brain metastases known patients history active subjects presence patient treated leptomeningeal disease manifestation history presence evidence patients diffuse spread untreated meningitis carcinomatous subjects known history brain presence leptomeningeal patients metastases suspected metastasis leptomeningeal brain known active disease subject needing carcinomatosis leptomeningeal metastasis brain disease history known symptomatic presence active patients leptomeningeal metastases brain active cns evidence history known disease patients