The difference between "Brain Metastasis" and "Brain Metastases" is primarily grammatical (singular vs. plural) and has clinical relevance:

✅ Brain [[Metastasis]] (singular)
Refers to a single metastatic tumor in the brain.

Example: “The patient presented with a solitary brain metastasis from lung cancer.”

Important when planning surgical resection, radiosurgery, or assessing prognosis, as single lesions often have a better outlook.

✅ [[Brain Metastases]] (plural)
Refers to multiple metastatic tumors in the brain.

Example: “MRI revealed multiple brain metastases.”

Often associated with a more advanced stage of systemic disease and may require whole-brain radiotherapy (WBRT) or systemic therapy instead of focal treatment.