Intraoperative overlay of optic radiation tractography during anteromesial temporal resection: a prospective validation study

Abstract

OBJECTIVE Anteromesial temporal lobe resection (ATLR) results in long-term seizure freedom in patients with drug-resistant focal mesial temporal lobe epilepsy (MTLE). There is significant anatomical variation in the anterior projection of the optic radiation (OR), known as Meyer’s loop, between individuals and between hemispheres in the same individual. Damage to the OR results in contralateral superior temporal quadrantanopia that may preclude driving in 33%–66% of patients who achieve seizure freedom. Tractography of the OR has been shown to prevent visual field deficit (VFD) when surgery is performed in an interventional MRI (iMRI) suite. Because access to iMRI is limited at most centers, the authors investigated whether use of a neuronavigation system with a microscope overlay in a conventional theater is sufficient to prevent significant VFD during ATLR. METHODS Twenty patients with drug-resistant MTLE who underwent ATLR (9 underwent right-side ATLR, and 9 were male) were recruited to participate in this single-center prospective cohort study. Tractography of the OR was performed with preoperative 3-T multishell diffusion data that were overlaid onto the surgical field by using a conventional neuronavigation system linked to a surgical microscope. Phantom testing confirmed overlay projection errors of < 1 mm. VFD was quantified preoperatively and 3 to 12 months postoperatively by using Humphrey and Esterman perimetry. RESULTS Perimetry results were available for all patients postoperatively, but for only 11/20 (55%) patients preoperatively. In 1/20 (5%) patients, a significant VFD occurred that would prevent driving in the UK on the basis of the results on Esterman perimetry. The VFD was identified early in the series, despite the surgical approach not transgressing OR tractography, and was subsequently found to be due to retraction injury. Tractography was also used from this point onward to inform retractor placement, and no further significant VFDs occurred. CONCLUSIONS Use of OR tractography with overlay outside of an iMRI suite, with application of an appropriate error margin, can be used during approach to the temporal horn of the lateral ventricle and carries a 5% risk of VFD that is significant enough to preclude driving postoperatively. OR tractography can also be used to inform retractor placement. These results warrant a larger prospective comparative study of the use of OR tractography–guided mesial temporal resection.

Visual outcomes after anterior temporal lobectomy and transsylvian selective amygdalohippocampectomy: A quantitative comparison of clinical and diffusion data

“…Ultimately, it is important to acknowledge that despite transgression of the OpR, other factors such as intraoperative tissue retraction 11 can also influence visual outcomes. These alternative pathomechanisms of visual system damage may provide a tenable explanation for discrepant imaging and perimetry findings.…”

“…OpR tractography, therefore, may help to effectively stratify operation risk. If available, postsurgical VFDs may be further prevented by using intraoperative tractography guidance 11–13 …”

“…If available, postsurgical VFDs may be further prevented by using intraoperative tractography guidance. [11][12][13] Although the importance of diffusion-based imaging techniques to predict postsurgical VFDs is widely accepted, findings derive predominantly from patients who have undergone ATL. However, well-validated parameters for VFD prediction following epilepsy surgery are Vienna 1090, Austria.…”

Advanced neuroimaging techniques in epilepsy

“…In epilepsy surgery, the visualization of the optic radiation with neuronavigation during surgery reduces the risk of causing damage and visual field deficits [21 ▪ ]. The same principles may be applied to other tracts, for example, sustaining motor and language functions, to minimize risk of postoperative deficits.…”

Applications of diffusion tensor imaging integrated with neuronavigation to prevent visual damage during tumor resection in the optic radiation area

“…During tumor resection, the protection of Meyer’s loop remains challenging, which is responsible for patients’ prost-operative visual function and quality of life (QOL) ( 1 ). Notably, tractography of the OpR has been shown to limit surgical damage to visual function during tumor resection involving the OpR area ( 2 ).…”