Transitory Fourth Cranial Nerve Palsy due to Foramen Ovale Electrode Placement

We report on a 56 year old female patient with a drug-resistant localization-related epilepsy with complex-partial and secondary generalized seizures of unknown aetiology. Video-EEG-monitoring with scalp-electrodes bad not been sufficient to determine the primary epileptogenic zone, so that we decided to perform a second EEG-monitoring phase with scalp electrodes and additional FOE. Flexible 4-contact FOE (AD-Tech Medical Instrument Corporation, Racine, WI, U.S.A.) with a diameter of 1 mm were placed through the foramen ovale bilaterally using a 17 gauge introducing needle. For local anaesthesia bupivacain 0.5% was given. The implantation technique has been described in detail by Wieser [3, 4]. Under x-ray control, bilateral implantations were performed without complications. The implantation time was five minutes on the left and 13 minutes on the right side, the latter due to several positioning adjustments prior to the placement in loco typico (Fig. 1). After dural penetration on the left side, a considerable loss of cerebrospinal fluid was observed the amount of which could not be measured precisely. Oral amoxicilline, which we use prophylactically, was started on the implantation day and continued until one day after explantation. Continuous monitoring was performed for 5 days. The FOE were explanted immediately after the end of the monitoring without complications. A few hours after implantation correlating with the diminishing effect of local anaesthesia the patient complained of moderate pain in both cheeks increased by chewing. This side-effect is not unusual [4] and disappeared after a few days. One day after the implantation the patient complained about blurred vision. In a first orientating physical examination we found a palsy of the left N. trochlearis persisting after explantation of the FOE. A neuro-ophthalmological examination confirmed our diagnosis of a palsy of the left N. trochlearis. A computer-tomography immediately afte r explantation and magnetic resonance imaging with additional sequences of the brain stem six days after explantation showed no morphological abnormality. In the course of the following days, the patient reported gradual improvement. Sixty-seven days after explantation of the FOE all pre-existing subjective symptoms were no longer present. The physical examination confirmed normal findings.