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 int
o the lumbar region with minor or no symptoms. Possible explanations f
or the migration are the circulation of CSF and the gravity. A new obs
ervation was that an infection may develop at the site where the forei
gn 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.