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EDITORIAL
Year : 2013  |  Volume : 61  |  Issue : 4  |  Page : 343--344

Intracranial arachnoid cysts: Epileptic seizures

J.M.K. Murthy 
 Department of Neurology, Continental Institute of Neuroscience and Rehabilitation, Continental Hospitals, Gachibowli, Hyderabad, Andhra Pradesh, India

Correspondence Address:
J.M.K. Murthy
Department of Neurology, Continental Institute of Neuroscience and Rehabilitation, Continental Hospitals, Gachibowli, Hyderabad-500 001, Andhra Pradesh
India




How to cite this article:
Murthy J. Intracranial arachnoid cysts: Epileptic seizures.Neurol India 2013;61:343-344


How to cite this URL:
Murthy J. Intracranial arachnoid cysts: Epileptic seizures. Neurol India [serial online] 2013 [cited 2017 Dec 16 ];61:343-344
Available from: http://www.neurologyindia.com/text.asp?2013/61/4/343/117580


Full Text

Intracranial arachnoid cysts are benign developmental cysts containing cerebrospinal fluid (CSF) and are often incidental finding in magnetic resonance imaging (MRI) done for other reasons. These cysts are slowly growing and often asymptomatic and when symptomatic the present features include focal neurologic deficits, raised intracranial pressure, and/or epileptic seizures. There is a debate whether arachnoid cysts in patients with epilepsy reflect the location of the seizure focus. [1],[2],[3],[4],[5] In the retrospective epilepsy clinic-based study by Arroyo and Santamaria, [3] of the 867 with epilepsy, 17 (1.96%) patients had associated arachnoid cysts. In six of them other possible or predisposing factors for epilepsy could be established. Of the remaining 12 patients, one had benign epilepsy with centrotemporal spikes and one had bilateral frontal and parietal band heterotopia. In the rest of the patients, clinical and electroencephalography (EEG)/video-EEG features localized seizure focus adjacent to the arachnoid cyst in only four patients. In the study by Yalcin and colleagues, [4] of the 20 patients with epilepsy and associated arachnoid cysts, eight patients could be categorized under either idiopathic generalized or localization related epilepsies by clinical and EEG features. Of the remaining 12 patients, only one patient had focal epileptiform abnormalities corresponding to arachnoid cyst location. In both the studies; the seizure focus localization was mostly based on clinical and interictal EEG features, video-EEG was done in very few cases. Such an approach has significant limitations as shown in the study by Remi and colleagues. [6] This study showed that the occurrence and localization of interictal and ictal EEG findings differ vastly for lesions in different brain regions, more so with extratemporal epilepsies. In the adult surgical series, preoperative video-EEG recordings and intraoperative electrocorticography (ECoG) findings showed good congruence with the location of arachnoid cysts and these patients had good seizure outcome following arachnoid cyst excision in adults with drug resistant arachnoid cyst-related epilepsy. [7] Similar were the findings in the pediatric patients in the study by the same group published in this issue of the journal. [7] Thus, the available data suggests that in patients with generalized and localization related idiopathic epilepsies [3],[4] and some specific epilepsy syndromes, [1],[5] the arachnoid cysts are more likely an incidental finding. In patients with identifiable possible or predisposing factors for epilepsy, arachnoid cysts may be incidental and these patients require multimodality workup to establish the causal relationship between the two. In patients with no other identifiable factor for epilepsy, the association between epilepsy and arachnoid cysts is more likely and these patients need detailed preoperative surgical evaluation before considering for epilepsy surgery to establish the causal relation.

The exact pathogenic mechanism of epileptogenesis in arachnoid cyst-related epilepsy is not unknown. Compression of the surrounding brain structures has been proposed as the possible mechanism. Okada and colleagues [8] studied the relationships among seizures, the volume of arachnoids cysts, and regional cerebral blood perfusion around arachnoid cysts. The volume of arachnoid cysts in patients without epilepsy was significantly larger than in patients with epilepsy. Single photon emission computed tomography (SPECT) demonstrated hyperperfusion around arachnoid cysts in patients with no epilepsy, whereas in patients with epilepsy SPECT demonstrated hypoperfusion. Lesional side to normal side ratio of region of interests in the posterior temporal area and irregular region of interests in the temporal area were significantly lower in patients with epilepsy than in patients without. These results suggest that the epileptogenic focus probably lies in compressed cerebral cortex surrounding the arachnoid cyst is probably the epileptogenic focus. These authors had also proposed that the associated parenchymal lesions in the surrounding brain may also participate in the epileptogenesis. This needs confirmation by histological studies of the excised surrounding brain tissue.

The surgical indication in patients with arachnoid cyst-related drug resistant epilepsy is localizing electroencephalographic interictal, ictal, and ECoG abnormalities. [7],[9] In pediatric [7] and adult [8] patients with arachnoid cyst-related epilepsy, pre-surgical video-EEG studies revealed epileptiform discharges strongly correlating to location of the cyst. Intraoperative ECoG in both adults and children demonstrated epileptiform discharges correlating to the cyst location. [7]

The place of surgery in arachnoid cyst-related epilepsy has not been systematically studied and the data is limited to a few case series. In these studies no details of presurgical evaluation in regard to localization of epileptogenic zone were given. In a recent surgical series in adults, good seizure outcome was observed in 87.5% of patients. [7] The same group reported good seizure outcome in 77.7% of pediatric patients. [7] These encouraging results in both the series may be related to the surgical techniques, cyst excision, and either anterior temporal lobectomy or thermocoagulation of the adjacent cortex. The extent of surgical resection was based on the intraoperative ECoG findings. The variable results in the earlier studies may be related to imprecise localization and inadequate resection of the epileptogenic zone. [2],[10],[11]

In patients with arachnoid cyst-related epilepsy, the choice of the most appropriate surgical approach is still debated. The two recent studies both in adults and children with arachnoid cyst-related epilepsy, the surgical approach was microsurgical craniotomy. Full space microsurgical craniotomy ensures the ability to perform to another operation for cyst-related epilepsy and also intraoperative ECoG monitoring. [7]

To establish the causal relationship between arachnoid cysts and epilepsy in patients with epilepsy and arachnoid cysts, probably a multimodality workup is essential. There is an urgent need for systematic studies to determine the ideal surgical approach and also the extent of resection to get a good seizure outcome in patients with arachnoid cyst-related drug resistant epilepsy with a large sample size.

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