A Case of Rectal Dissemination of Gastric Cancer Diagnosed by Simultaneous 18 F-FDG PET/MRI.

Metastatic rectal cancer is rare and difficult to differentiate from primary rectal cancer. A 79-year-old man with a rectal mass detected by CT during postoperative follow-up of gastric cancer underwent 18 F-FDG PET/MRI. Fused PET/MRI images revealed a lower FDG uptake within the mass, which appeared to surround the outside of the rectum, than in the rectal wall, suggesting rectal dissemination of gastric cancer. PET/MRI was useful for differentiating between mass and rectal wall uptake, because of the high contrast resolution of MRI and precise image fusion made possible by simultaneous image acquisition.