Endoscopic third ventriculostomy (ETV) has been accepted for obstructive hydrocephalus (OH). We herein present a case of OH and optic nerve sheath edema (ONSE). Although ETV was successful, ONSE worsened. Discussion is focused on the relationship among intracranial hypertension (IH), ETV, and ONSE. The patient was a 19-year-old woman with complaints of headache and emesis. Papilledema was prominent. Radiological examination showed OH as an aqueductal tumor. Endoscopic tumorectomy and ETV were accomplished. Although headache and emesis disappeared, papilledema persisted. On the 4th day, the patient lost light perception. On magnetic resonance imaging, the third ventricular stroma and aqueduct were patent. Nevertheless, ONSE was prominent. After lumbar drainage, her vision was restored. Finally, ventriculoperitoneal shunting was performed, following which ONSE disappeared. IH is not always accompanied by ONSE. However, once it occurs, it may act separately from IH, and ETV may even exacerbate ONSE due to alteration of cerebrospinal fluid (CSF) flow into the chiasmatic cistern. In the optic nerve sheath, CSF pressure is not easily transmitted across different areas; this should explain the dissociation between ONSE and other symptoms of IH. Furthermore, we suggest that ONSE and acute optic dysfunction should be considered an independent crisis as “hydronervus opticus.”
