No abstract

There is little information available relevant to long-term seizure outcome after anterior temporal lobectomy, particularly at extended postoperative periods. The aim of this study was an in-depth examination of patterns of longitudinal outcome and potential risk factors for seizure recurrence after lobectomy, utilizing a large patient sample with long follow-up. Included were 325 patients who underwent anterior temporal lobectomy between 1978 and 1998 (mean follow-up 9.6 +/- 4.2 years). Retrospective data were analysed using survival analysis and multivariate regression with Cox proportional hazard models. The probability of complete seizure freedom at 2 years post-surgery was 55.3% [95% confidence interval (CI) 50-61]; at 5 years, 47.7% (95% CI 42-53); and at 10 postoperative years it was 41% (95% CI 36-48). Patients with discrete abnormalities preoperatively (i.e. lesions and hippocampal sclerosis) had a significantly higher probability of seizure freedom than patients without obvious abnormality. The latter group had a pattern of recurrence similar to that in patients with lesions outside the area of excision. After adjustment for preoperative pathology, only the presence of preoperative secondarily generalized seizures had a significant association with recurrence [occasional preoperative generalized seizures, hazard ratio (HR) 1.6, 95% CI 1.1-2.3; frequent seizures, HR 2.0, 95% CI 1.4-2.9 compared with absence of preoperative generalized seizures]. Duration of preoperative epilepsy, age of seizure onset and age at surgery did not have an effect on outcome. Patients with two seizure-free postoperative years had a 74% (95% CI 66-81) probability of seizure freedom by 10 postoperative years. This late seizure recurrence was not associated with any identified risk factors. Specifically, patients with hippocampal sclerosis were not at higher risk. Surprisingly, complete discontinuation of anti-epileptic drugs (AEDs) after two postoperative years was not associated with an increased risk of recurrence (HR 1.03, 95% CI 0.5-2.1). This may be because selection of patients for AED discontinuation is biased towards those individuals perceived as 'low risk'. The results of this study indicate that the lack of an obvious abnormality or the presence of diffuse pathology, and preoperative secondarily generalized seizures are risk factors for recurrence after surgery. Late recurrence after initial seizure freedom is not a rare event; risk factors specific to this phenomenon are as yet unidentified.

We used actuarial methods to study outcome after temporal lobectomy in 135 consecutive patients classified into subgroups according to preoperative MRI findings. Sixty months after surgery, 69% of patients with foreign tissue lesions, 50% with hippocampal sclerosis, and 21% with normal MRIs had no postoperative seizures. An eventual seizure-free state of 2 years or more, whether the patient was seizure-free since surgery or not, was achieved by 80% of patients with foreign tissue lesions, 62% of those with hippocampal sclerosis, and 36% of those with normal MRIs. Outcome was worse in those with normal MRIs than in the other two groups. Early postoperative seizures with later remission (the "running down" phenomenon) occurred in all groups. Late seizure recurrence was present only in the hippocampal sclerosis group. These data show that preoperative MRI is a useful predictor of outcome and that actuarial analysis provides insight into different longitudinal patterns of outcome in MRI subgroups. This information can now be used in preoperative counseling.

T he advent of clinically available white matter fiber tracking, a technique that maps white matter pathways from diffusion-weighted MRI data 27 promises the ability to visualize a range of eloquent white matter tracts in individual patients. 12,17,24,30,33 The potential power of this information in many clinical situations is such that 3D maps are already being integrated with neurosurgical navigation systems, often being relied upon for the purpose of presurgical planning and intraoperative navigation. 10,23,33 Although the fundamental limitations of the most commonly used tractography method, namely DTI 6 -based tractography, are well described in the tech- Object. Diffusion-based MRI tractography is an imaging tool increasingly used in neurosurgical procedures to generate 3D maps of white matter pathways as an aid to identifying safe margins of resection. The majority of white matter fiber tractography software packages currently available to clinicians rely on a fundamentally flawed framework to generate fiber orientations from diffusion-weighted data, namely diffusion tensor imaging (DTI). This work provides the first extensive and systematic exploration of the practical limitations of DTI-based tractography and investigates whether the higher-order tractography model constrained spherical deconvolution provides a reasonable solution to these problems within a clinically feasible timeframe.Methods. Comparison of tractography methodologies in visualizing the corticospinal tracts was made using the diffusion-weighted data sets from 45 healthy controls and 10 patients undergoing presurgical imaging assessment. Tensor-based and constrained spherical deconvolution-based tractography methodologies were applied to both patients and controls.Results. Diffusion tensor imaging-based tractography methods (using both deterministic and probabilistic tractography algorithms) substantially underestimated the extent of tracks connecting to the sensorimotor cortex in all participants in the control group. In contrast, the constrained spherical deconvolution tractography method consistently produced the biologically expected fan-shaped configuration of tracks. In the clinical cases, in which tractography was performed to visualize the corticospinal pathways in patients with concomitant risk of neurological deficit following neurosurgical resection, the constrained spherical deconvolution-based and tensor-based tractography methodologies indicated very different apparent safe margins of resection; the constrained spherical deconvolution-based method identified corticospinal tracts extending to the entire sensorimotor cortex, while the tensor-based method only identified a narrow subset of tracts extending medially to the vertex.Conclusions. This comprehensive study shows that the most widely used clinical tractography method (diffusion tensor imaging-based tractography) results in systematically unreliable and clinically misleading information. The higher-order tractography model, using the same diffusion-weighted data, clea...