23.1 Goals

1. 
   

   Review the indications, technique, and complications of transarterial embolization of spinal tumors in the setting of a case example.

   
   
2. 
   

   Analyze the literature evaluating the efficacy of preoperative embolization of spinal metastases in reducing intraoperative blood loss during tumor resection surgery.

   
   
3. 
   

   Review other factors that may influence success of transarterial embolization such as degree of embolization, timing of surgery following embolization, and tumoral histology.

23.2 Case Example

23.2.1 History of Present Illness

A 51-year-old male with a history of renal cell carcinoma presented with 6 months of progressive back pain. He denied any neurologic symptoms including loss of bowel or bladder function, weakness, numbness, or paresthesias. He underwent a CT and MRI which demonstrated a pathologic fracture of the LI vertebral body.

Past medical history: Renal cell carcinoma diagnosed 9 monthsearlier,currentlyonchemotherapy. Priordeep venous thrombosis, not currently on anticoagulation.

Past surgical history: Prior left hydrocele repair.

Family history: Sister with colon cancer.

Social history: None.

Review of systems: As per the above.

Neurological examination: Unremarkable.

Imaging studies: See Fig. 23.1 and Fig. 23.2.

In Fig. 23.1a-d, computed tomography (CT) demonstrates a lytic lesion in the posterior vertebral body and left pedicle of the LI vertebral body. Magnetic resonance imaging (MRI) shows the lesion is enhancing and T2 hyperintense. There is epidural tumor extension resulting in left lateral recess stenosis and severe left neural foraminal narrowing. In Fig. 23.2a-d, spinal angiogram at the level of LI demonstrates tumoral blush of hypervascular LI vertebral body metastasis. Follow-up spinal angiography status postparticle and coil embolization of the LI tumor demonstrates no residual tumoral vascularity.

23.3 Case Summary

1. 
   

   What are the treatment options for this patient’s spinal tumor?

   
   

   The spine is the most common site of osseous metastatic disease and affects up to 40% of cancer patients, thought to be a result of its close proximity to regional venous and lymphatic drainage pathways. ¹² Spinal metastases can cause significant morbidity with up to 10% of patients suffering from cord compression. ³ Currently, the standard of care for treatment of spinal metastases is radiotherapy. ⁴ However for patients with mechanical instability or radioresistant tumors, surgery is indicated. Surgical treatment is aimed at pain control and preservation of mechanical and neurologic function. ⁵

   
   
2. 
   

   What are the purposes of transarterial embolization of tumors?

   
   

   Surgery in patients with hypervascular tumors may be hazardous due to excessive blood loss. One technique for reducing intraoperative blood loss is preoperative transarterial embolization. Preoperative embolization not only reduces blood loss but may allow for more complete tumor resection and shorter intraoperative time. ^{6 , 7 , 8 , 9 , 10} Embolization may also be indicated in patients with unresectable tumors as it can help to reduce pain and slow growth. ¹¹ A less common application is in cases where a large vessel is encased within the tumor confines (i.e., vertebral artery). In order to have an en-bloc resection of the tumor, it may be necessary to deconstruct this vessel after showing patency of the contralateral vessel.

   
   
3. 
   

   What spinal tumors can be treated with transarterial embolization?

   
   

   Preoperative embolization is described for a wide variety of tumors including those known to be at high risk for intraoperative hemorrhage such as thyroid carcinoma, renal cell carcinoma, and melanoma but also for more common malignancies such as breast, prostate, and lung carcinoma. ^{12 , 13} Embolization has also been successfully used in patients with hypervascular primary bone tumors such as aneurysmal bone cysts, hemangiomas, giant cell tumors, and chordomas ^{14 , 15 , 16 , 17}

   
   
4. 
   

   What is the technique for embolization of spinal tumors?

   
   

   Spinal arterial embolizations should be performed under general anesthesia with somatosensory-evoked potential (SSEP) monitoring. A preshaped guide catheter is used to access the corresponding bilateral segmental arteries, including two levels above and below the lesion. Angiography through the guide catheter is performed to identify tumor feeders, arterial supply to the spinal cord, and normal en passage vessels. Based on the configuration and origin of the feeder artery as well as the embolysate that will be used for the particular case, the microcatheter is selected. Once the microcatheter is in position, embolic material is delivered into the feeding pedicle.

   
   
5. 
   

   What embolic agents are available for use and what are the pros and cons of each?

   
   
   
   
   1. 
      

      PVA (Polyvinyl Alcohol)

      
      
      
      
      1. 
         

         PVA was first introduced as an intravascular embolization agent in 1975 and is now routinely used for preoperative spinal tumor embolization. ^{7 , 10 , 18 , 19} PVA particles are formed from PVA foam sheets and are available in sizes ranging from 100 to 1,100 mm. PVA particles adhere to the vessel wall and result in slow flow, causing thrombus formation and eventual angionecrosis. ²⁰ When using PVA, the preferred method of delivery is direction infusion into the pedicle supplying the tumor. If that vessel is unable to be catheterized and PVA must be injected from a more proximal vessel, flow control techniques can be used to direct particles into the tumor pedicle while avoiding normal branches. Post-embolization angiography is obtained immediately after embolization to evaluate for any residual angiographic blush or nontarget embolization.

      
      
   2. 
      

      NBCA (n-butyl cyanoacrylate)

      
      
      
      
      1. 
         

         NBCA is a low-viscosity cyanoacrylate glue that forms a polymer upon contact with ionic mediums such as water or blood. It is FDA approved for embolization of cerebral AVMs but is used off-label for tumor embolization. ^{7 , 21 , 22 , 23} NBCA is injected together with lipiodol under fluoroscopic guidance. NBCA is very adherent, which requires a rapid infusion time and can make the delivery difficult to control. The two main complications are nontarget embolization and catheter retention. These complications can be minimized by injecting rapidly and flushing the catheter with a nonheparinized 5% dextrose solution, which is nonionic and delays polymerization of NBCA within the catheter tip upon contact with blood or saline. ²⁴

      
      
   3. 
      

      Onyx

      
      
      
      
      1. 
         

         Onyx is a liquid embolic agent that has been successfully used for preoperative spinal tumor embolization. ^{13 , 25 , 26} It is composed of a polymer (ethylene-vinyl alcohol) dissolved in dimethyl sulfoxide (DMSO) that forms a cast within vessels upon contact with blood. It is a useful alternative to PVA when the tumor pedicle is close to the anterior spinal artery, and there is a risk of nontarget particle embolization. Onyx is available in two formulations (Onyx 18 and Onyx 34). Onyx 34 is higher viscosity and used primarily for high flow lesions such as AV malformations. The Onyx 18 formulation is used for tumor embolization because the lower viscosity results in better distal vascular penetration. Onyx is prepared per the manufacturer instructions, which involves agitation of the Onyx vials for 20 minutes and priming of the dead space of the microcatheter (typically an Echelon or Marathon microcatheter) with DMSO. Onyx is subsequently injected into the microcatheter under the blank roadmap technique. A small plug often forms along the distal tip of the microcatheter, which is desirable because it prevents retrograde reflux. Unlike NBCA, Onyx is nonadhesive. This decreases the chances of gluing the microcatheter in place and allows for a slow administration that can be evaluated angiographically in real-time. Onyx is administered until the vascular pedicle is occluded.

   
   
6. 
   

   What are the potential complications of transarterial embolization?

   
   

   The most clinically significant complication of transarterial embolization in the spine is nontarget embolization, which can result in ischemia and infarction of the spinal cord. ^{27 , 28} The true incidence of this complication is not known, likely because it occurs infrequently and is underreported. To prevent this complication, superselective catheterization and vigilant inspection of the pre-embolization angiograms must be performed to avoid spinal and radiculomedullary arteries and identify any intersegmental anastomoses. The neurological status of the patient should be monitored throughout the procedure and frequent angiograms should be obtained to evaluate for nontarget flow. For cervical tumors that are supplied by branches of the vertebral arteries, vertebrobasilar strokes from nontarget embolization are a risk. ⁸ If the tumor pedicle cannot be selectively catheterized, flow diversion via temporary balloon occlusion of the vertebral artery can be performed to protect against nontarget embolization. Although less common since the development of hydrophilic and detachable-tip microcatheters, catheter retention remains a potential complication of transarterial embolization with liquid embolics. ^{29 , 30} For adhesives such as NBCA, there is a risk gluing the microcatheter to the vessel wall due to reflux along the microcatheter tip. ³¹ With the use of Onyx, the chance of catheter retention is lower since Onyx is non-adhesive. However, the microcatheter is still at risk for retention due to encasement within the Onyx cast. ³² There is no literature currently available regarding the management of retained catheters within the spine possibly related to the short distance from the guide catheter to the target site. For retained catheters within cerebral lesions, the catheters are usually retrieved endovascularly or surgically, ^{33 , 34 , 35} although in some cases they have been left in place without ill-effect. ^{31 , 32}

   
   

   Other complications are common to all catheter angiographic procedures and include access site sequelae (groin hematoma, pseudoaneurysm, or AV fistula), radiation exposure, iodinated contrast (acute kidney injury, anaphylaxis), and vascular injury (spasm, dissection, rupture).

   
   
7. 
   

   What is the postprocedure care for embolization patients and when should surgery be performed?

   
   

   A neurological examination should be performed after the procedure to assess for any neurologic changes. Patients are admitted to the neurological intensive care unit overnight for observation and pain management. Patients undergo frequent neurological checks to monitor for any change in their neurologic status as postembolization edema may occur, resulting in myelopathy. ^{36 , 37} They are also monitored for postembolization syndrome. Although postembolization syndrome most commonly occurs after solid organ embolization, it has been reported to occur in patients treated with spinal tumor embolization. ³⁸ It is a self-limited syndrome consisting of fever, nausea, vomiting, pain, and leukocytosis. It usually manifests within 72 hours after the procedure and resolves after a week following supportive treatment. The optimal timing of when to perform surgery after embolization is somewhat debated, but most authors advocate for surgical resection within 72 hours of the embolization procedure to prevent angiogenesis. ^{9 , 39} In cases where the spinal canal is compromised by the tumor, the embolization may worsen the local edema and compress the cord even further, ultimately requiring an earlier surgical resection.