Primary hepatic neuroendocrine tumor: gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging
A 71-year-old man presented to our outpatient clinic 3 years ago for the evaluation of metastasis with documented prostate cancer, which was diagnosed elsewhere. The patient reported no clinical symptoms, such as flushing, fever, or abdominal pain. A physical examination revealed no abnormal findings. The results of other laboratory evaluations, including liver tests and blood level of tumor markers (i.e. alpha-fetoprotein, CA-19–9, and carcinoembryonic antigen), were within normal limits. An ultrasound examination revealed a heterogeneous mixed echoic solid mass in the left lateral segment of the liver that was approximately 3.7 cm in maximal diameter (Fig. ). Abdominal multidetector CT revealed a well-circumscribed, heterogeneous, and hypodense mass, with mild peripheral constant enhancement during the arterial, portal, and equilibrium phases (Fig. ). The liver background was not cirrhotic. MR images (Fig. ) were obtained with a 1.5 T unit using a liver-specific contrast agent (gadoxetic acid disodium [Gd-EOB-DTPA], Primovist®, Bayer Healthcare, Berlin, Germany). On T2-weighted fast spin-echo MR (TR/TE, 3646.3/107.0) and diffusion images (diffusion b-factor, 800), the mass was mainly with mild high signal intensity correlated with normal liver parenchyma with several foci of hyperintense foci. This mass demonstrated hypointensity on T1-weighted gradient echo images (TR/TE, 3.6/1.4), and the previously highly hyperintense foci on T2-weighted images showed also slightly hyperintense on T1-weighted image, suggesting a hemorrhagic component. Gadoxetic acid-enhanced T1-weighted MR images demonstrated peripheral enhancement of the solid tumor portion on early arterial phase, contrast wash-out pattern on portal venous phase and definite defect on 20 min delayed hepatobiliary phase. The patient underwent ultrasound-guided biopsy of the hepatic mass, and histology suggested a malignant neoplasm that originated from a neuroendocrine cell (well-differentiated neuroendocrine carcinoma, Grade 2). After a meticulous examination for the primary origin, including positron emission tomography-computed tomography (18F-FDG-PET/CT), colonoscopy, gastroscopy, and chest CT, there was no evidence of a primary focus. On 18F-FDG-PET/CT, there was no definite increase of glucose metabolism in the hepatic tumor (Fig. ). Although grade 2 neuroendocrine tumors demonstrate slow growth, surgical resection is the treatment of choice. Based on this pathologic diagnosis, a left hemihepatectomy was performed. During the operation, no evidence of ascites or liver cirrhosis was found. The gross features of the tumor appeared approximately 3.3 cm in size with well-defined margins and a pink-yellowish appearance. The tumor consisted of multiple small hemorrhagic vascular lakes with old blood. Microscopic examination revealed that the neoplasm comprised cell atypia and mitotic activity (8/10 HPF, Fig. ). Small-intermediate-sized tumor cells demonstrated uniformly round nuclei with abundant cytoplasm and vesicular nuclei chromatin. Immunohistochemical studies were performed (Fig. ), and the tumor cells were strongly positive for the neuroendocrine marker synaptophysin, focally positive for neural adhesion molecule (CD56)/chromogranin and negative for cytokeratin 7 (a marker for cholangiocarcinoma). Ki-67 proliferative index is positive in 5% of cells. Microscopic and immunohistochemical findings were compatible with a well-differentiated G2 neuroendocrine carcinoma based on the WHO 2010 criteria (). Based on this finding, we performed a more thorough study to rule out the possibility that the liver tumor was a metastatic NET during the 3-year follow-up period. This work-up included multiple upper gastrointestinal endoscopies, colonoscopy, abdominal ultrasound examination, chest and abdominal CT scans, 123I-MIBG scan, and 123I-Octreotide SPECT-CT. All imaging findings were normal, except mild duodenitis. Thus, we concluded that the final diagnosis in this case was primary hepatic NET.