Primary hepatic angiomyolipoma: immunohistochemistry and electron microscopic observations: a case report

BACKGROUND Hepatic angiomyolipomas are a rare, benign group of mesenchymal tumors in the liver. Hepatic angiomyolipoma is sometimes misdiagnosed as hepatocellular carcinoma, and there is the possibility of a malignant transformation. Hence, the accurate diagnosis of this disorder is necessary. CASE PRESENTATION A 64-year-old Japanese man was observed to have a space-occupying lesion of 15-mm diameter in the liver during a follow-up examination for a previously resected cecal carcinoma. He underwent lateral segmentectomy of the liver with a provisional diagnosis of hepatic metastatic recurrence of the carcinoma based on gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging and diffusion-weighted imaging. CONCLUSIONS We have explored the combination of gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging and histological examination to confirm our diagnosis of hepatic angiomyolipoma comprising an intimate mixture of numerous abnormal blood vessels, adipocytes, and epithelioid spindle cells of various sizes. Immunohistochemical examination revealed characteristic pathological findings associated with positive qualitative immunoreactions for human melanoma black 45 and desmin. Electron microscopic findings revealed the presence of melanosomes in the epithelioid cells. Diffusion-weighted imaging provides a more accurate diagnostic image with the characteristic macroscopic appearance of hepatic angiomyolipoma. Through immunohistochemistry and electron microscopy, we also show that this benign tumor comprises tissue elements.