37 Central Nervous System Tumors

10.1055/b-0040-175284

37 Central Nervous System Tumors

Kunal Vakharia, Muhammad Waqas, Elad I. Levy, and Adnan H. Siddiqui

General Description

Central nervous system (CNS) tumors that tend to be highly vascular can be effectively embolized and treated endovascularly prior to surgical intervention. Tumors most suited to such intervention include meningiomas, hemangioblastomas, paragangliomas, and juvenile angiofibromas. These tumors tend to have distinct locations and arterial feeders that are frequently hypertrophied on angiography. Understanding anatomical location and external carotid artery (ECA) anatomy becomes crucial in surgical planning and preoperative embolization. In addition, surgical planning with respect to timing after embolization becomes increasingly important because tumors that have recently undergone embolization tend to swell and generate perilesional edema. In addition, there is a growing body of literature on endovascular therapy for retinoblastoma as well as possible endovascular intervention for glioblastomas and other tumors of CNS origin.

Evidence for Tumor Embolization

Teasdale et al in 1984 ¹ and Wakhloo et al in 1993 ² demonstrated that embolization of meningiomas can reduce the need for blood transfusions intraoperatively as well as decrease the length of the surgical procedure.
Data suggest a 1.6%–9% reported incidence of cranial nerve palsy after small-particle embolization of feeding vessels primarily in meningiomas and paragangliomas.
It has been suggested that waiting 7–10 days postembolization may allow for collateral vessels to supply the tumor with blood, warranting early surgical resection after embolization.
Roberson et al. in 1979 ³ first described embolization of vascular pedicles for juvenile angiofibromas. Since then, embolization of ECA feeders to such tumors has shown a reduction in intraoperative blood loss.
Embolization of hemangioblastomas and hemangiopericytomas has shown some effectiveness in reducing intraoperative blood loss.
White et al. in 2008 ⁴ demonstrated that risk for preoperative embolization for cervical paragangliomas was low and the procedure offered significant hemostasis intraoperatively.
Most studies on embolization for spinal tumors lack a control arm; yet preoperative embolization is widely accepted to reduce the intraoperative blood loss in these cases.

Indications

Highly vascular tumors may potentially warrant embolization for selective delivery of chemotherapeutic medications or embolizates. Embolization is considered in this chapter, although the principles of chemotherapeutic delivery are similar. Embolization is performed for highly vascular skullbase lesions. Preoperatively, the goals of treatment should be discussed with patients and specifically identified. Typical indications include devascularizing tumor beds, embolizing deep or difficult to find arterial pedicles, or palliative management in select cases. Operations for vascular spinal tumors like hemangioblastoma, hemangioma, aneurysmal bone cyst, giant cell tumor, osteoblastoma, and metastatic deposits from renal cell carcinoma or the thyroid gland are considered technically difficult cases. Patients can have massive blood loss during the surgical resection of these tumors. In addition to vascularity, extent of disease, number of vertebral levels involved and bleeding during approach to the tumor can still cause significant blood loss.

Neuroendovascular Anatomy

External Carotid Artery Anatomy

The ECA primarily supplies tissues of the face, neck, and scalp. There are many extracranial-to-intracranial anastomoses that are crucial to understanding therapeutic embolization in this vasculature. Understanding the unique anatomy for each tumor is important, although they may have the same blood supply pattern because of a similar location (i.e., typical locations tend to be fed by typical arterial branches). Meningiomas and other dural-based lesions tend to arise in certain locations. Parasagittal meningiomas are often fed by ethmoidal arteries and the falcine artery; parasellar meningiomas are often fed by accessory and recurrent meningeal arteries from the internal maxillary artery; frontobasal meningiomas, including planum sphenoidale and sphenoid wing meningiomas, are often supplied by the inferolateral trunk from the internal carotid artery (ICA) as well as anterior and posterior ethmoidal vessels from the internal maxillary artery and the artery of the foramen rotundum. Tentorial meningiomas have been shown to have a robust supply from the tentorial artery off the ICA, petrosquamosal branch of the middle meningeal artery, and transmastoid branch off the occipital artery. Similarly, understanding the complex anatomy of the ascending pharyngeal artery is important when planning for embolization of paragangliomas in both the jugular foramen and cervical region. The intricate nature of the anterior ascending pharyngeal branches tends not to contribute to the vascular supply for paragangliomas. The posterior neuromeningeal and jugal branches are the most common sources of blood supply for these tumors. Planning for access as distally as possible while understanding the relation of the vessel to the skull base can help avoid cranial nerve palsies.

Spinal Cord Anatomy

The spinal cord is supplied by three longitudinal arteries (one anterior spinal artery and two posterior spinal arteries) that receive contributions from the spinal branches of the segmental arteries, also called radiculomedullary arteries. The radiculomedullary arteries also supply the spinal roots, dura, and bony wall of the spinal canal. Each radiculomedullary divides into an anterior and a posterior branch. The anterior radiculomedullary arteries divide into ascending and descending branches that anastomose to form the anterior spinal artery in the midline. The descending branch of the anterior radiculomedullary artery joins the midline anterior spinal artery in a characteristic “hairpin” configuration that can be identified on spinal angiography. The junctions between the posterior radiculomedullary arteries and the posterior spinal arteries also exhibit a characteristic hairpin configuration but are located off the midline. The great anterior radiculomedullary artery, commonly known as the artery of Adamkiewicz, arises at the T9 to T12 vertebral level in 75% of individuals, most often on the left side. When it arises above the T8 vertebral level or below the L2 level, there is usually a second major radiculomedullary arterial supply to the anterior spinal artery. At the cervical level, the radiculomedullary arteries arise from the vertebral artery and the ascending and deep cervical arteries. Additional contributions may be present from anastomoses with the ECA via the occipital and ascending pharyngeal arteries. At the thoracolumbar level, the radiculomedullary arteries arise from the supreme intercostal, posterior intercostal, and lumbar arteries. The blood supply to the sacrum and the cauda equina are via the lateral sacral and the iliolumbar arteries from the internal iliac artery. There is also a small contribution from the median sacral artery.

Periprocedural Medications

Preprocedurally, patients should be started on corticosteroids for large tumors and those causing neural compression. In addition, premedication before surgery or endovascular therapy may be necessary for patients taking medications specific to the pathology of their tumor; for example, β-blockers may need to be administered preoperatively to patients with paragangliomas.

Lidocaine can be administered at the site of the skin puncture prior to embolization to help prevent local edema and pain. Injections of dimethylsulfoxide into the tumor before embolization can potentially be helpful in liquefying the tumor during procedural resection, although reports of this therapy are anecdotal.

Systemic heparinization is administered during the procedure because of the risk of intraprocedural thrombus formation. A weight-based intravenous bolus of heparin aimed at an activated coagulation time of 250–300 s may limit thromboembolic complications. Heparin is administered before selective angiography of the feeding vessels. For acute thrombus formation during the procedure, a glycoprotein IIb/IIIa inhibitor (e.g., eptifibatide) is injected intra-arterially.

Specific Technique and Key Steps

The key steps for embolization of arterial pedicles to CNS tumors are described here ( Fig. 37.1–37.3, Video 37.1–37.3 ). The principles also apply to the delivery of chemotherapeutic agents.

A 6 or 8 French (F) sheath is inserted in the femoral artery.
After the femoral angiogram has been performed to confirm the absence of any irregularity or dissection, a guide catheter is advanced over a curved wire (0.035-inch angled Glidewire, Terumo) into the aorta. This maneuver is completed under fluoroscopic guidance.
Depending on the arch anatomy, the guide catheter can be brought up directly over the 0.035-inch angled Glidewire or advanced over a 4–5F intermediate diagnostic catheter, such as a Vitek (Cook Medical) or Berenstein catheter (Cook Medical).
Cerebral angiography is performed to obtain a baseline set of images of the intracranial vasculature and extracranial vasculature to identify arterial pedicles ( Video 37.1–37.3 ).
Bilateral ECA injections are important to obtain an understanding of the vascular supply to these tumors.
When the tumor is supplied by meningeal vessels, superselective catheterization of target meningeal vessels is important to understanding the anastomoses as well.
Microcatheter navigation is performed distally into the target vessel. Selective microcatheter injections are performed to demonstrate tumor vascularity and to confirm that the catheter is as distal in the vessel as possible to prevent cranial nerve injury ( Fig. 37.1–37.3, Video 37.1–37.3 ).
Choice of embolic agents including Onyx (Medtronic), N-butyl-2-cyanoacrylate polyvinyl alcohol and acrylic particles are important. Smaller particles tend to penetrate the tumor vasculature although the risk of neurological complication is higher. Typically, particles > 150 µm are suggested.
Wada testing can be performed if there is concern for anastomoses to the ophthalmic artery or other intracranial vessels.
Embolic agents are injected in a free-flow manner under negative roadmap imaging to clearly visualize how much tumor penetration has been achieved.
The embolic agent plug is broken, and the microcatheter is removed from the guide catheter.
A final (i.e., control) cerebral angiogram is recommended to assess for smooth synchronized perfusion, looking specifically for delayed capillary filling or other larger occlusion (i.e., vessel dropout).