Visual field defects after radiosurgery for mesial temporal lobe epilepsy.

Area of Science:

• Neurosurgery
• Epilepsy treatment
• Radiosurgery

Background:

• Gamma knife radiosurgery (RS) is a potential alternative to open surgery for mesial temporal lobe epilepsy (MTLE).
• The precise mechanisms and potential morbidities, such as visual field defects (VFDs), associated with RS for MTLE remain unclear.
• VFDs are a known complication of open surgery for MTLE, occurring in 52-100% of patients.

Purpose of the Study:

• To investigate the incidence and characteristics of VFDs following RS for MTLE.
• To explore the relationship between VFDs and treatment parameters, including radiation dose and seizure outcomes.
• To provide insights into the underlying mechanisms of RS in epilepsy treatment.

Main Methods:

• A multicenter prospective trial randomized MTLE patients to low (20 Gy) or high (24 Gy) doses of RS targeting the amygdala, hippocampal head, and parahippocampal gyrus.
• Postoperative perimetry was conducted at 24 months to quantify VFDs using visual field defect ratios (VFDRs).
• Results were analyzed against patient age, RS dose, radiation-induced changes, quality of life, and seizure remission.

Main Results:

• No patients reported subjective visual changes or had abnormal bedside visual field examinations.
• Fifteen out of 24 patients (62.5%) developed postoperative VFDs, specifically homonymous superior quadrantanopsias.
• VFDs correlated significantly with VFDRs, and patients achieving seizure remission had smaller (more severe) VFDRs.

Conclusions:

• VFDs occurred after RS for MTLE at rates comparable to historical data from open surgery.
• The pattern of VFDs suggests injury to the optic radiations, supporting a mechanism involving tissue damage.
• These findings indicate that RS for MTLE may induce localized tissue damage, contributing to its anticonvulsant effects.