General Description

Paragangliomas are rare neuroendocrine tumors derived from extra-adrenal paraganglia of the autonomic nervous system. Carotid body tumors are typically situated at the bifurcation of the common carotid artery and located within the adventitia of the common carotid artery. This is the most common neck paraganglioma and is typically supplied by branches off the external carotid artery (ECA), most commonly the ascending pharyngeal artery. Carotid body tumors have been described as slow-growing tumors with a growth rate of < 0.5 cm per year. Observation may be warranted in elderly patients who are otherwise asymptomatic from this lesion. Radiotherapy may be warranted in certain patient populations after considering the potential risks and benefits to the patient. Since the first embolization of a carotid body tumor prior to surgical resection was performed in 1980 by Schick et al ¹ , there has been significant controversy over the potential benefit in this particular situation. It is important to weigh the potential risks associated with endovascular intervention against the potential intraoperative benefits to the patient and surgeon.

Evidence Regarding Tumor Embolization

• 
  

  Since the initial report by Shick et al., many authors have reported their experience with preoperative embolization and the associated impact on intraoperative blood loss, cranial nerve injury, need for transfusion, and risk of stroke. A multivariate meta-analysis by Abu-Ghanem et al ² in 2015 found that there is no statistically significant impact of preoperative embolization for any of the above criteria.

  
  
• 
  

  All studies to date provide only retrospective analyses comparing preoperative embolization versus no embolization.

  
  
• 
  

  Power et al ³ in 2012 reported the single largest retrospective study consisting of 131 patients who underwent resection of carotid body tumors with and without preoperative embolization. They found a statistically significant difference in estimated blood loss during the surgical resection (263 mL in the pre-embolization group vs. 599 mL in the nonembolized group [P = 0.002]). In addition, 21 of 33 (64%) patients who underwent preoperative embolization had a cranial nerve injury compared with 39 of 71 (55%) patients who did not undergo embolization (these differences were not statistically significant). The most common cranial nerve neuropathies involved cranial nerves IX, X, and XII.

  
  
• 
  

  Gwon et al ⁴ showed that the Shamblin classification was related to the risk of stroke (P = 0.041) and that tumor size was not.

Indications

Highly vascular carotid body tumors may potentially warrant embolization. Although several studies and a meta-analysis have demonstrated that there is no statistically significant difference between outcomes during surgery for carotid body tumors that have undergone preoperative embolization versus those that have not, reducing intraoperative blood loss can be an important adjunct. In addition, no prospective trial has evaluated the potential benefits of Shamblin class II and III lesions or lesions invading the media or intima of the carotid artery, which may warrant preoperative embolization to aid in safer dissection as well as limiting operative time and cranial nerve injury.

Neuroendovascular Anatomy

The ECA primarily supplies the tissues of the face, neck, and scalp. The ECA has many anastomoses with the internal carotid artery (ICA), which are important to recognize when planning preoperative embolization for carotid body tumors. In addition, recognition of collateral ECAs that supply the tissues around the tumor is critical because collateral branches should be avoided during embolization to allow for the best chance of postoperative wound healing.

The ascending pharyngeal artery territory is the key to understanding the blood supply to carotid body tumors as well as the blood supply to the skull base because the artery supplies the intermediate zone bordered anteriorly by the internal maxillary artery territory and posteriorly by the occipital artery territory. Embryologically, the ascending pharyngeal artery originates from the third branchial arch artery and is derived from the ICA. It is important to recognize the importance of the ascending pharyngeal artery in supplying cranial nerves as they exit the skull base.

The pharyngeal branches tend to arise from the anterior division of the main artery or pharyngeal trunk. There are many branches that anastomose with the internal maxillary artery territory and have potential collaterals to the inferolateral trunk of the ICA. The neuromeningeal trunk has two principal branches, the hypoglossal artery and the jugular artery. The hypoglossal artery supplies the hypoglossal canal as well as dura of the anterior posterior fossa and foramen magnum region, contributing to the odontoid arcade. The jugular artery tends to travel through the jugular foramen supplying cranial nerves IX, X, and XI and has multiple anastomoses with the posterior circulation.

Periprocedural Medications

Preprocedurally, patients with large tumors and tumors causing neural compression should be placed on corticosteroids. In addition, medications specific to tumor pathology may need to be administered prior to surgery or endovascular therapy, meaning potentially administering β-blockers preoperatively for paragangliomas.

Lidocaine can be administered prior to embolization to help prevent local edema and pain. Injections of dimethylsulfoxide into the tumor prior to embolization can potentially be helpful in liquefying the tumor during procedural resection, although the evidence for this is anecdotal.

Systemic heparinization is administered during the procedure because of the ever-present risk of intraprocedural thrombus formation. A weight-based intravenous bolus of heparin aimed at an activated coagulation time of 250–300 seconds may limit thromboembolic complications. Administration of the heparin before crossing the stenotic lesion may limit thrombus formation on devices positioned within the ICA. For acute thrombus formation during the procedure, a glycoprotein IIb/IIIa inhibitor (e.g., eptifibatide) is utilized.