Background/aims Persistent diplopia secondary to a fourth cranial nerve palsy is poorly documented after open cranial base surgery.

Methods Six cases of fourth cranial nerve palsy after cranial base surgery were drawn from the Neuro-Ophthalmology and Head and Neck Surgery Clinics at the University of Michigan from 2004 to 2012.

Results Six patients developed diplopia and ocular misalignment in a pattern suggestive of superior oblique palsy following dissection of the medial orbital periosteum as part of a surgical approach to the anterior cranial base. Among the four patients in whom follow-up examination was available, the misalignment improved spontaneously in three patients and was stable in the fourth patient, but did not completely resolve in any patient.

Conclusions This sparsely documented phenomenon is likely caused by dysfunction of the superior oblique muscle, possibly the result of malposition of the trochlea after spontaneous reattachment of the periosteum. Special factors such as invasive tumours, repeated surgeries of this nature, prior radiation, or chemical cementing material that adversely affects wound healing may be contributory.