Indications and Preoperative Considerations
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Falcine meningiomas are extradural lesions that arise from the falx cerebri. They might be classified based on their relationship with the superior sagittal sinus (SSS) into anterior, middle or posterior lesions, each requiring different techniques for surgical resection.
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Meningiomas that arise both from the falx and tentorium are named falcotentorial meningiomas. These lesions may rise in any portion of the straight and transverse sinuses, up to and including the region adjacent to the torcula.
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Clinical symptoms associated with these lesions depend on the position of the lesion. Frontal falcine meningiomas may present with headache, seizures and frontal lobe syndrome. Middle third lesions can present with contralateral leg weakness secondary to compression of the paracentral lobule, while posterior third falcine and falcotentorial meningiomas can be associated with homonymous hemianopsia or even bilateral visual deficits when bilateral tumor extension is present.
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As in parasagittal meningiomas, evaluation of the relationship of the tumor to venous sinuses and draining veins is critical. Falcine meningiomas may grow superiorly into the SSS and/or inferiorly into the inferior sagittal sinus (ISS), whereas falcotentorial lesions might be closely related to the straight sinus, ISS, transverse sinus and torcula.
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The relationship between falcine meningiomas and the callosomarginal and pericallosal artery needs to be evaluated prior to surgery. These arteries are closely related to deep seated meningiomas especially at the middle portion of the SSS.
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Preoperative work-up must include MRI with gadolinium enhancement, MRA or angiogram and MRV, so the location and vascular relation of tumor with major vessels and dural sinuses can be adequately evaluated.
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Large falcotentorial meningiomas benefit from the insertion of a lumbar drain or external ventricular drainage (EVD) before surgery.
Surgical Procedure
Patient Positioning
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Different positions are required for falcine meningiomas depending on the lesion’s relation with the SSS. Anterior lesions typically require a supine position with slight elevation of the head. Middle third tumors can be approached using a semi-sitting position, a lateral position with the midline parallel to the ceiling, or a supine position with head slightly extended.
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Posterior third and falcotentorial meningiomas can be approached either using prone positioning with head elevation and slight flexion, semi-sitting or park bench positioning with slight flexion and 45 degree ipsilateral rotation of the head. With this technique the falx will act as a natural retractor of the contralateral hemisphere, and the ipsilateral hemisphere will fall away by gravity to enhance exposure of the lesion.
Skin Incision
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A bicoronal skin incision is performed in cases of tumors located at the anterior third of the SSS. For lesions located at the middle third, a U-shaped incision with its base at the temporal region is typically recommended. For falcine meningiomas close to the posterior third portion of the SSS and falcotentorial meningiomas, a U-shaped incision is typically performed, with the pedunculated part of the flap at the occipital region. When significant contralateral extension is present, a skin incision crossing the midline is recommended.
Craniotomy
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The craniotomy needs to be large enough to expose the borders of the tumor as well as 1–2 cm of normal brain tissue.
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For unilateral falcine lesions, the craniotomy crosses 1–2 cm of the midline in order to expose the SSS. Several burr holes and adequate dural detachment must be performed before using the craniotome over the SSS ( Figure 11.1 ). In smaller lesions, exposing the contralateral side of the sinus may not be necessary.
Figure 11.1
Craniotomy for falcine meningiomas. Typically, 2–3 burr holes are placed 1–2 cm in the contralateral side of the SSS and 2–3 burr holes in the ipsilateral side. A No. 3 Penfield dissector is used to detach the dura off the overlying bone.Related posts:
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