S5576 Silent Invaders: Anaerobic Pyogenic Liver Abscess in Complicated Diverticulitis

Introduction: A 37-year-old man with prior diverticulitis and intra-abdominal abscess (2021) presented with 3 months of fatigue, right upper quadrant pain, weight loss, and anorexia. Exam revealed hepatomegaly and diminished right lung base sounds. Labs showed sodium 128 mEq/L, bilirubin 1.9 mg/dL, aspartate aminotransferase 70 U/L, and lactate 4.4 mmol/L. Computed tomography (CT) revealed a 20.2 cm multiloculated hypodense liver mass with adjacent sigmoid colon thickening. Differential included diverticulitis-related abscess versus malignancy. CT-guided drainage yielded 1600 mL of purulent fluid; cultures grew Fusobacterium and Peptostreptococcus anaerobius. The patient improved on intravenous piperacillin-tazobactam, followed by outpatient ertapenem. He was referred for colonoscopy and tumor marker evaluation (CEA). Case Description/Methods: Fusobacterium and Peptostreptococcus are gut commensals that may translocate to the liver via the portal system after mucosal disruption. Though typically seen in immunocompromised patients, anaerobic PLAs can occur in immunocompetent individuals, especially those with diverticular disease. Prompt imaging, percutaneous drainage, and anaerobe-directed antibiotics are essential. Empiric therapy includes beta-lactam/beta-lactamase inhibitors, cephalosporins with metronidazole, or carbapenems. This case highlights the importance of early recognition, tailored antimicrobial therapy, and evaluation for underlying colonic pathology to prevent recurrence. Discussion: Anaerobic PLAs are uncommon but clinically significant. Fusobacterium and Peptostreptococcus, commensals of the gut and oral cavity, may access the liver through the portal system following mucosal disruption. Although most anaerobic PLAs occur in immunocompromised patients, this case underscores their relevance in immunocompetent hosts with predisposing gastrointestinal pathology. Diagnosis is often delayed due to nonspecific symptoms and culture challenges. Prompt imaging, drainage, and anaerobe-directed antibiotics are critical. This patient’s size of abscess warranted percutaneous drainage, followed by a 6-week antibiotic course. Empiric regimens include beta-lactam/beta-lactamase inhibitors, third-generation cephalosporins with metronidazole, or carbapenems. This case emphasizes early recognition and aggressive management of anaerobic PLAs, especially in those with diverticular disease. It also reinforces the need for further investigation into potential underlying malignancy, as colonic neoplasia may serve as a nidus for such infections.