Most intracranial tumors are characterized by several interesting biologic differences from tumors elsewhere in the body. Regardless of their rate of growth, degree of aggressiveness, ability to infiltrate and other characteristics usually associated with cancers, they do not metastasize to distant parts of the body. Cancers which arise elsewhere can metastasize freely into the central nervous system, indicating that the incompatibility of protoplasms is not absolute. When intracranial tumors metastasize they do so by implantation.
Using medulloblastomas as an example, Abbott and Kernohan1 recently considered some additional special problems in the behavior of these tumors. They accept the statements that tumor cells are often free in the cerebrospinal fluid and that they spread by circulation of the fluid and by gravity. Such free cells from medulloblastoma, they point out, frequently become implanted, whereas in other tumors which are equally cellular they usually fail to grow. Thus this system appears
BIOLOGIC PECULIARITIES OF INTRACRANIAL NEOPLASMS. JAMA. 1943;122(17):1187–1188. doi:10.1001/jama.1943.02840340035014