Recurrence of convexity meningiomas: tumor cells in the arachnoid membrane.

BACKGROUND

It remains open to debate why totally removed benign meningiomas recur. Two recurrent cases forced us to reconsider something corresponding to their recurrence that we had overlooked during Simpson grade I surgery.

METHODS

This study is based on 24 recent and 9 earlier cases in which benign convexity meningiomas were totally removed by Simpson's grade I surgery. Tough or thick arachnoid membranes continuing to normal arachnoid membranes and contiguous to meningiomas but different from dura mater were encountered in 11 recent and at least 2 earlier cases. Such thick arachnoid membranes were left in place or only partially resected in two earlier cases but extensively resected in all recent cases.

RESULTS

Light microscopy showed clusters of meningioma cells not in the removed dura mater but in the thick arachnoid membranes of an earlier case and 10 out of the 11 recent cases. Six and twelve years after initial surgery, recurrence of the 2 earlier cases was confirmed at subsequent surgery or diagnosed by neuro-imaging. By contrast, neuro-imaging from 30 to 132 months after initial surgery showed no recurrence in the 10 recent cases. A follow-up study over 5 years showed a significant difference in recurrence between Simpson's grade I surgery with and without extensive removal of surrounding thick arachnoid membranes (Fisher's exact test: p < 0.05).

CONCLUSION

This study emphasizes the possibility that thick arachnoid membranes contiguous to meningiomas and continuous to normal arachnoid membranes, involving clusters of tumor cells, may relate to meningioma recurrence.