Visual field deficits following laser ablation of the hippocampus.

OBJECTIVE

To qualify the incidence of and risk factors for visual field deficits (VFD) following laser interstitial thermal ablation (LITT) for mesial temporal lobe epilepsy (MTLE) and to relate this to anterior temporal lobectomy (ATL).

METHODS

Fifty-seven patients underwent LITT of the amygdalo-hippocampal complex (AH) for MTLE. Masks of ablation volumes, laser probe trajectories, and visual radiations (VRs) from individual subject space were transformed into standardized space using nonlinear registration. Voxel-wise statistics were performed to model relationships between VFDs vs ablation volumes, laser trajectories, VRs, and AH asymmetry. A review of VFDs following ATLs was performed.

RESULTS

The incidence of VFD after LITT is much lower than after ATLs. A total of 37.5% of patients developed a VFD, with the probability of this being much higher after left (50%) vs right hemisphere LITT (10%) (Fisher test, = 0.05). This laterality effect on VFDs is mirrored but underappreciated in ATL series. The most consistent LITT-VFD occurred in the superior vertical octant. Ablation of Meyer loop as well as the summed probability of VRs within laser trajectories correlated with VFDs ( < 0.05). Left and right hippocampi have significantly distinct orientations in axial and coronal planes, which may be one reason for the variation in VFD probability.

CONCLUSIONS

LITT results in lower rates of and smaller VFDs-typically an octantanopsia. VRs are at greater risk during surgery for left than right MTLE. Anatomical asymmetries in hippocampal anatomy may explain the hemispheric differences in deficits, and should factor into trajectory planning and also into preoperative patient counseling. Overall the incidence and extent of visual deficits following LITT for MTLE is lower than the reported data following anterior temporal lobectomy. VF tractography incorporated into LITT planning may reduce the occurrence of VFDs.