gms | German Medical Science

Objective: Visual field defects (VFDs) due to optic radiation (OR) injury are a common complication of temporal lobe surgery. The authors analyzed whether preoperative visualization of the optic tract will be able to reduce this complication by influencing the surgeon’s decision making about surgical approaches. Secondly, it was assessed, whether white matter shifts caused by temporal lobe tumors follow predetermined patters based on the tumor’s respective topography.

Method: 68 patients with intraaxial tumors of the temporal lobe received pre- and postoperative DTI-fibertracking (FT). In 37 of those pre- and postoperative visual field defects were documented by Goldmann perimetry. Brain Lab’s iPlan 2,5 navigation software was used for tumor reconstruction and fiber visualization after fusion of the respective DTIs with their MPRAGEs. The tracking algorithm used was: minimum fiber length: 50 mm; fractional anisotropy threshold: 0.15. The lateral geniculate body and the calcarine cortex were employed as tract seeding points. Shifts of the optic radiation caused by the tumor were visualized by comparison to the FTs of the respective patient’s healthy hemisphere.

Results: The shift of white matter tracts always followed fixed patterns dependent on tumor location: Temporomesial tumors → lateral and superior shift → transsylvian/trans-cisternal approach recommended; temporo-lateral tumors → medial shift → lateral transcortical approach recommended; temporo-polar tumors → posterior shift, always including Meyer’s loop → pterional transcortical approach recommended; temporocentric/-intrinsic tumors → lateral and inferior shift → transsylvian/trans-opercular approach recommended; tumors of the fusiform gyrus → superior (and medial) shift → subtemporal approach recommended. Using the approaches, recommended above, new or worsened VFDs occurred in 4% of the patient cohort. Total neurological and surgical morbidity were 10% respectively. In 88% a gross total resection was accomplished.

Conclusions: Pre-operative visualization of the OR may help in avoiding post-operative VFDs. In general, subtemporal and lateral transcortical approaches to mesial and intrinsic tumors bear the greatest risk of injury to the OR.