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Epilepsy surgery, vision, and driving: what has surgery taught us and could modern imaging reduce the risk of visual deficits?

ABSTRACT: Up to 40% of patients with temporal lobe epilepsy (TLE) are refractory to medication. Surgery is an effective treatment but may cause new neurologic deficits including visual field deficits (VFDs). The ability to drive after surgery is a key goal, but a postoperative VFD precludes driving in 4-50% of patients even if seizure-free. VFDs are a consequence of damage to the most anterior portion of the optic radiation, Meyer's loop. Anatomic dissection reveals that the anterior extent of Meyer's loop is highly variable and may clothe the temporal horn, a key landmark entered during temporal lobe epilepsy surgery. Experience from surgery since the 1940s has shown that VFDs are common (48-100%) and that the degree of resection affects the frequency or severity of the deficit. The pseudowedge shape of the deficit has led to a revised retinotopic model of the organization of the optic radiation. Evidence suggests that the left optic radiation is more anterior and thus at greater risk. Alternative surgical approaches, such as selective amygdalo-hippocampectomy, may reduce this risk, but evidence is conflicting or lacking. The optic radiation can be delineated in vivo using diffusion tensor imaging tractography, which has been shown to be useful in predicting the postoperative VFDs and in surgical planning. These data are now being used for surgical guidance with the aim of reducing the severity of VFDs. Compensation for brain shift occurring during surgery can be performed using intraoperative magnetic resonance imaging (MRI), but the additional utility of this expensive technique remains unproven.

SUBMITTER: Winston GP

PROVIDER: S-EPMC4030586 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Epilepsy surgery, vision, and driving: what has surgery taught us and could modern imaging reduce the risk of visual deficits?

Winston Gavin P GP

Epilepsia 20130920 11

Up to 40% of patients with temporal lobe epilepsy (TLE) are refractory to medication. Surgery is an effective treatment but may cause new neurologic deficits including visual field deficits (VFDs). The ability to drive after surgery is a key goal, but a postoperative VFD precludes driving in 4-50% of patients even if seizure-free. VFDs are a consequence of damage to the most anterior portion of the optic radiation, Meyer's loop. Anatomic dissection reveals that the anterior extent of Meyer's loo ...[more]

PMID: 24199825

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Project description:This article emphasizes the role of the technological progress in changing the landscape of epilepsy surgery and provides a critical appraisal of robotic applications, laser interstitial thermal therapy, intraoperative imaging, wireless recording, new neuromodulation techniques, and high-intensity focused ultrasound. Specifically, (a) it relativizes the current hype in using robots for stereo-electroencephalography (SEEG) to increase the accuracy of depth electrode placement and save operating time; (b) discusses the drawback of laser interstitial thermal therapy (LITT) when it comes to the need for adequate histopathologic specimen and the fact that the concept of stereotactic disconnection is not new; (c) addresses the ratio between the benefits and expenditure of using intraoperative magnetic resonance imaging (MRI), that is, the high technical and personnel expertise needed that might restrict its use to centers with a high case load, including those unrelated to epilepsy; (d) soberly reviews the advantages, disadvantages, and future potentials of neuromodulation techniques with special emphasis on the differences between closed and open-loop systems; and (e) provides a critical outlook on the clinical implications of focused ultrasound, wireless recording, and multipurpose electrodes that are already on the horizon. This outlook shows that although current ultrasonic systems do have some limitations in delivering the acoustic energy, further advance of this technique may lead to novel treatment paradigms. Furthermore, it highlights that new data streams from multipurpose electrodes and wireless transmission of intracranial recordings will become available soon once some critical developments will be achieved such as electrode fidelity, data processing and storage, heat conduction as well as rechargeable technology. A better understanding of modern epilepsy surgery will help to demystify epilepsy surgery for the patients and the treating physicians and thereby reduce the surgical treatment gap.

Project description:OBJECTIVEThis study is aimed at improving the clinical utility of diffusion-weighted imaging maximum a posteriori probability (DWI-MAP) analysis, which has been reported to be useful for predicting postoperative motor, language, and visual field deficits in pediatric epilepsy surgery. The authors determined the additive value of a new clustering mapping method in which average direct-flip distance (ADFD) reclassifies the outliers of original DWI-MAP streamlines by referring to their minimum distances to the exemplar streamlines (i.e., medoids).METHODSThe authors studied 40 children with drug-resistant focal epilepsy (mean age 8.7 ± 4.8 years) who had undergone resection of the presumed epileptogenic zone and had five categories of postoperative deficits (i.e., hemiparesis involving the face, hand, and/or leg; dysphasia requiring speech therapy; and/or visual field cut). In pre- and postoperative images of the resected hemisphere, DWI-MAP identified a total of nine streamline pathways: C1 = face motor area, C2 = hand motor area, C3 = leg motor area, C4 = Broca's area-Wernicke's area, C5 = premotor area-Broca's area, C6 = premotor area-Wernicke's area, C7 = parietal area-Wernicke's area, C8 = premotor area-parietal area, and C9 = occipital lobe-lateral geniculate nucleus. For each streamline of the identified pathway, the minimal ADFD to the nine exemplars corrected the pathway membership. Binary logistic regression analysis was employed to determine how accurately two fractional predictors, Δ1-9 (postoperative volume change of C1-9) and γ1-9 (preoperatively planned volume of C1-9 resected), predicted postoperative motor, language, and visual deficits.RESULTSThe addition of ADFD to DWI-MAP analysis improved the sensitivity and specificity of regression models for predicting postoperative motor, language, and visual deficits by 28% for Δ1-3 (from 0.62 to 0.79), 13% for Δ4-8 (from 0.69 to 0.78), 13% for Δ9 (from 0.77 to 0.87), 7% for γ1-3 (from 0.81 to 0.87), 1% for γ4-8 (from 0.86 to 0.87), and 24% for γ9 (from 0.75 to 0.93). Preservation of the eloquent pathways defined by preoperative DWI-MAP analysis with ADFD (up to 97% of C1-4,9) prevented postoperative motor, language, and visual deficits with sensitivity and specificity ranging from 88% to 100%.CONCLUSIONSThe present study suggests that postoperative functional outcome substantially differs according to the extent of resected white matter encompassing eloquent cortex as determined by preoperative DWI-MAP analysis. The preservation of preoperative DWI-MAP-defined pathways may be crucial to prevent postoperative deficits. The improved DWI-MAP analysis may provide a complementary noninvasive tool capable of guiding the surgical margin to minimize the risk of postoperative deficits for children.

Project description:BackgroundLaser interstitial thermal therapy (LITT) has recently gained popularity as a minimally invasive surgical option for the treatment of mesiotemporal epilepsy (mTLE). Similar to traditional open procedures for epilepsy, the most frequent neurological complications of LITT are visual deficits; however, a critical analysis of these injuries is lacking.ObjectivesTo evaluate the visual deficits that occur after LITT for mTLE and their etiology.MethodWe surveyed five academic epilepsy centers that regularly perform LITT for cases of self-reported postoperative visual deficits. For these patients all pre-, intra- and postoperative MRIs were co-registered with an anatomic atlas derived from 7T MRI data. This was used to estimate thermal injury to early visual pathways and measure imaging variables relevant to the LITT procedure. Using logistic regression, we then compared 14 variables derived from demographics, mesiotemporal anatomy, and the surgical procedure for the patients with visual deficits to a normal cohort comprised of the first 30 patients to undergo this procedure at a single institution.ResultsOf 90 patients that underwent LITT for mTLE, 6 (6.7%) reported a postoperative visual deficit. These included 2 homonymous hemianopsias (HHs), 2 quadrantanopsias, and 2 cranial nerve (CN) IV palsies. These deficits localized to the posterior aspect of the ablation, corresponding to the hippocampal body and tail, and tended to have greater laser energy delivered in that region than the normal cohort. The patients with HH had insult localized to the lateral geniculate nucleus, which was -associated with young age and low choroidal fissure CSF volume. Quadrantanopsia, likely from injury to the optic radiation in Meyer's loop, was correlated with a lateral trajectory and excessive energy delivered at the tail end of the ablation. Patients with CN IV injury had extension of contrast to the tentorial edge associated with a mesial laser trajectory.ConclusionsLITT for epilepsy may be complicated by various classes of visual deficit, each with distinct etiology and clinical significance. It is our hope that by better understanding these injuries and their mechanisms we can eventually reduce their occurrence by identifying at-risk patients and trajectories and appropriately tailoring the ablation procedure.

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Epilepsy surgery, vision, and driving: what has surgery taught us and could modern imaging reduce the risk of visual deficits?

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Epilepsy surgery, vision, and driving: what has surgery taught us and could modern imaging reduce the risk of visual deficits?

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