Imaging Characterization of a Cystic Duct Neuroendocrine Carcinoma in a Dog Using Contrast‐Enhanced Ultrasonography and Multiphasic Computed Tomography

We describe a cystic duct neuroendocrine carcinoma in a dog evaluated with CEUS and multiphasic CT. The lesion was initially suspected to be hepatic but was reclassified as an intraluminal biliary mass on imaging. CEUS showed arterial hyperenhancement with early washout, and CT demonstrated a strongly enhancing intraluminal mass with progressive washout and biliary dilation. These findings enabled accurate localization and supported surgical management. Histopathology confirmed neuroendocrine carcinoma. Neoplasia of the canine gallbladder and biliary tract is uncommon, and tumors arising from the biliary ducts are rarely reported. Differentiating between hepatic and biliary origin can be challenging, particularly when intraductal lesions cause disproportionate biliary dilation relative to their size. Contrast-enhanced ultrasonography and multiphasic CT enable assessment of vascular characteristics and lesion localization, which may aid in distinguishing intraluminal biliary lesions from hepatic masses. This report describes a cystic duct neuroendocrine carcinoma characterized using CEUS, multiphasic CT, and histopathology, highlighting the role of multimodal imaging in accurate lesion localization.