Giant arachnoid cyst in adult presented with secondary epileptiform activity

INTRODUCTION

Arachnoid cysts (ACs) are common benign congenital intracranial lesions, most of them are an accidental finding.[1] Pathogenesis of cysts formation is not clear and presumably associated with splitting of arachnoid layer during embryogenesis. Rare localization of supratentorial ACs is interhemispheric fissure. Usual clinical appearances of such ACs are headache, seizures, and focal deficit. There is no generally accepted approach to surgical treatment of ACs. We discuss a case of giant AC with sings of brain compression and epileptiform activity on electroencephalography (EEG) without seizures.

CASE DESCRIPTION

A Left handed adult patient with head deformity and everyday intensive headaches in the right temporal region, worsening with straining, presented in our neurosurgical department. Magnetic resonance imaging (MRI) scans showed giant arachnoid cyst of the right hemisphere [Figure 1].

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Figure 1:: Axial (a), coronal (b), and sagittal (c) T1 gadolinium-enhanced brain MRI of arachnoid cyst (7 × 8 × 7 cm).

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No cognitive impairment was found: Mini Mental State Examination scale 30/30, Frontal Assessment Battery 18/18, Montreal Cognitive Assessment scale 30/30, Trial Making Test (TMT) A 27 s, TMT B 69 s, and Hamilton depression rating scale 5. Neurological examination showed no focal deficit. Ophthalmological examination reviled no signs of increased intracranial pressure (ICP). EEG detected epileptiform activity from the right frontal lobe [Figures 2a and b]. Computed tomography (CT) cisternography confirmed that cyst was isolated from subarachnoid space [Figures 2c and d]. Lumbar cerebrospinal fluid (CSF) opening pressure during lumbar puncture was 18 cm.

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Figure 2:: Monopolar (a) and bipolar (b) EEG showing epileptiform activity. T2-FLAIR MRI (c) revealed signs of local swallowing of brain tissue. CT cisternography (d) shows no signs of contrast in the cyst’s cavity despite filling of lateral ventricles with contrast.

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Taking into account headaches, abnormal EEG, MRI signs of brain compression, and isolated type of cyst, we performed microsurgical cystostomy [Figure 3].

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Figure 3:: Patients positioning (a), intraoperative findings (b and c).

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Based on light microscopic findings, a histologic diagnosis of AC was made [Figure 4a and b].

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Figure 4:: Histological findings (a and b) and postoperative monopolar (c) and bipolar (d) EEG.

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Postoperative course was fine, headaches disappeared, EEG showed resolution of epileptiform activity [Figure 4c and d]. The patient was symptom free at 12 months follow-up and EEG showed no signs of previously seen epileptiform activity.

DISCUSSION

The common prevalence of ACs in adults is estimated at 1.4% and slightly higher in men then in women.[1] The most cases are clinically silent. Sometimes, natural history of ACs includes spontaneous or traumatic rupture,[6] cysts enlargement with brain compression, and hydrocephalus, increasing focal deficit. ACs could be presented with parkinsonism,[7] cognitive impairment,[3] anxiety, and depression,[4] however, described case had no such presentation. Even large and giant ACs could be asymptomatic.[5]

Four main theories of cyst’s enlargement are as follows: (1) CSF secretion by inner surface of the cyst, (2) osmotic gradient between the cystic content and the CSF, (3) slit-valve mechanism between cyst and the subarachnoid space, and (4) pulsation of intracystic fluid of venous or arterial origin.[10] We did not find any valve-like structures during intraoperative examination.

Presented case characterized by unspecific symptoms, so treatment has been controversial. Despite the benefits from surgery of symptomatic arachnoid cysts, some authors proposed that seizures and headaches often persist after treatment.[2] Wang et al. supported the view that patients with unspecific symptoms may profit from surgical cyst decompression.[9] At the same time, Rabiei et al. found no changes in surgically treated patients despite self-reported improvement.[8] Some authors recommend medical treatment for patients with headache or seizures.[9] The current case had been suspected symptomatic despite absence of raised ICP. Indications for surgery were signs of brain compression, epileptiform activity, and isolated cyst during CT cisternography.

Surgical modalities available for ACs are as follows: microsurgical resection of cyst’s wall with or without connection with ventricles or basal cisterns; endoscopic fenestration; and cyst-peritoneal shunting. Several studies propose independence of clinical outcome from surgical modality.[9] We prefer to avoid cyst shunting due to the patient’s young age and not to cause shunt dependence.

Yamasaki et al. noted that epileptic seizures may remain unchanged or worsen after surgery on interhemispheric ACs.[10] Apparently, we present rare observation of normalization of EEG after cyst’s fenestration.

CONCLUSION

ACs are rare reasons of headaches and seizures in adults. Surgery could be preferable treatment option despite minimal clinical presentation. Indications for surgery are as follows: increased ICP, evidences of cyst’s enlargement, hydrocephalus, signs of brain compression, and epileptiform activity. CT cisternography is useful for establishing indications for surgery while isolated cyst confirmed.