Jo

Figure 16-7. Angiogram of JNA.

Figure 16-7. Angiogram of JNA.

Paragangliomas Introduction

The extra-adrenal paraganglia are neural crest-derived rests of tissue that migrate to sites in the body in close association with cranial nerves, the aorta and its branches.48 These paraganglia are composed of two predominant cell types: the sustentac-ular cells and the chief cells. The sustentacular cells are modified Schwann cells whereas the chief cells produce and can release catecholamines and other neurotransmitter substances.19,48 The tumors that arise from these cell rests, the paragangliomas, can occasionally release neurotransmitter substances or demonstrate malignant behavior.49,50

While paragangliomas produce symptoms of neurotransmitter excess (tachycardia, flushing, palpitations) only very rarely (< 5%),49 when this occurs, the hemodynamic effects of such functional tumors can be dramatic.51 Moreover, physical manipulation of nonfunctional tumors can occasionally result in the intravenous release of neurotransmitters and subsequent symptoms.52

As surgery is the most commonly employed treatment for these tumors, pre- and intraoperative anesthetic precautions for potential neurotransmitter release must be observed.51 Such precautions include careful preoperative questioning regarding the intermittent occurrence of any symptoms referable to neurotransmitter release (tachycardia, palpitations, headache, flushing) and a detailed family history seeking to identify relatives with similar tumors or symptoms (see below). When potential symptoms of a functional tumor are suggested, preoperative screening should include the measurement of plasma and urinary levels of catecholamines as well as their metabolites (metanephrine, VMA).51 The pre- and intraoperative use of a- and ^-adrenergic blockade are important agents that can reduce the anesthetic risk associated with the treatment of these tumors.

Jugulo-tympanic

Vagal body Carotid body

Aoritcal pulmonary

Figure 16-8. Location of non-chromaffin paragangliomas of the head and neck.

Jugulo-tympanic

Vagal body Carotid body

Aoritcal pulmonary

An additional consideration in the treatment of patients with paragangliomas relates to the familial incidence of these tumors as well as the occurrence of multiple paragangliomas in the same patient. Although the vast majority of paragangliomas occur spontaneously, as many as 10 percent can occur as part of an autosomal dominantly-inherited condition with incomplete penetrance.53 Recently, genetic linkage studies have suggested that the gene responsible for familial paragangliomas is located on the long arm of chromosome 1 1.54,55 These familial paragan-gliomas, as compared to their sporadic counterparts, are more commonly bilateral, multicentric, and become clinically apparent at a younger age.53-56-57

Paragangliomas of the head and neck are commonly named according to the major neurovascular structures with which they are associated. Within the head and neck, three of the most common paragan-gliomas are the carotid body tumor, the glomus jugulare, and the glomus intravagale (Figure 16-8).

Carotid Body

Figure 16-10. MRA showing carotid body tumor splaying the carotid arteries.

Anatomy

The carotid body is a discrete paraganglion located in the adventitia of the posteromedial aspect of the carotid bifurcation.58 It functions as a chemoreceptor, responding to changes in arterial oxygen, carbon diox ide, and pH by regulating ventilation.58,59 Individuals who live at high altitudes, chronically exposed to oxygen of a lower partial pressure than that at sea level,

Figure 16-11. Carotid body MRI ("salt and pepper" enhancement with flow voids).

Figure 16-9. Carotid body tumor.

Figure 16-11. Carotid body MRI ("salt and pepper" enhancement with flow voids).

appear to have an increased risk of developing sporadic (non-familial) carotid body tumors.59,60

Diagnosis

A carotid body tumor most commonly presents as a painless neck mass with limited superior-inferior mobility, near the angle of the mandible, during the fifth decade of life (Figure 16-9).58,59 Computed tomography (CT) and magnetic resonance imaging (MRI) characteristically reveal splaying of the internal and external carotid arteries (Figure 16-10). While intense contrast enhancement on CT is seen, a "salt and pepper" pattern on MRI may be appreciated secondary to the presence of flow voids within the tumor (Figure 16-11).61,62 The pattern of displacement of the neurovascular structures in the vicinity of the mass, coupled with the clinical examination, usually is sufficient to confirm the diagnosis of a carotid body tumor.

Treatment

The treatment for carotid body tumors is surgical excision. The surgical approach to these tumors is via a horizontal neck incision at approximately the level of the carotid bifurcation. Meticulous hemostasis at all stages of the operative procedure, and the establishment of proximal and distal control of the carotid artery are mandatory, as is proficiency in vascular surgery (or assistance) if patch grafting or venous replacement become necessary. When preoperative evaluation suggests that carotid body tumor removal might require intraoperative interruption of carotid artery flow, balloon occlusion studies to assess the cerebral blood flow should be obtained.63 Careful identification and preservation of the integrity of the marginal branch of the facial nerve and the lower cranial nerves is to be expected. Due to the location of the carotid body, a sub-adventitial plane of tumor dissection is required, a maneuver that does not appear to compromise the integrity of the artery.64

Surgical resection of these tumors with minimal morbidity should be the treatment goal. The structures most likely to be injured when resecting a carotid body tumor include the superior laryngeal nerve, vagus nerve, and the hypoglossal nerve.58 In patients with bilateral carotid body tumors, surgical resection of the smaller tumor should be attempted first with a period of 3 to 6 months elapsing prior to resection of the contralateral tumor. Patients undergoing bilateral carotid body resection may demonstrate markedly labile postoperative blood pressure, a phenomenon thought to be due to the complete loss of carotid sinus function as a secondary consequence of the dissection and removal of the carotid body tumors.58 However, this lability diminishes with time as alternative blood pressure regulatory mechanisms appear to compensate.

While meticulously-performed surgical resection is unquestionably the treatment of choice for carotid body tumors, the use of radiotherapy as primary treatment for these neoplasms (particularly extensive tumors whose excision might be associated with significant morbidity) has been reported.65 The rationale for such treatment derives from the fact that although these tumors are minimally radiosensitive, radiotherapy likely produces fibrosis of the tumor's vasculature and therefore can arrest tumor growth.65

Glomus Jugulare

The jugulotympanic region is the site of origin for two types of paragangliomas. The glomus tympan-icum arises from either a branch of the vagus nerve (posterior auricular branch of Arnold) or a branch of the glossopharyngeal nerve (tympanic branch of Jacobson), while the glomus jugulare arises from the jugular bulb itself. As the majority ofjugulotympanic tumors are of jugular bulb origin, the discussion that follows will focus exclusively on these tumors.19

Anatomy

The glomus jugulare tumor is a slow-growing lesion that arises from the paraganglionic tissue of the jugular bulb at the skull base.48 Anatomically, this area of the cranial base is in close proximity to the internal carotid artery, cranial nerves IX, X, XI, XII, and the internal auditory canal. As lesions of the skull base are exceedingly difficult to appreciate clinically, these tumors are often not identified until they begin to cause some degree of cranial nerve dysfunction from expansile growth.64

Figure 16-12. MRI showing Glomus jugulare at the base of the skull.

Diagnosis

The most common presenting symptoms of a glomus jugulare tumor include tinnitus, hearing loss, vocal cord paralysis, diminished gag reflex, and tongue deviation.67 On physical examination, the presence of a vascular mass medial to an intact tympanic membrane (due to tumor erosion of the bony hypotympanum) can be seen.66 Radiographically, these tumors are best diagnosed and subsequently assessed by a combination of CT and MRI with contrast enhancement.68 While CT imaging can best demonstrate the details of bony erosion at the skull base as well as the proximity of the tumor to the structures of the temporal bone (Figure 6-12), MRI can delineate the relationship of the tumor mass to adjacent neurovascular structures.68

Treatment

The optimal treatment of a glomus jugulare tumor depends upon a combination of both patient and tumor factors. The morbidity that can often accompany the surgical resection of these tumors primarily relates to paresis or paralysis of the facial nerve as well as the lower cranial nerves.67 While the treatment of a particular tumor in a specific patient needs to be individualized, there is general agreement that the optimal treatment of this benign, slow-growing tumor of the skull base in older patients is nonsurgi-cal.67,68 In younger patients, however, the issue of what is the optimal treatment is unresolved.

Radiotherapy for glomus jugulare tumors, as is the case with carotid body tumors, is believed to cause fibrosis of the tumor's vascular elements, leading to growth arrest.65,69 In an extensive review of 24 major series of glomus jugulare tumors treated by either primary surgery or radiotherapy, both modalities yielded similar rates of post-treatment persistent and recurrent disease (8% and 7% respectively).70 While there was extensive variability among the studies with respect to follow-up and treatment modality selection, the similar results suggest that the morbidity of a particular treatment may be the most important determinant for treatment selection.

The surgical approach to glomus jugulare tumors requires adequate access and visualization of both the tumor and the vital neurovascular structures of

Figure 16-12. MRI showing Glomus jugulare at the base of the skull.

the cranial base. Based upon a careful review of preoperative imaging studies (CT, MRI, MRA), the likelihood of intraoperative interruption of carotid circulation needs to be assessed and, if deemed to be a significant risk, a preoperative balloon occlusion study should be obtained.

The most common approach for these tumors is some variation of the approach to the infratemporal fossa first described by Fisch.71 In this approach, which includes exposure of the mastoid segment of the facial nerve and the upper lateral neck, the facial nerve is identified and then anteriorly translocated. While this approach permits safe access to both the internal carotid artery and the jugular bulb at the skull base, it can potentially result in paresis or paralysis of the facial mimetic musculature.67,71

The morbidity of surgical resection of glomus jugulare tumors, with paresis or paralysis of the lower cranial nerves (IX through XII), can be rehabilitated in order to improve postoperative function and quality of life. In particular, vocal cord paralysis that results from injury to the vagus nerve is frequently compensated for by the contralateral vocal cord over a period of months. However, in those cases where inadequate compensation is present with aspiration and/or incomplete adduction, the paralyzed vocal cord can be surgically medialized, restoring glottic closure.72 Isolated paralysis of the spinal accessory nerve mandates the institution of an aggressive postoperative physical therapy regimen to minimize the development of significant shoulder pain and joint restriction.73 While isolated paralysis of either the glossopharyngeal or hypoglossal nerves will not cause significant morbidity and may only require speech and swallowing therapy for rehabilitation, bilateral paralyses of these or the other nerves as well as combinations of nerve injuries (ie, simultaneous hypoglossal and vagus injuries) may cause significant problems with deglutition and/or respiration—necessitating tracheostomy, gastrostomy or both.

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