Case Report: Contrast-enhanced US and CT imaging features of nodule-in-nodule hepatocellular carcinoma in a dog

A spayed female Maltese dog weighing 3 kg found to have a hepatic nodule during a routine health examination. B-mode ultrasonography revealed a focal, round, heterogeneous mass located in the left lateral liver lobe, characterized by a target-like appearance with a hyperechoic center surrounded by a hypoechoic peripheral region. On contrast-enhanced ultrasonography, the lesion exhibited a central defect during the Kupffer phase. Multiphasic computed tomography (CT) demonstrated marked diffuse enhancement during the arterial phase, followed by heterogeneous washout in the portal phase. Delayed-phase CT images further revealed a hyperattenuating central nodule within a hypoattenuating peripheral component. To our knowledge, this is the first report describing the B-mode, ultrasonographic, contrast-enhanced ultrasonographic, and multiphasic CT features of nodule-in-nodule hepatocellular carcinoma in a dog, closely resembling imaging characteristics reported in human medicine.