Meningiomas: a quest for the optimum therapy

I T is not surprising that meningiomas, the most common benign intracranial tumor, have fascinated neurosurgeons since the inception of the subspecialty. As with other benign tumors of the central nervous system, surgical excision should be expected to cure the affected individual. This has not always been the case. Harvey Cushing, always alert to the deficiencies of his evolving subspecialty, discussed problems of recurrence in the greatest of his monographs. Why did surgical excision fail to cure these patients? Cushing noted a more rapid growth with angioblastic meningiomas compared with the more benign course of meningothelial or fibroblastic variants. Differences in histology, 3,22,z3 however, were only a small part of the answer. The most obvious reason for recurrent tumor was primary failure to completely excise the lesion. Published studies confirm the higher incidence of recurrence associated with incomplete excision. 1,29,3~ This could be attributed to three factors: 1) failure to appreciate the extent of the meningioma; 2) premature termination of surgery related to hemorrhage often obstructing visualization or even compromising the stability of the patient; and 3) involvement of critical neural, vascular, or paracranial structures. Neuroimaging has made a dramatic impact on the first of these problems our ability to recognize the extent of the tumor. It is sometimes difficult for those who finished training within the last 20 years to appreciate just how much of a change in clinical practice was produced by the introduction of computerized tomography (CT) scanning? Subsequent use of magnetic resonance (MR) imaging, especially with gadolinium enhancement, has even better outlined the true size of meningiomas. We can thus not only preoperatively outline the extent of the tumor but also recognize postoperative residual tumor or detect recurrence. 8 Improvement in hemostasis intraoperatively can be attributed to the use of bipolar coagulation and newer hemostatic agents. Preoperative angiography can define the tumor vascular supply. Adjunctive embolization can substantially reduce bleeding when performed prior to surgery. The third problem, the involvement of critical structures, has been addressed by parallel improvements in surgical techniques. This has had its most dramatic effect in dealing with tumors of the sphenoid wing and parasellar region. While complete resection rates of 91% are claimed for tumors affecting the lateral aspect, only 47% of inner sphenoid meningiomas could be completely excised. 34 Among the surgical trends has been the recognition of the advantages of a joint approach to lesions of the skull base. By combining the talents of head and neck surgeons, otologists, plastic surgeons, and ophthalmologists with those of the neurosurgeorl, morbidity may be reduced and more extensive tumors addressed. Direct surgical approach to lesions of the cavernous sinus, an area previously considered sacrosanct, represents a second area of surgical advance. 36 The use of the microscope, high-speed drills, laser, and ultrasound fragmentation have all contributed to better visualization, less tissue manipulation, and more selective protection of surrounding structures. In spite of these advances, meningiomas continue to recur. The problem of involvement of adjacent critical vascular or neural structures, in particular, continues to be an issue. Even with surgery within the cavernous sinus, extension to the wall of the carotid artery limits complete microscopic resection without en bloc removal with or without reconstruction of the carotid artery itself. 37 Aggressive excision in the medial sphenoid area can result in substantial problems with the major cranial vessels. 13 Whether the risks and effort involved in this procedure are outweighed by the potential benefits remains to be seen. Finally, even when complete excision is accomplished tumors may recur. While the recurrence rates vary among papers, applications of statistical analysis and life-table studies suggest that the long-term recurrence rates are much higher 1,3~ than suggested in earlier articles 4~ or even in more recent ones when the