- Email: [email protected]
The impact of new imaging technologies in neurosurgery
review article R. D. Johnson R. J. Stacey Department of Neurosurgery, John Radcliffe Hospital, Headington, Oxford Correspondence to: R. D. Johnson, Department of Neurosurgery, West Wing, John Radcliffe Hospital, Headley Way, Headington, Oxford, OX3 9DU Tel: + 44(0)7980 224193 email: reubenjohnson@ doctors.org.uk
THE IMPACT OF NEW IMAGING TECHNOLOGIES IN NEUROSURGERY Neurosurgery has primarily been concerned with resective or ablative techniques for the accurate removal of pathological tissue with the minimal disruption of surrounding healthy neuronal matter. There have been numerous advances in neurosurgery which have aided the neurosurgeon to achieve this aim including the development of microsurgical, endoscopic and endovascular techniques. Functional neurosurgery has also seen a particular resurgence over the last 15 years with the identication of new anatomical targets and clinical indications. Technological advances in neuroimaging are providing many new adjuncts to the neurosurgeon’s armamentarium. Neuronavigation systems and intra-operative imaging have improved success in surgical removal of tumours from the central nervous system. Accurate epilepsy surgery requires imaging of the epileptogenic zone and accurate identication of adjacent eloquent cortex. New imaging modalities such as PET, SPECT, and fMRI can now be used in order to reduce neurological decits resulting from surgery. This review highlights some of the major advances in neurosurgery and discusses the impact of neuronavigation and functional imaging in tumour surgery and epilepsy surgery. keywords: neurosurgical technique, neuronavigation, intraoperative imaging, functional imaging, positron emission tomography (PET), functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI) Surgeon, 1 December 2008, pp.344-9
Introduction Neurosurgery is a rapidly changing discipline with many new frontiers and there have been many advances over the last 50 years. Some of the most important advances have been summarised in Table 1. The operative microscope is perhaps the single most significant advance in modern neurosurgery and has enabled better visualisation of vessels and nerves. Gazi Yasargil is credited with popularising the use of the operating microscope in neurosurgery, and microsurgical techniques have allowed more radical resection of central nervous system lesions. Yasargil has described microneurosurgery as a field with two arms. On the one hand there is the equipment: the operative microscope and the delicate, specialised instruments. On the other hand there is the skill of the neurosurgeon, who has to develop new indirect eye-hand co-ordination. Indirect hand-eye coordination skills have also allowed advances in neurosurgery by way of the development of endoscopic and endovascular techniques. Endoscopy of the ventricular system has become routine, particularly for paediatric neurosurgeons, in order to treat hydrocephalus and also to biopsy and debulk ventricular-based lesions such as colloid cysts. In aqueduct stenosis, the endoscope can be used to perform a third ventriculostomy in which a hole is made in the floor of the third ventricle. 344
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the royal colleges of surgeons of edinburgh and ireland
This procedure removes the need for ventriculoperitioneal shunts in these patients and the associated complications of shunt systems. There has been a revolution in vascular neurosurgery with endovascular treatment of aneurysms with the insertion of platinum coils. Table 1. Some of the key advances in neurosurgery over the last 50 years 1. Introduction of the operative microscope and development of microsurgical techniques 2. Endovascular treatment of intracranial aneurysms 3. Endoscopic techniques such as ventriculostomy for treatment of hydrocephalus 4. Spinal xation techniques for spinal stabilisation 5. Minimally invasive spinal surgery techniques 6. Deep brain stimulation techniques in functional neurosurgery 7. Neuronavigation – frameless stereotaxy. 8. Intraoperative MRI
© 2008 Surgeon 6; 6: 344-9
The International Subarachnoid Aneurysmal Trial (ISAT), a largescale trial involving 43 centres and 2143 patients, compared surgical versus endovascular treatments for ruptured aneurysms in cases where both treatments were deemed to be equally appropriate.1 ISAT has provided Class I evidence of improved outcomes for coiling over surgical clipping of small anterior circulation aneurysms. Spinal neurosurgery has seen the development of microsurgical techniques and also the widespread introduction of spinal fusion techniques. Perhaps the most widespread advance has been the introduction of pedicle screws for spinal fixation. The use of implants to replace the use of iliac crest grafts in anterior cervical discectomy is another example of a recent change in neurosurgical practice, although it remains to be seen whether this results in better outcome for patients. Functional neurosurgery has seen a particular resurgence over the last 15 years with new subthalamic targets being identified for several clinical indications. Deep-brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is now considered the treatment of choice for pharmacologically resistant Parkinson’s disease. DBS has also been applied with considerable success for dystonia, cluster headache, epilepsy and chronic pain syndromes.2 There is also a renewed interest in psychosurgery following reports of the successful use of DBS for treatment of resistant depression.3 Primate research in the field of functional neurosurgery is one of the best examples of the successful application of findings from pre-clinical studies to clinical practice. These examples demonstrate that advances in neurosurgery have been the result of the skilled application by neurosurgeons of new technologies to assist in the treatment of neurological pathology. New imaging modalities have become available in recent years that are destined to aid neurosurgeons in their work. Perhaps one of the main changes is the introduction of these imaging modalities into the operating theatre. It must be emphasised that none of these technologies will ever replace the surgeon and it will always be the surgeon’s skill that is required to treat the patient. However, one of the aspects of neurological pathology is that it is sometimes not visible to the naked eye even with the aid of the operating microscope. This is particularly true of some epileptic foci and of the border between brain tumours and normal brain. Neuronavigation, particularly combined with intraoperative MRI, is likely to have a significant impact on neurosurgical practice. As availability of these technologies becomes more widespread more studies can be done to evaluate their effectiveness in improving patient outcome.
Neuronavigation and functional imaging in intracranial tumour surgery The maximal removal of diseased tissue whilst minimising the risk of neurological damage is the main challenge faced during intracranial tumour surgery. For intracranial mass lesions, such as primary or secondary tumours, the boundary between normal and abnormal tissue can be very ill defined. Even when an intracranial mass lesion is discrete from the surrounding brain, optimal planning of the surgical approach is paramount in performing a safe excision. Neuronavigation techniques are set to have a major impact on intracranial tumour surgery, allowing for more accurate resection and more minimally invasive techniques for tumour biopsy. Cerebral metastases are the most common form of brain tumour, © 2008 Surgeon 6; 6: 344-9
and surgical management depends upon the number of lesions and upon the presence or absence of a known primary. Debulking surgery is certainly an option for symptomatic metastases, and biopsy may be indicated if there is no known primary lesion. Gliomas are the most common primary brain tumour and management depends upon the type and grade of the tumour. For malignant gliomas, the gold standard is surgical excision and radiotherapy. For low-grade gliomas, and other less aggressive primary tumours such as meningiomas, surgical resection may be indicated for large lesions, particularly in young or symptomatic patients. Although still a matter of controversy, there is increasing evidence to suggest that, at least in low-grade gliomas, length of survival is related to the degree of resection, with long-term survival being associated with a greater degree of resection.4,5 Imaging modalities in intracranial tumour surgery can be used to locate the intracranial lesion and assist the operating surgeon to navigate within the cranial cavity in order to resect the lesion (neuronavigation). In addition, there is a role for neuro-imaging technologies which help define the location of eloquent areas of the brain and how these are related to the tumour. Victor Horsley and Robert Clarke developed a stereotactic method of locating deep-seated brain lesions in 1908 by assigning coordinates in three planes to neuroanatomical structures, based on cranial landmarks. Although this stereotactic system was successful in experiments with small animals, it was never used clinically. Neuronavigation technology made its first impact on clinical neurosurgery in the framebased stereotaxy introduced in 1947 by Spiegel et al, who introduced a plaster head cap, known as a stereoencephalatome, which combined pre-operative radiology with anatomical landmarks to locate deep cortical structures.6 Frame-based stereotaxy is still one of the mainstay techniques in neurosurgery and is routinely used for the biopsy of deep-seated cerebral tumours.7 The advent of new imaging technologies has led to the development of frameless stereotaxy. The first frameless stereotactic system was reported by Roberts in 1986 and was based on a system of acoustic triangulation.8 The term ‘neuronavigator’ was first used by Watanabe in 1987, in association with the use of a localising aluminium arm in combination with CT images.9 Improved quality of digital image data and the wide availability of appropriate computer technology has allowed the development of increasingly sophisticated frameless neuronavigation systems. All frameless neuronavigation systems rely on the integration of pre-operatively acquired CT or MRI data with patient reference points. These patient reference points can be either anatomical or topically applied fiducial points. The transformed data set allows the guidance of surgical instruments within a three-dimensional coordinate system which integrates pre-operative ‘virtual-world’ images and ‘real-world’ patient anatomy (Figure 1). Frameless stereotactic neuronavigation has several advantages over frame-based systems. Frameless navigation dispenses with the need for large frames that interfere with the operative field, and there is potentially an unlimited number of targets navigable within the cranial vault. Frameless neuronavigation is, therefore, a highly versatile technique which can be used in much more invasive procedures than are allowed by frame-based systems. Validating the usefulness of neuronavigation systems in tumour surgery requires the systematic assessment of the available systems by direct comparison with conventional microneurosurgical techniques. Retrospective studies in small groups of patients have found that
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Figure 1. A frameless neuronavigation system being used to assist resection of an intracranial tumour. The pre-operative ‘virtual-world’ images can be seen on the screen and these are integrated with the ‘real-world’ patient anatomy extent of radical tumour resection was greater, and patient survival time longer, for patients undergoing surgery with neuronavigation for glioblastomas or malignant astrocytomas than it was in patients in whom conventional techniques were used.10,11 Although similar benefits of neuronavigation have been seen in a prospective study of glioma surgery, selection bias may have had an effect on clinical outcome.12 One of the main drawbacks of neuronavigation systems has been the problem of brain-shift. This is the positional change of tissue intraoperatively. Brain-shift can be due to a number of factors, including CSF drainage, tumour resection and brain swelling.13 Intra-operative MRI (ioMRI) has been developed in order to overcome this problem and has been found to increase the extent of tumour resection.14-16 Although there is some controversy regarding the value of gross tumour resection there are numerous studies which indicate that, for a variety of tumours, the degree of tumour removal correlates with prognosis; this is particularly the case in paediatric tumours.17 Neuronavigation systems which utilise ioMRI are likely to be of particular value in tumour surgery where maximal resection is paramount. 346
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In addition to delineating the intra-operative anatomy of intracranial lesions, new imaging modalities have been employed in order to understand better the anatomy of surrounding eloquent grey matter and critical white matter tracts. Intra-operative electrocortical stimulation has been the main method by which eloquent areas of cortex have been functionally mapped. Motor areas may be mapped by observing movements following electricocortical stimulation in patients anaesthetised without paralysing agents.18 Mapping of language function by this method requires that the patient is awake for a brief period intra-operatively.19 Neuronavigation systems now allow the integration of functional and anatomical imaging data so that eloquent areas adjacent to tumours can be visualised. Functional MRI (fMRI) and positon emission tomography (PET) scanning have been employed to delineate the position of eloquent grey matter areas in the operative field, thereby allowing them to be avoided in the tumour resection.20-23 The principle underlying both fMRI and PET in functional mapping is that localised changes in cerebral blood flow or metabolism are used as an indicator of neuronal activity. PET utilises either H215O as a blood tracer to measure blood flow or [18F]-fluorodeoxglucose uptake to measure cerebral metabolism. fMRI measures blood oxygen level dependent (BOLD) changes in the magnetic resonance signal due to alterations in the ratio of oxyhaemoglobin and deoxyhaemoglobin in the most metabolically active brain regions.24 In both imaging modalities, the blood flow signals in areas of the brain during a specific task are compared with blood flow signals at rest (control conditions). PET and fMRI have theoretical advantages over conventional electrocortical stimulation techniques in that they are non-invasive and also allow mapping of cortical activity deep into the sulci of the brain. Of the two techniques, fMRI is considered less invasive as it does not require the use of radioisotopes, and spatial resolution appears to be far better than with PET.25 Similar principles have been applied to the visualisation of eloquent white matter tracts using a form of MRI known as diffusion-tensor imaging. The random thermally-driven motion, or diffusion, of water molecules has been shown to occur directionally along white matter tracts due to the presence of axons and myelin sheaths which act as barriers.26 In diffusion tensor imaging (DTI), MRI gradients are adjusted to be sensitive to this diffusion and a mathematical model, or tensor, is used to visualise the direction of maximal diffusivity.27 DTI has been shown to be useful in providing intraoperative imaging of eloquent white matter tracts, such as descending motor tracts and optic tracts.28,29 It is also possible to combine DTI with fMRI in order to map cortical motor areas and their descending tracts together.30,31 Increasingly sophisticated neuronavigation systems, and the integration of pre-operative data with functional imaging modalities and intraoperative MRI, are set to become a part of routine neurosurgical practice. Early clinical results are promising but larger studies with a wider range of patients are needed. Nonetheless, integrated neuronavigation systems are likely to play a major role by increasing the extent of tumour resection and lowering the operative morbidity.
Imaging in epilepsy surgery Epilepsy is one of the most frequently occurring chronic neurological conditions, affecting 0.5–1% of the population. Although current drug therapy provides many patients with good seizure control,
the royal colleges of surgeons of edinburgh and ireland
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a substantial number of patients remain without adequate seizure control.32 In patients with medically refractory epilepsy, surgery to remove a seizure focus can result in long-term remission in up to 75% of patients.33,34 In these patients it may be the most successful treatment option. Epilepsy surgery requires detailed pre-operative planning in order to define the seizure focus. The most commonly performed resective procedure is anterior temporal lobectomy for removal of a sclerotic hippocampus which may be visualised with conventional MRI imaging. However, hippocampal sclerosis is MRI-negative in some patients, and there are many other patients with other pathologies that cause localised epilepsy with seizure foci not visible with conventional imaging modalities. In such cases, localisation of the seizure focus has been achieved with intracranial recording of epileptogenic activity using subdural grids or strips.35 PET studies using [18F]-fluorodeoxyglucose can identify areas of hypometabolism during seizures, such areas having been shown to correlate with the seizure focus.36 Single photon emission computed tomography (SPECT), using ictal injection of tracers, has also proven extremely useful in localising seizure foci as localised blood flow changes leave a ‘signature’ which can be seen hours later.37 fMRI has been investigated for its potential as a less invasive method of locating seizure foci. Correlating coincident electroencephalography (EEG) recording with fMRI can provide localisation information on seizure foci; although still experimental, this is an exciting development for the non-invasive location of surgical targets in pharmacoresistant epilepsy patients.38,39 Functional mapping and neuronavigation are also of major importance in epilepsy surgery. In patients with temporal lobe epilepsy, the cortical functions which are at greatest risk are memory and language.40,41 Lateralisation of language and memory function has been traditionally examined using Wada testing whereby the unilateral injection of barbiturate into the internal carotid artery temporarily disables first one hemisphere and then the other. fMRI has been compared with Wada testing in order to evaluate its potential as a much less invasive tool in the pre-operative assessment of patients in epilepsy surgery, and although results are conflicting it is possible that refinement of fMRI protocols will make this a valuable technique, particularly in the paediatric population.42,43 It is likely that, in the future, multimodal imaging will be used in the assessment and presurgical work-up of patients with pharmacoresistant epilepsy.44
Conclusions Neuroimaging modalities do not perform the operation for the surgeon but are a useful adjunct to the neurosurgeon’s toolbox. Advances in available imaging modalities help neurosurgeons to delineate the anatomy of intracranial lesions and to understand better the anatomy of surrounding eloquent grey matter and critical white matter tracts that cannot otherwise be visualised. Good resection of the pathological lesions will, however, remain dependent upon the skill of the operating surgeon. Functional neuronavigation, combined with intra-operative imaging, is likely to become more widely available over the next few years. This has already had a major impact on surgery for tumours and epileptic foci. These technologies are set to have a similar impact on other neurosurgical sub-specialties. For example, functional imaging techniques may have a role in defining specific brain regions to target with DBS, and may provide a means of overcoming small anatomical differences between individuals.45 Intra-operative fMRI may also be © 2008 Surgeon 6; 6: 344-9
effective in investigating the brain activity changes induced by DBS and in establishing the efficacy of a DBS procedure at the earliest possible stage.46-48 The integration of neuronavigation systems and intra-operative functional imaging is likely to impact on DBS by further refining the surgical technique and by revealing new functional targets. Image-guidance systems are also beginning to be used in spinal surgery. Spinal surgery poses particular challenges because of the need for placement of implant devices such as pedicle screws to fuse spinal segments. An accurate trajectory is paramount in the placement of pedicle screws in order to avoid neurovascular structures, including exiting nerve roots. Success in the use of three-dimensional image guidance systems in the placement of pedicle screws has already been reported.49 Neurosurgical skill will ultimately be the determining factor, and it may be that neuronavigation in spinal surgery may have a role in facilitating learning curves of the operating surgeon.
Copyright © 31 March 2008 REFERENCES 1. Molyneux AJ, Kerr RS, Yu LM et al. International Subarachnoid Aneurysm Trial (ISAT) Collaborative Group. International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet 2005; 366: 809-17 2. Pereira ACS, Green AL, Nandi D et al. Deep brain stimulation: indications and evidence. Future Drugs 2007; 4: 591-603 3. Mayberg HS, Lozano HS, Voon V et al. Deep brain stimulation for treatment-resistant depression. Neuron 2005; 45: 651-60 4. Berger MS, Deliganis AV, Dobbins J et al. The effect of extent of resection on recurrence in patients with low grade cerebral hemisphere gliomas. Cancer 1994; 74: 1784-91 5. Wissoff JH, Boyett JM, Berger MS et al. Current neurosurgical management and the impact of the extent of resection in the treatment of malignant gliomas of childhood: a report of the children’s cancer group trial no. CCG-945. J Neurosurg 1998; 89: 52-59 6. Spiegal EA, Wycis HT, Marks M et al. Stereotactic apparatus for operations on the human brain. Science 1947; 106: 349–50 7. Smith JS, Quiñones-Hinojosa A et al. Frame-based stereotactic biopsy remains an important diagnostic tool with distinct advantages over frameless stereotactic biopsy. J Neurooncol 2005; 73: 173–79 8. Roberts DW, Strohbehn JW, Hatch JF et al. A frameless stereotaxic integration of computerised tomographic imaging and the operating microscope. J Neurosurg 1986; 65: 545–49 9. Watanabe E, Watanabe T, Manaka S et al. Threedimensional digitiser (neuronavigator): new equipment for computed tomography-guided stereotaxic surgery. Surg Neurol 1987; 27: 543–47 10. Wirtz CR, Albert FK, Schwaderer M et al. The benet of neuronavigation for neurosurgery analyzed by its impact on glioblastoma surgery. Neurol Res 2000; 22: 354–60
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11. Kurimoto M, Hayashi N, Kamiyama H et al. Impact of neuronavigation and image-guided extensive resection for adult patients with supratentorial malignant astrocytomas: a single-institution retrospective study. Minim Invasive Neurosurg 2004; 47: 278–83 12. Litofsky NS, Bauer AM, Kasper RS et al. Imageguided resection of high-grade glioma: patient selection factors and outcome. Neurosurg Focus 2006; 20: 354–60 13. Nabavi A, Black PM, Gering DT et al. Serial intraoperative imaging of brain shift. Neurosurgery 2001; 48: 787–97 14. Tronnier VM, Wirtz CR, Knauth M et al. Intraoperative magnetic resonance imaging in neurosurgery. Neurosurgery 1997; 40: 891–900 15. Knauth M, Wirtz CR, Tronnier VM et al. Intraoperative MR imaging increases the extent of tumor resection in patients with high-grade gliomas. AJNR Am J Neuroradiol 1999; 20: 1642–46 16. Wirtz CR, Knauth M, Staubert A et al. Clinical evaluation and follow-up results for intraoperative magnetic resonance imaging in neurosurgery. Neurosurgery 2000; 46: 1112–20 17. Cohen KJ, Broniscer A, Glod J. Pediatric glial tumours. Curr Treat Options Oncol 2001; 2: 529–36 18. Ojemann G, Ojemann J, Lettich E et al. Cortical language localisation in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients. J Neurosurgery 1989; 71: 316–26 19. Meyer FB, Bates LM, Goerss SJ et al. Awake craniotomy for aggressive resection of primary gliomas located in eloquent brain. Mayo Clinic Proc 2001; 76: 677–87 20. Bittar RG, Olivier A, Sadikot AF et al. Localization of somatosensory function by using positron emission tomography scanning: a comparison with intraoperative cortical stimulation. Neurosurgery 1999; 44: 1249–55 21. Schreckenberger M, Spetxger U, Sabri O et al. Localisation of motor areas in brain tumour patients: a comparison of preoperative [18F]FDG-PET and intraoperative cortical electrostimulation. Eur J Nucl Med 2001; 28: 1394–1403 22. Nimsky C, Ganslandt O, Fahlbusch R. Functional neuronavigation and intraoperative MRI. Adv Tech Stand Neurosurg 2004; 29: 229–63 23. Majos A, Tybor K, Stefanczyk L et al. Cortical mapping by functional magnetic resonance imaging in patients with brain tumours. Eur Radiol 2005; 15: 1148–58 24. Ogawa S, Lee TM, Kay AR et al. Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proc Natl Acad Sci USA 1990; 87: 9868–72 25. Yoo SS, Talos IF, Golby AJ et al. Evaluating requirements for spatial resolution of fMRI for neurosurgical planning. Hum Brain Mapp 2004; 21: 34–43 26. Moseley ME, Cohen Y, Kucharczyk J et al. Diffusionweighted MR imaging of anisotropic water diffusion in cat central nervous system. Radiology 1990; 176: 439–46
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27. Jellison BJ, Field AS, Medow J et al. Diffusion tensor imaging of cerebral white matter: a pictoral review of physics, bre tract anatomy, and tumor imaging patterns. AJNR Am J Neuroradiol 2004; 25: 356–69 28. Berman JI, Berger MS, Mukherjee P et al. Diffusion-tensor imaging-guided tracking of bers of the pyramidal tract combined with intraoperative cortical stimulation mapping in patients with gliomas. J Neurosurg 2004; 101: 66–72 29. Tummala RP, Chu RM, Liu H et al. Application of diffusion tensor imaging to magnetic-resonanceguided brain tumour resection. Paediatr Neurosurg 2003; 39: 39–43 30. Parmer H, Sitoh YY, Yeo TT. Combined magnetic resonance tractography and functional magnetic resonance imaging in evaluation of brain tumours involving the motor system. J Comput Assist Tomogr 2004; 28: 551–56 31. Niminsky C, Grummich P, Sorensen AG et al. Visualisation of the pyramidal tract in glioma surgery by integrating diffusion tensor imaging in functional neuronavigation. Zentralbl Neurochir 2005; 66: 133–41 32. Stefan H, Steinhoff BJ. Emerging drugs for epilepsy and other treatment options. Eur J Neurol 2007; 14: 1154–61 33. Duncan JS. Epilepsy surgery. Clin Med 2007; 7: 137–42 34. Wiebe S, Blume WT, Girvin JP et al. Effectiveness and efciency of surgery for temporal lobe epilepsy study group. a randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001; 345: 311–18 35. Ikeda A, Miyamato S, Shibasaki H. Cortical mapping in epilepsy patients: information from subdural electrodes in presurgical evaluation. Epilepsia 2002; 43: 56–60 36. Chugani HT, Shields WD, Shewmon DA et al. Infantile spasms: I. PET identies focal cortical dysgenesis in cryptogenic cases for surgical treatment. Ann Neurol 1990; 27: 406–13 37. Van Paesshcen W. Ictal SPECT. Epilepsia 2004; 45: 35–40 38. Lemieux L. Electroencephalography-correlated functional MR imaging studies of epileptic activity. Neuroimaging Clin N Am 2004; 14: 487–506 39. Lemieux L, Salek-Haddadi A, Lund TE et al. Modelling large motion events in fMRI studies of patients with epilepsy. Magn Reson Imaging 2007; 25: 894–901 40. Scoville WB, Milner B. Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiatry 1957; 20: 11–21 41. Ferguson SM, Rayport M, Schell CA. Life after surgery for temporolimbic seizures. Int Rev Neurobiol 2006; 76: 87–116 42. Benke T, Köylü B, Visani P et al. Language lateralization in temporal lobe epilepsy: a comparison between fMRI and the Wada Test. Epilepsia 2006; 47: 1308–19
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43. Kesavadas C, Thomas B, Sujesh S et al. Real-time functional MR imaging (fMRI) for presurgical evaluation of paediatric epilepsy. Pediatr Radiol 2007; 37: 964–74 44. Kurian M, Spinelli L, Delavelle J et al.Multimodality imaging for focus localization in pediatric pharmacoresistant epilepsy. Epilep Dis 2007; 9: 20–31 45. Kringelbach ML, Jenkinson N, Owen SL, Aziz TZ. Translational principles of deep brain stimulation. Nat Rev Neurosci 2007; 8: 623–35 46. Georgi JC, Stippich C, Tronnier VM et al. Active deep brain stimulation during MRI: a feasibility study. Magn Res Med 2004; 51: 380–88 47. Hesselmann V, Sorger B, Girnus R et al. Intraoperative functional MRI as a new approach to monitor deep brain stimulation in Parkinson’s disease. Eur Radiol 2004; 14: 686–90 48. Hesselmann V, Maarouf M, Hunsche S et al. Functional MRI for immediate monitoring stereotactic thalamotomy in a patient with essential tremor. Eur Radiol 2006; 16: 2229–33 49. Lekovic GP, Potts EA, Karahalios DG et al. A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 2007; 7: 393–98
RCSI
DATE FOR YOUR DIARY
CHARTER DAY MEETINGS Thursday 12 - Saturday 14 February 2009
RCSI-ANTHONY WALSH/IPSEN TRAVELLING FELLOWSHIP IN UROLOGY 2009 The Royal College of Surgeons in Ireland in conjunction with Ipsen Pharmaceuticals Limited have made available a Urology Travelling Fellowship to enable a trainee to attend a meeting or to visit a centre of urological excellence in the year 2009. The value of the award is €6,000. Applications for the Fellowship are invited from Fellows and Members of the Royal College of Surgeons in Ireland who are Higher Surgical Trainees in Urology within the Republic of Ireland or Northern Ireland.
Incorporating:
Annual video surgery meeting & Annual meeting of the Irish higher surgical training group
Closing date Friday 2 January 2009 Professor W Arthur Tanner Director of Surgical Affairs Application form and further details may be obtained from: Ms G Conroy Ofce of the Director of Surgical Affairs 123 St. Stephen’s Green, Dublin 2 Tel: +353 4022187 e-mail: [email protected] http://www.rcsi.ie
© 2008 Surgeon 6; 6: 344-9
Programmes will be circulated shortly Communications Department Royal College of Surgeons in Ireland 123 St. Stephen’s Green, Dublin 2 Tel: +353 (1)4022238 Fax: +353 (1)4022458 e-mail: [email protected] http://www.rcsi.ie
the royal colleges of surgeons of edinburgh and ireland | 349
THE IMPACT OF NEW IMAGING TECHNOLOGIES IN NEUROSURGERY Neurosurgery has primarily been concerned with resective or ablative techniques for the accurate removal of pathological tissue with the minimal disruption of surrounding healthy neuronal matter. There have been numerous advances in neurosurgery which have aided the neurosurgeon to achieve this aim including the development of microsurgical, endoscopic and endovascular techniques. Functional neurosurgery has also seen a particular resurgence over the last 15 years with the identication of new anatomical targets and clinical indications. Technological advances in neuroimaging are providing many new adjuncts to the neurosurgeon’s armamentarium. Neuronavigation systems and intra-operative imaging have improved success in surgical removal of tumours from the central nervous system. Accurate epilepsy surgery requires imaging of the epileptogenic zone and accurate identication of adjacent eloquent cortex. New imaging modalities such as PET, SPECT, and fMRI can now be used in order to reduce neurological decits resulting from surgery. This review highlights some of the major advances in neurosurgery and discusses the impact of neuronavigation and functional imaging in tumour surgery and epilepsy surgery. keywords: neurosurgical technique, neuronavigation, intraoperative imaging, functional imaging, positron emission tomography (PET), functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI) Surgeon, 1 December 2008, pp.344-9
Introduction Neurosurgery is a rapidly changing discipline with many new frontiers and there have been many advances over the last 50 years. Some of the most important advances have been summarised in Table 1. The operative microscope is perhaps the single most significant advance in modern neurosurgery and has enabled better visualisation of vessels and nerves. Gazi Yasargil is credited with popularising the use of the operating microscope in neurosurgery, and microsurgical techniques have allowed more radical resection of central nervous system lesions. Yasargil has described microneurosurgery as a field with two arms. On the one hand there is the equipment: the operative microscope and the delicate, specialised instruments. On the other hand there is the skill of the neurosurgeon, who has to develop new indirect eye-hand co-ordination. Indirect hand-eye coordination skills have also allowed advances in neurosurgery by way of the development of endoscopic and endovascular techniques. Endoscopy of the ventricular system has become routine, particularly for paediatric neurosurgeons, in order to treat hydrocephalus and also to biopsy and debulk ventricular-based lesions such as colloid cysts. In aqueduct stenosis, the endoscope can be used to perform a third ventriculostomy in which a hole is made in the floor of the third ventricle. 344
|
the royal colleges of surgeons of edinburgh and ireland
This procedure removes the need for ventriculoperitioneal shunts in these patients and the associated complications of shunt systems. There has been a revolution in vascular neurosurgery with endovascular treatment of aneurysms with the insertion of platinum coils. Table 1. Some of the key advances in neurosurgery over the last 50 years 1. Introduction of the operative microscope and development of microsurgical techniques 2. Endovascular treatment of intracranial aneurysms 3. Endoscopic techniques such as ventriculostomy for treatment of hydrocephalus 4. Spinal xation techniques for spinal stabilisation 5. Minimally invasive spinal surgery techniques 6. Deep brain stimulation techniques in functional neurosurgery 7. Neuronavigation – frameless stereotaxy. 8. Intraoperative MRI
© 2008 Surgeon 6; 6: 344-9
The International Subarachnoid Aneurysmal Trial (ISAT), a largescale trial involving 43 centres and 2143 patients, compared surgical versus endovascular treatments for ruptured aneurysms in cases where both treatments were deemed to be equally appropriate.1 ISAT has provided Class I evidence of improved outcomes for coiling over surgical clipping of small anterior circulation aneurysms. Spinal neurosurgery has seen the development of microsurgical techniques and also the widespread introduction of spinal fusion techniques. Perhaps the most widespread advance has been the introduction of pedicle screws for spinal fixation. The use of implants to replace the use of iliac crest grafts in anterior cervical discectomy is another example of a recent change in neurosurgical practice, although it remains to be seen whether this results in better outcome for patients. Functional neurosurgery has seen a particular resurgence over the last 15 years with new subthalamic targets being identified for several clinical indications. Deep-brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is now considered the treatment of choice for pharmacologically resistant Parkinson’s disease. DBS has also been applied with considerable success for dystonia, cluster headache, epilepsy and chronic pain syndromes.2 There is also a renewed interest in psychosurgery following reports of the successful use of DBS for treatment of resistant depression.3 Primate research in the field of functional neurosurgery is one of the best examples of the successful application of findings from pre-clinical studies to clinical practice. These examples demonstrate that advances in neurosurgery have been the result of the skilled application by neurosurgeons of new technologies to assist in the treatment of neurological pathology. New imaging modalities have become available in recent years that are destined to aid neurosurgeons in their work. Perhaps one of the main changes is the introduction of these imaging modalities into the operating theatre. It must be emphasised that none of these technologies will ever replace the surgeon and it will always be the surgeon’s skill that is required to treat the patient. However, one of the aspects of neurological pathology is that it is sometimes not visible to the naked eye even with the aid of the operating microscope. This is particularly true of some epileptic foci and of the border between brain tumours and normal brain. Neuronavigation, particularly combined with intraoperative MRI, is likely to have a significant impact on neurosurgical practice. As availability of these technologies becomes more widespread more studies can be done to evaluate their effectiveness in improving patient outcome.
Neuronavigation and functional imaging in intracranial tumour surgery The maximal removal of diseased tissue whilst minimising the risk of neurological damage is the main challenge faced during intracranial tumour surgery. For intracranial mass lesions, such as primary or secondary tumours, the boundary between normal and abnormal tissue can be very ill defined. Even when an intracranial mass lesion is discrete from the surrounding brain, optimal planning of the surgical approach is paramount in performing a safe excision. Neuronavigation techniques are set to have a major impact on intracranial tumour surgery, allowing for more accurate resection and more minimally invasive techniques for tumour biopsy. Cerebral metastases are the most common form of brain tumour, © 2008 Surgeon 6; 6: 344-9
and surgical management depends upon the number of lesions and upon the presence or absence of a known primary. Debulking surgery is certainly an option for symptomatic metastases, and biopsy may be indicated if there is no known primary lesion. Gliomas are the most common primary brain tumour and management depends upon the type and grade of the tumour. For malignant gliomas, the gold standard is surgical excision and radiotherapy. For low-grade gliomas, and other less aggressive primary tumours such as meningiomas, surgical resection may be indicated for large lesions, particularly in young or symptomatic patients. Although still a matter of controversy, there is increasing evidence to suggest that, at least in low-grade gliomas, length of survival is related to the degree of resection, with long-term survival being associated with a greater degree of resection.4,5 Imaging modalities in intracranial tumour surgery can be used to locate the intracranial lesion and assist the operating surgeon to navigate within the cranial cavity in order to resect the lesion (neuronavigation). In addition, there is a role for neuro-imaging technologies which help define the location of eloquent areas of the brain and how these are related to the tumour. Victor Horsley and Robert Clarke developed a stereotactic method of locating deep-seated brain lesions in 1908 by assigning coordinates in three planes to neuroanatomical structures, based on cranial landmarks. Although this stereotactic system was successful in experiments with small animals, it was never used clinically. Neuronavigation technology made its first impact on clinical neurosurgery in the framebased stereotaxy introduced in 1947 by Spiegel et al, who introduced a plaster head cap, known as a stereoencephalatome, which combined pre-operative radiology with anatomical landmarks to locate deep cortical structures.6 Frame-based stereotaxy is still one of the mainstay techniques in neurosurgery and is routinely used for the biopsy of deep-seated cerebral tumours.7 The advent of new imaging technologies has led to the development of frameless stereotaxy. The first frameless stereotactic system was reported by Roberts in 1986 and was based on a system of acoustic triangulation.8 The term ‘neuronavigator’ was first used by Watanabe in 1987, in association with the use of a localising aluminium arm in combination with CT images.9 Improved quality of digital image data and the wide availability of appropriate computer technology has allowed the development of increasingly sophisticated frameless neuronavigation systems. All frameless neuronavigation systems rely on the integration of pre-operatively acquired CT or MRI data with patient reference points. These patient reference points can be either anatomical or topically applied fiducial points. The transformed data set allows the guidance of surgical instruments within a three-dimensional coordinate system which integrates pre-operative ‘virtual-world’ images and ‘real-world’ patient anatomy (Figure 1). Frameless stereotactic neuronavigation has several advantages over frame-based systems. Frameless navigation dispenses with the need for large frames that interfere with the operative field, and there is potentially an unlimited number of targets navigable within the cranial vault. Frameless neuronavigation is, therefore, a highly versatile technique which can be used in much more invasive procedures than are allowed by frame-based systems. Validating the usefulness of neuronavigation systems in tumour surgery requires the systematic assessment of the available systems by direct comparison with conventional microneurosurgical techniques. Retrospective studies in small groups of patients have found that
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Figure 1. A frameless neuronavigation system being used to assist resection of an intracranial tumour. The pre-operative ‘virtual-world’ images can be seen on the screen and these are integrated with the ‘real-world’ patient anatomy extent of radical tumour resection was greater, and patient survival time longer, for patients undergoing surgery with neuronavigation for glioblastomas or malignant astrocytomas than it was in patients in whom conventional techniques were used.10,11 Although similar benefits of neuronavigation have been seen in a prospective study of glioma surgery, selection bias may have had an effect on clinical outcome.12 One of the main drawbacks of neuronavigation systems has been the problem of brain-shift. This is the positional change of tissue intraoperatively. Brain-shift can be due to a number of factors, including CSF drainage, tumour resection and brain swelling.13 Intra-operative MRI (ioMRI) has been developed in order to overcome this problem and has been found to increase the extent of tumour resection.14-16 Although there is some controversy regarding the value of gross tumour resection there are numerous studies which indicate that, for a variety of tumours, the degree of tumour removal correlates with prognosis; this is particularly the case in paediatric tumours.17 Neuronavigation systems which utilise ioMRI are likely to be of particular value in tumour surgery where maximal resection is paramount. 346
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In addition to delineating the intra-operative anatomy of intracranial lesions, new imaging modalities have been employed in order to understand better the anatomy of surrounding eloquent grey matter and critical white matter tracts. Intra-operative electrocortical stimulation has been the main method by which eloquent areas of cortex have been functionally mapped. Motor areas may be mapped by observing movements following electricocortical stimulation in patients anaesthetised without paralysing agents.18 Mapping of language function by this method requires that the patient is awake for a brief period intra-operatively.19 Neuronavigation systems now allow the integration of functional and anatomical imaging data so that eloquent areas adjacent to tumours can be visualised. Functional MRI (fMRI) and positon emission tomography (PET) scanning have been employed to delineate the position of eloquent grey matter areas in the operative field, thereby allowing them to be avoided in the tumour resection.20-23 The principle underlying both fMRI and PET in functional mapping is that localised changes in cerebral blood flow or metabolism are used as an indicator of neuronal activity. PET utilises either H215O as a blood tracer to measure blood flow or [18F]-fluorodeoxglucose uptake to measure cerebral metabolism. fMRI measures blood oxygen level dependent (BOLD) changes in the magnetic resonance signal due to alterations in the ratio of oxyhaemoglobin and deoxyhaemoglobin in the most metabolically active brain regions.24 In both imaging modalities, the blood flow signals in areas of the brain during a specific task are compared with blood flow signals at rest (control conditions). PET and fMRI have theoretical advantages over conventional electrocortical stimulation techniques in that they are non-invasive and also allow mapping of cortical activity deep into the sulci of the brain. Of the two techniques, fMRI is considered less invasive as it does not require the use of radioisotopes, and spatial resolution appears to be far better than with PET.25 Similar principles have been applied to the visualisation of eloquent white matter tracts using a form of MRI known as diffusion-tensor imaging. The random thermally-driven motion, or diffusion, of water molecules has been shown to occur directionally along white matter tracts due to the presence of axons and myelin sheaths which act as barriers.26 In diffusion tensor imaging (DTI), MRI gradients are adjusted to be sensitive to this diffusion and a mathematical model, or tensor, is used to visualise the direction of maximal diffusivity.27 DTI has been shown to be useful in providing intraoperative imaging of eloquent white matter tracts, such as descending motor tracts and optic tracts.28,29 It is also possible to combine DTI with fMRI in order to map cortical motor areas and their descending tracts together.30,31 Increasingly sophisticated neuronavigation systems, and the integration of pre-operative data with functional imaging modalities and intraoperative MRI, are set to become a part of routine neurosurgical practice. Early clinical results are promising but larger studies with a wider range of patients are needed. Nonetheless, integrated neuronavigation systems are likely to play a major role by increasing the extent of tumour resection and lowering the operative morbidity.
Imaging in epilepsy surgery Epilepsy is one of the most frequently occurring chronic neurological conditions, affecting 0.5–1% of the population. Although current drug therapy provides many patients with good seizure control,
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a substantial number of patients remain without adequate seizure control.32 In patients with medically refractory epilepsy, surgery to remove a seizure focus can result in long-term remission in up to 75% of patients.33,34 In these patients it may be the most successful treatment option. Epilepsy surgery requires detailed pre-operative planning in order to define the seizure focus. The most commonly performed resective procedure is anterior temporal lobectomy for removal of a sclerotic hippocampus which may be visualised with conventional MRI imaging. However, hippocampal sclerosis is MRI-negative in some patients, and there are many other patients with other pathologies that cause localised epilepsy with seizure foci not visible with conventional imaging modalities. In such cases, localisation of the seizure focus has been achieved with intracranial recording of epileptogenic activity using subdural grids or strips.35 PET studies using [18F]-fluorodeoxyglucose can identify areas of hypometabolism during seizures, such areas having been shown to correlate with the seizure focus.36 Single photon emission computed tomography (SPECT), using ictal injection of tracers, has also proven extremely useful in localising seizure foci as localised blood flow changes leave a ‘signature’ which can be seen hours later.37 fMRI has been investigated for its potential as a less invasive method of locating seizure foci. Correlating coincident electroencephalography (EEG) recording with fMRI can provide localisation information on seizure foci; although still experimental, this is an exciting development for the non-invasive location of surgical targets in pharmacoresistant epilepsy patients.38,39 Functional mapping and neuronavigation are also of major importance in epilepsy surgery. In patients with temporal lobe epilepsy, the cortical functions which are at greatest risk are memory and language.40,41 Lateralisation of language and memory function has been traditionally examined using Wada testing whereby the unilateral injection of barbiturate into the internal carotid artery temporarily disables first one hemisphere and then the other. fMRI has been compared with Wada testing in order to evaluate its potential as a much less invasive tool in the pre-operative assessment of patients in epilepsy surgery, and although results are conflicting it is possible that refinement of fMRI protocols will make this a valuable technique, particularly in the paediatric population.42,43 It is likely that, in the future, multimodal imaging will be used in the assessment and presurgical work-up of patients with pharmacoresistant epilepsy.44
Conclusions Neuroimaging modalities do not perform the operation for the surgeon but are a useful adjunct to the neurosurgeon’s toolbox. Advances in available imaging modalities help neurosurgeons to delineate the anatomy of intracranial lesions and to understand better the anatomy of surrounding eloquent grey matter and critical white matter tracts that cannot otherwise be visualised. Good resection of the pathological lesions will, however, remain dependent upon the skill of the operating surgeon. Functional neuronavigation, combined with intra-operative imaging, is likely to become more widely available over the next few years. This has already had a major impact on surgery for tumours and epileptic foci. These technologies are set to have a similar impact on other neurosurgical sub-specialties. For example, functional imaging techniques may have a role in defining specific brain regions to target with DBS, and may provide a means of overcoming small anatomical differences between individuals.45 Intra-operative fMRI may also be © 2008 Surgeon 6; 6: 344-9
effective in investigating the brain activity changes induced by DBS and in establishing the efficacy of a DBS procedure at the earliest possible stage.46-48 The integration of neuronavigation systems and intra-operative functional imaging is likely to impact on DBS by further refining the surgical technique and by revealing new functional targets. Image-guidance systems are also beginning to be used in spinal surgery. Spinal surgery poses particular challenges because of the need for placement of implant devices such as pedicle screws to fuse spinal segments. An accurate trajectory is paramount in the placement of pedicle screws in order to avoid neurovascular structures, including exiting nerve roots. Success in the use of three-dimensional image guidance systems in the placement of pedicle screws has already been reported.49 Neurosurgical skill will ultimately be the determining factor, and it may be that neuronavigation in spinal surgery may have a role in facilitating learning curves of the operating surgeon.
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11. Kurimoto M, Hayashi N, Kamiyama H et al. Impact of neuronavigation and image-guided extensive resection for adult patients with supratentorial malignant astrocytomas: a single-institution retrospective study. Minim Invasive Neurosurg 2004; 47: 278–83 12. Litofsky NS, Bauer AM, Kasper RS et al. Imageguided resection of high-grade glioma: patient selection factors and outcome. Neurosurg Focus 2006; 20: 354–60 13. Nabavi A, Black PM, Gering DT et al. Serial intraoperative imaging of brain shift. Neurosurgery 2001; 48: 787–97 14. Tronnier VM, Wirtz CR, Knauth M et al. Intraoperative magnetic resonance imaging in neurosurgery. Neurosurgery 1997; 40: 891–900 15. Knauth M, Wirtz CR, Tronnier VM et al. Intraoperative MR imaging increases the extent of tumor resection in patients with high-grade gliomas. AJNR Am J Neuroradiol 1999; 20: 1642–46 16. Wirtz CR, Knauth M, Staubert A et al. Clinical evaluation and follow-up results for intraoperative magnetic resonance imaging in neurosurgery. Neurosurgery 2000; 46: 1112–20 17. Cohen KJ, Broniscer A, Glod J. Pediatric glial tumours. Curr Treat Options Oncol 2001; 2: 529–36 18. Ojemann G, Ojemann J, Lettich E et al. Cortical language localisation in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients. J Neurosurgery 1989; 71: 316–26 19. Meyer FB, Bates LM, Goerss SJ et al. Awake craniotomy for aggressive resection of primary gliomas located in eloquent brain. Mayo Clinic Proc 2001; 76: 677–87 20. Bittar RG, Olivier A, Sadikot AF et al. Localization of somatosensory function by using positron emission tomography scanning: a comparison with intraoperative cortical stimulation. Neurosurgery 1999; 44: 1249–55 21. Schreckenberger M, Spetxger U, Sabri O et al. Localisation of motor areas in brain tumour patients: a comparison of preoperative [18F]FDG-PET and intraoperative cortical electrostimulation. Eur J Nucl Med 2001; 28: 1394–1403 22. Nimsky C, Ganslandt O, Fahlbusch R. Functional neuronavigation and intraoperative MRI. Adv Tech Stand Neurosurg 2004; 29: 229–63 23. Majos A, Tybor K, Stefanczyk L et al. Cortical mapping by functional magnetic resonance imaging in patients with brain tumours. Eur Radiol 2005; 15: 1148–58 24. Ogawa S, Lee TM, Kay AR et al. Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proc Natl Acad Sci USA 1990; 87: 9868–72 25. Yoo SS, Talos IF, Golby AJ et al. Evaluating requirements for spatial resolution of fMRI for neurosurgical planning. Hum Brain Mapp 2004; 21: 34–43 26. Moseley ME, Cohen Y, Kucharczyk J et al. Diffusionweighted MR imaging of anisotropic water diffusion in cat central nervous system. Radiology 1990; 176: 439–46
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27. Jellison BJ, Field AS, Medow J et al. Diffusion tensor imaging of cerebral white matter: a pictoral review of physics, bre tract anatomy, and tumor imaging patterns. AJNR Am J Neuroradiol 2004; 25: 356–69 28. Berman JI, Berger MS, Mukherjee P et al. Diffusion-tensor imaging-guided tracking of bers of the pyramidal tract combined with intraoperative cortical stimulation mapping in patients with gliomas. J Neurosurg 2004; 101: 66–72 29. Tummala RP, Chu RM, Liu H et al. Application of diffusion tensor imaging to magnetic-resonanceguided brain tumour resection. Paediatr Neurosurg 2003; 39: 39–43 30. Parmer H, Sitoh YY, Yeo TT. Combined magnetic resonance tractography and functional magnetic resonance imaging in evaluation of brain tumours involving the motor system. J Comput Assist Tomogr 2004; 28: 551–56 31. Niminsky C, Grummich P, Sorensen AG et al. Visualisation of the pyramidal tract in glioma surgery by integrating diffusion tensor imaging in functional neuronavigation. Zentralbl Neurochir 2005; 66: 133–41 32. Stefan H, Steinhoff BJ. Emerging drugs for epilepsy and other treatment options. Eur J Neurol 2007; 14: 1154–61 33. Duncan JS. Epilepsy surgery. Clin Med 2007; 7: 137–42 34. Wiebe S, Blume WT, Girvin JP et al. Effectiveness and efciency of surgery for temporal lobe epilepsy study group. a randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001; 345: 311–18 35. Ikeda A, Miyamato S, Shibasaki H. Cortical mapping in epilepsy patients: information from subdural electrodes in presurgical evaluation. Epilepsia 2002; 43: 56–60 36. Chugani HT, Shields WD, Shewmon DA et al. Infantile spasms: I. PET identies focal cortical dysgenesis in cryptogenic cases for surgical treatment. Ann Neurol 1990; 27: 406–13 37. Van Paesshcen W. Ictal SPECT. Epilepsia 2004; 45: 35–40 38. Lemieux L. Electroencephalography-correlated functional MR imaging studies of epileptic activity. Neuroimaging Clin N Am 2004; 14: 487–506 39. Lemieux L, Salek-Haddadi A, Lund TE et al. Modelling large motion events in fMRI studies of patients with epilepsy. Magn Reson Imaging 2007; 25: 894–901 40. Scoville WB, Milner B. Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiatry 1957; 20: 11–21 41. Ferguson SM, Rayport M, Schell CA. Life after surgery for temporolimbic seizures. Int Rev Neurobiol 2006; 76: 87–116 42. Benke T, Köylü B, Visani P et al. Language lateralization in temporal lobe epilepsy: a comparison between fMRI and the Wada Test. Epilepsia 2006; 47: 1308–19
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43. Kesavadas C, Thomas B, Sujesh S et al. Real-time functional MR imaging (fMRI) for presurgical evaluation of paediatric epilepsy. Pediatr Radiol 2007; 37: 964–74 44. Kurian M, Spinelli L, Delavelle J et al.Multimodality imaging for focus localization in pediatric pharmacoresistant epilepsy. Epilep Dis 2007; 9: 20–31 45. Kringelbach ML, Jenkinson N, Owen SL, Aziz TZ. Translational principles of deep brain stimulation. Nat Rev Neurosci 2007; 8: 623–35 46. Georgi JC, Stippich C, Tronnier VM et al. Active deep brain stimulation during MRI: a feasibility study. Magn Res Med 2004; 51: 380–88 47. Hesselmann V, Sorger B, Girnus R et al. Intraoperative functional MRI as a new approach to monitor deep brain stimulation in Parkinson’s disease. Eur Radiol 2004; 14: 686–90 48. Hesselmann V, Maarouf M, Hunsche S et al. Functional MRI for immediate monitoring stereotactic thalamotomy in a patient with essential tremor. Eur Radiol 2006; 16: 2229–33 49. Lekovic GP, Potts EA, Karahalios DG et al. A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 2007; 7: 393–98
RCSI
DATE FOR YOUR DIARY
CHARTER DAY MEETINGS Thursday 12 - Saturday 14 February 2009
RCSI-ANTHONY WALSH/IPSEN TRAVELLING FELLOWSHIP IN UROLOGY 2009 The Royal College of Surgeons in Ireland in conjunction with Ipsen Pharmaceuticals Limited have made available a Urology Travelling Fellowship to enable a trainee to attend a meeting or to visit a centre of urological excellence in the year 2009. The value of the award is €6,000. Applications for the Fellowship are invited from Fellows and Members of the Royal College of Surgeons in Ireland who are Higher Surgical Trainees in Urology within the Republic of Ireland or Northern Ireland.
Incorporating:
Annual video surgery meeting & Annual meeting of the Irish higher surgical training group
Closing date Friday 2 January 2009 Professor W Arthur Tanner Director of Surgical Affairs Application form and further details may be obtained from: Ms G Conroy Ofce of the Director of Surgical Affairs 123 St. Stephen’s Green, Dublin 2 Tel: +353 4022187 e-mail: [email protected] http://www.rcsi.ie
© 2008 Surgeon 6; 6: 344-9
Programmes will be circulated shortly Communications Department Royal College of Surgeons in Ireland 123 St. Stephen’s Green, Dublin 2 Tel: +353 (1)4022238 Fax: +353 (1)4022458 e-mail: [email protected] http://www.rcsi.ie
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