Neurophysiological intraoperative monitoring during an optic nerve schwannoma removal

This paper reports the case of a patient with optic nerve schwannoma and the first use of neurophysiological intraoperative monitoring of visual evoked potentials during the removal of such tumor with no postoperative visual damage. Schwannomas are benign neoplasms of the peripheral nervous system arising from the neural crest-derived Schwann cells, these tumors are rarely located in the optic nerve and the treatment consists on surgical removal leading to high risk of damage to the visual pathway. Case report of a thirty-year-old woman with an optic nerve schwannoma. The patient underwent surgery for tumor removal on the left optic nerve through a left orbitozygomatic approach with intraoperative monitoring of left II and III cranial nerves. We used Nicolet Endeavour CR IOM (Carefusion, Middleton WI, USA) to performed visual evoked potentials stimulating binocularly with LED flash goggles with the patient´s eyes closed and direct epidural optic nerve stimulation delivering rostral to the tumor a rectangular current pulse. At follow up examinations 7 months later, the left eye visual acuity was 20/60; Ishihara score was 8/8 in both eyes; the right eye photomotor reflex was normal and left eye was mydriatic and arreflectic; optokinetic reflex and ocular conjugate movements were normal. In this case, the epidural direct electrical stimulation of optic nerve provided stable waveforms during optic nerve schwannoma resection without visual loss.