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Excision of Carotid Body Tumors


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 ).

Fig. 73.1, 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.

Fig. 73.2, 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

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

  • 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.

  • 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.

  • 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

History

  • 1.

    History of present illness

    • a.

      Presence of a mass in the lateral neck

    • b.

      Labile or difficult to control hypertension

    • c.

      Sudden flushing

    • d.

      Palpitations

    • e.

      Changes in voice

    • f.

      Dysphagia

    • g.

      Weakness of the tongue

    • h.

      Tinnitus (may be present on the side of the tumor from the high-flow state)

  • 2.

    Past medical history

    • a.

      Prior neck surgery

    • b.

      Comorbid medical illnesses (particularly hypertension that requires multiple medications for control)

    • c.

      Pheochromocytoma

    • d.

      Carotid atherosclerotic disease

    • e.

      Transient ischemic attacks (TIAs)

  • 3.

    Family history

    • a.

      Familial PGLs

    • b.

      Disorders of bleeding/clotting

  • 4.

    Medications

    • a.

      Antiplatelet drugs

    • b.

      Herbal products

    • c.

      Allergies to antibiotics

Physical Examination

  • 1.

    Complete examination of the head and neck evaluating for a neck mass, which may be either unilateral or bilateral. Evaluation of cranial nerves with particular attention to involvement of the vagus or hypoglossal nerves. Assessment of any scars in the neck from prior surgery

  • 2.

    Flexible fiberoptic examination

    • a.

      Evaluation of both superior and recurrent laryngeal nerve function especially vocal fold mobility

Imaging

  • 1.

    CT scan with contrast—Provides excellent resolution and the CBT will enhance intensely with contrast. The tumor will splay the internal and external carotid arteries (“Lyre sign”). The CT scan may also reveal other PGLs.

  • 2.

    MR angiography

    • a.

      T1 imaging will show an isointense or hypointense lesion when compared with muscle. Larger lesions will have a “salt and pepper” appearance representing small regions of slow blood flow (salt) and flow voids (pepper). The lesion will have intense enhancement with gadolinium contrast ( Fig. 73.3 ).

      Fig. 73.3, Magnetic resonance angiogram of a 21-year-old woman with bilateral carotid body tumors (arrows) .

    • b.

      T2 imaging—CBT will be hyperintense to muscle, and there will also be a speckled appearance with flow voids.

  • 3.

    Transfemoral angiography—Remains the gold standard for true identification and assessment of tumor vascularity ( Fig. 73.4 ). The senior author (ENM) has had at least one case of misdiagnosis based on history, physical examination, and a vascular blush seen on MR scanning. What was thought to be a CBT was surprisingly identified intraoperatively as an aneurysm of the internal carotid artery ( Fig. 73.5 ).

    Fig. 73.4, Angiogram of the same patient demonstrates a carotid body tumor.

    Fig. 73.5, Magnetic resonance angiogram of a mass in the neck mistakenly diagnosed as a carotid body tumor. Transfemoral angiography revealed an aneurysm of the internal carotid artery.

  • 4.

    Octreotide or metaiodobenzylguanidine (MIBG) scintigraphy—A sensitive but not specific test for phenochromocytoma. A variety of neuroendocrine tumors including other PGLs (glomus tumors) will enhance, as will non-neuroendocrine tumors (lymphoma, Merkel cell carcinoma). This test can be helpful when evaluating the patient for multiple lesions.

Indications

  • 1.

    Small tumors that have recently been discovered should be removed, as should tumors demonstrating growth, whether accelerated or steady, with or without involvement of the lower cranial nerves. Patients who are in the Shamblin I or II classification may have this tumor removed safely.

  • 2.

    Patients demonstrating neuropathy, such as vocal cord paralysis or paralysis of the tongue, should also have the tumor removed. These tumors are usually Shamblin type III and require resection and replacement of the carotid artery.

  • 3.

    Secreting CBT

Contraindications

Patients who are elderly, have severe comorbidities, refuse surgery, or fail a balloon occlusion test should be considered for observation, including yearly CT scans or radiation therapy.

Preoperative Preparation

  • 1.

    All patients who have the preoperative diagnosis suggestive of PGL should have examination of a 24-hour urine specimen for catecholamines (vanillylmandelic acid) before surgery. If an abnormality is identified, then an MRI of the abdomen should be performed to try to identify a pheochromocytoma. Pheochromocytomas should be removed before removing the PGL to avoid a potentially fatal intraoperative hypertensive crisis.

  • 2.

    If the abnormal catecholamines are present but no pheochromocytoma is identified, it must be assumed that an unusual catecholamine-secreting PGL is present. The anesthesiologist should be consulted in advance and a program for the management of a potential hypertensive crisis planned.

  • 3.

    Preoperative embolization is not required in most cases because the tumors that do not encase the carotid artery can be dissected off of the muscularis of the carotid artery using dissection in the subadventitial plane. We believe that the preoperative embolization may induce an intense inflammatory response that may lead to obliteration of the subadventitial plane, making dissection of the tumor dangerous.

  • 4.

    Discussion with a vascular surgeon is recommended in all cases. If there is an injury to the internal carotid artery during resection, vessel repair with a patch or graft should be performed. It is essential to schedule these cases on days when a vascular surgeon can be available.

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