Brain metastases on imaging typically show lesions at which anatomic region?

• A. Ring-enhancing lesions
• B. Calcifications
• C. Lesions at the gray-white border
• D. Diffuse edema with no focal lesions

Answer: (C)

This question tests where brain metastases tend to appear on imaging. Tumor cells spread through the bloodstream and tend to lodge where the vascular architecture changes at the gray–white matter junction. The transition from the thick, perpendicular white-matter tracts to the more densely packed gray matter creates a site where embolic tumor cells arrest and seed. As a result, metastases are classically multiple and located at the gray–white border, often with surrounding vasogenic edema. Central necrosis can give ring-like enhancement after contrast, but the key imaging pattern is the preference for the gray–white junction. Calcifications aren’t typical for most metastases, and diffuse edema without focal lesions suggests other processes.