Magnetic Resonance Imaging of Patients with Epilepsy

Clinical Radiology (2001) 56: 787±801 doi:10.1053/crad.2001.0744, available online at http://www.idealibrary.com on Review Magnetic Resonance Imaging of Patients with Epilepsy S E J CO N NO R , J M J A RO S Z Department of Neuroradiology, King's College Hospital, London, U.K Received: 27 October 2000 Revised: 29 January 2001 Accepted: February 2001 Magnetic resonance imaging (MRI) is the radiological investigation of choice for the evaluation of patients with epilepsy It is able to detect and characterize the structural origin of seizures, and signi®cantly in¯uences treatment planning and prognosis The indications for MRI, protocols used for MRI in epilepsy and the relevant imaging anatomy are discussed The major categories of epileptogenic lesions which result in chronic seizures are reviewed and illustrated Mesial temporal sclerosis is emphasized, re¯ecting its major importance as a cause of medically intractable epilepsy The role of MRI in the planning and assessment of epilepsy surgery is considered Connor, S E J and Jarosz, J M # 2001 The Royal College of Radiologists (2001) Clinical Radiology 56, 787±901 Key words: epilepsy, magnetic resonance imaging Epilepsy is a disorder of spontaneously recurrent seizures which are caused by abnormal electrical discharges in the brain It a€ects between 0.5% and 1% of the world's population [1] Seizures may be divided into those that begin with a local discharge of epileptic activity and which appear focal on electroencephalograms (EEGs), termed partial seizures, and those that are initiated simultaneously throughout the brain, called generalized seizures [2] The most common focus for a partial seizure is the temporal lobe Complex partial seizures are a subset of partial seizures which are characterized by impairment of consciousness or memory; they most frequently originate from the temporal lobe Although only a small percentage of patients with seizures are refractory to medical treatment, complex partial seizures are responsible for the majority of such cases [3,4] Surgical treatment of epileptogenic structural disorders such as mesial temporal sclerosis, tumours and vascular malformations may eliminate seizures in these patients with medically intractable epilepsy Such surgery is targeted at the `epileptogenic zone' which is that part of the cortex which must be resected to eliminate seizures [5] but does not necessarily correspond to the `epileptogenic lesion' seen on structural imaging [6,7] The role of imaging is to detect and characterize the structural basis of focal seizures Computed tomography (CT) is able to identify large structural abnormalities and Author for correspondence and guarantor of study: Dr S E J Connor, Department of Neuroradiology, King's Healthcare NHS Trust, King's College Hospital, Denmark Hill, London SE5 9RS, U.K Fax: ‡44 (0)207 346 3120; E-mail: s.connor@talk21.com 0009-9260/01/100787+15 $35.00/0 remains adequate in the emergency or perioperative setting CT is also more frequently used than MRI for the investigation of recent onset seizures in adults in the U.K., despite MRI being more sensitive to the detection of early disease A speci®c cause for seizures, usually either cerebrovascular disease, primary or secondary brain tumour, is identi®ed in fewer than 50% of patients with such recent onset seizures [8] However, the superiority of MRI for the identi®cation of hippocampal sclerosis, cortical abnormalities and other surgically correctable epileptogenic lesions means that it is generally preferred for the assessment of chronic epilepsy, and particularly when complex partial seizures are present Up to 80% of patients with chronic temporal lobe epilepsy have structural lesions identi®ed by MRI [9,10] The MRI assessment of chronic epilepsy will be emphasized and illustrated in this review since most radiologists will be familiar with the MRI appearances of tumour, infection and in¯ammation which result in new onset seizures in adulthood [8] THE ROLE AND INDICATIONS FOR MRI IN CHRONIC EPILEPSY The demonstration of epileptogenic lesions by MRI is important for the treatment and prognosis of individual cases and helps select those patients with medically intractable seizures who are surgical candidates [8,10±14] Physiological imaging investigations such as single photon emission computed tomography (SPECT), positron emission tomography (PET) and functional MRI all # 2001 The Royal College of Radiologists 788 CLINICAL RADIOLOGY provide complementary information in those patients considered for epilepsy surgery, both to help delineate the `epileptogenic zone' and to identify functionally eloquent cortex [7]; however, they are inadequate for the assessment of brain structure MRI alone is currently recommended for the neuro-imaging evaluation of patients with chronic epilepsy [14] MRI should, ideally, be performed on all patients with an electroclinical diagnosis of partial seizures or partial seizures evolving to secondary generalized seizures since partial epilepsy is often associated with a structural abnormality of the brain [15] Some seizures that appear generalized from the start on clinical and EEG criteria are actually rapidly spreading partial seizures [16,17] and so MRI studies are also warranted when there are unclassi®ed or apparently generalized seizures in the ®rst year of life (when seizure type is particularly dicult to di€erentiate) or in adulthood [14,18] MRI is essential when seizures are poorly controlled with medication or are associated with progressive neurological or neuropsychological de®cit [14, 19] CT is only indicated in the patient with chronic epilepsy if MRI is not readily available, if it is contraindicated, or when it may provide complementary information, for instance to detect calci®cation in patients with a history of congenital infection or stigmata of tuberous sclerosis MRI PROTOCOLS Patients with chronic epilepsy should be examined with a speci®c imaging protocol which best demonstrates the likely abnormalities Because most partial seizures and medically intractable seizures arise from the temporal lobe, and in particular from the hippocampus, oblique coronal imaging, orthogonal to the hippocampal structures, is most useful The hippocampus lies in a plane which is seen on a midline sagittal section as the line joining the splenium of the corpus callosum to the posteroinferior frontal lobe [11] The optimum protocol includes an oblique coronal high resolution T1-weighted volume data set through the whole brain which allows reformatting in any plane, measurement of hippocampal volumes and co-registration with functional data A spoiled gradient recalled echo acquisition with a 1.5 mm partition size is one such sequence An oblique coronal T2-weighted sequence, typically using mm thin sections, should also be obtained with either a fast spin echo or conventional spin echo technique in order to detect hippocampal signal abnormalities [20,21] A coronal ¯uid attenuated inversion recovery (FLAIR) sequence is helpful to increase conspicuity of high T2 signal cortical lesions adjacent to the cerebrospinal ¯uid (CSF) spaces [22] although its increased yield of abnormalities in epilepsy relative to standard sequences is disputed [23±25] Gadolinium-DTPA enhanced T1-weighted images are required to look for primary or secondary tumours, infection or in¯ammation in the presence of recent onset epilepsy [8] However, intravenous gadolinium does not increase the detection of structural abnormalities in chronic epilepsy and it is not routinely administered [26] although it is useful for the characterization of abnormalities STRUCTURAL LESIONS IN CHRONIC EPILEPSY The histological ®ndings in patients undergoing surgery for temporal lobe epilepsy reveal mesial temporal sclerosis (50±70%) to be the commonest abnormality, with tumours, developmental abnormalities of neuronal migration and cortical organization, vascular malformations and posttraumatic, in¯ammatory or ischaemic gliosis being found less frequently [27±30] A non-speci®c or normal histological examination is found in 10±25%, while dual abnormalities, which are usually due to a combination of hippocampal sclerosis and either glioma, heterotopia or vascular abnormalities [31], are present in 8±22% of patients A similar distribution of structural abnormalities is diagnosed in patients undergoing MRI for temporal lobe epilepsy or medically refractory epilepsy [9,10,32] In patients with extratemporal refractory epilepsy, coexistent hippocampal pathology is rare [33], and MRI reveals tumours and vascular malformations to be the commonest lesions in the frontal lobe, tumours and cortical dysgenesis in the parietal lobe, and cortical dysgenesis and vascular malformations in the occipital lobe [32] Lesions are less commonly identi®ed in the presence of extratemporal seizures [34] Mesial Temporal Sclerosis Mesial temporal sclerosis (MTS) refers to neuronal loss and gliosis of the hippocampus which leads to reorganization of neuronal pathways and the formation of an epileptogenic focus [35] It may be a consequence of childhood febrile seizures, encephalitis, pre- and perinatal insults or may represent a pathological response to repeated seizures [35±37] It is the commonest abnormality in medically intractable epilepsy and surgical resection of the hippocampus and anterior temporal lobe renders up to 90% of these patients seizure-free [3,38] The MRI assessment of MTS requires some knowledge of hippocampal anatomy The macroscopic anatomy and internal architecture, together with imaging correlation, of the hippocampus has been extensively reviewed [39,40] Coronal sections demonstrate the normal grey matter of the hippocampus to be isointense to cortex with T1-weighting [41] and slightly hyperintense to cortex with FLAIR sequences [42] The hippocampal head (also called pes or foot) is bulbous and is seen in the same coronal plane as the interpeduncular cistern (Fig 1a) It lies posteroinferior to the amygdala from which it is separated by the uncal recess of the temporal horn and the alveus, which is a thin layer of white matter Prominent interdigitations are seen on its superior aspect at the lateral ventricular surface (Fig 1b) The body of the hippocampus (Fig 1c) is seen at the level of the midbrain It is ovoid in shape and is the most uniform portion It lies inferior to the choroidal ®ssure and sits on the subiculum of the parahippocampal gyrus from which it is separated by the hippocampal ®ssure (which may be obliterated or only partially visualized) The tail of the hippocampus is located (Fig 1d) at or behind the midbrain where it is seen adjacent to the crura of the fornices The two primary MRI ®ndings of mesial temporal sclerosis are hippocampal atrophy (usually recognized by MRI OF PATIENTS WITH EPILEPSY 789 Fig ± Normal hippocampal anatomy (a) T2-weighted coronal image at the level of the interpeduncular cistern demonstrates the hippocampal head (arrowhead) separated from the amygdala (star) by the uncal recess of the temporal horn (curved arrow) (b) T1-weighted coronal image demonstrates the interdigitations on the ventricular surface of the hippocampal head (c) T2-weighted coronal image at the level of the midbrain demonstrates the ovoid hippocampal body (curved arrow) inferior to the choroidal ®ssure (d) T2-weighted coronal image posterior to the midbrain shows the hippocampal tail (arrowhead) adjacent to the crus of the fornix (curved arrows) 790 CLINICAL RADIOLOGY Fig ± Fifteen-year-old girl with complex partial seizures and mesial temporal sclerosis (a) T2-weighted coronal image at the level of the hippocampal head demonstrates an atrophic hyperintense hippocampal head (arrow) and a small ipsilateral mamillary body (arrowhead) (b) T2-weighted coronal image more posteriorly shows an atrophic anterior ipsilateral thalamus with an area of encephalomalacia more superiorly (arrows) and poor grey±white matter di€erentiation of the ipsilateral parahippocampal gyrus (c) T1-weighted coronal image at the same level demonstrates a slender ipsilateral fornix (curved arrow) (d) T2-weighted coronal image further posteriorly reveals an atrophic, hyperintense hippocampal body (arrow) which is dicult to distinguish from the adjacent enlarged temporal horn asymmetry in the case of unilateral atrophy) and increased signal intensity of the hippocampus on T2-weighted imaging (Figs 2a±d) [38,43±45] The most recent MR investigations using visual inspection of these features have demonstrated sensitivities of 87±100% [12,44,46,47] In analysing these features it must be appreciated that minor asymmetry of hippocampal volumes is normal [41]; however, signi®cant asymmetry is speci®c for MTS and is not prevalent in normal patients [48,49] Hyperintensity on T2-weighted sections may also be seen in the proximity of the hippocampus owing to partial volume averaging of the CSF, tumour, oedema, blood products, ¯ow artifact [50] and developmental cysts [41] In addition, mesial temporal hyperintensity on FLAIR sequences is mimicked by MRI OF PATIENTS WITH EPILEPSY 791 Fig ± Thirteen-year-old (boy) with complex partial seizures and dual pathology (a) Post-gadolinium T1-weighted axial image and (b) T2weighted coronal image reveal an irregular heterogenous lesion in the left anterior temporal lobe There are poorly enhancing areas (arrowheads) There are some hypointense components (curved arrows) which result from calci®cation The lesion was resected and found to represent a DNET (c) T2-weighted coronal image demonstrates the left hippocampal body to be small, so indicating coexisting MTS temporal horn choroid plexus or incomplete CSF signal suppression [11,51] However, if the high T2 signal is truly localized to the hippocampus, it has been shown to be a highly speci®c ®nding for MTS [12,20,52] and may occur in the absence of atrophy [12,53] The whole hippocampus must be carefully studied for atrophy and signal abnormality since the changes are non-uniform in 44% of patients, most frequently being localized to the body [54] Visual assessment of hippocampal asymmetry may be hampered by head rotation The position of the internal auditory canals on T2 weighting and the ventricular atria [41] or middle cerebellar peduncles on T1 weighting are useful landmarks to ensure that the same coronal anatomical sections are being compared for each hippocampus Visual assessment may reliably detect hippocampal asymmetry of more than 20%; however, quantitative analysis is 792 CLINICAL RADIOLOGY Fig ± Sixteen-year-old girl with band heterotopia (a) T1-weighted coronal and (b) T2-weighted coronal images show a thin band of grey matter isointensity within the subcortical white matter of both frontal lobes (arrows) required to assess smaller hippocampal volume ratios [55] When hippocampal volumetric analysis is compared to qualitative analysis, the sensitivity for MTS is slightly increased [3,56] However, the commonly used methodology of manual outlining of the hippocampus on contiguous thin section T1-weighted images (usually over 20 images) is demanding and time-consuming, and automated methods are still in their infancy [50] It is therefore impractical in routine clinical practice and is generally only used in the pre-operative assessment of selected cases Measurements of the T2 relaxation time may also be quanti®ed and this improves the sensitivity for hippocampal abnormalities [57] Fig ± Thirty-four-year-old woman with complex partial seizures and subependymal grey matter heterotopia (a) T1-weighted coronal and (b) T2-weighted coronal images demonstrate bilateral nodular areas of grey matter isointensity (curved arrows) adjacent to the lateral walls of the ventricular trigones There are numerous secondary MR features which support a diagnosis of MTS These include temporal horn dilatation (Fig 2d) [58], loss of hippocampal internal architecture [59], decreased hippocampal signal on T1weighted images and poor parahippocampal grey±white matter de®nition (Fig 2d) Other ®ndings, such as MRI OF PATIENTS WITH EPILEPSY 793 Fig ± Thirteen-year-old girl with complex partial seizures and tuberous sclerosis (a) T2-weighted axial and (b) FLAIR axial images reveal multiple high signal areas on T2-weighted sequence (arrowheads) and FLAIR sequence, within the cortex and subcortical white matter of both frontal lobes These represent hamartomata (tubers) ipsilateral atrophy of the temporal lobe [60], thalamus (Fig 2b) [61], fornix (Fig 2c) and mamillary body (Fig 2a) [62], are related to the a€erent and e€erent pathways of the hippocampus (Fig 3) These secondary features are present in 40±60% of patients with MTS [9,38] and help improve the diagnostic accuracy when used with the primary ®ndings, but they are unreliable signs in their own right Loss of hippocampal interdigitations has recently been proposed as a further major criterion for the MR diagnosis of MTS [63] Bilateral, roughly symmetrical hippocampal atrophy is present on MRI and pathological studies in 10±15% of patients with MTS [31,64] Assessment of bilateral abnormalities is dicult, both visually and with volumetric techniques It is best studied by measuring absolute hippocampal volumes [62] which have a de®ned normative range [65], should be calculated for each centre and may be corrected for total intracranial volume [66] The visual search for MTS must continue even in the presence of another focal lesion on MRI since dual pathology is not uncommon (Fig 3) If an extrahippocampal lesion is surgically resected, but coexistent sclerosed hippocampus remains, there is a poor prognosis [11,67] Similarly, undetected subtle extrahippocampal pathology is responsible for poor outcome following surgery for MTS [68] Disorders of Neuronal Migration and Cortical Organization Disorders of neuronal migration and cortical organization are being identi®ed more often in patients undergoing MRI for seizure disorders [69] An incidence of 4±7% in patients with epilepsy referred for MRI has been reported [10,70] and it is the most common presentation of these disorders [71] They are the most common underlying lesion in infants and young children with epilepsy, accounting for up to 40% of children with infantile spasms [72] The range of abnormalities includes cortical dysplasia (agyria, pachygyria, polymicrogyria), abnormal location of grey matter (band, laminar or nodular heterotopias) (Figs & 5), schizencephaly, hemimegalencephaly, tuberous sclerosis (Fig 6) and dysembryoplastic neuroepithelial tumour (DNET; a mixed glioneuronal neoplasm with evidence of mild dyplasia in the adjacent cortex) The MRI features of these conditions are well described [73±77] The interpretation of these MR ®ndings, requires particular attention to the analysis of cortical grey matter, grey±white matter 794 CLINICAL RADIOLOGY Fig ± Twenty-nine-year-old woman with complex partial seizures and cortical dysplasia (a) T1-weighted coronal image demonstrates a thickened superior frontal gyrus with loss of grey±white matter di€erentiation (arrow) Subcortical hyperintensity is seen on the (b) T2-weighted coronal image (arrow) and accentuated on the (c) FLAIR coronal image boundary, white matter and the periventricular region Minor derangements may only be detected when the volumetric data is reformatted as a tangential slice or as a surface display of the 3D reconstruction [69] Focal cortical dysplasia (Fig 7) is the most common major malformation and is the most frequently considered for surgical resection [78,79] It is often located in the central and pre-central cortex [71,79] The MRI features are of broad gyri with thick cortex (greater than mm), indistinct grey±white matter junction and abnormal signal in the underlying subcortical white matter [11,72,77] Focal polymicrogyria [80], a forme fruste of tuberous sclerosis, DNETs [81] and other low grade tumours [82] may have similar MRI appearances Some clinical syndromes due to disorders of neuronal migration and cortical organization have characteristic MRI appearances described Pseudobulbar palsy and cognitive impairment are associated with bilateral perisylvian and perirolandic malformation [83] whilst gelastic epilepsy, precocious puberty and cognitive impairment are the typical clinical features of a hypothalamic hamartoma (Fig 8) [84] Tumours Tumours are the principal structural abnormality in 12% of patients with medically intractable epilepsy referred for MRI [32] Most of the tumours for which epilepsy surgery MRI OF PATIENTS WITH EPILEPSY 795 Fig ± Thirty-seven-year-old man with a 20 year history of gelastic seizures and a hypothalamic hamartoma (a) T1-and (b) T2-weighted coronal images demonstrate a pedunculated lesion which is isointense on the T1-weighted image (arrow), and hyperintense on the T2weighted image, which arises from the left side of the hypothalamus is performed are located in the temporal lobe cortex [3,85] These tumours tend to be low grade and very indolent There was a mean pre-operative history of 14 years of chronic seizures in one series [85] Gangliogliomas are the tumours most commonly associated with an epileptogenic focus, and there is a good prognosis following resection [85,86] These lesions have a low signal on T1-weighted and high signal on T2-weighted sequences, and may demonstrate gadolinium enhancement and mass e€ect [87] Other frequent tumours in epileptic patients are pilocytic and Fig ± Thirty-two-year-old woman with longstanding complex partial seizures secondary to a histologically proven oligoastrocytoma (a) T1-weighted coronal image post-gadolinium and (b) T2-weighted axial image reveal a non-enhancing lesion which is hypointense on the T1-weighted image, and hyperintense on the T2-weighted image (arrows), within the right superior frontal gyrus 796 CLINICAL RADIOLOGY Fig 10 ± Twenty-®ve-year-old man with complex partial seizures secondary to an arteriovenous malformation (a) T2-weighted axial and (b) coronal images demonstrate multiple vascular ¯ow voids within the left parietal lobe with a dilated branch of the right middle cerebral artery (arrow in a) feeding the nidus and a dilated cortical vein (arrow in b) draining the nidus and ultimately communicating with the superior sagittal sinus (not shown) ®brillary astrocytomas, DNETs and oligodendrogliomas (Fig 9) [3,85,88] Vascular Malformations Vascular malformations are the cause of intractable epilepsy in 2±3% of patients in surgical series [18,29,30] Patients have an 18% risk of developing a seizure disorder when managed conservatively over 20 years [89] Arteriovenous malformations (AVMs) have a distinctive MR appearance owing to the cluster of round and linear signal voids (Fig 10) Cavernous haemangiomas (Fig 11) are considered more epileptogenic than AVMs [90], possibly owing to the greater reactive gliosis Cavernous haemangiomas are seen as circumscribed lesions on MRI with a central area of heterogeneity corresponding to methaemoglobin, deoxyhaemoglobin and calci®cation and a haemosiderin ring giving a low signal on T2-weighted imaging [91] Epileptogenic vascular malformations are more often super®cial and associated with surrounding T2 hyperintensity than their non-epileptogenic counterparts [92] Local resection of vascular malformations carries the best prognosis of all epileptogenic lesions, with an excellent chance of seizure remission [11,79] Other MR Features Associated with Epilepsy Epileptogenic cortical encephalomalacia and gliosis secondary to trauma, infarction or infection are well demonstrated with MRI Destructive lesions are an important cause of childhood seizures [72] Cerebral insults during the ®rst months of gestation result in smooth porencephalic cavities not lined by gliosis [93], while late gestational, perinatal or post-natal injury leads to focal or generalized encephalomalacia (Fig 12) [72] At the opposite end of the age spectrum, MRI has proved useful in the demonstration of ischaemic lesions associated with late onset epilepsy [94] MRI has recently shown subcortical plaques to be responsible for seizure activity in the 4% of multiple sclerosis patients with epilepsy [95] Tuberculomas and cysticercosis (Fig 13) are the most commonly identi®ed causes of epilepsy in developing countries and MRI may demonstrate the various stages in the development of the non-calci®ed cortical cysticercosis lesion [96] Complex partial and generalized status epilepticus may result in reversible hyperintense lesions on T2-weighted images in the supratentorial grey matter [97,98] and di€use hippocampal and gyral high signal on T2-weighted sequences with additional swelling [99,100] Focal lesions in the splenium of the corpus callosum have also been noted MRI OF PATIENTS WITH EPILEPSY 797 Fig 11 ± Fifty-year-old man with complex partial seizures and a cavernous angioma T2-weighted axial image shows `popcorn' central hyperintensity surrounded by a rim of hypointensity (curved arrows) within the right uncus Fig 12 ± Thirty-two-year-old man with complex partial seizures secondary to ischaemic damage in early life (a) T2-weighted axial image shows hyperintense encephalomalacia within the left frontal lobe secondary to a branch middle cerebral artery infarct The left cerebral hemisphere is smaller than the right and there is enlargement of the left frontal paranasal sinus (arrow) (b) FLAIR coronal image reveals much of the left frontal encephalomalacia to be isointense to CSF with a rim of hyperintensity corresponding to gliosis 798 CLINICAL RADIOLOGY Fig 13 ± Thirty-six-year-old Indian man, who last visited India years previously, developed focal motor seizures secondary to cerebral cysticercosis (a) T1-weighted post gadolinium sagittal image and (b) T2-weighted axial image at clinical presentation show a super®cial ring enhancing lesion within the left frontal lobe which has a hypointense rim (arrow) and surrounding hyperintensity on the T2-weighted image The enhancing rim of the ®brous capsule and the pericystic oedema result from death of the larva The patient was treated with antiepileptic drugs alone Eight weeks later (c) T2-weighted axial image demonstrates resolution of the pericystic oedema 799 MRI OF PATIENTS WITH EPILEPSY in epileptic patients and may be the result of antiepileptic drug toxicity [101] MRI FOR EPILEPSY SURGERY Epilepsy surgery requires an MRI examination [11] This may be supplemented by a variety of functional imaging investigations ( functional MRI, MR spectroscopy, PET, ictal SPECT), although the minimal imaging requirements and cost-e€ectiveness of these examinations have not been established [34] The role of these other techniques in epilepsy imaging is well reviewed elsewhere [7,11,50] Functional imaging techniques can be particularly helpful when there is discordance between the EEG focus and the lesion or when no lesion is evident on high quality MRI [102] Cortical dysplasia is the abnormality most frequently detected with PET but not with MRI in patients with intractable epilepsy [102] Patients may also bene®t from invasive EEG monitoring, either with depth electrodes, which are usually implanted into the mesial temporal lobes or deep frontal structures depending on EEG surface recording, and subdural mats, which are surgically implanted onto the surface of the brain MRI based stereotactic procedures are commonly employed to place intracranial depth recording electrodes [103] MRI also allows accurate assessment of location and detection of complications, when depth electrodes [104] and subdural electrode grids [105] are placed freehand MRI based surgical guidance systems have also been developed which allow three-dimensional imaging to be presented to the surgeon with superimposed real time information concerning the position of the surgeons `pointer' [106] and this has proved useful in epilepsy surgery Post-operative MRI performed a minimum of months following surgery is useful, if seizures have not remitted [7] If MRI demonstrates surgery to be incomplete then a second operation will allow a more extensive resection and consequently a better prognosis [7,110] The MRI appearances of cortical resection [107], corpus callosotomy [108] and hemispherectomy [109] have all been de®ned FUTURE DEVELOPMENTS IN MR EPILEPSY IMAGING The future relevant technical improvements in MRI include increased spatial resolution and improved postprocessing of data Phased array surface coils [111] have aided detection and characterization of seizure foci and high ®eld strength systems may improve resolution Threedimensional surface displays or curvilinear reconstructions may be used to display the gyral morphology and aid the visual interpretation [69] Advances in quantitative MRI have helped assess the relative volume and infolding of cortical grey matter and may overcome the limitations of subjective visual assessment 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