Clinical Evaluation

Glomus tumors, or paragangliomas or chemodectomas, are neuroendocrine tumors from the adventitia of the jugular bulb (glomus jugulare) or from the carotid body (carotid body tumor). They also occur in other regions of the head and neck in proximity with the parasympathetic system. Local mass effect leads to lower cranial nerve dysfunction. Glomus jugulare may also be associated with tinnitus and carotid body tumors may be a palpable pulsatile mass. In some, particularly glomus jugulare and vagale, the catecholamines in the clusters of neurosecretory granules may cause hypertension. This is less common in carotid body tumors. Patients should routinely be screened with urinary and serum catecholamine levels because treatment may occasionally cause acute changes in systemic catecholamine with resultant cardiovascular collapse.

JNAs form at the sphenopalatine foramen and are thought to be from the vascular plexus of the first branchial arch. These present with nasal fullness, obstruction, or epistaxis. Furthermore, patients with JNA and metastatic tumors may present with acute hemorrhage refractory to conservative management. In the head and neck region, this may manifest as acute airway compromise due to pharyngeal hemorrhage. Tumor hemorrhage has also been reported to result in consumptive coagulopathy, which may resolve upon treatment of the hypervascular tumor.

Imaging

Radiographic workup of paragangliomas demonstrates “salt-and-pepper” appearance on T1- and T2-weighted MRI and occasionally occlusion of the sigmoid sinus and internal jugular vein. Hyperintensity CT imaging will better demonstrate the osseous abnormality, which is an eroded pattern due to growth of the mass. Cross-sectional imaging is also useful in identifying multiplicity of lesions, which occurs in 30 to 40% of familial presentations. In paragangliomas, angiography is helpful in defining the extent of hypervascularity (3, 5, 6 in algorithm). Occasionally, radioactively labeled octreotide uptake is used on single-photon emission CT (SPECT) study.

MR of a JNA will demonstrate flow voids consistent with hypervascularity, with prominent enhancement of the lesion. Angiography is helpful to further delineate the vascular supply from the internal and external carotid arteries, such as the internal maxillary, ascending pharyngeal, or ophthalmic arteries (3, 5, 6 in algorithm).

In comparison with intracranial tumors, tumors of the head and neck are more likely to have multiple arterial supplies with collateralization between multiple major arteries, such as bilateral carotid supply or carotid and vertebral supply. In contrast, tumors of the vertebral column are typically supplied by segmental vessels at that level or at the immediately adjacent levels (5, 6 in algorithm).

Embolization Objective

To decrease intraoperative blood loss, embolic agents can be employed to sacrifice specific arterial pedicles or devascularize the parenchymal capillary base of the tumor. In cases of hypervascular metastasis (▶ Fig. 70.1 ) or JNA (▶ Fig. 70.2 ) presenting with acute hemorrhage, embolization may also be a temporizing measure to arrest active hemorrhage while awaiting definitive management. There is not a widely applied scale to describe the extent of embolization, but a general framework is based on this distinction between the main arterial pedicles and the intralesional capillaries.

Endovascular Management—Operative Nuances

Access to the tumor hypervascularity can be accomplished via a transarterial route. This may involve femoral or radial access. Navigation into the tumor arterial supply is complicated by tortuosity of vessels, which typically increases with increasing age as well as hypertension. Transarterial embolization typically devascularizes only the pedicle via which the access is achieved. Therefore, multiplicity of arterial supply to the tumor requires multiple catheterizations, and may be more common in tumors of the head and neck than in intracranial tumors (▶ Fig. 70.1 ). However, tumors of the vertebral column may have fewer total arterial pedicles, favoring transarterial access.

Percutaneous access to the tumor parenchyma is an alternative means of delivering embolic agent (▶ Fig. 70.3 ). A percutaneous route avoids the complexity of multiple significant arterial feeders and bypasses tortuous anatomy. In both the head and neck and the spine, most tumors are accessible via a percutaneous route with appropriate image guidance. In the distinct case of JNA, direct puncture of the tumor parenchyma can be accomplished via endoscopic-guided endonasal needle infiltration via the nasal mucosa.

The choice of access, whether transarterial or direct puncture is guided by ease of embolization. Tortuous anatomy, multiple arterial feeders, and collateral supply to sensitive vascular territories determine the difficulty of transarterial access. Direct puncture can be limited by local normal anatomy or body habitus but is overall less variable. However, most cases would require a pre-embolization angiogram to assess the tumor vascularity; therefore, transarterial access in a tumor with a single main arterial pedicle may still present an attractive approach. Patterns of typical arterial supply may suggest an appropriately focused angiographic evaluation; for example, the ascending pharyngeal is typically the primary arterial supply to glomus tumor. As discussed earlier, safely achieving the embolization objective is the primary concern. This distinction may be a result of multiple arterial supplies, including arterial collateral supply which is subangiographic or inaccessible via transarterial catheterization. Despite comparable angiographic outcomes, the principal objective is optimizing intraoperative hemostasis without an increase in overall risk. This would suggest that when feasible, a direct puncture approach with extensive embolization of the tumor capillary bed is most appropriate. In our previously reported experience, direct puncture also provided faster embolization, with direct puncture taking an average of 39 minutes, while transarterial access required 50 minutes for embolization of a JNA. Patients should be informed that in the direct puncture approach, there is occasionally skin induration at the puncture sites, but rare occurrence of skin necrosis.

Options for tumor embolization agent include particle embolic agents, liquid embolic agents, and less commonly coils or other devices. Coils and other embolic devices are employed embolize larger vessels, which can help with flow modulation when high flow interferes with delivery control. Coaxial dual-lumen balloon catheters such as the ASCENT (Codman Johnson and Johnson, Raynham, MA) now offer a temporary alternative tool for flow modulation. Attributes of an ideal embolic agent for safe and effective delivery include visibility, controlled deployment, noninflammatory, and nonneurotoxicity. For effective embolization, the agent needs to penetrate the small vasculature. For subsequent resection, the embolic agent should not interact with electrocautery and should be mechanically manipulable and transectable.

Durability of the agent is important for solitary embolization but less important when the patient will undergo operative resection within 72 hours of the embolization. However, it is important to consider the durability of embolization in cases where total resection may not be accomplished. Historically, recanalization is thought to occur following particle embolization, with as much as a 20% rate of rehemorrhage over the course of 2 months if the source is otherwise untreated. Most preoperative embolization is followed by the definitive surgical procedure within 1 to 3 days in the absence of clear increased risk from serial endovascular and open surgical procedures. Occasionally, when tumor swelling is of particular concern, embolization is immediately followed by operative resection, but this can be logistically limited if the embolization and operation are each complicated and time-consuming.

Parenchymal penetration is determined by liquid viscosity or particle size. Unfortunately, there is not a well-defined technique for determining the size of the hypervascular channels. Therefore, in practice, embolic agents are delivered via manually modulated delivery that is titrated on fluoroscopic feedback. Successful embolization with particles leads to increasing contrast stagnation and reflux, while the liquid embolic agents are mixed with tantalum or Ethiodol (Savage Laboratories, Melville, NY) which demonstrate the extent of polymerization but do not demonstrate the nature of the perfusion. It is easier to assess the extent of embolization with the liquid embolic agents. Particles such as polyvinyl alcohol (PVA; Cook Medical, Bloomington, IN; Contour, Boston Scientific, Marlborough, MA) or Embospheres (Merit Medical, South Jordan, UT) can penetrate vessels from 40 to 1,300 µm depending on selection of particle size. Ethylene vinyl alcohol copolymer (Onyx; Covidien Medtronic, Plymouth, MN) is reported to penetrate vessels as small as 5 µm, while N-butyl cyanoacrylate (NBCA; Codman Johnson and Johnson, Raynham, MA) penetrates less deeply into vessels as small as 20 µm.

Each embolic agent also has particular attributes which can complicate delivery. Some types of particles form aggregates, leading to irregular vascular penetration and occlusion. Other particles may have nonuniform size and penetrate in an inconsistent fashion. These particles may also accumulate in the inside of the catheter or completely occlude the hub of the catheter. Associated with this, particle delivery generally requires a larger catheter than may be required for the liquid embolic agents. Particle embolization does not typically form a coherent cast which is observed or manipulated during surgical exposure (▶ Fig. 70.3 ). Delivery of particle embolic agents has not been described in direct puncture techniques. There may be limited by the ability to propagate upstream against capillary flow. The liquid embolic agents have been well described with transarterial techniques and are increasingly described with the direct puncture technique. Direct puncture also obviates catheter entrapment by the liquid embolic agent because the delivery is achieved via a rigid needle. However, the slowly diffuse nature of injection via direct puncture makes application of NBCA, which polymerizes relatively quickly, difficult in comparison to Onyx embolization. Reflux of NBCA into the intracranial supply has been reported both intraprocedurally due to unexpectedly low resistance, and in a delayed fashion following completion of embolization due to delayed polymerization. With gradual centripetal polymerization and diffusely infiltrative spread of the agent into low resistance channels, Onyx can be effectively delivered throughout the hypervascular capillary network via a single direct puncture and intervals of injection. In addition to varying viscosity of liquid embolic agents, variation in needle caliber used for direct puncture may alter the embolic penetration.

The liquid embolic agents are delivered with nonionic solutes. In comparing the liquid embolic agents, NBCA is mixed with Ethiodol (Savage Laboratories), which is radiopaque and conveys viscosity to the agent, while Onyx is delivered in dimethyl sulfoxide (DMSO), which has been reported to cause vasospasm and discomfort when delivered quickly. However, NBCA polymerizes more quickly and is at higher risk of trapping the catheter and due to its adhesive nature. In contrast, Onyx delivery can be started and stopped on the order of several minutes at a time due to a slower precipitating reaction, and Onyx is cohesive in nature and therefore less likely to cause catheter retention. The Apollo detachable-tip catheter (Covidien Medtronic) is also designed to minimize complication from catheter tip trapping by the embolic agents. Although some groups hesitate to deploy a retained catheter device in addition to embolic agents, this catheter can be particularly useful in preoperative embolizations since the mass itself will be resected shortly thereafter. Furthermore, the Onyx cast is more brittle and there are reports of complications with monopolar electrocautery due to conductivity of the tantalum radio-opaque agent. However, NBCA can be delivered with a larger variety of catheters, including highly navigable catheters such as the Magic (Balt), while the DMSO solvent for Onyx is restricted to use in specifically designed catheters.

Consider the following example and decisions of embolization technique. A patient with JNA presents with recurrent epistaxis and supplied by multiple branches from bilateral internal maxillary arteries, which also supplies significant transethmoidal collateral supply to the ipsilateral choroidal blush. In such a case, the number of arterial pedicles that must be catheterized to achieve successful devascularization of the tumor and the risk of embolizing an “en passant” vessel with retinal embolization may lead one to use a direct puncture approach with Onyx. This can be accomplished via a percutaneous or an endonasal–transmucosal–endoscopic-guided approach. The ability to penetrate diffuse hypervascularity from multiple arterial sources would enable cerebral embolization, while the controlled distribution and high visibility of Onyx decrease the risk of off-target embolization.