The Role of Delayed Imaging at MRI in Rare Non-enhancing Prostate Cancer Brain Metastases: A Case Report.

Brain metastases in prostate cancer are rare (<2% of cases). In magnetic resonance imaging, nearly all brain metastases exhibit contrast-enhancement, which may be affected by the time elapsed since the administration of the contrast agent. We discuss a case where the brain metastases in a patient with prostate cancer do not show a clear contrast-enhancement on magnetic resonance imaging using a standard brain metastases protocol. It also emphasizes the usefulness of delayed imaging in identifying blood-brain barrier damage. We present the case of a 69-year-old man diagnosed with prostate adenocarcinoma, currently in castration-resistant phase (last value of serum prostate-specific antigen: 45.1 ng/mL) with bone, mediastinal and inguinal lymph nodes, pulmonary, and hepatic metastases. In a contrast-enhanced whole-body computed tomography examination, the appearance of intra-axial brain lesions suspicious for metastases was documented. The subsequent contrast-enhanced brain magnetic resonance imaging showed the presence of 5 intra-axial lesions consistent with brain metastases. These lesions exhibited hyperintense signals in T2-fluid-attenuated inversion recovery images; after contrast agent administration, a ring-like contrast-enhancement was more clearly visible in T1-weighted images acquired later (about 15 minutes after contrast agent administration) than in those acquired earlier (about 5-7 minutes after contrast agent administration). In conclusion, for oncological subjects with multiple brain lesions lacking obvious contrast-enhancement using a standard magnetic resonance imaging protocol, we suggest acquiring late images. These might allow for the detection of even minimal post-contrast impregnation, improving confidence in the diagnosis of brain metastases.