Visual field defects after temporal lobectomy -- comparing methods and analysing resection size

Hypometabolism in the Posteromedial Temporal and Medial Occipital Cortex on Preoperative 2-Deoxy-2-(18F) Fluoro-D-Glucose Positron Emission Tomography Suggests Exacerbation of Visual Field Defects After Surgery for Temporal Lobe Epilepsy: A Retrospective Long-Term Follow-Up Study

OBJECTIVE

Surgery is a good treatment option for drug-resistant temporal lobe epilepsy (TLE). 2-deoxy-2-(18F) fluoro-D-glucose (FDG) positron emission tomography (PET) is used to detect epileptic foci as hypometabolic lesions in presurgical evaluation. Visual field defects (VFDs) in the contralateral homonymous upper quadrant are common postoperative complications in TLE. This study aimed to quantify VFDs using pattern deviation probability plots (PDPPs) and examine the effect of hypometabolism in FDG-PET on VFDs.

METHODS

This study included 40 patients. Both visual fields were assessed using the Humphrey field analyzer preoperatively and 3 months and 2 years postoperatively. PDPPs with <0.5% confidence level counted in the contralateral homonymous upper quadrant. FDG-PET results were compared between groups with (15 patients) and without (24 patients) hypometabolism in the optic radiation.

RESULTS

All 40 patients were evaluated by Humphrey field analyzer at 3 months postoperatively and 39 at 2 years postoperatively. The incidence of VFDs 3 months postoperatively was 35/40 (87.5%), and 17/40 (42.5%) patients had severe VFDs. In cases of surgery on the left temporal lobe, ipsilateral eyes appeared to be more significantly affected than contralateral eyes. VFDs were more severe in patients with FDG hypometabolism than in those without hypometabolism in posteromedial temporal and medial occipital cortex (P < 0.01); however, 85% of patients with FDG hypometabolism had a reduced VFD 2 years postoperatively.

CONCLUSIONS

PDPP counting is useful for quantifying VFDs. Preoperative dysfunction indicated by preoperative FDG-PET in the posteromedial temporal and medial occipital cortex could enhance VFDs early after TLE surgery.

Diffusion spectrum imaging based semi-automatic optic radiation tractography for vision preservation in SEEG-guided radiofrequency thermocoagulation

OBJECTIVE

To assess the efficacy and safety of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC), using diffusion spectrum imaging (DSI) tractography to preoperatively delineate the optic radiation (OR) and reduce the risk of visual field defects (VFDs) where the epileptogenic zones (EZs) are located in or close to the eloquent visual areas.

METHODS

We prospectively followed up twenty-four consecutive patients (12 males and 12 females) who underwent SEEG-guided RFTC in or near the OR pathway. A distance of ≥ 3.5 mm away from the OR on the targeted electrodes contacts that exhibited relevant ictal onset patterns, IEDs and EES during SEEG recordings, was required as our selection criterion prior to performing RFTC, enough to theoretically prevent VFDs. Using default tracking parameters, the optic radiation was tracked semi-automatically in DSI-studio.

RESULTS

There were 12 male and 12 female patients ranging in age from 6 to 57 years, with follow-up period ranging from 6 to 37 months. Nineteen patients responded to RFTC (R+, 79.16 %), and 5 patients did not benefit from RFTC (R-, 20.83 %). The preoperative application of DSI semi-automatic based OR tractography was successful in the protection of the OR in all 24 patients. Three patients experienced a neurologic deficit following RFTC, and five patients had a partial quadrant visual field deficit prior to surgery that did not worsen, and none of the remaining nineteen patients had a quadrant visual field deficit.

CONCLUSION

Our study validates the safety and efficacy of SEEG-RFTC as a viable therapeutic approach for epileptic foci situated in or adjacent to the visual eloquent regions. We demonstrate that DSI-based tractography offers superior precision in delineating the OR compared to DTI. We establish that implementing a criterion of a minimum distance of ≥ 3.5 mm in radius from the OR on the targeted electrode contacts prior to conducting RFTC can effectively mitigate the risk of VFDs.

Surgery procedures in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common cause of refractory epilepsy amenable for surgical treatment and seizure control. Surgery for TLE is a safe and effective strategy. The seizure-free rate after surgical resection in patients with mesial or neocortical TLE is about 70%. Resective surgery has an advantage over stereotactic radiosurgery in terms of seizure outcomes for mesial TLE patients. Both techniques have similar results for safety, cognitive outcomes, and associated costs. Stereotactic radiosurgery should therefore be seen as an alternative to open surgery for patients with contraindications for or with reluctance to undergo open surgery. Laser interstitial thermal therapy (LITT) has also shown promising results as a curative technique in mesial TLE but needs to be more deeply evaluated. Brain-responsive stimulation represents a palliative treatment option for patients with unilateral or bilateral MTLE who are not candidates for temporal lobectomy or who have failed a prior mesial temporal lobe resection. Overall, despite the expansion of innovative techniques in recent years, resective surgery remains the reference treatment for TLE and should be proposed as the first-line surgical modality. In the future, ultrasound therapies could become a credible therapeutic option for refractory TLE patients.

Postoperative outcomes and surgical ratio at a newly established epilepsy center: The first 100 procedures

PURPOSE

To describe the patients' characteristics, surgical ratio, and outcomes following epilepsy surgery at the newly established Epilepsy Center Frankfurt Rhine-Main.

METHODS

We retrospectively studied the first 100 consecutive patients, including adult (n = 77) and pediatric (n = 23) patients, with drug-resistant epilepsy who underwent resective or ablative surgical procedures at a single, newly established epilepsy center. Patient characteristics, seizure and neuropsychological outcomes, histopathology, complications, and surgical ratio were analyzed.

RESULTS

The mean patient age was 28.8 years (children 10.6 years, adults 34.2 years). The mean epilepsy duration was 11.9 years (children 3.9 years, adults 14.3 years), and the mean follow-up was 1.5 years. At the most recent visit, 64% of patients remained completely seizure free [Engel IA]. The rates of perioperative complications and unexpected new neurological deficits were 5%, each. The proportion of patients showing deficits in one or more cognitive domains increased six months after surgery and decreased to presurgical proportions after two years. Symptoms of depression were significantly decreased and quality of life was significantly increased after surgery. The surgical ratio was 25.3%.

CONCLUSION

Similar postsurgical outcomes were achieved at a newly established epilepsy center compared with long-standing epilepsy centers. The lower time to surgery may reflect a general decrease in time to surgery over the last decade or the improved accessibility of a new epilepsy center in a previously underserved area. The surgical ratio was not lower than reported for established centers.

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, p = 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 (p < 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.

Optic Radiation Tractography in Pediatric Brain Surgery Applications: A Reliability and Agreement Assessment of the Tractography Method

Background

Optic radiation (OR) tractography may help predict and reduce post-neurosurgical visual field deficits. OR tractography methods currently lack pediatric and surgical focus.

Purpose

We propose a clinically feasible OR tractography strategy in a pediatric neurosurgery setting and examine its intra-rater and inter-rater reliability/agreements.

Methods

Preoperative and intraoperative MRI data were obtained from six epilepsy and two brain tumor patients on 3 Tesla MRI scanners. Four raters with different clinical experience followed the proposed strategy to perform probabilistic OR tractography with manually drawing anatomical landmarks to reconstruct the OR pathway, based on fiber orientation distributions estimated from high angular resolution diffusion imaging data. Intra- and inter-rater reliabilities/agreements of tractography results were assessed using intraclass correlation coefficient (ICC) and dice similarity coefficient (DSC) across various tractography and OR morphological metrics, including the lateral geniculate body positions, tract volumes, and Meyer's loop position from temporal anatomical landmarks.

Results

Good to excellent intra- and inter-rater reproducibility was demonstrated for the majority of OR reconstructions (ICC = 0.70-0.99; DSC = 0.84-0.89). ICC was higher for non-lesional (0.82-0.99) than lesional OR (0.70-0.99). The non-lesional OR's mean volume was 22.66 cm³; the mean Meyer's loop position was 29.4 mm from the temporal pole, 5.89 mm behind of and 10.26 mm in front of the temporal ventricular horn. The greatest variations (± 1.00-3.00 mm) were observed near pathology, at the tract edges or at cortical endpoints. The OR tractography were used to assist surgical planning and guide lesion resection in all cases, no patient had new visual field deficits postoperatively.

Conclusion

The proposed tractography strategy generates reliable and reproducible OR tractography images that can be reliably implemented in the routine, non-emergency pediatric neurosurgical setting.

Predicting verbal memory decline following temporal lobe resection for epilepsy

OBJECTIVES

The aim of the study was to develop a prediction model for verbal memory decline after temporal lobe resection (TLR) for epilepsy. The model will be used in the preoperative counselling of patients to give individualized information about risk for verbal memory decline.

MATERIALS AND METHODS

A sample of 110 consecutive patients who underwent TLR for epilepsy at Sahlgrenska University Hospital between 1987 and 2011 constituted the basis for the prediction model. They had all gone through a formal neuropsychological assessment before surgery and 2 years after. Penalized regression and 20 × 10-fold cross-validation were used in order to build a reliable model for predicting individual risks.

RESULTS

The final model included four predictors: side of surgery; inclusion or not of the hippocampus in the resection; preoperative verbal memory function; and presence/absence of focal to bilateral tonic-clonic seizures (TCS) the last year prior to the presurgical investigation. The impact of a history of TCS is a new finding which we interpret as a sign of a more widespread network disease which influences neuropsychological function and the cognitive reserve. The model correctly identified 82% of patients with post-operative decline in verbal memory, and the overall accuracy was 70%-85% depending on choice of risk thresholds.

CONCLUSIONS

The model makes it possible to provide patients with individualized prediction regarding the risk of verbal memory decline following TLR. This will help them make more informed decisions regarding treatment, and it will also enable the epilepsy surgery team to prepare them better for the rehabilitation process.

Mechanisms and Risk Factors Contributing to Visual Field Deficits following Stereotactic Laser Amygdalohippocampotomy

Selective laser amygdalohippocampotomy (SLAH) is a minimally invasive surgical treatment for medial temporal lobe epilepsy. Visual field deficits (VFDs) are a significant potential complication. The objective of this study was to determine the relationship between VFDs and potential mechanisms of injury to the optic radiations and lateral geniculate nucleus. We performed a retrospective cross-sectional analysis of 3 patients (5.2%) who developed persistent VFDs after SLAH within our larger series (n = 58), 15 healthy individuals and 10 SLAH patients without visual complications. Diffusion tractography was used to evaluate laser catheter penetration of the optic radiations. Using a complementary approach, we evaluated evidence for focal microstructural tissue damage within the optic radiations and lateral geniculate nucleus. Overablation and potential heat radiation were assessed by quantifying ablation and choroidal fissure CSF volumes as well as energy deposited during SLAH.SLAH treatment parameters did not distinguish VFD patients. Atypically high overlap between the laser catheter and optic radiations was found in 1/3 VFD patients and was accompanied by focal reductions in fractional anisotropy where the catheter entered the lateral occipital white matter. Surprisingly, lateral geniculate tissue diffusivity was abnormal following, but also preceding, SLAH in patients who subsequently developed a VFD (all p = 0.005).In our series, vision-related complications following SLAH, which appear to occur less frequently than following open temporal lobe -surgery, were not directly explained by SLAH treatment parameters. Instead, our data suggest that variations in lateral geniculate structure may influence susceptibility to indirect heat injury from transoccipital SLAH.

[Visual field disorder after surgery of temporal lobe epilepsy associated to hippocampus sclerosis]

OBJECTIVE

Assessment of frequency and severity of visual field disorders after neurosurgical operations at patients with pharmacoresistant form of epilepsy in hippocampus sclerosis.

MATERIAL AND METHODS

The study included 48 patients having surgical operations for a pharmacoresistant form of temporal lobe epilepsy due to hippocampus sclerosis. Anterior lobectomy with amygdalohippocampectomy (LE + AHE) was performed in 25 patients; Selective amygdalohippocampectomy (SAHE) was performed in 23 patients. We evaluated both the frequency of cases of homonymous visual field disorders and their severity.

RESULTS

After surgery the normal visual field was preserved at 7 (14.6%) patients. The appearance of visual field disorder by the type of homonymous hemianopsia was observed at 41 (85.4%) patients. When assessing the severity of visual field disorder, the smallest disorder was at patients who underwent sub-temporal access of SAHE: a statistically significant difference in the frequency of severe visual field disorder was revealed when comparing this group with patients having LE + AHE (p<0.02), as well as with patients having SAHE with access through sylvian gap (p<0.02).

CONCLUSION

SAHE with sub-temporal access allows maintaining or minimally injuring the central optic neuron fibers, including the Meyer loop at patients operated for symptomatic temporal lobe epilepsy.

Visual field defects after radiosurgery versus temporal lobectomy for mesial temporal lobe epilepsy: Findings of the ROSE trial

PURPOSE

Stereotactic radiosurgery (SRS) may be an alternative to anterior temporal lobectomy (ATL) for mesial temporal lobe epilepsy (MTLE). Visual field defects (VFD) occur in 9-100% of patients following open surgery for MTLE. Postoperative VFD after minimally invasive versus open surgery may differ.

METHODS

This prospective trial randomized patients with unilateral hippocampal sclerosis and concordant video-EEG findings to SRS versus ATL. Humphries perimetry was obtained at 24 m after surgery. VFD ratios (VFDR = proportion of missing homonymous hemifield with 0 = no VFD, 0.5 = complete superior quadrantanopsia) quantified VFD. Regressions of VFDR were evaluated against treatment arm and covariates. MRI evaluated effects of volume changes on VFDR. The relationships of VFDR with seizure remission and driving status 3 years after surgery were evaluated.

RESULTS

No patients reported visual changes or had abnormal bedside examinations, but 49 of 54 (91%) of patients experienced VFD on formal perimetry. Neither incidence nor severity of VFDR differed significantly by treatment arm. VFDR severity was not associated with seizure remission or driving status.

CONCLUSION

The nature of VFD was consistent with lesions of the optic radiations. Effective surgery (defined by seizure remission) of the mesial temporal lobe results in about a 90% incidence of typical VFD regardless of method.

Relation of Structural and Functional Changes in Auditory and Visual Pathways after Temporal Lobe Epilepsy Surgery

Auditory and visual pathways may be affected as a consequence of temporal lobe epilepsy surgery because of their anatomical relationships with this structure. The purpose of this paper is to correlate the results of the auditory and visual evoked responses with the parameters of tractography of the visual pathway, and with the state of connectivity between respective thalamic nuclei and primary cortices in both systems after the surgical resection of the epileptogenic zone in drug-resistant epileptic patients. Tractography of visual pathway and anatomical connectivity of auditory and visual thalamus-cortical radiations were evaluated in a sample of eight patients. In general, there was a positive relationship of middle latency response (MLR) latency and length of resection, while a negative correlation was found between MLR latency and the anatomical connection strength and anatomical connection probability of the auditory radiations. In the visual pathway, significant differences between sides were found with respect to the number and length of tracts, which was lower in the operated one. Anatomical connectivity variables and perimetry (visual field defect index) were particularly correlated with the latency of P100 wave which was obtained by quadrant stimulation. These results demonstrate an indirect functional modification of the auditory pathway and a direct traumatic lesion of the visual pathway after anterior temporal lobectomy in patients with drug resistant epilepsy.

Visual field deficits after epilepsy surgery: a new quantitative scoring method

Background

Anterior temporal lobectomy (ATL) as a treatment for drug-resistant temporal lobe epilepsy (TLE) frequently causes visual field deficits (VFDs). Reported VFD encompasses homonymous contralateral upper quadrantanopia. Its reported incidence ranges from 15 to 90%. To date, a quantitative method to evaluate postoperative VFD in static perimetry is not available. A method to quantify postoperative VFD, which allows for comparison between groups of patients, was developed.

Methods

Fifty-five patients with drug-resistant TLE, who underwent ATL with pre- and postoperative perimetry, were included. Temporal lobe resection length was measured on postoperative MRI. Percentage VFD was calculated for the total visual field, contralateral upper quadrant, or other three quadrants combined.

Results

Patients were divided into groups by resection size (< 45 and ≥ 45 mm) and side of surgery (right and left). We found significant higher VFD in the ≥ 45 vs. < 45 mm group (2.3 ± 4.4 vs. 0.7 ± 2.4%,p = 0.04) for right-sided ATL. Comparing VFD in both eyes, we found more VFD in the right vs. left eye following left-sided ATL (14.5 ± 9.8 vs. 12.9 ± 8.3%, p = 0.03). We also demonstrated significantly more VFD in the < 45 mm group for left- vs. right-sided surgery (6.7 ± 6.7 vs. 13.1 ± 7.0%, p = 0.016). A significant quantitative correlation between VFD and resection size for right-sided ATL was shown (r = 0.52, p < 0.01).

Conclusions

We developed a new quantitative scoring method for the assessment of postoperative visual field deficits after temporal lobe epilepsy surgery and assessed its feasibility for clinical use. A significant correlation between VFD and resection size for right-sided ATL was confirmed.

Parahippocampectomy as a New Surgical Approach to Mesial Temporal Lobe Epilepsy Caused By Hippocampal Sclerosis: A Pilot Randomized Comparative Clinical Trial

BACKGROUND AND OBJECTIVE

The parahippocampal gyrus plays an important role in the epileptogenic pathways of mesial temporal lobe epilepsy caused by hippocampal sclerosis (mTLE-HS); its resection could prevent epileptic seizures with fewer complications. This study evaluates the initial efficacy and safety of anterior temporal lobectomy (ATL), selective amygdalohipppocampectomy (SAH), and parahippocampectomy (PHC) surgical approaches in mTLE-HS.

METHODS

A randomized comparative pilot clinical trial (2008-2011) was performed that included patients with mTLE-HS who underwent ATL, trans-T3 SAH, and trans-T3 PHC. Their sociodemographic characteristics, visual field profiles, verbal and visual memory profiles, and Engel scale outcome at baseline and at 1 and 5 years are described, using descriptive statistics along with parametric and nonparametric tests.

RESULTS

Forty-three patients with a mean age of 35.2 years (18-56 years), 65% female, were analyzed: 14 underwent PHC, 14 ATL, and 15 SAH. The following percentages refer to those patients who were seizure free (Engel class IA) at 1-year and 5-year follow-up, respectively: 42.9% PHC, 71.4% ATL, and 60% SAH (P = 0.304); 28.6% PHC, 50% ATL, and 53.3% SAH (P = 0.353). Postoperative visual field deficits were 0% PHC, 85.7% ATL, and 46.7% SAH (P = 0.001). Verbal and/or visual memory worsening were present in 21.3% PHC, 42.8% ATL, and 33.4% SAH (P = 0.488) and preoperative and postoperative visual memory scores were significantly different in the SAH group only (P = 0.046).

CONCLUSIONS

PHC, ALT, and SAH show a preliminary similar efficacy in short-term seizure-free rates in patients with mTLE-HS. However, PHC efficacy in the long-term decreases compared with the other surgical techniques. PHC does not produce postoperative visual field deficits.

Visual field defects following different resective procedures for mesiotemporal lobe epilepsy

INTRODUCTION

One of the most common side effects of mesiotemporal lobe resection in patients with medically intractable epilepsy are visual field defects (VFD). While peripheral defects usually remain unnoticed by patients, extended VFD influence daily life activities and can, in particular, affect driving regulations. This study had been designed to evaluate frequency and extent of VFD following different surgical approaches to the mesiotemporal area with respect to the ability to drive.

MATERIALS AND METHODS

This study comprises a consecutive series of 366 patients operated at the Epilepsy Center in Freiburg for intractable mesiotemporal lobe epilepsy from 1998 to 2016. The following procedures were performed: standard anterior temporal lobectomy (ATL: n=134; 37%), anterior temporal or keyhole resection (KH: n=53; 15%), and selective amygdalohippocampectomy via the transsylvian (tsAHE: n=145; 40%) and the subtemporal (ssAHE: n=34; 9%) approach. Frequency and extent of postoperative VFD were evaluated in relation to different surgical procedures. According to the German driving guidelines, postoperative VFD were classified as driving-relevant VFD with the involvement of absolute, homonymous central scotoma within 20° and driving-irrelevant VFD with either none or exclusively minor VFD sparing the center.

RESULTS

Postoperative visual field examinations were available in 276 of 366 cases. Postoperative VFD were observed in 202 of 276 patients (73%) and were found to be driving-relevant in 133 of 276 patients (48%), whereas 69 patients (25%) showed VFD irrelevant for driving. Visual field defects were significantly less likely following ssAHE compared with other temporal resections, and if present, they were less frequently driving-relevant (p<0.05), irrespective of the side of surgery.

CONCLUSION

Subtemporal sAHE (ssAHE) caused significantly less frequently and less severely driving-relevant VFD compared with all other approaches to the temporal lobe, irrespective of the side of surgery.

Somatic complications of epilepsy surgery over 25 years at a single center

INTRODUCTION

Epilepsy surgery is an effective treatment for refractory focal epilepsy. Risks of surgery need to be considered when advising individuals of treatment options. We describe the frequency and nature of physical adverse events associated with epilepsy surgery in a single center.

MATERIAL AND METHODS

We reviewed the prospectively maintained records of adults who underwent epilepsy surgery at our center between 1990 and 2014 to identify peri/postsurgical adverse events. These were categorized into neurological deficits and those related to surgery (e.g. wound infections). Neurological deficits were categorized as expected or unexpected and into transient (≤3 months) or persistent (>3 months), RESULTS: There were 911 procedures with no peri-operative deaths. Persistent neurological adverse events were seen following 157 (17.2%) procedures. The most common persistent expected complication was quadrantanopia after temporal lobe resections (72/764, 9.4%). Unexpected persistent neurological complications occurred in 20 procedures (2.2%) and included: quadrantanopia (6, 0.7%); hemianopia (2, 0.2%); hemi/mono-paresis/sensory loss (9, 1%); dysphasia (10, 1%); frontalis muscle weakness (2, 0.2%); and oculomotor weakness (1, 0.1%). 106 surgery related adverse events occurred in 83 procedures, with severe infections requiring bone-flap removal in 24 (2.6%) procedures and intracranial infections in 8 (0.9%). The risk of post-resective severe infection increased by 4 fold (OR 4.32, 95% CI 2.1-8.9, p<0.001) with use of subdural EEG monitoring prior to resection. In consequence, in August 2011 we introduced antibiotic coverage in all individuals undergoing intracranial monitoring. Also, after August 2011 there was greater use of Stereo-EEG (SEEG) than subdural (OR 9.0 CI 0.36-224.2, p=0.18ns). One complicated by severe infection. Other surgical complications included haematoma (0.3%), hydrocephalus (0.3%) and CSF leak (1.2%). None had permanent complications.

CONCLUSIONS

Adverse event rates are similar to other series. Epilepsy surgery carries well defined surgical and neurological risks. The risks of somatic adverse events, in addition to neuropsychiatric and neuropsychological complications need to be made clear to individuals considering this treatment option.

Factors predicting the outcome following surgical treatment of mesial temporal epilepsy due to mesial temporal sclerosis

BACKGROUND

Mesial temporal sclerosis (MTS) is the most common disease found in an epilepsy surgery series. Early age of onset, a history of febrile convulsions, epileptiform discharges on EEG, duration of epilepsy, number of generalized seizures and severity of psychiatric disorders are possible prognostic factors in patients with MTS.

OBJECTIVE

The aim of this study is to review the clinical, semiotic, psychological, electrophysiological and neuroradiological researches and relate their findings to the prognosis of patients with MTS who underwent anteromedial temporal lobectomy (ATL).

METHODS

Of 1,214 patients evaluated for surgery in the epilepsy Center of Faculdade de Medicina de São Jose do Rio Preto (FAMERP), a tertiary Brazilian epilepsy center, 400 underwent ATL for MTS. Examinations and clinical data were analyzed and compared with the Engel Outcome Classification.

RESULTS

Of all the items analyzed, the MRI showed the greatest influence on patient outcome. As for the clinical evaluation and pathological antecedents, age at surgery, epilepsy duration, perinatal insults, family history of epilepsy, febrile seizures, neuropsychological abnormalities and presence of generalized tonic-clonic seizure all had statistical significance.

CONCLUSION

In order to identify the most appropriate candidates for ATL, it is very important to consider the prognostic factors associated with a favorable outcome for counseling patients in daily practice.

The white matter tracts of the cerebrum in ventricular surgery and hydrocephalus

OBJECTIVE The relationship of the white matter tracts to the lateral ventricles is important when planning surgical approaches to the ventricles and in understanding the symptoms of hydrocephalus. The authors' aim was to explore the relationship of the white matter tracts of the cerebrum to the lateral ventricles using fiber dissection technique and MR tractography and to discuss these findings in relation to approaches to ventricular lesions. METHODS Forty adult human formalin-fixed cadaveric hemispheres (20 brains) and 3 whole heads were examined using fiber dissection technique. The dissections were performed from lateral to medial, medial to lateral, superior to inferior, and inferior to superior. MR tractography showing the lateral ventricles aided in the understanding of the 3D relationships of the white matter tracts with the lateral ventricles. RESULTS The relationship between the lateral ventricles and the superior longitudinal I, II, and III, arcuate, vertical occipital, middle longitudinal, inferior longitudinal, inferior frontooccipital, uncinate, sledge runner, and lingular amygdaloidal fasciculi; and the anterior commissure fibers, optic radiations, internal capsule, corona radiata, thalamic radiations, cingulum, corpus callosum, fornix, caudate nucleus, thalamus, stria terminalis, and stria medullaris thalami were defined anatomically and radiologically. These fibers and structures have a consistent relationship to the lateral ventricles. CONCLUSIONS Knowledge of the relationship of the white matter tracts of the cerebrum to the lateral ventricles should aid in planning more accurate surgery for lesions within the lateral ventricles.

Tractography of Meyer's loop for temporal lobe resection—validation by prediction of postoperative visual field outcome‬‬‬‬

BACKGROUND

Postoperative visual field defects are common after temporal lobe resection because of injury to the most anterior part of the optic radiation, Meyer's loop. Diffusion tensor tractography is a promising technique for visualizing the optic radiation preoperatively. The aim of this study was to assess the anatomical accuracy of Meyer's loop, visualized by the two most common tractography methods—deterministic (DTG) and probabilistic tractography (PTG)—in patients who had undergone temporal lobe resection.

METHODS

Eight patients with temporal lobe resection for temporal lobe pathology were included. Perimetry and diffusion tensor imaging were performed pre- and postoperatively. Two independent operators analyzed the distance between the temporal pole and Meyer's loop (TP-ML) using DTG and PTG. Results were compared to each other, to data from previously published dissection studies and to postoperative perimetry results. For the latter, Spearman's rank correlation coefficient (r(s)) was used.

RESULTS

Median preoperative TP-ML distances for nonoperated sides were 42 and 35 mm, as determined by DTG and PTG, respectively. TP-ML assessed with PTG was a closer match to dissection studies. Intraclass correlation coefficients were 0.4 for DTG and 0.7 for PTG. Difference between preoperative TP-ML (by DTG and PTG, respectively) and resection length could predict the degree of postoperative visual field defects (DTG: r(s) = -0.86, p < 0.05; PTG: r(s) = -0.76, p < 0.05).

CONCLUSION

Both DTG and PTG could predict the degree of visual field defects. However, PTG was superior to DTG in terms of reproducibility and anatomical accuracy. PTG is thus a strong candidate for presurgical planning of temporal lobe resection that aims to minimize injury to Meyer's loop.

Strengths and limitations of tractography methods to identify the optic radiation for epilepsy surgery

Diffusion tensor imaging (DTI) tractography (TG) can visualize Meyer's loop (ML), providing important information for the epilepsy surgery team, both for preoperative counseling and to reduce the frequency of visual field defects after temporal lobe resection (TLR). This review highlights significant steps in the TG process, specifically the processing of raw data including choice of TG algorithm and the interpretation and validation of results. A lack of standardization of TG of the optic radiation makes study comparisons challenging. We discuss results showing differences between studies and uncertainties large enough to be of clinical relevance and present implications of this technique for temporal lobe epilepsy surgery. Recent studies in temporal lobe epilepsy patients, employing TG intraoperatively, show promising results in reduction of visual field defects, with maintained seizure reduction.

Complications of epilepsy surgery in Sweden 1996–2010: a prospective, population-based study

OBJECT

Detailed risk information is essential for presurgical patient counseling and surgical quality assessments in epilepsy surgery. This study was conducted to investigate major and minor complications related to epilepsy surgery in a large, prospective series.

METHODS

The Swedish National Epilepsy Surgery Register provides extensive population-based data on all patients who were surgically treated in Sweden since 1990. The authors have analyzed complication data for therapeutic epilepsy surgery procedures performed between 1996 and 2010. Complications are classified as major (affecting daily life and lasting longer than 3 months) or minor (resolving within 3 months).

RESULTS

A total of 865 therapeutic epilepsy surgery procedures were performed between 1996 and 2010, of which 158 were reoperations. There were no postoperative deaths. Major complications occurred in 26 procedures (3%), and minor complications in 65 (7.5%). In temporal lobe resections (n = 523), there were 15 major (2.9%) and 41 minor complications (7.8%); in extratemporal resections (n = 275) there were 9 major (3.3%) and 22 minor complications (8%); and in nonresective procedures (n = 67) there were 2 major (3%) and 2 minor complications (3%). The risk for any complication increased significantly with age (OR 1.26 per 10-year interval, 95% CI 1.09–1.45). Compared with previously published results from the same register, there is a trend toward lower complication rates, especially in patients older than 50 years.

CONCLUSIONS

This is the largest reported prospective series of complication data in epilepsy surgery. The complication rates comply well with published results from larger single centers, confirming that epilepsy surgery performed in the 6 Swedish centers is safe. Patient age should be taken into account when counseling patients before surgery.

Diffusion tensor imaging tractography of Meyer's loop in planning resective surgery for drug-resistant temporal lobe epilepsy

PURPOSE

Whether Meyer's loop (ML) tracking using diffusion tensor imaging tractography (DTIT) can be utilized to avoid post-operative visual field deficits (VFD) after anterior temporal lobectomy (ATL) for drug-resistant temporal lobe epilepsy (TLE) using a large cohort of controls and patients. Also, we wanted to create a normative atlas of ML in normal population.

METHODS

DTIT was used to study ML in 75 healthy subjects and 25 patients with and without VFD following ATL. 1.5T MRI echo-planar DTI sequences with DTI data were processed in Nordic ICE using a probabilistic method; a multiple region of interest technique was used for reconstruction of optic radiation trajectory. Visual fields were assessed in patients pre- and post-operatively.

RESULTS

Results of ANOVA showed that the left ML-TP distance was less than right across all groups (p = 0.01). The average distance of ML from left temporal pole was 37.44 ± 4.7 mm (range: 32.2-46.6 mm) and from right temporal pole 39.08 ± 4.9 mm (range: 34.3-49.7 mm). Average distance of left and right temporal pole to tip of temporal horn was 28.32 ± 2.03 mm (range: 26.4-32.8 mm) and was 28.92 ± 2.09 mm, respectively (range: 25.9-33.3 mm). If the anterior limit of the Meyer's loop was ≤38 mm on the right and ≤35 mm on the left from the temporal pole, they are at a greater risk of developing VFDs.

CONCLUSIONS

DTIT is a novel technique to delineate ML and plays an important role in planning surgical resection in TLE to predict post-operative visual performance and disability.

Evaluating contextual processing in diffusion MRI: application to optic radiation reconstruction for epilepsy surgery

Diffusion MRI and tractography allow for investigation of the architectural configuration of white matter in vivo, offering new avenues for applications like presurgical planning. Despite the promising outlook, there are many pitfalls that complicate its use for (clinical) application. Amongst these are inaccuracies in the geometry of the diffusion profiles on which tractography is based, and poor alignment with neighboring profiles. Recently developed contextual processing techniques, including enhancement and well-posed geometric sharpening, have shown to result in sharper and better aligned diffusion profiles. However, the research that has been conducted up to now is mainly of theoretical nature, and so far these techniques have only been evaluated by visual inspection of the diffusion profiles. In this work, the method is evaluated in a clinically relevant application: the reconstruction of the optic radiation for epilepsy surgery. For this evaluation we have developed a framework in which we incorporate a novel scoring procedure for individual pathways. We demonstrate that, using enhancement and sharpening, the extraction of an anatomically plausible reconstruction of the optic radiation from a large amount of probabilistic pathways is greatly improved in three healthy controls, where currently used methods fail to do so. Furthermore, challenging reconstructions of the optic radiation in three epilepsy surgery candidates with extensive brain lesions demonstrate that it is beneficial to integrate these methods in surgical planning.

Preventing visual field deficits from neurosurgery

OBJECTIVE

We assessed whether display of optic radiation tractography during anterior temporal lobe resection (ATLR) for refractory temporal lobe epilepsy (TLE) can reduce the severity of postoperative visual field deficits (VFD) and increase the proportion of patients who can drive and whether correction for brain shift using intraoperative MRI (iMRI) is beneficial.

METHODS

A cohort of 21 patients underwent ATLR in an iMRI suite. Preoperative tractography of the optic radiation was displayed on the navigation and operating microscope displays either without (9 patients) or with (12 patients) correction for brain shift. VFD were quantified using Goldmann perimetry and eligibility to drive was assessed by binocular Esterman perimetry 3 months after surgery. Secondary outcomes included seizure freedom and extent of hippocampal resection. The comparator was a cohort of 44 patients who underwent ATLR without iMRI.

RESULTS

The VFD in the contralateral superior quadrant were significantly less (p = 0.043) with iMRI guidance (0%-49.2%, median 14.5%) than without (0%-90.9%, median 24.0%). No patient in the iMRI cohort developed a VFD that precluded driving whereas 13% of the non-iMRI cohort failed to meet UK driving criteria. Outcome did not differ between iMRI guidance with and without brain shift correction. Seizure outcome and degree of hippocampal resection were unchanged.

CONCLUSIONS

Display of the optic radiation with image guidance reduces the severity of VFD and did not affect seizure outcome or hippocampal resection. Correction for brain shift is possible but did not further improve outcome. Future work to incorporate tractography into conventional neuronavigation systems will make the work more widely applicable.

Visualizing Meyer's loop: A comparison of deterministic and probabilistic tractography

BACKGROUND

Diffusion tensor tractography of the anterior extent of the optic radiation - Meyer's loop - prior to temporal lobe resection (TLR) may reduce the risk for postoperative visual field defect. Currently there is no standardized way to perform tractography.

OBJECTIVE

To visualize Meyer's loop using deterministic (DTG) and probabilistic tractography (PTG) at different probability levels, with the primary aim to explore possible differences between methods, and the secondary aim to explore anatomical accuracy.

METHODS

Twenty-three diffusion tensor imaging exams (11 controls and 7 TLR-patients, pre- and post-surgical) were analyzed using DTG and PTG thresholded at probability levels 0.2%, 0.5%, 1%, 5% and 10%. The distance from the tip of the temporal lobe to the anterior limit of Meyer's loop (TP-ML) was measured in 46 optic radiations. Differences in TP-ML between the methods were compared. Results of the control group were compared to dissection studies and to a histological atlas.

RESULTS

For controls and patients together, there were statistically significant differences (p<0.01) for TP-ML between all methods thresholded at PTG ≤1% compared to all methods thresholded at PTG ≥5% and DTG. There were no statistically significant differences between PTG 0.2%, 0.5% and 1% or between PTG 5%, 10% and DTG. For the control group, PTG ≤1% showed a closer match to dissection studies and PTG 1% showed the best match to histological tracings of Meyer's loop.

CONCLUSIONS

Choice of tractography method affected the visualized location of Meyer's loop significantly in a heterogeneous, clinically relevant study group. For the controls, PTG at probability levels ≤1% was a closer match to dissection studies. To determine the anterior extent of Meyer's loop, PTG is superior to DTG and the probability level of PTG matters.

Temporal lobe resective surgery for medically intractable epilepsy: a review of complications and side effects

Object. It is widely accepted that temporal resective surgery represents an efficacious treatment option for patients with epilepsy of temporal origin. The meticulous knowledge of the potential complications, associated with temporal resective procedures, is of paramount importance. In our current study, we attempt to review the pertinent literature for summating the complications of temporal resective procedures for epilepsy. Method. A PubMed search was performed with the following terms: “behavioral,” “cognitive,” “complication,” “deficit,” “disorder,” “epilepsy,” “hemianopia,” “hemianopsia,” “hemorrhage,” “lobectomy,” “medial,” “memory,” “mesial,” “neurobehavioral,” “neurocognitive,” “neuropsychological,” “psychological,” “psychiatric,” “quadranopia,” “quadranopsia,” “resective,” “side effect,” “surgery,” “temporal,” “temporal lobe,” and “visual field.” Results. There were six pediatric, three mixed-population, and eleven adult surgical series examining the incidence rates of procedure-related complications. The reported mortality rates varied between 0% and 3.5%, although the vast majority of the published series reported no mortality. The cumulative morbidity rates ranged between 3.2% and 88%. Conclusions. Temporal resective surgery for epilepsy is a safe treatment modality. The reported morbidity rates demonstrate a wide variation. Accurate detection and frank reporting of any surgical, neurological, cognitive, and/or psychological complications are of paramount importance for maximizing the safety and improving the patients' overall outcome.

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

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.

Visual field defects after radiosurgery for mesial temporal lobe epilepsy

PURPOSE

Gamma knife radiosurgery (RS) may be an alternative to open surgery for mesial temporal lobe epilepsy (MTLE), but morbidities and the anticonvulsant mechanisms of RS are unclear. Examination of visual field defects (VFDs) after RS may provide evidence of the extent of a postoperative fixed lesion. VFDs occur in 52-100% of patients following open surgery for MTLE.

METHODS

This multicenter prospective trial of RS enrolled patients with unilateral hippocampal sclerosis and concordant video-electroencephalography (EEG) findings. Patients were randomized to low (20 Gy) or high (24 Gy) doses delivered to the amygdala, hippocampal head, and parahippocampal gyrus. Postoperative perimetry were obtained at 24 months after RS. Visual field defect ratios (VFDRs) were calculated to quantify the degree of VFDs. Results were contrasted with age, RS dose and 50% isodose volume, peak volume of radiation-induced change at the surgical target, quality of life measurements, and seizure remission.

KEY FINDINGS

No patients reported visual changes and no patients had abnormal bedside visual field examinations. Fifteen (62.5%) of 24 patients had postoperative VFDs, all homonymous superior quadrantanopsias. None of the VFDs were consistent with injury to the optic nerve or chiasm. Clinical diagnosis of VFDs correlated significantly with VFDRs (p = 0.0005). Patients with seizure remission had smaller (more severe) VFDRs (p = 0.04). No other variables had significant correlations.

SIGNIFICANCE

VFDs appeared after RS in proportions similar to historical comparisons from open surgery for MTLE. The nature of VFDs was consistent with lesions of the optic radiations. The findings support the hypothesis that the mechanism of RS involves some degree of tissue damage and is not confined entirely to functional changes in neuromodulation.

Optimization of tractography of the optic radiations

Imaging and delineation of the optic radiations (OpRs) remains challenging, despite repeated attempts to achieve reliable validated tractography of this complex structure. Previous studies have used varying methods to generate representations of the OpR which differ markedly from one another and, frequently, from the OpR's known structure. We systematically examined the influence of a key variable that has differed across previous studies, the tractography seed region, in 13 adult participants (nine male; mean age 31 years; SD 8.7 years; range 16-47). First, we compared six seed regions at the lateral geniculate nucleus (LGN) and sagittal stratum based on the literature and known OpR anatomy. Three of the LGN regions seeded streamlines consistent with the OpR's three "bundles," whereas a fourth seeded streamlines consistent with each of the three bundles. The remaining two generated OpR streamlines unreliably and inconsistently. Two stratum regions seeded the radiations. This analysis identified a set of optimal regions of interest (ROI) for seeding OpR tractography and important inclusion and exclusion ROI. An optimized approach was then used to seed LGN regions to the stratum. The radiations, including streamlines consistent with Meyer's Loop, were streamlined in all cases. Streamlines extended 0.2 ± 2.4 mm anterior to the tip of the anterior horn of the lateral ventricle. These data suggest some existing approaches likely seed representations of the OpR that are visually plausible but do not capture all OpR components, and that using an optimized combination of regions seeded previously allows optimal mapping of this complex structure.

Optic radiation tractography and vision in anterior temporal lobe resection

Objective

Anterior temporal lobe resection (ATLR) is an effective treatment for refractory temporal lobe epilepsy but may result in a contralateral superior visual field deficit (VFD) that precludes driving in the seizure-free patient. Diffusion tensor imaging (DTI) tractography can delineate the optic radiation preoperatively and stratify risk. It would be advantageous to incorporate display of tracts into interventional magnetic resonance imaging (MRI) to guide surgery.

Methods

We studied 20 patients undergoing ATLR. Structural MRI scans, DTI, and visual fields were acquired before and 3 to 12 months following surgery. Tractography of the optic radiation was performed on preoperative images and propagated onto postoperative images. The anteroposterior extent of the damage to Meyer's loop was determined, and visual loss was quantified using Goldmann perimetry.

Results

Twelve patients (60%) suffered a VFD (10–92% of upper quadrant; median, 39%). Image registration took <3 minutes and predicted that Meyer's loop was 4.4 to 18.7mm anterior to the resection margin in these patients, but 0.0 to 17.6mm behind the resection margin in the 8 patients without VFD. The extent of damage to Meyer's loop significantly correlated with the degree of VFD and explained 65% of the variance in this measure.

Interpretation

The optic radiation can be accurately delineated by tractography and propagated onto postoperative images. The technique is fast enough to propagate accurate preoperative tractography onto intraoperative scans acquired during neurosurgery, with the potential to reduce the risk of VFD. ANN NEUROL 2012;

Diffusion tensor imaging tractography of the optic radiation for epilepsy surgical planning: a comparison of two methods

The optic radiation is a key white matter structure at risk during epilepsy surgery involving the temporal, parietal or occipital lobes. It shows considerable anatomical variability, cannot be delineated on clinical MRI sequences and damage may cause a disabling visual field deficit. Diffusion tensor imaging tractography allows non-invasive mapping of this pathway. Numerous methods have been published but direct comparison is difficult as patient, acquisition and analysis parameters differ.

Two methods for delineating the optic radiation were applied to 6 healthy controls and 4 patients with epileptogenic lesions near the optic radiation. By comparing methods with the same datasets, many of the parameters could be controlled. The first method was previously developed to accurately identify Meyer's loop for planning anterior temporal lobe resection. The second aimed to address limitations of this method by using a more automated technique to reduce operator time and to depict the entire optic radiation.

Whilst the core of the tract was common to both methods, there was significant variability between the methods. Method 1 gave a more consistent depiction of Meyer's loop with fewer spurious tracts. Method 2 gave a better depiction of the entire optic radiation, particularly in more posterior portions, but did not identify Meyer's loop in one patient.

These results show that whilst tractography is a promising technique, there is significant variability depending on the method chosen even when the majority of parameters are fixed. Different methods may need to be chosen for surgical planning depending on the individual clinical situation.

Apical temporal lobe resection; "tailored" hippocampus-sparing resection based on presurgical evaluation data

BACKGROUND

It is the aim of epilepsy surgery in patients with lesional epilepsy for the surgeon to not only remove the lesion itself, but also the epileptogenic zone. Here, we report our experience with a modified temporal resection technique confined to the apical temporal lobe, i.e., sparing the hippocampal formation in patients with epileptogenic lesions in the anterior part of the temporal lobe. This apical temporal lobe resection (aTLR) includes tailored lesionectomy, amygdalectomy, and resection of the mesial structures only in the apex of the temporal lobe. This paper presents our surgical technical details and the outcome of aTLR.

METHODS

Between 2001 and 2008, aTLR was performed in 61 patients. All patients underwent comprehensive presurgical evaluation including video-EEG monitoring, magnetic resonance imaging (MRI), and neuropsychological testing. All patients had a lesion in the apex of the temporal lobe and a normal hippocampus as seen in MRI, as well as intact memory functions in neuropsychological examination. There were 33 males (54.1%) and 28 females (45.9%). The mean age in years at epilepsy onset was 20.2 ± 13.4, the mean age at epilepsy surgery was 32.1 ± 11.9, the mean preoperative epilepsy duration was 11.8 ± 8.8 years and the mean duration of follow-up was 2.1 ± 1.3 years (range 0.5-6 years).

RESULTS

Fifty-four (88.5%) of 61 patients were in Engel Class 1 at 6 months, 38 (80.9%) of 47 at 2 years and nine (81.8%) of 11 at the 5 year follow-up. Histopathological examination showed tumors in 31 patients, FCD in ten patients, amygdala sclerosis in seven patients, cavernomas in six patients, unspecific reactions in eight patients, and gliosis in one patient. Surgical complications occurred in four patients: one had a permanent and three had transient complications which could be successfully treated. Fifty (82%) resections were considered to be complete resections as evaluated by serial postoperative MRI, seven patients (11.5%) had incomplete resection of the preoperative MRI lesion and in four patients (6.6%) it remained unclear. Fifteen patients (29.4%) were withdrawn from antiepileptic drugs for more than 2 years without relapse. Postoperative neuropsychological examination revealed worsening of memory performance in two patients (3.2%) and improved or no changes in the rest of the patients.

CONCLUSIONS

Apical temporal resection sparing the mesial temporal structures is an effective procedure with good long-term seizure outcome in patients with refractory epilepsy due to lesions confined to the apex of the temporal lobe.

Disorders of the optic tract, radiation, and occipital lobe

Disorders of the optic tract, lateral geniculate nucleus, optic radiation, and occipital lobe - collectively called the retrochiasmal visual pathways - are commonly encountered in neurological practice, and may result from a number of causes. The major visual morbidity of retrochiasmal disease is the homonymous visual field defect, which is found in approximately 8% of stroke patients. A homonymous visual field defect may have profound legal, occupational, and financial consequences for patients, with many patients unable to read, drive, or return to work after sustaining retrochiasmal damage. Some homonymous hemianopias may improve, usually within days of a cerebral infarction, but remain stable after 3 months. Although treatment options are limited to those of the underlying cause, appropriate counseling and low-vision rehabilitation may be helpful.

Epilepsy surgery provides new insights in retinotopic organization of optic radiations. A systematic review

PURPOSE OF REVIEW

Visual field defects (VFDs) produced by temporal lobe resections provide valuable information on the retinotopic organization of the optic radiations. The results of this systematic review of the literature will be translated into a revised--and evidence-based--map of the retinotopic anatomy of the anterior optic radiations.

RECENT FINDINGS

Recent studies provide best evidence by combining automatic static perimetry and modern imaging techniques. VFDs occur in 83% of patients undergoing temporal lobectomy. There is a significant correlation between size of resection and amount of VFD. Most defects appear incongruous. Macular involvement is seen in more than 50% of cases. The inferolateral defect border is of a sloping nature and sometimes crosses the horizontal meridian. On the basis of these findings, the classical theory on the retinotopic anatomy of the optic radiation should be revised.

SUMMARY

This article systematically reviews the literature on VFDs after temporal lobe resection. Frequency, size, congruity, macular involvement and defect borders are related to size of resection. The classical theory on the retinotopic organization of the anterior optic radiations should be revised.

Defining Meyer's loop-temporal lobe resections, visual field deficits and diffusion tensor tractography

Anterior temporal lobe resection is often complicated by superior quadrantic visual field deficits (VFDs). In some cases this can be severe enough to prohibit driving, even if a patient is free of seizures. These deficits are caused by damage to Meyer's loop of the optic radiation, which shows considerable heterogeneity in its anterior extent. This structure cannot be distinguished using clinical magnetic resonance imaging sequences. Diffusion tensor tractography is an advanced magnetic resonance imaging technique that enables the parcellation of white matter. Using seed voxels antero-lateral to the lateral geniculate nucleus, we applied this technique to 20 control subjects, and 21 postoperative patients. All patients had visual fields assessed with Goldmann perimetry at least three months after surgery. We measured the distance from the tip of Meyer's loop to the temporal pole and horn in all subjects. In addition, we measured the size of temporal lobe resection using postoperative T₁-weighted images, and quantified VFDs. Nine patients suffered VFDs ranging from 22% to 87% of the contralateral superior quadrant. In patients, the range of distance from the tip of Meyer's loop to the temporal pole was 24–43 mm (mean 34 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was −15 to +9 mm (mean 0 mm). In controls the range of distance from the tip of Meyer's loop to the temporal pole was 24–47 mm (mean 35 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was −11 to +9 mm (mean 0 mm). Both quantitative and qualitative results were in accord with recent dissections of cadaveric brains, and analysis of postoperative VFDs and resection volumes. By applying a linear regression analysis we showed that both distance from the tip of Meyer's loop to the temporal pole and the size of resection were significant predictors of the postoperative VFDs. We conclude that there is considerable variation in the anterior extent of Meyer's loop. In view of this, diffusion tensor tractography of the optic radiation is a potentially useful method to assess an individual patient's risk of postoperative VFDs following anterior temporal lobe resection.

VISUAL FIELD DEFECTS IN SELECTIVE AMYGDALOHIPPOCAMPECTOMY FOR HIPPOCAMPAL SCLEROSIS

OBJECTIVE

Meyer's loop, the most vulnerable part of the optic radiations during approaches to the temporomedial region, extends to the tip of the temporal horn and is often encountered in epilepsy surgery. The risk of damaging Meyer's loop during transsylvian selective amygdalohippocampectomy peaks while accessing the temporal horn through its roof by opening the inferior limiting sulcus of the insula. In this prospective study, we sought to evaluate and identify the incidence of visual field deficits in a homogeneous group of patients who had temporal lobe epilepsy with hippocampal sclerosis and who underwent transsylvian selective amygdalohippocampectomy.

METHODS

We studied 30 patients who were referred for epilepsy surgery for intractable complex partial and/or secondary generalized seizures and evaluated according to a noninvasive protocol. All patients underwent selective amygdalohippocampectomy for temporal lobe epilepsy with hippocampal sclerosis using the standard transsylvian approach. Visual field deficits were examined preoperatively in 30 patients, by either a confrontation method (n = 18) or standard Goldmann perimetry (n = 12) and postoperatively in all patients using standard Humphrey digital perimetry.

RESULTS

Visual field examination was normal in all patients before surgery. Humphrey perimetric measurement revealed visual field deficits in 11 patients (36.6%) after surgery.

CONCLUSION

We have shown that there is a considerable risk of having visual field deficits after standard transsylvian selective amygdalohippocampectomy owing to the interruption of the anterior bundle of the optic radiation fibers, which most likely occurs while opening the temporal horn through the inferior limiting sulcus of the insula.

VISUAL FIELD DEFECTS IN SELECTIVE AMYGDALOHIPPOCAMPECTOMY FOR HIPPOCAMPAL SCLEROSIS

OBJECTIVE

Meyer's loop, the most vulnerable part of the optic radiations during approaches to the temporomedial region, extends to the tip of the temporal horn and is often encountered in epilepsy surgery. The risk of damaging Meyer's loop during transsylvian selective amygdalohippocampectomy peaks while accessing the temporal horn through its roof by opening the inferior limiting sulcus of the insula. In this prospective study, we sought to evaluate and identify the incidence of visual field deficits in a homogeneous group of patients who had temporal lobe epilepsy with hippocampal sclerosis and who underwent transsylvian selective amygdalohippocampectomy.

METHODS

We studied 30 patients who were referred for epilepsy surgery for intractable complex partial and/or secondary generalized seizures and evaluated according to a noninvasive protocol. All patients underwent selective amygdalohippocampectomy for temporal lobe epilepsy with hippocampal sclerosis using the standard transsylvian approach. Visual field deficits were examined preoperatively in 30 patients, by either a confrontation method (n = 18) or standard Goldmann perimetry (n = 12) and postoperatively in all patients using standard Humphrey digital perimetry.

RESULTS

Visual field examination was normal in all patients before surgery. Humphrey perimetric measurement revealed visual field deficits in 11 patients (36.6%) after surgery.

CONCLUSION

We have shown that there is a considerable risk of having visual field deficits after standard transsylvian selective amygdalohippocampectomy owing to the interruption of the anterior bundle of the optic radiation fibers, which most likely occurs while opening the temporal horn through the inferior limiting sulcus of the insula.

Diffusion tensor tractography of the Meyer loop in cases of temporal lobe resection for temporal lobe epilepsy: correlation between postsurgical visual field defect and anterior limit of Meyer loop on tractography

BACKGROUND AND PURPOSE

Visual field defects sometimes occur after temporal resection surgery. Our purpose was to evaluate the correlation between visual field defects caused by temporal lobe resection and the degree of resection of the Meyer loop, as assessed by diffusion tensor tractography.

MATERIALS AND METHODS

We examined 14 patients who underwent temporal resection for temporal lobe epilepsy. We obtained presurgical tractographies and then measured the distance between the temporal tip and the anterior limit of the Meyer loop (T-M distance). The degree of resection of the Meyer loop was defined as the distance from the anterior limit of the Meyer loop to the posterior limit of the temporal lobe resection (M-R distance). This was calculated by subtracting the T-M distance from the measured distance between the temporal tip and the posterior limit of the resection (T-R distance).

RESULTS

The mean T-M distance was 36.6 mm. The interindividual variation of the distance ranged from 30.0 to 43.2 mm. Although there was no statistically significant correlation between the extent of the visual field defect and the T-R distance, there was a statistically significant correlation between the degree of the visual field defect and the M-R distance.

CONCLUSION

The range of interindividual variation for the position of the Meyer loop was rather large, indicating that this variation is the key factor in visual field defects after temporal lobectomy, and the visual field defect appears to be predicted by presurgical tractography. Evaluation of the Meyer loop through the use of tractography seems to be a feasible method, which can be used to predict the visual field defect after temporal lobe resection.

Intersubject variability in the anterior extent of the optic radiation assessed by tractography

INTRODUCTION

Temporal lobe resection for epilepsy involves a risk of damaging the anterior part of the optic radiation, Meyer's loop, causing a contralateral upper quadrant visual field defect. This study aims to assess the intersubject variability in the course of Meyer's loop in vivo by diffusion tensor imaging and tractography.

METHODS

Seven healthy volunteers and two patients with previous temporal lobe resection were recruited. Diffusion tensor imaging and tractography were used to visualize the optic radiation. The distances from the anterior edge of Meyer's loop to landmarks in the temporal lobe were calculated.

RESULTS

In the healthy subjects, the mean distance between the most anterior part of Meyer's loop and the temporal pole was 44 mm (range 34-51 mm). Meyer's loop did not reach the tip of the temporal horn in any subject. A disruption in Meyer's loop could be demonstrated in the patient with quadrantanopia after temporal lobe resection.

CONCLUSIONS

Meyer's loop has a considerable variability in its anterior extent. Tractography may be a useful method to visualize Meyer's loop, and assess the risk of a visual field defect, prior to temporal lobe resection.

Temporal lobe resections

INTRODUCTION

In the 50 years since Penfield outlined the requirements of the epilepsy surgeon, we have seen the introduction of the digitised electroencephalogram (EEG), video telemetry and the magnetic resonance imaging (MRI) scan. In the operating room, advances in neuro-anaesthesia, the introduction of the operating microscope, image guidance and the ultrasonic aspirator have greatly enhanced the surgeons' technical ability. Despite these changes, the thesis encapsulated in Penfield's statement is that the surgeon needs to understand and interpret the preoperative data in such a way as to identify as closely as possible the epileptogenic zone where he must carry out surgery with the utmost care and diligence, and finally, in the context of audit and follow-up of his surgical patients, he must be able to predict for each individual case the likelihood of success and failure of any particular procedure.

CONCLUSION

Previous articles in this supplement have looked at the specific investigations carried out to identify the epileptogenic zone, but once this data has been gathered, it is the responsibility of the neurosurgeon, within the context of the multidisciplinary team, to decide whether surgery is both feasible and advisable and then to discuss this in depth with the patient and their family and carers. The multidisciplinary epilepsy surgery meeting allows cases to be discussed in an open forum and the decisions made in this meeting can then be discussed with the family. The process of consent will begin from the moment any surgical procedure is discussed and should, wherever possible, be reinforced with written, as well as verbal, information. The process of consent should be a continuum until the actual day of surgery. All parties involved in the care and management of the patient should be regarded as stakeholders in this decision, and it is vital that all these stakeholders are working towards a common goal.

OBJECTIVES

In this article, I will consider the specific aspects of the presurgical investigations that are applicable to the temporal lobe and the differing types of surgery that are likely to be indicated. I will then describe, in detail, the surgical technique of temporal lobe resection, highlighting some of the pitfalls and successes that such surgery can provide.

The field defects of anterior temporal lobectomy: a quantitative reassessment of Meyer's loop

Temporal lobectomy is often complicated by superior quadrantanopia. The relation of field loss to sagittal resection length can inform us about the functional anatomy of Meyer's loop, with ramifications for surgical planning. However, the literature has produced highly variable results. We studied 29 patients with anterior temporal lobectomies using Goldmann perimetry. 24 patients had post-operating neuroimaging, with which we assessed resection length relative to each patient's temporo-occipital dimensions. For the field defect we calculated the proportion of area lost for three isopters. We found a significant correlation between resection size and field loss for both nasal and temporal defects. Linear regressions suggested an anterior limit of Meyer's loop at 24 to 28 mm from the anterior temporal pole, and involvement of the lower quadrant when resections reached 70 to 79 mm, with significant inter-subject variability. The nasal defect was 15% greater than the temporal defect for all degrees of quadrantanopia, with no difference between right and left hemispheres. Macular involvement began when field defects reached 61% of quadrant area, corresponding to a resection of about 58 mm. Patterns of field loss showed that the lower margins were most often horizontal or with a slight slope towards fixation, rather than true wedge defects. We conclude that field loss is related to resection length and that Meyer's loop extends more anteriorly than estimated in traditional surgical studies, in agreement with modern MRI and dissection studies. The patterns of field loss support a revised retinotopic model in which the most anterior fibers of Meyer's loop represent the superior field, not the vertical meridian as traditionally proposed.