noun

• 1Pathology
  A condition characterized by the presence of an increased number of neuroglial or satellite cells surrounding neurons, especially in the central nervous system; an instance of this. In later use also: the presence of tumour cells around neurons, characteristic of certain types of brain tumour.

• 2Medicine
  The spread of a melanoma or other malignant or (occasionally) infectious lesion into tissue near the original lesion, especially when forming visible secondary nodules; a secondary lesion of this kind.