Epidemiology

Temporal bone paragangliomas are much more common than any other middle ear neoplasm. These tumors are second only to vestibular schwannoma as the most common tumor affecting the temporal bone.7 Temporal bone paragangliomas account for 15% of all neoplasms at the skull base.8 The incidence of this tumor is 1: 1,300,000. The peak incidence is at 45 and 55 years of age, although this is highly variable. There is a predominant incidence in females7,9 with a sex ratio of 4:1. There is no racial or ethnic predilection.

Although paragangliomas arise sporadically, a positive family history has been reported in 9.5 to 50% of patients.10-12 The mode of inheritance in the familial form is currently attributed to the genetic imprinting mode of inheritance.12

The familial form is distinct from the nonfamilial form in that there is no female preponderance, and it is associated with a higher incidence (48%) of multicentric paragangliomas.12 Multicentricity is found in about 5 to 15% of patients with the nonfamilial form. The most common second tumor is a carotid body tumor.

Pathology

Temporal bone paragangliomas are typically vascular reddish purple lobulated masses. Histologically, paragangliomas resemble paraganglia, displaying the same organoid pattern with zellballen composed of chief cell-like elements. Mitotic figures are rare. The histopathology is characterized by a rich vascularity.

Although usually histologically benign, paragangliomas of the temporal bone are characterized as locally destructive. Their growth is characteristically very slow, but rapid progression can occur and is unpredictable.13'14 Spread occurs along the pathways of least resistance, often initially after the air cell tracts of cancellous and spongiotic temporal bone. Eventually, the tumor spreads outside the temporal bone via the jugular foramen and other neurovascular foramina.15'16

Paragangliomas overall have an incidence of malignancy of 2 to 4%, but this is far less common with temporal bone paragan-gliomas than with glomus vagale tumors. There is no histologic distinction between benign and malignant lesions. Malignancy is reserved for the presence of local, regional, and distal metastases. Distal metastases occur most commonly to the lungs.

Functional activity in skull base paragangliomas is 1 to 2%.8,17-19 In these cases, the continuous or episodic secretion of catecholamines may produce clinical symptoms mimicking a pheochromocytoma. These features include persistent or paroxysmal hypertension, tachycardia, excessive perspiration, and anx-iousness. When manipulated surgically, catecholamine-secreting paragangliomomas can potentially initiate a life-threatening hypertensive crisis, constituting an anesthetic emergency.

Paragangliomas of the temporal bone are associated with other neoplasms, both benign and malignant, in 7% of patients.7 Tumors most commonly associated are pheochro-mocytomas, thyroid C-cell carcinoma, parathyroid adenomas, and visceral neoplasms of neural crest origin. There is also a reported association with the multiple endocrine neoplasm (MEN) syndromes.

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