Meningiomas are regarded as benign dural tumors that can be totally removed; however, after a resection that appears to the naked eye to be total, their recurrence rate is high. Malignancy in a few cases and an erroneous belief in many others that the excision was total are among the most accepted explanations. Few studies have mentioned multicentricity as a cause of "relapse." Therefore, the authors decided to examine the dura mater around globular meningiomas for evidence of regional multifocality. A radial strip of dura was removed from the line of attachment of globular meningiomas in 14 consecutive patients. Meningotheliomatous cell aggregates were demonstrated in 100% of these dural strips in the form of either intradural clusters or nodes protruding from the inner aspect of the dura. The benign appearance of the cells and the great prevalence in this study of the benign types of meningioma seem to exclude malignancy; the intradural position of the clusters and their independence from blood vessels apparently negate seeding and dural metastasis. Control strips of convexity dura mater taken from 10 neurosurgical patients without meningioma failed to show these meningotheliomatous conglomerates. These findings indicate that solitary globular meningiomas represent only the most visible growth in the midst of a neoplastic field change spreading over a wide area of dura mater. The authors believe that this can explain some unexpected "recurrences," and that a wide resection of dura around globular meningiomas, whenever possible, could reduce the incidence of clinical growth after true total excision of the most visible lesion. It remains to be determined what factors cause the acceleration of growth of these cell aggregates after removal of the dominant tumor.

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Globular single meningiomas are generally regarded as benign tumors that can be completely removed. Nevertheless, after a total macroscopic resection including the insertion zone (Grade 1 operation according to Simpson's classification), the incidence of recurrence ranged from 9% to 14% at the 5-year follow-up review. The authors have shown that single meningiomas represent only the visible predominant growth in the midst of a wide neoplastic field in the dura mater. Regional multiplicity in meningiomas would thus seem to be the rule. With this in mind, the authors propose to divide recurrences after Grade 1 operations into true local and false regional. A local recurrence is defined as a regrowth within the limits of the previous dural flap. Regional recurrence is when new growth develops outside the previous craniotomy site; this should not be considered as a recurrence but as a new primary site. These regional recurrences might explain some unexpected late tumor growth occurring after a Grade 1 operation. Five illustrative cases in which regional recurrence was detected by computerized tomography are presented. The authors also propose to add a supplementary grade to Simpson's surgical grading: Grade 0. This operation would entail a wide resection of the dura around the attachment zone of the meningioma. The authors hope that with a Grade 0 operation the incidence of recurrence might be reduced.

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A case of metastasizing invasive carcinoma of breast to an expanding extradural frontal meningioma is presented. The peculiar tendency of meningioma to be the host tumor for carcinoma is discussed. The literature pertaining to such rare occurrences is reviewed.