Primary hepatic signet ring cell neuroendocrine tumor is extremely rare and is characterized by distinct intracytoplasmic hyaline vacuoles that are mucin negative and cytokeratin positive. The unique histological features may cause difficulty in diagnosis and delay patient care. Here the authors report a 49-year-old man with an incidental finding of a 2.7 cm liver mass in the absence of chronic liver disease. The resected tumor was grossly unencapsulated but well demarcated with friable tissue texture. Microscopically, the entire tumor consisted of sheets of monotonous cells separated by delicate microvasculature. The tumor cells had granular chromatin, inconspicuous nucleoli, and eosinophilic cytoplasm. Many of the tumor cells had eccentric, pale intracytoplasmic vacuoles resembling signet ring cells in adenocarcinoma. Immunohistochemical studies showed that the tumor cells were positive for neuroendocrine markers and that the intracytoplasmic vacuoles were negative for mucin but strongly positive for cytokeratins. Careful systemic search including OctreoScan scintigraphy (Mallinckrodt Medical, Inc., St. Louis, MO) and capsule endoscopy failed to reveal any other tumors. A diagnosis of primary hepatic signet ring cell neuroendocrine tumor was established. Ten months after surgery, the patient is well without any other detectable tumor on radiology. Serological neuroendocrine markers are also within normal limits.
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