Introduction

Most of the tumors that originate in the poststyloid parapharyngeal space (PPS) are tumors of neural origin. Most of these are paragangliomas (PGLs), the most common of which is the carotid body tumor (CBT). It is usually possible to tell preoperatively, by imaging studies, whether these tumors are in fact CBT, glomus vagale tumors, or schwannomas. The computed tomography (CT) scan with contrast is very helpful in the differential diagnosis. The CBT is located at the bifurcation of the carotid artery, whereas the glomus vagale tumor, because of its site of origin from the vagus nerve, arises posterior to the carotid artery.

The Shamblin classification of CBT and its relationship to the carotid artery ( Fig. 73.1 ) has proved to be very useful in the assessment of CBT. The Shamblin I and Shamblin II types of tumors are amenable to surgery by dissecting the tumor off of the carotid artery using the subadventitial technique. However, the Shamblin III tumors in which the carotid artery is encased by tumor, cannot be removed safely by this technique. Not only is the artery encased in the tumor but the tumor may actually invade into the muscularis of the artery and cannot be dissected free. Further dissection then creates an opening in the wall of the carotid artery with resultant hemorrhage. Patients with Shamblin III tumors should undergo a complete resection of the artery by a vascular surgeon with reconstruction using either a vein graft or a synthetic graft ( Fig. 73.2 ).

Carotid body paragangliomas. Shamblin classification scheme: type I—small and easy to dissect, type II—medium and more intimately attached to the carotid artery, and type III—large with transmural invasion of the wall of the carotid artery requiring resection and grafting.

With permission from Shamblin WR, ReMine WH, Sheps SG, et al: Carotid body tumors. Am J Surg 122:733-739, 1971.

A, Patient with a mass in the neck, which has increased in size over a 10-year period. B, Magnetic resonance imaging demonstrates a large carotid body tumor with numerous flow voids. C, Lateral view of mass extending to prevertebral fascia.

Although most CBTs are the result of sporadic mutations, there is a subset of PGLs that are inherited. They are referred to as the familial form (PGL1). These PGLs are multiple and usually involve the carotid body so that there may be unilateral CBT or bilateral CBT with additional PGLs arising from unnamed arteries in the vicinity. Tumors in the familial PGL group, in addition to being multiple, are also more likely to be malignant and more likely to have an associated pheochromocytoma.

The familial form of PGL has an autosomal dominant inheritance pattern. Baysal et al. reported in Science the analysis of families carrying the PGL1 gene, which revealed mutations in the succinate dehydrogenase (SDHD), a mitochondrial complex 11 gene in hereditary PGL, on chromosome 11q23. In this paternal inheritance pattern, the father may pass the gene along to the son, who has a 50% chance of having a PGL, who may pass it along to successive males. However, it may also pass to the female, who may develop a tumor but cannot pass the gene to her offspring because of genetic imprinting. The families of patients who have PGL1 should undergo genetic testing. For patients who are found not to have the gene, this is reassuring, and no further testing is required. Patients who test positive should undergo magnetic resonance imaging (MRI) screening. If the MRI discloses a tumor, this should be removed. If the MRI is negative, it should be repeated annually so that if a tumor develops it may be identified at an early stage and may be removed safely.

Key Operative Learning Points

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  Modern imaging techniques permit the surgeon to formulate a plan of management without a preoperative biopsy.

  
  
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  Attempting to remove a Shamblin III type of CBT using a subadventitial approach will eventuate in massive bleeding due to invasion of the wall of the artery by tumor.

  
  
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  Failure to evaluate for abnormal catecholamines in patients with PGL may result in intraoperative hypertensive crisis in the presence of a secreting PGL or pheochromocytoma.

  
  
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  Failure to preserve the lower cranial nerves during the excision of a CBT will result in hoarseness and aspiration in the postoperative period.

Preoperative Period