sensitive; good initial low cost screening test;
--> hypoechoic mass, irregular borders, 
- experience helps to differentiate necrotic tumours.
- particularly useful for evaluating the gallbladder and hepatic ducts
- less useful when pts obese or tumours under R diaphragm

CT is best overall
- sensitivity 95-100%
--> typically hypodense, well demarcated, peripheral enhancement with contrast, gas in 20%,
--> if amoebic, boundaries may be poorly defined
- allows thorough exam of abdomen for other causes
- guides perc drainage.

MRI
- equally sensitively cf CT but routinely unavailable

Reminder:
Evaluate gallstones, colon, appendix.
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MANAGEMENT

Potentially lethal without timely management

Principles
1. Identify source
2. Gain sample for MC&S
3. Treat with antibiotics +/- drainage

Note on Differentials
Necrotic tumours and non-infected haematomas can be mistaken for abscesses.
- usually tumours are in patients with disseminated malignancies receiving chemo (particularly large colorectal Ca, or GISTs on Glivec).
- prognosis for cancers can be negatively affected by aspiration
- tumour markers: AFP, Ca 19.9, CEA in suspect cases.
- non-resolving lesions should be treated as malignant

Conservative
Untreated abscess are uniformly fatal.
Medical management alone may be necessary in patients with multiple small abscesses
- many months of therapy likely

Non-Operative
Pyogenic: blood cultures, broad spectrum cover.
- drainage is important to determine the bacteriology.
- bacteria found usually correlate to source (see above).
Bacterial
- antibiotics for 4-6 weeks typically, however may be shorter if appropriate drainage achieved.
- beta lactam / beta-lactamase inhibitor, carbapenems, 2nd gen cephalosporins
- anaerobic cover (metronidazole or clindamycin)
- e.g. regimens: tazosin (piperacillin-tazobactam), meropenem, ticarcillin-clavulanate (timentin).
- but if multiple episodes of cholangitis and stents, might need cover for VRE, eg linezolid.
- for presumed colonic source, ceftriaxone and metronidazole useful.
- if suspicion of endocarditis, then MRSA cover with vancomycin
--> then adjust regimen once actual bugs are defined.
Amoebic
Metronidazole highly effective (often alone, without drainage).
- this has made drainage virtually obsolete.
- dramatic response to metronidazole can help confirm the diagnosis.
--> drainage only reqd when questionable diagnosis, bacterial coinfection or complications of the abscess.
--> or if no clinical response after 5-7d, high risk large abscess esp in L lobe.
--> surgery rarely needed e.g. haemorrhage, erosion or secondary abscesses failing primary drainage
Metronidazole can reach high concs in the liver.
- use 750mg tds for 5-10d
- caution in breast feeding or pregnancy.
- 90% respond after 10d, whereas 10% are resistant and require other agents.
- Most will improve after 3d
Luminal antimicrobials (e.g. iodoquinol) should also be used to eradicate intestinal colonization
- 10% relapse rate otherwise
Follow-up stool examination to check luminal eradication
Fungal
Amphotericin B

Drainage
Standard of care now moved away from surgery to percutaneous procedures.
One reasonable approach is:
<5 cm : Aspirate to dryness to speed up resolution
- advantages of decreased cost, reduced invasiveness and less drain pain cf drainage.
>5 cm : drain insertion; flushed to prevent blockage
--> 95% resolution with these regimens (Dennison & Maddern).
--> Fewer repeat procedures, fewer failures but same morbidity cf surgery.
Perform repeat USS or CTs weekly
Maintain drains until <10 cc/day
Persistent fever after 2 weeks indicates need for more aggressive therapy
Drainage not appropriate if:
- known intra-abdominal source that requires surgery
- multiple large abscesses
- ascites
- transpleural drainage required.
Amoebic
Drainage only critical if:
- to differentiate from pyogenic
- >5cm
- older patient (>55)
- failure of medical therapy >7d
--> is viscous, and bacterial superinfection can occur.
Amoeba rarely isolated from the drainage (they are in invading the adjacent liver)
--> acellular proteinaceous debris

Recurrent / Refractory Abscesses
Usually when large, multiple or communicating with biliary tract.
Recurrence --> drain insertion.
Refractory --> drain insertion.
Surgery occasionally required
- laparoscopy, 26 Fr drainage tube insertion;
- caution for fungal super-infection in this context.

Surgical
Surgery may be required to manage an abdominal or pelvic source
- and drain the liver.
Remove gallbladders associated with abscesses.
Surgery is the only consistently effective treatment for hydatids.

Drainage Technique
Midline or subcostal incision
Address underlying pathology within the abdomen if present
Locate abscess; intra-op USS if reqd
Isolate area with packs, and aspirate fully for culture and to reduce contamination
Create a tract through parenchyma to the cavity, ideally allowing dependent drainage.
Irrigate and suction cavity, enlarge tract and debride abscess to remove loculations.
Place a large drain into the cavity +/- drain perihepatic space
- bring these drains out through separate incisions.
Biopsy all to rule out tumour and to evaluate for trophozoites of E. histolytica.


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References
Dennison & Maddern
Medscape