No mass image formation of metastatic neuroendocrine tumors to the liver on ultrasound: A case report.

A 65-year-old woman showed abnormal positron emission tomography findings in the liver after breast cancer surgery. Computed tomography showed a hepatic mass with faint ring enhancement. Magnetic resonance imaging (MRI) of the liver mass showed low signals on T1-weighted images, faint high signals on fat-suppressed T2-weighted images, nominal enhancement both on early and late phase images, and distinct low signals on hepatobiliary images. Ultrasound, however, could not depict any mass images in the liver. The patient underwent diagnostic endoscopic laparotomy, revealing a visible liver tumor through the liver surface in the segment 5. Laparoscopic ultrasound was also unable to depict any tumor images even by directly placing the ultrasound probe just on the exposed tumor. Pathological study of the resected mass showed that a well-circumscribed mass was composed of atypical cells growing in solid and trabecular fashions with little nuclear atypia, focal shelf-like arrangement of nuclei, a fine vascular network, small interstitial components between tumor cell clusters, and no peri-tumoral inflammatory cells/fibrous components, and had 3 daughter nodules. In addition, CD56, synaptophysin, and chromogranin positivities of the tumors led to the diagnosis of metastatic neuroendocrine tumors (NET). Diagnostic physicians should note that ultrasound may fail to show mass images even of well-circumscribed metastatic NETs to the liver.