A 9-year-old spayed female mixed breed dog weighing 6.8 kg with a history of previous splenectomy for hemangiosarcoma 4 years earlier was referred for a hepatic mass lesion. Although the dog did not have a clinical sign, a computed tomography revealed a solitary mass in the left medial lobe of the liver. Spleen-like tissue was observed on needle core biopsy of the mass, leading to the diagnosis of intrahepatic splenosis. Therefore, hepatic lobectomy of the left medial lobe of the liver was performed. Histopathological evaluation of the excised tumor confirmed the diagnosis of intrahepatic splenosis. No further development of splenosis was detected on CT performed 217 days after the surgery. The dog died of suspected aspiration pneumonia without any event or clinical signs related to intrahepatic splenosis on postoperative 272 days. The cause of the intrahepatic splenosis observed in this dog was unknown
however, hematogeneous dissemination and autoimplantation of splenic tissue via the portal venous flow was speculated. This case shows the utility of needle core biopsy for the preoperative diagnosis of splenosis. The intrahepatic splenosis in this case was considered to have developed as a long-term sequelae after splenectomy, as in humans.