Single and multiple clusters of magnetoencephalographic dipoles in neocortical epilepsy: significance in characterizing the epileptogenic zone

PURPOSE: To characterize the epileptogenic zone in neocortical epilepsy (NE) by using magnetoencephalography (MEG). METHODS: We defined and compared locations of single and multiple clusters of equivalent current dipoles (ECDs) for interictal spikes with MRI findings, ictal-onset zones (IOZs) from subdural electroencephalography (SDEEG), resected areas, and postsurgical outcomes of 20 patients who underwent cortical resection for medically intractable NE. RESULTS: Fourteen patients had single clusters; six had multiple clusters. Overlap of clusters and IOZs defined group A (nine patients), in which a single cluster coincided with the IOZ; group B1 (four patients), in which a single cluster was within or partially overlapped the IOZ; group B2 (five patients), in which multiple-cluster sections overlapped IOZs; group C (two patients; one single; one multiple), in which no overlap was seen. More single clusters (nine of 14) than multiple clusters (none of six) coincided with the IOZ (p = 0.014). More patients with single clusters (10 of 14) than patients with multiple clusters (one of six) had seizure-free outcomes (p = 0.049). Eight of nine patients in group A, versus three of 11 in groups B1, B2, and C, achieved seizure-free outcomes (p = 0.0098). Correlations between MRI findings and postsurgical outcomes were not statistically significant; eight of 13 patients with single lesions, one of four with no lesions, and two of three with multifocal lesions had seizure-free outcomes. CONCLUSIONS: In neocortical epilepsy, MEG ECD clusters correlated with SDEEG IOZs. Single clusters indicated discrete epileptogenic zones that required complete resection for seizure-free outcome. Multiple clusters necessitated that the multiple or extensive epileptogenic zones be completely identified and delineated by SDEEG.     

Topographic movie of ictal high-frequency oscillations on the brain surface using subdural EEG in neocortical epilepsy

PURPOSE: To understand the rapid dynamic changes of ictal intracranial high-frequency oscillations (HFOs) in neocortical epilepsy. METHODS: We integrated multiple band frequency analysis and brain-surface topographic maps of HFOs from ictal subdural EEG (SDEEG) recordings. We used SDEEG to record partial seizures consisting of right-arm jerks with secondary generalization in a 17-year-old right-handed girl. We selected 20-s EEG sections that included preclinical seizure recordings. We averaged the HFO power between 60 and 120 Hz for 25 selected electrodes, made topographic maps from these averaged powers, and superimposed the maps on the brain-surface image. We filmed consecutive HFO maps at a 10-ms frame rate. RESULTS: Before clinical seizure onset, high-power HFOs emerged at the superior portion of the left precentral gyrus, then appeared in the middle of the left postcentral gyrus, and subsequently reverberated between both regions as well as the posterior portion of the left postcentral gyrus. Right-arm extension and facial grimacing started as the HFO power decreased. As generalized tonic-clonic seizures evolved, HFO power increased but remained within the central region. CONCLUSIONS: Topographic movies of intracranial HFOs on the brain surface allow visualization of the dynamic ictal changes in neocortical epilepsy.     

Magnetoencephalographic spike sources associated with auditory auras in paediatric localisation-related epilepsy

Objective

To characterise magnetoencephalographic spike sources in paediatric patients with auditory auras and recurrent localisation‐related epilepsy.

Methods

Six patients (four boys and two girls (ages 7–14 years) were retrospectively studied. All patients had auditory auras as part of their initial seizure manifestation, including four patients who underwent previous brain surgery. Scalp video electroencephalography and magnetoencephalography (MEG) were carried out in six patients, intraoperative electrocorticography in three patients and extraoperative intracranial video electroencephalography in one patient. MEG auditory‐evoked fields (AEFs) were studied in four patients.

Results

Three patients had elementary auditory auras, one had complex auditory aura and two had both complex and elementary auras. All six patients had clustered MEG spike sources with coexisting scattered spike sources. MEG clusters were localised in the superior temporal gyrus with surrounding scatters in four patients (two left and two right); two patients had scattered spikes in the superior temporal gyrus in addition to clustered MEG spike sources in the left inferior and middle frontal gyri or parieto‐occipital region. AEFs were located within an MEG cluster in one patient and within 3 cm of a cluster in two patients. Surgical resection, including the regions of MEG clusters, was carried out in four patients. Three of four patients who had previous surgeries were seizure free at 2 years after excision of the MEG cluster region.

Conclusions

MEG spike sources clustered in the superior temporal gyrus in six patients with auditory auras. These spike sources were in close proximity or seemed to engulf the magnetic AEF. Areas with MEG spike sources contained the residual or recurrent epileptogenic zone after incomplete cortical excision for lesional epilepsy.Auditory auras are considered to be reliable indicators of temporal‐lobe seizure onset.^1,2,3,4 Epileptic auditory phenomena include elementary and complex auras. Elementary auditory auras are simple sounds, such as buzzing or ringing, provoked either by direct cortical stimulation of the medial part of Heschl''s gyrus or by spontaneously elicited epileptic discharges involving the primary auditory cortex.^3,5 Complex auditory auras can be hallucinations or illusions of sounds. The auditory hallucinations consist of elaborate phenomena of music or voices, whereas the illusions consist of modifications of intensity, tonality or resonance of surrounding voices. Unlike elementary auditory auras, which have a focal origin on the auditory cortex, complex auditory hallucinations and illusions tend to be elicited from more widespread areas involving the planum temporale or the lateral part of the superior temporal gyrus.^3,5Magnetoencephalography (MEG) localises the sources of intraneuronal electric currents that contribute to extracranial magnetic fields. MEG analysis uses an equivalent current dipole (ECD) model overlaid on to magnetic resonance images to localise sources of interictal epileptiform discharges. This technique can provide unique information about epileptogenic zones as reflected by interictal epileptiform discharges in patients with neocortical localisation‐related epilepsy secondary to lesions.^6,7 As magnetic fields are comparatively unaffected by the different electrical conductivities of the brain, cerebrospinal fluid, skull and skin, MEG can non‐invasively and accurately localise the residual epileptic spike sources in patients with recurrent seizures, even in the presence of skull defects after brain surgery.^8,9In a previous article,¹⁰ we reported on the significance of ear plugging as a behavioural manifestation of auditory auras in three patients. We now report on the localising value of MEG spike sources in six patients with localisation‐related epilepsy and auditory auras as the initial manifestations of their seizures. To our knowledge, this is the first report of MEG spike sources associated with auditory auras in paediatric patients with epilepsy.     

Psoas abscess in hemodialysis patients

Background  

The insidious onset and occult characteristic of psoas abscess can cause diagnostic delays, resulting in high mortality and morbidity rates. Here, we investigated the characteristics of psoas abscess in hemodialysis patients.     

Spatially filtered magnetoencephalography compared with electrocorticography to identify intrinsically epileptogenic focal cortical dysplasia

This study was carried out to evaluate Synthetic Aperture Magnetometry-kurtosis (SAM(g(2))), a spatially filtered source localization technique in magnetoencephalography (MEG), for identification of epileptogenic areas of focal cortical dysplasia (FCD). Three children with FCD were investigated to localize the ictal onset zone (IOZ). All patients subsequently had extraoperative electrocorticography (ECoG) for intractable epilepsy and surgical resection. SAM(g(2)) analysis showed overlapping of interictal MEG spike sources with the IOZ on ECoG in all children. We recommend MEG-SAM(g(2)) and MEG interictal spike source localization in patients with epileptogenic FCD.     

Astrocytic inclusions in epilepsy: expanding the spectrum of filaminopathies

We report the finding of unique astrocytic inclusions in a series of pediatric epilepsy patients, all of whom presented with seizures in their first year of life and had mild-to-moderate developmental delay. All eventually underwent surgical treatment for refractory epilepsy and, on pathological examination, were found to have distinctive, eosinophilic, globular cytoplasmic inclusions confined to cortical astrocytes. These inclusions were almost exclusively juxtanuclear, highly refractile, spared distal subpial, or perivascular astrocytic processes and were strongly and exclusively immunopositive for filamin A, an actin binding protein involved in neuronal migration. Identical inclusions have been identified and characterized in cases of Aicardi syndrome, a rare neurodevelopmental disease. The presence of the same inclusions in the cortex of epilepsy patients, some of whom had concomitant brain anomalies related to migrational problems, prompted us to consider that these patients may lie within a spectrum of disease involving dysfunction of filamin or filamin-interacting proteins. The term "filaminopathy" is tentatively proposed as a distinct pathological entity for this condition in which clinical manifestations range from epilepsy in mildly neurologically impaired patients to severe mental and physical handicap in the Aicardi syndrome. Future studies will be necessary to unravel the exact nature of the filamin A protein or gene aberrations in these patients.     

Bell-shaped relationship between central blood volume and spontaneous baroreflex function

Spontaneous baroreflex function can be altered by acute changes in central blood volume. Both a reduction in spontaneous baroreflex function at central hypovolemia and augmentation at hypervolemia suggest a dose-effect relationship between central blood volume and spontaneous baroreflex function. However, this relationship has not been quantified over stepwise widespread changes in central blood volume. Twelve individuals underwent central hypovolemia at two levels of lower body negative pressure (LBNP) (-15 mm Hg, LBNP15; -30 mm Hg, LBNP30) and hypervolemia with two discrete infusions of normal saline (NS) (15 ml kg(-1), NS15; total 30 ml kg(-1), NS30). Spontaneous baroreflex function was assessed using transfer function analysis and the sequence method between blood pressure and R-R interval. Both central venous pressure (-0.6-7.9 mm Hg) and left ventricular end-diastolic volume (72.4-133.1 ml) decreased during LBNP and increased after saline infusion. Both spontaneous baroreflex indices of high-frequency transfer function gain (LBNP30, 17.4+/-3.2; LBNP15, 22.3+/-3.8; baseline, 25.6+/-4.1; NS15, 28.5+/-4.2 ms mm Hg(-1), ANOVA P=0.001) and of the sequence slope (LBNP30, 14.4+/-2.2; LBNP15, 17.2+/-2.5; baseline, 20.5+/-2.8; NS15, 24.5+/-3.1 ms mm Hg(-1), ANOVA P=0.001) increased stepwise from hypovolemia of LBNP30 to hypervolemia of NS15. However, these indices were lower at NS30 (high-frequency transfer function gain, 22.0+/-2.2 ms mm Hg(-1), post-hoc P=0.071; sequence slope, 17.7+/-1.7 ms mm Hg(-1), post-hoc P<0.05) than NS15 during hypervolemia. These results indicated that the relationship between central blood volume and spontaneous baroreflex function is apparently bell-shaped, with maximal augmentation at moderate hypervolemia.