Diagnostic Cerebral Angiogram

It is critical to perform a thorough diagnostic cerebral angiographic evaluation before meningioma embolization. Interpreted in conjunction with findings evident on noninvasive imaging, this will enable a detailed appraisal of the dural, pial, and transosseous arterial supply to the tumor and assessment of the patency and drainage pattern of the venous sinuses. Superselective angiograms afford an opportunity to delineate the nature of dangerous anastomoses involving the internal carotid and vertebral arteries and identify small branches that supply the cranial nerves. Anatomical variants, especially those of the middle meningeal and ophthalmic arteries, must be noted.

The classic angiographic appearance of a meningioma is that of a uniform hypervascular tumor blush that appears in the early arterial phase and persists through the late venous phase. A dense network of small vascular branches supplying the tumor is arranged in a “sunburst pattern,” centered on larger feeding vessels8 ( Figs. 14.1 and 14.2 ). The vascularity of meningiomas is variable, however, with some lesions demonstrating relatively little angiographic evidence of contrast staining. The predominant supply to intracranial meningiomas occurs via the dural vasculature. This includes branches of both the external carotid artery and the internal carotid artery/vertebrobasilar system. Secondary supply commonly derives from small, pial branches.

The middle meningeal artery, which supplies the dura of the anterior and middle cranial fossa, is the vessel most commonly associated with meningiomas. There is often bilateral middle meningeal arterial supply to tumors in the parasagittal region. Not infrequently, transosseous supply from the superficial temporal artery is also noted ( Fig. 14.3 ). Olfactory groove and planum sphenoidale meningiomas often receive additional blood supply from the ethmoidal divisions and anterior falcine branch of the ophthalmic artery. Meningeal branches of the cavernous internal carotid artery contribute significantly to the blood supply of tentorial, sphenoid wing, and petroclival meningiomas.9 Posterior fossa meningiomas residing at the cerebellopontine angle or located along the cerebellar convexities are often fed by the ascending pharyngeal artery and transosseous branches of the occipital artery, in addition to the petrosquamosal branch of the middle meningeal artery. Midline posterior fossa and foramen magnum lesions are more often supplied by posterior meningeal branches of the vertebral artery ( Fig. 14.4 ).

Embolization

After a diagnostic cerebral angiogram is performed to identify blood supply and assess for feasibility and safety of embolization, a microcatheter is advanced over a microguidewire through the larger diagnostic or guide catheter. Under real-time digital subtraction fluoroscopy, the microsystem is advanced into the vascular pedicle supplying the tumor. Superselective angiography is performed through the microcatheter to confirm proper position and to identify any distal branches supplying normal tissue and to assess for the presence of dangerous anastomoses. Provocative testing with intraarterial sodium amytal or lidocaine may aid in the detection of unsafe collaterals or cranial nerve supply distal to the microcatheter tip.3,7 After proper positioning of the microcatheter, injection of embolic material is performed under constant real-time digital subtraction fluoroscopy. Distal tumoral penetration prevents flow to the mass via collateral vessels and results in devascularization and subsequent tumor necrosis.

Several agents have been utilized to embolize meningiomas, including particles,10,11 n-butyl cyanoacrylate,12 Onyx (ev3 Neurovascular, Irvine, CA),13 platinum coils,14 ethanol,15 fibrin glue,16 and Gelfoam pledgets (Pfizer, Inc., NY).5,17 Particulate agents are favored over liquid embolic materials due to their ease of use and relative safety. Because the precise penetration capacity of particles is dependent on their size, appropriate selection precludes infiltration into the small arterioles supplying cranial nerves. Because the vasa nervorum are small, the use of particles larger than 150 μm in diameter has been suggested to lessen the risk of ischemic cranial nerve injury.18,19 Polyvinyl alcohol (PVA) particles are believed to remain occlusive in vessels for time periods in the order of weeks, after which vascular recanalization may occur.20 This property is suitable for preoperative tumor embolization. Given that the tumor mass is excised during definitive surgical resection, a long-term durable embolization is not necessary. Trisacryl gelatin microspheres are deformable, homogeneous, and uniformly shaped. They are believed to result in less catheter obstruction and recanalization than do irregularly shaped and sized PVA particles.21 Although they may penetrate deeper than similar-sized PVA particles, they are also more likely to inadvertently enter and remain in small blood vessels. After particle embolization is performed, a platinum coil or Gelfoam pledget may be placed more proximally, in the treated vessel, to help prevent recanalization and aid in surgical resection3 ( Fig. 14.5 ). Care is taken to avoid proximal reflux of any embolic material into eloquent vascular branches.

In contrast to particles, liquid embolic materials such as glue (n-butyl cyanoacrylate) and Onyx can more easily enter anastomotic channels that supply cranial nerves or cortical vessels not evident on the initial diagnostic angiogram. The operator must be acutely aware of this possibility when utilizing such agents for tumor embolization. Additionally, microcatheter retention can result in vessel rupture or ischemic sequelae. The use of particles, rather than liquid embolic agents, eliminates the prospect of this complication. As such, meningiomas located distant from the skull base foramina and exiting cranial nerves are most suitable for embolization with liquid agents. ( Fig. 14.6 ).

Determining which vessels to embolize is not always straightforward. Most agree that large, external carotid artery vessels that directly supply the tumor mass and are distant from dangerous anastomoses may be treated. However, meningiomas supplied by both the external and internal carotid artery are reported to exhibit increase pial supply subsequent to embolization of external branches.5 Augmented blood flow and hypertrophy of the small, deep intracranial vessels may increase the difficulty of the surgical resection because this vascular supply is often not encountered until the end of the operation.

Preoperative embolization of pial blood supply is generally not performed because the benefit of embolization is usually outweighed by the potential risk of ischemia and stroke ( Fig. 14.7 ). However, some authors advocate embolization of hypervascular tumors purely, or predominantly, supplied by internal carotid artery or pial branches.7,22 This technique requires the ability to advance a microcatheter just proximal to the tumor bed, excluding any en passage vessels from inadvertent embolization. Furthermore, there must be no adjacent normal brain staining evident on superselective angiography. Preexisting irreversible neurological deficits may decrease the subsequent risks inherent to embolization of pial vessels before surgical resection.7