Functional brain mapping of ictal activity in gelastic epilepsy associated with hypothalamic hamartoma: A case report

Intraoperative changes in large-scale thalamic circuitry following laser ablation of hypothalamic hamartomas

BACKGROUND AND OBJECTIVES

Gelastic seizures due to hypothalamic hamartomas (HH) are challenging to treat, in part due to an incomplete understanding of seizure propagation pathways. Although magnetic resonance imaging-guided laser interstitial thermal therapy (MRgLITT) is a promising intervention to disconnect HH from ictal propagation networks, the optimal site of ablation to achieve seizure freedom is not known. In this study, we investigated intraoperative post-ablation changes in resting-state functional connectivity to identify large-scale networks associated with successful disconnection of HH.

METHODS

Children who underwent MRgLITT for HH at two institutions were consecutively recruited and followed for a minimum of one year. Seizure freedom was defined as Engel score of 1A at the last available follow-up. Immediate pre- and post- ablation resting-state functional MRI scans were acquired while maintaining a constant depth of general anesthetic. Multivariable generalized linear models were used to identify intraoperative changes in large-scale connectivity associated with seizure outcomes.

RESULTS

Twelve patients underwent MRgLITT for HH, five of whom were seizure-free at their last follow-up. Intraprocedural changes in thalamocortical circuitry involving the anterior cingulate cortex were associated with seizure-freedom. Children who were seizure-free demonstrated an increase and decrease in connectivity to the pregenual and dorsal anterior cingulate cortices, respectively. In addition, children who became seizure-free demonstrated increased thalamic connectivity to the periaqueductal gray immediately following MRgLITT.

DISCUSSION

Successful disconnection of HH is associated with intraoperative, large-scale changes in thalamocortical connectivity. These changes provide novel insights into the large-scale basis of gelastic seizures and may represent intraoperative biomarkers of treatment success.

Advances in epileptic network findings of hypothalamic hamartomas

Hypothalamic hamartomas (HHs) are congenital developmental malformations located in the hypothalamus. They are associated with a characteristic clinical manifestation known as gelastic seizures (GS). However, the traditional understanding of HHs has been limited, resulting in insufficient treatment options and high recurrence rates of seizures after surgery. This is consistent with the network hypothesis of focal epilepsy that the epileptogenic zone is not only limited to HH but may also involve the distant cerebral cortex external to the HH mass. The epilepsy network theory, on the other hand, provides a new perspective. In this study, we aim to explore HH-related epilepsy as a network disease, challenging the conventional notion of being a focal lesional disease. We analyze various aspects of HHs, including genes and signaling pathways, local circuits, the whole-brain level, phenotypical expression in terms of seizure semiology, and comorbidities. By examining HHs through the lens of network theory, we can enhance our understanding of the condition and potentially identify novel approaches for more effective management and treatment of epilepsy associated with HHs.

MRI-Negative Occipital Lobe Epilepsy Presenting as Gelastic Seizures

Although gelastic seizures (GSs) with extrahypothalamic epileptogenic zones such as the frontal, temporal, or parietal lobes have been previously reported, reports of GSs arising from the occipital region are rare. Herein, we describe the seizure propagation pattern of mirthless GSs confirmed by intracranial EEG in a case of MRI-negative occipital lobe epilepsy. In this patient, EEG onset was localized to the right occipital lobe while the onset of laughter coincided with seizure propagation to the right basal temporal region. This finding suggested that the symptomatogenic area for GSs in the occipital lobe may reside in the basal temporal region, and the basal temporal region may play a role in laughing behaviors. This case demonstrated that an elaborate analysis of electroclinical features combined with imaging findings may lead to successful seizure localization.

Resting-state functional connectivity by independent component analysis-based markers corresponds to areas of initial seizure propagation established by prior modalities from the hypothalamus

OBJECTIVE

The aims of this study were to evaluate a clinically practical functional connectivity protocol designed to blindly identify the corresponding areas of initial seizure propagation and also to differentiate these areas from remote secondary areas affected by seizure. The patients in this cohort had intractable epilepsy caused by intrahypothalamic hamartoma, which is the location of the ictal focus. The ictal propagation pathway is homogeneous and established, thus creating the optimum situation for the proposed method validation study.

METHODS

Twelve patients with seizures from hypothalamic hamartoma and 6 normal control patients underwent resting state functional MRI, using independent component analysis to identify network differences in patients. This was followed by seed-based connectivity measures to determine the extent of functional connectivity derangement between hypothalamus and these areas. The areas with significant change in connectivity were compared with the results of prior studies' modalities used to evaluate seizure propagation.

RESULTS

The left amygdala-parahippocampal gyrus area, cingulate gyrus, and occipito-temporal gyrus demonstrated the highest derangement in connectivity with the hypothalamus, p < 0.01, corresponding to the initial seizure propagation areas established by prior modalities. Areas of secondary ictal propagation were differentiated from these initial locations by first being identified as an abnormal neuronal signal source via independent component analysis, but did not show significant connectivity directly with the known ictal focus.

CONCLUSION

Non-invasive connectivity measures correspond to areas of initial ictal propagation and differentiate such areas from secondary ictal propagation, which may aid in ictal focus surgical disconnection planning and support the use of this newer modality for adjunctive information in epilepsy surgery evaluation.

Epileptic network of hypothalamic hamartoma: An EEG-fMRI study

OBJECTIVE

To investigate the brain networks involved in epileptogenesis/encephalopathy associated with hypothalamic hamartoma (HH) by EEG with functional MRI (EEG-fMRI), and evaluate its efficacy in locating the HH interface in comparison with subtraction ictal SPECT coregistered to MRI (SISCOM).

METHODS

Eight HH patients underwent EEG-fMRI. All had gelastic seizures (GS) and 7 developed other seizure types. Using a general linear model, spike-related activation/deactivation was analyzed individually by applying a hemodynamic response function before, at, and after spike onset (time-shift model=-8-+4s). Group analysis was also performed. The sensitivity of EEG-fMRI in identifying the HH interface was compared with SISCOM in HH patients having unilateral hypothalamic attachment.

RESULTS

EEG-fMRI revealed activation and/or deactivation in subcortical structures and neocortices in all patients. 6/8 patients showed activation in or around the hypothalamus with the HH interface with time-shift model before spike onset. Group analysis showed common activation in the ipsilateral hypothalamus, brainstem tegmentum, and contralateral cerebellum. Deactivation occurred in the default mode network (DMN) and bilateral hippocampi. Among 5 patients with unilateral hypothalamic attachment, activation in or around the ipsilateral hypothalamus was seen in 3 using EEG-fMRI, whereas hyperperfusion was seen in 1 by SISCOM.

SIGNIFICANCE

Group analysis of this preliminary study may suggest that the commonly activated subcortical network is related to generation of GS and that frequent spikes lead to deactivation of the DMN and hippocampi, and eventually to a form of epileptic encephalopathy. Inter-individual variance in neocortex activation explains various seizure types among patients. EEG-fMRI enhances sensitivity in detecting the HH interface compared with SISCOM.

Pediatric applications of functional magnetic resonance imaging

Pediatric functional MRI has been used for the last 2 decades but is now gaining wide acceptance in the preoperative workup of children with brain tumors and medically refractory epilepsy. This review covers pediatrics-specific difficulties such as sedation and task paradigm selection according to the child's age and cognitive level. We also illustrate the increasing uses of functional MRI in the depiction of cognitive function, neuropsychiatric disorders and response to pharmacological agents. Finally, we review the uses of resting-state fMRI in the evaluation of children and in the detection of epileptogenic regions.

Hypothalamic hamartomas. Part 1. Clinical, neuroimaging, and neurophysiological characteristics

Hypothalamic hamartomas are uncommon but well-recognized developmental malformations that are classically associated with gelastic seizures and other refractory seizure types. The clinical course is often progressive and, in addition to the catastrophic epileptic syndrome, patients commonly exhibit debilitating cognitive, behavioral, and psychiatric disturbances. Over the past decade, investigators have gained considerable knowledge into the pathobiological and neurophysiological properties of these rare lesions. In this review, the authors examine the causes and molecular biology of hypothalamic hamartomas as well as the principal clinical features, neuroimaging findings, and electrophysiological characteristics. The diverse surgical modalities and strategies used to manage these difficult lesions are outlined in the second article of this 2-part review.

Transfer Function between EEG and BOLD Signals of Epileptic Activity

Simultaneous electroencephalogram (EEG)-functional Magnetic Resonance Imaging (fMRI) recordings have seen growing application in the evaluation of epilepsy, namely in the characterization of brain networks related to epileptic activity. In EEG-correlated fMRI studies, epileptic events are usually described as boxcar signals based on the timing information retrieved from the EEG, and subsequently convolved with a hemodynamic response function to model the associated Blood Oxygen Level Dependent (BOLD) changes. Although more flexible approaches may allow a higher degree of complexity for the hemodynamics, the issue of how to model these dynamics based on the EEG remains an open question. In this work, a new methodology for the integration of simultaneous EEG-fMRI data in epilepsy is proposed, which incorporates a transfer function from the EEG to the BOLD signal. Independent component analysis of the EEG is performed, and a number of metrics expressing different models of the EEG-BOLD transfer function are extracted from the resulting time courses. These metrics are then used to predict the fMRI data and to identify brain areas associated with the EEG epileptic activity. The methodology was tested on both ictal and interictal EEG-fMRI recordings from one patient with a hypothalamic hamartoma. When compared to the conventional analysis approach, plausible, consistent, and more significant activations were obtained. Importantly, frequency-weighted EEG metrics yielded superior results than those weighted solely on the EEG power, which comes in agreement with previous literature. Reproducibility, specificity, and sensitivity should be addressed in an extended group of patients in order to further validate the proposed methodology and generalize the presented proof of concept.

Dynamic Causal Modelling of epileptic seizure propagation pathways: a combined EEG-fMRI study

Simultaneous EEG-fMRI offers the possibility of non-invasively studying the spatiotemporal dynamics of epileptic activity propagation from the focus towards an extended brain network, through the identification of the haemodynamic correlates of ictal electrical discharges. In epilepsy associated with hypothalamic hamartomas (HH), seizures are known to originate in the HH but different propagation pathways have been proposed. Here, Dynamic Causal Modelling (DCM) was employed to estimate the seizure propagation pathway from fMRI data recorded in a HH patient, by testing a set of clinically plausible network connectivity models of discharge propagation. The model consistent with early propagation from the HH to the temporal-occipital lobe followed by the frontal lobe was selected as the most likely model to explain the data. Our results demonstrate the applicability of DCM to investigate patient-specific effective connectivity in epileptic networks identified with EEG-fMRI. In this way, it is possible to study the propagation pathway of seizure activity, which has potentially great impact in the decision of the surgical approach for epilepsy treatment.

Orbitozygomatic resection for hypothalamic hamartoma and epilepsy: patient selection and outcome

PURPOSE

This study aims to examine the outcomes of ten patients after orbitozygomatic (OZ) pterional surgery in cases of refractory epilepsy caused by hypothalamic hamartomas (HH).

METHODS

Ten patients with HH and treatment-resistant epilepsy (mean age 18.3 years, range 0.7 to 42.7) underwent HH resection with an OZ approach (n = 8) or an OZ approach combined with a transventricular endoscopic approach (n = 2). Follow-up for the patients ranged from 0.5 to 6.2 years (mean 3.1). Outcomes were prospectively monitored with the use of a proprietary database.

RESULTS

Four patients (40%) are seizure-free, and four (40%) have had greater than 50% reduction in seizures. One patient had no significant change in seizure frequency, and one patient died unexpectedly 2.8 years after surgery. Six patients had total or near-total HH resection (98-100% of HH lesion volume). Of these, four of six (66%) were seizure-free, and two had at least greater than 50% reduction in seizures. Residual complications include diabetes insipidus (n = 1), poikilothermia (n = 1), visual field deficit (n = 1), and hemiparesis (n = 1). Eight families (80%) reported improved quality of life.

CONCLUSIONS

Patients with treatment-resistant epilepsy and tumors with an inferior or horizontal plane of attachment to the hypothalamus should continue to be approached from below. Those with both intrahypothalamic and parahypothalamic components may require approaches from above and below, either simultaneously or staged. For appropriately selected patients, the success of controlling seizures with an OZ is comparable to results utilizing transcallosal or transventricular approaches. The likelihood of controlling seizures appears to correlate with extent of resection.

Surgical resection of hypothalamic hamartomas for severe behavioral symptoms

Hypothalamic hamartomas (HHs) are associated with treatment-resistant epilepsy. Many patients also experience severe and sometimes disabling psychiatric problems. The most common behavioral symptoms consist of paroxysms of uncontrolled anger related to poor frustration tolerance. These can include violence, resulting in disrupted family or school relationships, and legal consequences including incarceration. In a large cohort of patients undergoing surgical resection of HHs for refractory epilepsy, 88% of families described an improvement in overall behavioral functioning [1]. Here, we describe four patients (three males, mean age=11.9 years) who underwent surgical resection of HHs largely for behavioral indications. Three patients had relatively well controlled seizures, and one had no history of epilepsy. All patients had striking improvement in their psychiatric comorbidity. HH resection can result in significant improvement in behavioral functioning, even in patients with relatively infrequent seizures. Further investigation under approved human research protocols is warranted.

Transendoscopic intraoperative recording of gelastic seizures from a hypothalamic hamartoma

OBJECT

The differential diagnosis of hypothalamic masses in children includes hamartomas, which are associated with gelastic seizures and endocrine dysfunction. The purpose of this study was to utilize transendoscopic electroencephalography (EEG) recording at the time of tissue biopsy to further assist in diagnosis, determination of prognosis, and treatment planning.

METHODS

We present the case of an infant with gelastic seizures and a large hypothalamic mass lesion. Despite a clinical and radiographic presentation typical of hypothalamic hamartoma (HH), slight growth on serial imaging raised concern for a diagnosis of intrinsic neoplasm. Biopsy of the lesion was recommended.

RESULTS

Transventricular, endoscopic biopsy, was undertaken, with concurrent intraoperative, transendoscopic EEG recording using a standard epilepsy depth recording macroelectrode. Numerous electrographic seizures were recorded. Histopathology revealed a HH.

CONCLUSION

This is the first report of intraoperative macroelectrode recording of electrographic seizures transendoscopically from a HH. This technique may prove useful for diagnosis, prognosis and treatment planning, as well as to guide transendoscopic therapeutic interventions for HH.