Spontaneous migration of foreign bodies in the central nervous system.

The authors present four cases where foreign bodies within the central nervous system had spontaneously migrated. Two of these were surgical clips and two were bullets. The clips seemed to pass intradurally into the lumbar region with minor or no symptoms. Possible explanations for the migration are the circulation of CSF and the gravity. A new observation was that an infection may develop at the site where the foreign body had been situated before migration. From the clinical point of view, the removal of foreign bodies from the intradural space is not indicated, if the patient has no connected symptoms.