Preoperative Tumor Embolization.pptx

Preopeerative endovascular embolization of tumors - why ? How? Where? When? Also tenets of techniques of embolization and different materials used in the preoperative embolization and its advantages and disadvantages and evidence based current role in today’s neurosurgery.

1. Endovascular Techniques for Tumor Embolization Moderated by : Dr Saraj Kumar Singh Dr Anand Das Presented By:- Dr Rahul Jain SR-3 Neurosurgery

2. BACKGROUND Endovascular tumor embolization was first reported in the 1970s when technological advances made superselective catheterization possible. Common features of the lesions include high vascularity, deep or surgically difficult-to-access supplying arteries , and an intimate relationship to major arteries, dural sinuses, or cranial nerves. Meningioma treatment remains the most frequent indication.

3. INDICATIONS

4. Purpose – To facilitate subsequent resection by selectively permeating the neoplastic microvasculature with embolic material, while preserving the vascular supply to nonpathologic surrounding tissues. These goals must be balanced against the risks of embolization, which include occlusion of en passage vessels, pulmonary emboli, retained microcatheters , and compression of eloquent neural tissues by expanding intratumoral edema or hemorrhage . Rationale and Evidence

5. Prospective randomized trials comparing tumor resection with and without preoperative embolization have not been done , hence the available literature remains largely limited to retrospective single- center cohort series. Overall, these studies support reduced intraoperative blood loss with preoperative embolization for selected tumors with shortens the resection time and increases the possibility of radical tumor removal. Tumor embolization is typically followed by open surgery , patients therefore have both the risk of endovascular devascularization and the risk of subsequent surgery.

6. Broad Principles of the Arterial Supply Vessels of the head, neck, and spine supply the soft tissue surrounding the neural axis, the dural covering, the proximal nerves , and the parenchyma of the brain and spinal cord. Tumors may recruit supply from any of these sources, depending on both the origin and location of the tumor. Vessels supplying the parenchyma of the brain, the pial vessels , include the intradural branches of the internal carotid artery (ICA) and vertebral arteries as well as the anterior spinal artery.

7. Embolization in these vessels carries the risk of off-target embolization to the parenchymal vessels. Catheterization and removal of the catheter also present risk of dissection with associated hemorrhagic and ischemic complications of pial vessel embolization. Dural vessels derive from branches of the external carotid artery (ECA) as well as proximal branches of the ICA and vertebral artery. Before supplying the dura, these branches often supply the cranial nerves as they traverse the cranial foramina . Embolization is therefore safer after distally catheterizing these vessels.

8. Distal catheterization of the middle meningeal artery (MMA) offers effective embolization of the tumor capillary bed when the tumor is dural based. The structural support of the dura also reduces the risk of vessel avulsion during catheter removal . The dural and pial vessels do not exist in isolation but as an interconnected network, with anastomoses. The flow through these anastomoses varies from patient to patient and also varies with physiologic and therapeutic changes.

9. Preembolization diagnostic angiographic work-up is generally performed using a standard 4- or 5-French diagnostic catheter. A ngio -architectural features Type and number of feeding arteries number of compartments arterioarterial anastomoses [especially between extracranial and intracranial vessels] presence of arte- riovenous shunts) characteristics of venous drainage (e.g., obstruction of a sinus by intraluminal tumor extension or external compression ).

10. If vessel sacrifice is considered , the collateral circulation, including the circle of Willis and potential leptomeningeal and extracranial-to-intracranial collaterals, needs to be carefully assessed; a formal balloon test occlusion with or without hypotensive challenge may be beneficial for this purpose. Tumor embolization is typically performed using a 5- or 6-French guiding catheter. Selectively catheterize the vessel of choice with a microcatheter large enough to carry microparticles , pushable and detachable coils of various sizes, and other embolization material.

11. Microcatheters of smaller diameter (e.g., Excelsior SL-10 straight microcatheter , Stryker) and flow-directed microcatheters (e.g., Marathon , ev3) may come into play for catheterization of very distal tumor-feeding branches, but at the cost of precluding the use of larger size embolic materials. Most commonly, an over-the-wire or flow-directed microcatheter is used to perform superselective catheterization and angiography of the feeding pedicles. This technique allows targeted deposition of the embolic material into the pathologic tissue while avoiding the normal tissue. Alternatively , direct percutaneous puncture into the mass of the tumor can be performed in tumors accessible via a percutaneous route

12. General Considerations General medical condition must allow for a safe angiographic procedure. Renal function may limit the amount of contrast that can be safely administered, and vascular disease precludes endovascular access. General anesthesia provides comfort for the patient and reduces movement artifacts that limit angiographic interpretation in the treatment planning and may obscure images of the embolisate deposition.

13. SSEPs and MEPs, can signal angiographically occult ischemic or hemorrhagic complications. When embolization via the vertebral arteries, monitor brainstem auditory evoked responses to provide some understanding of the brainstem and cranial nerve function. Although cranial nerve monitoring is feasible during embolization, embolization is distinct from skull base microsurgery, where early diminishment of signals is potentially reversible . 6-French sheath is used with a transfemoral approach.

14. Intravenous heparin after the access site is obtained to achieve an activated clotting time between 200 and 300 seconds . A thorough understanding of the angioarchitecture of the feeding pedicles, en passage vessels, and EC-to-IC and anterior-to-posterior circulation anastomoses is required . In spinal cases, diligent evaluation of potential anastomoses with the anterior spinal artery is essential to prevent embolic complications. The goal in tumor embolization is not only to sacrifice the feeding vessels but also to obliterate the tumor capillary bed to the greatest extent possible.

15. For direct or percutaneous embolization, a fter catheter angiography demonstrates the vascular supply and anastomoses, a 20-gauge spinal needle is inserted percutaneously into the lesion under fluoroscopic road map guidance until blood return is observed. In this case, puncture of feeding vessels is intentionally avoided. Intratumoral angiography is performed through the spinal needle to confirm its location within the tumor. Direct access to the capillary bed can be advantageous if the feeding pedicles are difficult or impossible to catheterize.

16. Timing Many institutions routinely extirpate tumors the day after embolization . Some groups have reported peak devascularization 1 week postembolization , but some reports have noted advantages in reducing blood loss from earlier surgery. Because tumor necrosis has also been associated with hemorrhage , elevated intracranial pressure , and emergency neurologic decline, some authors have even reported delaying embolization until after a craniotomy is completed to avoid the potential for acute tumor edema from embolization.

17. Arguments in favor of early surgery (i.e., 1–3 days) include the anticipation of tissue swelling and the intention to prevent revascularization via collateralization. On the other hand , longer wait times allow for necrotic liquefaction, which can make resection technically simpler and faster—a soft, partially liquefied tumor can at times be removed with suction alone. Necrotic liquefaction becomes apparent around day 4 after devascularization and attains its maximum at 7 to 9 days , after which no significant additional tissue death seems to occur.

18. Embolic Agents Ideal embolisate is one that can penetrate deeply into the capillary bed while providing sufficient control over its injection to avoid occlusion of the norma l arterial or venous vasculature, radiopacity for visualization, ease of surgical handling, and nontoxicity. Given that the treatment goal is surgical extirpation of the tumor, the long-term durability of the embolisate is a less important. 3 types – solid occlusive, particles and liquid agents

19. Solid Occlusive Devices Coils and balloons used to occlude large vessels. Liquid, fibered, and detachable coils. Liquid coils are soft and injectable, while fibered coils are pushed mechanically through a coil pusher Detachable coils are released mechanically, electrically, or hydrostatically. The primary role of coils is to augment the effects of a secondary embolisate by dampening the high arterial flow and thereby eliminate dangerous EC-to- IC anastomoses to minimize embolic events before another occlusive agent is used.

20. Particles Although particles penetrate the capillary bed, they are unable to occlude additional arterial pedicles in a retrograde fashion, so additional arterial pedicles may need to be catheterized for further embolization to achieve the same degree of devascularization . Particles range from 50 to 1000 μm in size composed of PVA (non uniform) or microspheres. Gelfoam particles are typically 40 to 60 μm in size. Advantage lie in their ease of use and deep tumoral penetration .

21. Innate proteolysis of gelfoam particles can easily disintegrate these agents typically over the course of 4 to 6 weeks, thereby causing occluded vessels to recanalize . Because of the small size of these embolisates , they can potentially occlude the vasa vasorum of cranial nerves or cause other undesirable embolizations . PVA particles are the most commonly used agents for tumor embolization after introduction in 1960s. PVA is inert and insoluble; therefore, contrast is required to visualize it during injection . PVA can be long-lasting, but it is not permanent; it degrades over weeks to months.

22. Smaller particles are more effective than larger particles in penetrating tumors to facilitate tumor necrosis. PVA is associated with an increased risk of inadvertent embolization of en passage vessels or the pulmonary capillary bed compared to larger particles. PVA particles ranges from 50 to 1000 μ m. Unlike PVA , microspheres have a uniform shape and size. They may be associated with less clumping and clogging of microcatheters than PVA. They do not degrade and generate only a moderate inflammatory response.

23. Microspheres have been described to penetrate more distally than PVA during embolization and to result in significantly less operative blood loss. US FDA approved Embospheres ( BioSphere Medical, Rockland, MA ) are clear, radiolucent, acrylic microspheres composed of tris -acryl gelatin in the year 2000. Embozene ( CeloNova BioSciences,Newnan , GA) are hydrophilic-coated hydrogels. Particle size selection is a balance between the extent of penetration and the risk of penetration. For tumor embolization , we commonly use 200 to 350 μm particle s.

24. Smaller particles can migrate more distally before becoming lodged but are at risk of embolizing normal terminal branches. Embolization with smaller particles carries a greater risk of necrosis, edema , and hemorrhagic conversion within the lesion ( approximately 5 %) from occlusion of terminal branches or of draining veins. Larger particles can be trapped in the proximal branches and may not adequately occlude the tumor capillary bed despite significant contrast reflux.

25. When particles are used , the inner diameter of the delivery microcatheter must be bigger than the particles to prevent clogging. Some catheters are designed with a smooth transition between the hub and the catheter lumen to reduce clogging, but the main factor is related to maintaining the particles in a uniformly distributed suspension . An iodinated contrast medium is mixed with the particles as a surrogate indicator of where the embolisate is deposited. Therefore, there is a risk of particle deposition not correlating with the contrast marker if there is a non uniform suspension.

26. Liquid Embolic Agents The most common and widely available are cyanoacrylate monomers and ethylene vinyl alcohol (EVOH ). Alcohol is a potent sclerotic, devascularizing agent. It causes anoxic cellular damage and fibrinoid necrosis of the intimal lining. Although ethanol is a powerful embolisate , it must be used judiciously and with great caution to prevent infarction of normal tissue.

27. n- BCA was approved in 2000 for use in brain arteriovenous malformations. It is a nonabsorbable , adhesive liquid embolic agent that causes an inflammatory response in the endothelium and tumor . N -BCA must be mixed with ethiodized oil and tantalum powder to prolong the polymerization time and promotes radiopacity . This embolisate stimulates the development of necrosis and fibrous ingrowth in the arterial feeders , leading to permanent, durable occlusion . Compared to PVA, n- BCA tends to occlude both proximal and distal vessels, increasing the probability of injuring cranial nerves or causing infarctions.

28. The adhesive nature of the polymer can entrap the microcatheter , risking catheter fracture or vessel avulsion during removal. For most applications, we use a mixture between 1.5:1 and 3:1 of ethiodized oil to n- BCA for infusion. The microcatheter is cleared with 5% dextrose in water to flush all ionic catalysts from the lumen . The polymerization rate depends on the concentration of n- BCA monomer. EVOH copolymer–DMSO sold in US by name Onyx (Medtronic , Dublin, Ireland ), approved by USFDA in 205 for brain AVMs.

29. Unlike n- BCA, Onyx is a cohesive polymer delivered in an organic solvent containing a suspension of radiopaque tantalum powder . Before it is used, the Onyx solution must be shaken vigorously for 20 minutes to suspend the radiopaque tantalum powder. Otherwise, sedimentation of the tantalum causes inadequate opacification during infusion and misunderstanding of the distribution of the embolisate . Once prepared, Onyx continues to be injected under subtraction-mask imaging to demonstrate the slight radiopacity of the embolisate .

30. The slow, steady injection should be about 0.1 mL/min and should not exceed 0.25 mL/min to avoid the effects of angiotoxicity of the solvent . Whennreflux occurs proximally, the infusion is stopped for as long as 2 minutes to allow the Onyx to solidify around the catheter. This strategy – “Plug and Push” allows a plug to form at the catheter tip, increasing the resistance against retrograde flow and thereby increasing the probability of antegrade flow. The goal is to establish forward flow into the capillary bed of the tumor, which can then deliver embolisate throughout the tumor without selective catheterization of each feeding artery.

31. The advantages of Onyx are that it can penetrate much deeper than other agents and that the capillary network can be broadly occluded with a single pedicle injection. Unlike n- BCA, Onyx permits discontinuous injections on the order of minutes and allows continuous angiographic analysis of the angioarchitecture of the lesion . In particular, small collaterals not visualized on the initial angiogram may become apparent with progressive infusion of Onyx. Venous filling can be stopped temporarily without the threat of unintended migration of Onyx into draining veins. These advantages allow exceptional control of Onyx flow and its progression to enable a large amount to be delivered via a single injection.

32. Considerations for liquid embolics In general, a more distal catheterization, with a short distance to the target, is required for the use of n- BCA due to the shorter period of injection and due to its adhesive nature . Onyx is more often able to migrate along a longer arterial pedicle to reach the target capillary bed. However, despite the ability to deliver Onyx over a longer distance, the inflammatory nature of n- BCA is suggested to result in more effective embolization even with less embolisate .

33. The slowly controlled administration of Onyx is both favorable in allowing fine control of the embolisate but also unfavorable in longer procedure time and greater radiation exposure. With both Onyx and n- BCA embolization , the risk of catheter entrapment can be mitigated with detachable-tip microcatheters .

34. COMPLICATIONS Overall, the incidence of permanent neurologic deficits after tumor embolization is typically below 2% The most common complications from tumor embolization are fever and localized pain. Unintended embolization most often occurs in unrecognized anastomoses involving ECA-ICA, Carotid- Vertebrobasilar and spinal medullary artery with paraspinal vasculature.

35. The orbital, petrocavernous , and upper cervical regions harbor a particularly large number of these potentially dangerous pathways. Once the perfusion pressure across the arteriocapillary bed rises during embolization, these routes may become functionally active and therefore subject to potential embolization . Vessel injury and tumor hemorrhage - Microwire perforations of distal arterial branches and high injection pressure of the embolic material or contrast agent. Fortunately most often clinically silent or limited to transient headache, focal seizures , or focal neurological deficits.

36. Tumor swelling : Hypoxic swelling of the freshly devascularized tumor starts immediately following embolization and reaches its maximum at around 4 days . steroids bolus prior to embolization and continued until after surgery. Close neurological examination and preparedness for definitive surgery in case of mass effect. Reflux of embolic material - reflux along a selectively catheterized branch into a parent artery or when embolic material finds its way from a distal ECA branch into the ICA or vertebral artery circulation via one of a given set of arterioarterial anastomoses that cross the skull base.

37. Injection of embolic material is therefore best performed under live biplane digital subtraction angiography. Careful intermittent injection allows for the embolic material to be carried into the tumor bed by blood flow around the catheter; avoid induction of spasm in the target artery by means of careful catheterization. As embolization progresses, new portions of the tumor bed frequently open, often permitting embolization of a larger part of the mass. Therefore periodically monitor the state of the tumor vascular bed by washing the particles in with saline and performing intermittent biplane angiography through the embolization microcatheter .

38. Risk of blindness - Inadvertent central retinal artery embolization. Occurs when a dangerous anastomosis between branches of the internal maxillary artery or MMA and the ophthalmic artery has been overlooked. Cranial nerve injury : Terminal branches of the ECA system supply the transcranial and extracranial portions of cranial nerves. ECA branches notorious for putting cranial nerves at risk include the : ascending pharyngeal artery (cranial nerves [CNs] IX–XII) accessory meningeal artery (CN IV–VI), MMA ( CN VII ), and posterior auricular artery (CN VII).

39. Skin necrosis - obliteration of the cutaneous capillary bed may cause necrosis of the skin or prevent efficient wound healing after craniotomy. Particularly when using small particles (<150 μm ) or liquid embolics in the superficial temporal, posterior auricular, and occipital arteries.

40. COMPLICATION AVOIDANCE It is of particular importance to limit the morbidity of preoperative tumor embolization, and to keep in mind that aggressive embolization easily results in permanent postprocedural neurological deficits. The presence of dangerous anastomoses does not necessarily preclude embolization. The use of particles larger in size than the diameter of the anastomotic artery, positioning of the catheter tip distal to their origin on the parent artery, their temporary occlusion with embolic materials, and the use of temporary balloon inflation are part of a wide range of techniques allowing for selective flow control.

41. Conclusion Vascular craniospinal tumors can present formidable surgical challenges with high associated rates of operative morbidity and mortality. Diagnostic angiographic work-up, including a series of anatomic studies of the tumor vasculature using superselective microcatheters , is the key to safe embolization using particulates or liquid embolic agents.