The values of the base of the working zone have a wide distribution. Blind puncture of annulus by the working cannula or obturator may be dangerous. The safer procedure would be the direct viewing of the annulus by endoscopy before annulotomy; the working cannula should be inserted into the foramen as close as possible to the facet joint.

A 56-year-old man presented with a meningioma associated with hyperostotic bone containing little tumor cell infiltration. The patient presented with a growing mass on his right forehead and exophthalmos. Computed tomography (CT) taken 4 years previously revealed only hyperostosis without intracranial lesion. Repeat CT revealed an enhanced intracranial mass with overlying diffuse hyperostosis extending extracranially. The tumor and affected bone were widely removed. Histological examination confirmed rhabdoid meningioma in the intracranial and extracranial lesion. However, most of the hyperostotic bone showed no tumor cell infiltration. The cause of hyperostosis associated with meningioma is unclear, but tumor invasion is the generally accepted cause. In this case, hyperostosis occurred without tumor cell infiltration so another mechanism was probably involved. The extracranial extension occurred despite the disproportionately small tumor without global tumor cell infiltration of the bone or bony erosion.

TFLs are common structures in the IVF and may reduce the space available for the spinal nerve root within the IVF. In this circumstance, any compromise of the IVF may impinge on the nerve root.

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