Cytologic, Histologic, and Ultrasonographic Features of Hepatic Intravascular Lymphoma in a Dog.

A 6 year-old neutered male Mastiff cross dog was evaluated for gastrointestinal signs and increased liver enzyme activities. Ultrasonography revealed hepatomegaly with a heterogeneous parenchyma, hypoechoic regions, and echogenic material in hepatic veins, suggestive of thrombi. Fine-needle aspiration and core needle biopsies were obtained from the liver for cytologic and histopathologic evaluation. Cytology revealed a population of poorly cohesive, atypical round cells, raising suspicion for lymphoma or a primitive/blastemal neoplasm. Initial histopathology was inconclusive, but a subsequent surgical biopsy revealed a population of individualized round cells confined within the lumens of hepatic vessels. Using immunohistochemistry, a neoplastic population of CD3-immunoreactive lymphocytes lacking Pax5 immunoreactivity was identified, confirming the diagnosis of large T-cell intravascular lymphoma (IVL). This is considered a rare and aggressive lymphoma characterized by a solely intravascular proliferation of neoplastic lymphocytes. Despite initial core needle histopathologic evaluation, a definitive diagnosis was only achieved after evaluating a larger surgical biopsy. This is also the first report to describe the ultrasonographic appearance of hepatic IVL in dogs. This report adds to the limited veterinary literature on IVL and underscores the importance of obtaining representative samples for a reliable histopathologic diagnosis.