Neural stimulators: a guide to imaging and postoperative appearances.

Implantable neural stimulators have been developed to aid patients with debilitating neurological conditions that are not amenable to other therapies. The aim of this article is to improve understanding of correct anatomical placement as well as the relevant imaging methods used to assess these devices. Potential complications following their insertion and an overview of the current indications and potential mechanism of action of these devices is provided.

Simultaneous intracranial EEG-fMRI in humans: protocol considerations and data quality.

We have recently performed simultaneous intracranial EEG and fMRI recordings (icEEG-fMRI) in patients with epilepsy. In this technical note, we examine limited thermometric data for potential electrode heating during our protocol and found that heating was ≤0.1 °C in-vitro at least 10 fold less than in-vivo limits. We quantify EEG quality, which can be degraded by MRI scanner-induced artefacts, and fMRI image (gradient echo echo-planar imaging: GE-EPI) signal quality around the electrodes, which can be degraded by electrode interactions with B1 (radiofrequency) and B0 (static) magnetic fields. We recorded EEG outside and within the MRI scanner with and without scanning. EEG quality was largely preserved during scanning and in particular heartbeat-related artefacts were small compared to epileptic events. To assess the GE-EPI signal reduction around the electrodes, we compared image signal intensity along paths into the brain normal to its surface originating from the individual platinum-iridium electrode contacts. GE-EPI images were obtained at 1.5 T with an echo time (TE) of 40 ms and repetition time (TR) of 3000 ms and a slice thickness of 2.5 mm. We found that GE-EPI signal intensity reduction was confined to a 10 mm radius and that it was reduced on average by less than 50% at 5mm from the electrode contacts. The GE-EPI image signal reduction also varied with electrode orientation relative to the MRI scanner axes; in particular, cortical grid contacts with a normal along the scanner's main magnetic field (B(0)) axis have higher artefact levels relative to those with a normal perpendicular to the z-axis. This suggests that the artefacts were predominantly susceptibility-related rather than due to B1 interactions. This information can be used to guide interpretation of results of icEEG-fMRI experiments proximal to the electrodes, and to optimise artefact reduction strategies.

Premature mortality in refractory partial epilepsy: does surgical treatment make a difference?

BACKGROUND: Epilepsy carries an increased risk of premature death. For some people with intractable focal epilepsy, surgery offers hope for a seizure-free life. The authors aimed to see whether epilepsy surgery influenced mortality in people with intractable epilepsy. METHODS: The authors audited survival status in two cohorts (those who had surgery and those who had presurgical assessment but did not have surgery). RESULTS: There were 40 known deaths in the non-surgical group (3365 person years of follow-up) and 19 in the surgical group (3905 person-years of follow-up). Non-operated patients were 2.4 times (95% CI 1.4 to 4.2) as likely to die as those who had surgery. They were 4.5 times (95% CI 1.9 to 10.9) as likely to die a probable epilepsy-related death. In the surgical group, those with ongoing seizures 1 year after surgery were 4.0 (95% CI 1.2 to 13.7) times as likely to die as those who were seizure-free or who had only simple partial seizures. Time-dependent Cox analysis showed that the yearly outcome group did not significantly affect mortality (HR 1.3, 95% CI 0.9 to 1.8). CONCLUSION: Successful epilepsy surgery was associated with a reduced risk of premature mortality, compared with those with refractory focal epilepsy who did not have surgical treatment. To some extent, the reduced mortality is likely to be conferred by inducing freedom from seizures. It is not certain whether better survival is attributable only to surgery, as treatment decisions were not randomised, and there may be inherent differences between the groups.

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 T(1)-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.

The spatio-temporal mapping of epileptic networks: combination of EEG-fMRI and EEG source imaging.

Simultaneous EEG-fMRI acquisitions in patients with epilepsy often reveal distributed patterns of Blood Oxygen Level Dependant (BOLD) change correlated with epileptiform discharges. We investigated if electrical source imaging (ESI) performed on the interictal epileptiform discharges (IED) acquired during fMRI acquisition could be used to study the dynamics of the networks identified by the BOLD effect, thereby avoiding the limitations of combining results from separate recordings. Nine selected patients (13 IED types identified) with focal epilepsy underwent EEG-fMRI. Statistical analysis was performed using SPM5 to create BOLD maps. ESI was performed on the IED recorded during fMRI acquisition using a realistic head model (SMAC) and a distributed linear inverse solution (LAURA). ESI could not be performed in one case. In 10/12 remaining studies, ESI at IED onset (ESIo) was anatomically close to one BOLD cluster. Interestingly, ESIo was closest to the positive BOLD cluster with maximal statistical significance in only 4/12 cases and closest to negative BOLD responses in 4/12 cases. Very small BOLD clusters could also have clinical relevance in some cases. ESI at later time frame (ESIp) showed propagation to remote sources co-localised with other BOLD clusters in half of cases. In concordant cases, the distance between maxima of ESI and the closest EEG-fMRI cluster was less than 33 mm, in agreement with previous studies. We conclude that simultaneous ESI and EEG-fMRI analysis may be able to distinguish areas of BOLD response related to initiation of IED from propagation areas. This combination provides new opportunities for investigating epileptic networks.

Cognitive outcomes of temporal lobe epilepsy surgery in older patients.

PURPOSE: To examine the cognitive risks of temporal lobe surgery in patients aged 50 years and older. METHODS: We analysed data from 55 patients who underwent temporal lobe surgery (26 left-sided:29 right sided) from 1988 to 2012 at our centre. Pre-surgical and one year post-operative memory and naming capacity were compared to data obtained from two younger cohorts; 185 aged 18-30 and 220 aged 31-49. RESULTS: Pre-operative memory impairments were most marked for the oldest cohort and were associated with a longer duration of epilepsy. Naming capacity improved with age and better performance was associated with a later age at epilepsy onset. Post-operative declines were largest in older patients, achieving statistical significance for verbal memory, naming and subjective ratings. Left temporal lobe resections carried the greatest risk of memory and naming decline. Cognitive outcomes were unrelated to seizure outcome, VIQ or mood. CONCLUSION: Our findings indicate the cognitive risks of TLE surgery are greater for older patients. Cognitive outcomes need to be considered when assessing the efficacy of epilepsy surgery in older cohorts and pre-operative performance levels need to be taken into account.

Intramedullary thoracic cord metastasis managed effectively without surgery.

Spinal intramedullary metastases present with rapidly progressing neurological deficits and have an extremely poor prognosis. Prompt investigation and management are required. This case history illustrates that radiotherapy and steroids can be effective in returning motor function. The behaviour of the primary tumour and the stage of the disease influence whether surgery is appropriate.

Giant temporo-occipital sinus pericranii. A case report.

A rare case of a giant, temporo-occipital sinus pericranii is presented. A 38-year-old male presented with minor symptoms of headache and heaviness over an enlarging temporo-occipital bone defect. Within the defect a soft, compressible, mass lesion was observed, which varied in size with changes in intracranial pressure. Radiological imaging demonstrated bone erosion around a fluid filled mass, which on angiography communicated via a series of channels with the transverse sinus. A diagnosis of sinus pericranii was made. Due to the risk of future complication the patient elected to undergo surgery, which successfully resected the mass and obliterated the venous communications with the diploic veins and transverse sinus. The classification, aetiology, differential diagnosis, radiological characteristics and management options relating to sinus pericranii are discussed.

Subdural haematoma associated with an arachnoid cyst after repetitive minor heading injury in ball games.

We report the case of a chronic subdural haematoma caused by repetitive heading of a football which led to the diagnosis of a middle fossa arachnoid cyst. The association between arachnoid cysts and subdural haematoma is discussed as are safety implications in sporting injuries.

Balloon cells associated with granule cell dispersion in the dentate gyrus in hippocampal sclerosis.

Granule cell dispersion (GCD) is a common finding in hippocampal sclerosis in patients with intractable focal epilepsy. It is considered to be an acquired, post-developmental rather than a pre-existing abnormality, involving dispersion of either mature or newborn neurones, but the precise factors regulating it and its relationship to seizures are unknown. We present two cases of GCD with associated CD34-immunopositive balloon cells, a cell phenotype associated with focal cortical dysplasia type IIB, considered to be a developmental cortical lesion promoting epilepsy. This observation opens up the debate regarding the origin of balloon cells and CD34 expression and their temporal relationship to seizures.

Correlation of quantitative MRI and neuropathology in epilepsy surgical resection specimens--T2 correlates with neuronal tissue in gray matter.

Newer MRI methods can detect cerebral abnormalities not identified on routine imaging in patients with focal epilepsy. Correlation of MRI with histopathology is necessary to understand the basis of MRI abnormalities and subsequently predict histopathology from in vivo MRI. The aim of this study was to determine if particular quantitative MR parameters were associated with particular histological features. Nine patients with temporal lobe epilepsy were imaged at 1.5 T using standard presurgical volumetric and quantifiable sequences: magnetization transfer and FFT2. The resected temporal lobe was registered with the volumetric MRI data according to our previously described method to permit correlation of the modalities. Stereologically measured neuronal densities and field fraction of GFAP, MAP2, synaptophysin and NeuN immunohistochemistry were obtained. Analyses were performed in the middle temporal gyrus and compared with quantitative MRI data from the equivalent regions. There was a significant Spearman Rho negative correlation between NeuN field fraction and the T2 value in gray matter (correlation coefficient -0.72, p=0.028). There were no significant correlations between any neuropathological and MR measures in white matter. These preliminary findings suggest that T2 in gray matter is sensitive to the proportion of neuronal tissue. Novel quantitative MRI measures acquired with higher field strength magnets, and so with superior signal to noise ratios, may generate data that correlate with histopathological measures. This will enable better identification and delineation of the structural causes of refractory focal epilepsy, and will be of particular benefit in patients in whom current optimal MRI does not identify a relevant abnormality.

Anthropometric indices in normal elderly subjects.

Anthropometric data (triceps skinfold thickness, mid-arm circumference and arm muscle circumference) have been obtained from 114 normal elderly individuals and are presented as a suitable reference range for use in nutritional assessment of the elderly. In males the results did not differ significantly from existing standards for younger men but in females there was a significant difference from similar standards for younger women. These findings suggest that there is an increase in fat and a decrease in lean body mass with advancing age in females but not in males. This difference is discussed.

Rapid enlargement of a vestibular schwannoma following gamma knife treatment.

Stereotactic radiosurgery has been proposed as the first line treatment for acoustic tumours and has been particularly advocated in cases of Type 2 Neurofibromatosis (NF2) with bilateral acoustic nerve tumours. We present the case of a 22-year-old male with NF2 and bilateral acoustic nerve tumours. He underwent an uncomplicated excision of the larger, left sided lesion. Histology showed a benign acoustic schwannoma with no atypical features. One year later he underwent stereotactic radiosurgery (Gamma Knife 1500 cGy) to the right sided lesion. After initial swelling, within 12 months the tumour had reduced in size and undergone central necrosis. However, 2 years later MRI of the brain revealed a dramatic increase in the size of the right sided tumour, with considerable brain stem compression. The patient subsequently died. This highly unusual case highlights the need for careful clinical and radiological follow up. in patients with acoustic tumours, regardless of the treatment method employed.

Intracerebral haemorrhage and drug abuse in young adults.

The epidemic of abuse of the so-called 'designer drugs' amphetamine, cocaine and ecstasy--is fast replacing traditional aetiological factors as the largest cause of intracerebral haemorrhage among young adults. Traditional teaching is that these represent hypertensive haemorrhages. Recent reports, however, have indicated that these patients may harbour underlying vascular malformations. We review 13 patients with a positive history of drug abuse preceding the onset of intracerebral haemorrhage. These patients presented to the National Hospital for Neurology and Neurosurgery in central London over a 7-month period. Of the 13 patients (eight male, five female), average age 31 years (19-43) years), 10 were well enough to undergo cerebral angiography. Intracranial aneurysms were demonstrated in six patients and arteriovenous malformations in three patients. In only one of the patients was the angiogram normal. A further patient was subsequently shown to have a middle cerebral artery aneurysm at autopsy. The epidemiology, pharmacology and systemic effects of these drugs are considered. The mechanisms by which these compounds cause intracerebral complications and their influence on prognosis are discussed. The incidence of intracerebral haemorrhage (ICH), ischaemic cerebral infarctions and subarachnoid haemorrhage (SAH) following drug abuse is increasing. Contrary to historical opinion, drug-related ICH is frequently related to an underlying vascular malformation. Arteriography should be part of the evaluation of most young patients with nontraumatic ICH. A thorough history focusing on the use of illicit substances and toxicological screening of urine and serum should be part of the evaluation of any young patient with a stroke.

Bitemporal hemianopia caused by metastatic carcinoma in a patient with Wegener's granulomatosis: an unexpected finding.

Metastatic lesions in the suprasellar region are extremely rare. The differential diagnosis of a focal lesion at this site is wide ranging and lesions often have a similar radiological appearance. We present a woman with known Wegener's granulomatosis who lost vision while on medical treatment for a presumed granuloma at this site. Exploration revealed a metastatic carcinoma of unknown origin. Attention is drawn to the importance of making a histological diagnosis in cases of suprasellar lesions.

Haemangioblastoma of a cervical sensory nerve root in Von Hippel-Lindau syndrome.

Spinal haemangioblastomas are rare, accounting for only about 7% of all central nervous system cases. The case of a 40-year-old woman with a haemangioblastoma arising solely from a cervical sensory nerve root is presented. At operation via a cervical laminectomy, it was possible to resect the tumour en masse with the sensory ramus, by extending the laminectomy through the exit foramen for C6. Haemangioblastomas are commonly intramedullary, and have only been reported in this location on one previous occasion. The patient has Von Hippel-Lindau syndrome and a history of multiple solid tumours. The possible role of the Von Hippel-Lindau tumour suppressor gene in the pathogenesis of these neoplasms is discussed.

Intra-operative localisation of skull base tumours. A case report using the ISG viewing wand in the management of trigeminal neuroma.

Deep-seated skull base tumours provide as much a challenge to the surgeons' skills of localisation as to his technical abilities during the resection. These lesions are frequently inaccessible and lie adjacent to vital structures requiring extensive cerebral retraction for adequate exposure and direct visualisation. The ISG viewing wand is a newly developed image guidance system to aid direction of the operative approach and localisation of intracerebral pathology. We discuss its use in the management of a trigeminal neuroma.

Vitamin B12 absorption from the gut does not decline with age in normal elderly humans.

In 37 elderly subjects undergoing measurement of whole body retention of 58Co-B12 at 7 and/or 14 days it was observed that significant (greater than 5%) retention of an inert non-absorbable marker (51CrCl3) occurred at 7 days in 23% of subjects and at 14 days in 8% of subjects. In view of the substantial retention of marker at 7 days it is suggested, therefore, that 14-day measurements of B12 retention are more appropriate than 7-day measurements in the elderly. Whole body retention of vitamin B12 at 14 days was measured in 51 healthy elderly subjects. Results obtained did not correlate with age, between 60 and 96 years, and were no different from results obtained from younger subjects in previously reported studies. It is concluded that vitamin B12 absorption, per se, does not decline with age.