Radiographic, CT, MRI, and bone scintigraphy findings of patellar oligometastasis from rectal cancer.

Solitary metastasis or oligometastasis to the patella from colorectal cancer is rare, and multimodal imaging findings, including MRI, have not been well discussed. We report the case of a 74-year-old man with patellar oligometastasis from rectal cancer that was initially missed on whole-body positron emission tomography (PET) and misdiagnosed on bone scan. Radiographs and CT scans showed an osteolytic patellar tumor that was hypointense with ill-defined borders on T1-weighted imaging and hyperintense with well-defined borders on diffusion-weighted imaging. We discussed the characteristic MRI findings of patellar metastases and the pitfalls of PET and bone scan.