Locally metastatic mucinous rectal adenocarcinoma: Imaging diagnosis with DW-MRI in comparison with PET-CT.

A 56-year-old male patient with locally advanced mucinous rectal cancer underwent neoadjuvant chemoradiotherapy. Follow-up imaging with positron emission tomography-computed tomography (PET-CT) revealed a local response to chemoradiotherapy, whereas diffusion-weighted magnetic resonance imaging (DW-MRI) showed newly presented sacral bone metastasis. Histopathologically confirmed bone metastasis and the local tumor were surgically removed. Repeat DW-MRI revealed tumor recurrence in the sacral excision zone eight months after surgery, which was reconfirmed by histopathology. This case shows the superior imaging ability of DW-MRI in the diagnosis of mucinous tumors in comparison to PET-CT.