hepatic abscess

**Types and etiology** 1. Pyogenic (most common in developed countries) - Usually polymicrobial: E. coli, Klebsiella pneumoniae, Streptococcus milleri (anginosus) group, anaerobes (Bacteroides), Enterococcus. - Routes of seeding: (a) biliary tract disease (cholangitis, obstruction from stones or malignancy), the most common cause; (b) portal vein (pylephlebitis) from appendicitis, diverticulitis, or IBD; (c) hepatic artery (bacteremia, endocarditis); (d) direct extension or trauma; (e) cryptogenic. - Klebsiella pneumoniae (hypermucoviscous, K1/K2 serotypes) is associated with diabetes and East Asia. It can cause metastatic infection (endophthalmitis, meningitis). Also consider colorectal cancer when Klebsiella liver abscess is found. - Staphylococcus aureus is more likely with bacteremia, endocarditis, or in children (including chronic granulomatous disease). 2. Amebic - Entamoeba histolytica, acquired by fecal-oral ingestion of cysts in endemic areas (travel to or immigration from Mexico, India, Africa, Central/South America). - Trophozoites invade the colon (flask-shaped ulcers) and travel via the portal vein, usually to a single abscess in the right lobe. - Contents are "anchovy paste" (sterile, brownish, necrotic liquefied hepatocytes). Trophozoites are found at the abscess wall rather than in the pus. - Most often in men aged 20-40. Often without concurrent diarrhea. 3. Fungal (Candida): in immunocompromised or neutropenic patients, often with multiple small lesions ("bull's-eye" or "target" lesions on imaging). 4. Echinococcal (hydatid cyst): Echinococcus granulosus from sheepdog exposure. Do not aspirate because of the risk of anaphylaxis and spillage. Imaging shows a cyst with daughter cysts and calcified walls.

**Clinical features** - Fever, chills, RUQ pain, malaise, nausea, weight loss, tender hepatomegaly. The presentation can be subtle or nonspecific, especially in older adults. - Right pleural effusion, referred shoulder pain, or hiccups if there is diaphragmatic irritation. - Labs: leukocytosis, elevated alkaline phosphatase (most consistent abnormality), mild transaminase elevation, hypoalbuminemia, anemia of chronic disease.

**Diagnosis** - Imaging: ultrasound first, with CT (rim-enhancing hypodense lesion) as the most sensitive test. Look for the "cluster sign" (coalescing small abscesses) in pyogenic abscess. - Pyogenic: blood cultures (positive in about 50%) and aspirate Gram stain and culture. - Amebic: serology (anti-ameba IgG, positive in more than 90%) and stool antigen or PCR. Stool microscopy is often negative. Aspiration is usually unnecessary.

**Treatment** - Pyogenic: broad-spectrum IV antibiotics covering gram-negatives, anaerobes, and streptococci (e.g., a third-generation cephalosporin or piperacillin-tazobactam, plus metronidazole), typically 4-6 weeks total. Percutaneous catheter drainage (or needle aspiration) for abscesses larger than about 3-5 cm. Surgery if drainage fails, if there is rupture, or if the abscess has multiple loculations or an underlying surgical cause. Treat the source (e.g., biliary decompression). - Amebic: metronidazole (or tinidazole), followed by a luminal agent (paromomycin or iodoquinol) to eradicate intestinal cysts. Drainage is rarely needed, only for large abscesses, a left lobe abscess (rupture risk), or no response in 5-7 days.

**Complications** - Rupture into the peritoneum, pleural space (empyema), or pericardium (left lobe amebic abscess can rupture into the pericardium, with tamponade). - Sepsis, hepatic vein thrombosis, and metastatic infection.

**High-yield pearls** - Pyogenic abscess = polymicrobial, often biliary origin, and needs drainage plus antibiotics. - Amebic abscess = single right-lobe lesion, "anchovy paste" pus, travel history, and treatment with metronidazole, which is usually enough. - Never aspirate a suspected hydatid cyst without precautions (albendazole and PAIR or surgical approach). - Think of Klebsiella liver abscess in a diabetic patient from East Asia.