• Takafumi Nishizaki, Norio Ikeda, Shigeki Nakano, Tomomi Okamura, and Seisho Abiko.
• Department of Neurosurgery, Ube Industries Central Hospital, Nishikiwa, Yamaguchi, Japan. nishiza@jeans.ocn.ne.jp
• Acta Neurochir (Wien). 2009 Dec 1;151(12):1717-21.

ObjectiveThe optimal surgical approach for a trigone meningioma is still controversial. Here, we report two patients with trigone meningioma treated successfully via an occipital inter-hemispheric and trans-cortical approach in the lateral semi-prone position.Clinical PresentationA 53-year-old woman was admitted to a local hospital with sudden transient dizziness and vomiting. The CT brain scan demonstrated a right intra-ventricular tumour. She was therefore transferred to our hospital for surgical treatment. The other patient was a 67-year-old woman who was admitted to a local hospital after a traffic accident and a CT brain scan revealed an incidental right intra-ventricular tumour. After referral to our hospital, periodic MRI examinations revealed gradual tumour enlargement within a one-year period. Neither of the patients had any neurological deficits, including in the visual fields.InterventionThe head of each patient was positioned so that the tumour-containing right ventricle was oriented downwards and laterally. An occipital inter-hemispheric approach was performed and using a navigation system, the tumour was identified about 1 cm in depth from the cortical surface. After the medial part of the tumour was debulked, the posterior and then the anterior choroidal blood supplies to the tumour were identified. Occlusion of these vessels achieved tumour haemostasis. The tumours were totally removed via a 1.5-cm cortical incision. Brain retraction was minimal because the right hemisphere was pulled down by gravity. Therefore, the para-splenial cisterns were easily accessed, resulting in early release of cerebrospinal fluid. Post-operative MRI showed complete removal of the tumour and the patients had no neurological deficits. Anti-epileptic medication was withdrawn one week after the operation.ConclusionsThe occipital inter-hemispheric fissure lacks important bridging veins. The approach used and patient positioning minimized damage to the lateral aspect of the optic radiation and the corpus callosum. Except in patients with very large trigone meningiomas, this approach is useful for decreasing the risk of post-operative hemianopsia or epilepsy, and possibly speech disturbance, even in patients with a tumour in the dominant hemisphere.

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