Histopathological evidence of direct hepatic invasion by Anisakis from the liver surface: A case report.

Anisakis occasionally parasitizes extra-gastrointestinal organs, including the liver, pancreas, and ovary. We herein report a case of hepatic anisakiasis in which the route of hepatic invasion by Anisakis was histologically confirmed. A 50-year-old Japanese man with a history of left testicular seminoma underwent follow-up contrast-enhanced dynamic computed tomography, which revealed a liver mass suspicious for metastasis. The scan showed a low-attenuation area near the liver surface in segment 7. Laparoscopic partial hepatectomy was performed for diagnosis and treatment. Histologically, the mass showed necrosis and inflammatory infiltration, mainly by lymphocytes and neutrophils, with a parasite observed within the lesion. The parasite exhibited characteristic features-bifurcated Y-shaped lateral cords and a prominent renette cell-diagnostic of Anisakis larvae. A continuous linear band of granulation tissue connecting the liver surface to the lesion suggested the route of invasion. Retrospective imaging review confirmed that the hypodense linear band extending from the liver surface to the mass represented the direct invasion pathway. This case provides clear evidence of the hepatic invasion route in anisakiasis. Although rarely encountered, recognition of this feature may help distinguish hepatic anisakiasis from malignant liver tumors.