Secondary Brown's syndrome following fourth nerve palsy - case series and review of literature.

Introduction: Restriction of eye movements following fourth nerve palsy has been attributed to orbital injury in the past. In this report, we challenge this view. Methods: In a retrospective case series, we analyzed seven consecutive patients with a Brown's syndrome that evolved after a fourth nerve palsy. Results: All patients presented with fourth nerve palsies following trauma or meningioma surgery. After a delay of months, the fourth nerve palsy improved but the patients developed a limitation in adduction and upgaze in the same eye. None of the cases involved an injury to the orbit and the iatrogenic cases were secondary to neurosurgeries far from the orbit. A non-vascular fourth nerve palsy can evolve into a late onset motility limitation in the field of action of the antagonist in the absence of an orbital trauma. Discussion: We suspect an innervational mechanism as the cause of this secondary Brown's syndrome. This may involve aberrant-or compensatory innervation in different types of motoneurons innervating the superior oblique muscle.