Improvement of Isolated Abducens Nerve Palsy with Hydrocephalus after CSF Diversion: A Possible Evaluative Role of Retroclival-pontomedullary Distance.

Isolated abducens nerve palsy (IANP), caused by secondary communicating hydrocephalus, has been rarely documented; in addition, its mechanism and appropriate treatment are not understood well. This study presents a case of bilateral IANP with hydrocephalus in a 62-year-old man who was successfully treated with cerebrospinal fluid (CSF) diversion to correct an enlarged retroclival space during the follow-up of recurrent brain tumor in the right parieto-occipital lobe. The patient was treated with three resections, temozolomide, and irradiation before developing IANP. Magnetic resonance imaging (MRI) revealed a recurrent tumor and ventriculomegaly with an expanded retroclival cisternal space. The patient underwent subtotal tumor resection and external ventricular drain placement in the anterior horn of the lateral ventricle. His bilateral IANP persisted for 4 days after surgery but gradually improved and disappeared by Day 7. Four weeks later, the patient underwent ventriculoperitoneal (VP) shunt surgery to establish a permanent CSF diversion that continued to control the symptoms. Retrospective MRI review revealed the distance between the clivus and pontomedullary junction on the sagittal section (retroclival-pontomedullary distance; RPD) of 9.0, 12.8, 10.7, and 10.6 mm before IANP, on IANP onset, on postoperative Day 4, and post VP shunt surgery, respectively. In conclusion, VP shunt surgery was an appropriate approach for IANP with communicating hydrocephalus to correct the enlarged retroclival cisternal space. RPD thus may be used as one of possible evaluation methods for IANP with hydrocephalus, which can be caused by various factors.