Preoperative intracranial meningioma embolization: technical considerations affecting the risk-to-benefit ratio.

The most common rationale given for the preoperative embolization of an intracranial meningioma is the reduction of surgical blood loss (1 ). According to some surgeons, large or critically placed meningiomas may be easier to remove after embolization. However, objective data to validate these impressions are not readily available. The degree of surgical blood loss may be as or more dependent upon the type of meningioma and its inherent degree of vascularity , the surgical technique, and the position of the meningioma relative to other vascular structures, than upon whether the tumor was preoperatively embolized. The neurosurgeons with whom I have worked over the years have not believed it necessary to embolize every meningioma. A convexity meningioma of small to moderate size may be easily controlled by the surgeon, without the risk and expense of preoperative embolization. However, there certainly are meningiomas that represent more formidable challenges and in which preoperative embolization may play a significant role, including the following: 1) Meningioma of the skull base, where it may be difficult to control the vascular supply. Although it may be impossible to embolize the entire meningioma because of supply from critical vascular structures such as the internal carotid or middle cerebral arteries, some embolization in this difficult tumor may be better than none, and may reduce surgical blood loss. 2) A large meningioma with abundant edema in which retraction and definition of surgical planes may be difficult. 3) Tumorous involvement of a persistently patent dural sinus, from which there may be significant hemorrhage if complete resection is attempted. 4) Tumorous involvement of the scalp and calvarium , because of significant bleeding just getting to the tumor. 5) Predominant vascular supply from the external carotid artery is preferred; however, there may be benefit to embolization even with a moderate to large pial supply to the meningioma if embolization allows better separation of tumor from eloquent portions of brain tissue. If the goal of embolization is to decrease intraoperative bleeding, the embolic material must pass deep into the vasculature of the tumor. More proximal vascular occlusion is inadequate; the surgeon can do that. Superselective catheterization of vessels supplying the tumor must be performed. Then come the questions: What type and size of embolic agent must be used? How do we document the efficacy of the embolization procedure? How do we document the effect of embolization on the surgical procedure and on patient outcome? In sum, how do we get around purely subjective statements by the neurosurgeon that embolization helps, and "prove" that the procedure is really worth the risk and the expense? We must also examine the risk side of the equation. If tiny particles or a liquid are used, agents that could pass through anastomotic channels to normal tissues, do we increase the risk to the patient? In other words , by producing a more efficacious result of embolization, do we also increase the inherent risk of the procedure? This issue of the American Journal of !'feuraradiology contains two articles that attempt to measure the efficacy of preoperative meningioma embolization. In the paper by Grand et al (2) , the authors discuss their study of 15 patients undergoing preoperative meningioma emboliza-