Hepatic abscesses are uncommon in dogs and typically develop secondary to biliary tract disease or ascending bacterial infections. Although congenital extrahepatic portosystemic shunt (EHPSS) is known to impair hepatic perfusion and immune clearance, its potential role in predisposing geriatric dogs to hepatic abscess formation has not been previously reported. This case report describes the diagnostic approach, therapeutic decision-making, and clinical outcome of a geriatric dog in which a multidrug-resistant hepatic abscess occurred in association with congenital EHPSS, and to propose a pathophysiologic link between chronic portal hypoperfusion and intrahepatic infection. An 11-year-old neutered male Maltese dog with a known EHPSS presented with acute anorexia and lethargy. Diagnostic imaging revealed a hepatic abscess adjacent to the gallbladder, and cytology confirmed a septic process. Despite targeted meropenem therapy based on antimicrobial susceptibility testing, the abscess failed to regress and C-reactive protein levels continued to rise. Concern for persistent biliary contamination and impaired hepatic immune clearance led to surgical intervention. A combined procedure—partial hepatic lobectomy, cholecystectomy, and shunt attenuation—was performed. Postoperative hypotension was managed successfully with vasopressors and transfusion. The patient recovered uneventfully, and at four-month follow-up, hepatic enzyme activities normalized and liver size increased. These findings highlight the need to evaluate hepatic infections in dogs with EHPSS as a potential consequence of impaired hepatic immune clearance rather than an incidental finding.

Hepatic neuroendocrine carcinoma (NEC) in dogs is a rare malignancy with limited therapeutic guidance and no established standard of care. This report describes an adaptive, clinically guided multimodal treatment approach in a dog with advanced hepatic NEC with regional lymph node involvement. Sequential systemic therapies—including doxorubicin, mitoxantrone with lomustine and prednisolone, and subsequently toceranib—were administered based on clinical response assessment using imaging (VCOG RECIST), hematologic monitoring, and quality-of-life evaluation. Ex vivo drug sensitivity testing (DST) was performed to provide functional reference information but was interpreted as supportive rather than predictive. Notably, discordance was observed between strong in vitro sensitivity to doxorubicin and early clinical progression, underscoring the limitations of monoculture-based assays in recapitulating in vivo tumor biology. Sustained stable disease was observed following transition to toceranib with continued adjunct immunomodulatory therapy; however, the independent contribution of each treatment component cannot be determined. This case highlights the feasibility of iterative treatment refinement in rare canine malignancies and emphasizes that DST findings should be integrated cautiously within a broader clinical decision-making framework.