this section, only neoplasms of the carotid body and in-travagal paraganglia are discussed.
Carotid body paragangliomas are the most common tumours of the head and neck paraganglia, making up 60-70% of the tumours of this type [30, 61, 100]. Lack et al. found 69 paragangliomas of the head and neck in more than 600,000 operations (0.12%), and only 1 in 13,400 autopsies at Memorial Hospital in New York city .
The tumour, typically located in the carotid bifurcation, is typically found in individuals of either sex in the third to the eighth decades of life. It often presents as a painless, slowly enlarging mass. It is the only neoplasm that arises in that particular location. Carotid angiography is a valuable diagnostic aid. The risk of developing this tumour is higher in persons living at high altitudes than those living at sea level . Carotid body paragangliomas with endocrine activity are rare. The tumour seldom undergoes malignant transformation; histologic criteria are of little prognostic value. The incidence of metastasis is estimated to be less than 10% [14, 61].
The vagal region is the third most frequent site of involvement after the carotid body and jugulotympanic region. Unlike the circumscribed carotid body, the vagal paraganglioma represents collections of microscopic nests located along the vagus nerve distal to the ganglion nodosum. Because of the variability in location of the normal vagal paraganglia, paragangliomas arising from these structures also vary in location. At the time of diagnosis, patients are usually in the fourth to fifth decade of life, and there is a female predominance [14, 30].
Patients generally report a slowly growing neck mass, and, because of the intimate relationship with the vagus nerve, cranial nerve palsies may also be present [14, 30]. Vagal paragangliomas displace the carotid vessels anteriorly, are grossly round or fusiform, and abut the base of the skull. Multiple, also bilateral, and familial occurrences of paragangliomas have been documented.
Paragangliomas have a tan, soft cut surface. Para-gangliomas from all regions of the head and neck are histologically similar. They are well circumscribed and composed of chief cells arranged in nests known as Zellballen (Fig. 9.12). The tumour cells have granular cytoplasm and round nuclei with prominent nucleoli. Nuclear pleomorphism may be present, but mitosis is rare, and necrosis is usually present only if the patient underwent preoperative embolisation or if the nests of cells are very large. Compressed sustentacular cells and a rich capillary network surround each nest. A reticulin stain highlights the Zellballen arrangement of the cells. Malignant varieties are difficult to distinguish on histologic examination, but generally they have a higher mitotic rate and more necrosis than benign tumours. Vascular invasion may be present in both benign and malignant paragan-gliomas.
The chief cells are positive for neuroendocrine markers such as chromogranin and synaptophysin. They are usually negative for cytokeratin, but an occasional case has been reported to be positive . The sustentacular cells are positive for S-100 protein .
Electron microscopy studies show the tumour cells to contain neurosecretory granules. The cells have cy-toplasmic processes that surround neighbouring cells, and the cytoplasm contains abundant large mitochondria and inconspicuous Golgi apparatus, smooth and rough endoplasmic reticulum.
Although histologic findings are generally quite distinctive, the differential diagnosis of paragangliomas of the head and neck may include endocrine neoplasms arising from the thyroid (medullary carcinoma) or parathyroid glands and other neuroendocrine carcinomas. Less commonly, alveolar soft part sarcoma, melanoma, granular cell tumour and metastatic renal cell carcinoma are included in the differential diagnosis [14, 30, 55, 61].
Surgery is the treatment of choice for paraganglio-mas. If the neoplasm is completely excised, recurrence is relatively rare; recurrence rates are 10% for carotid body tumours and 5-25% for vagal paragangliomas [14, 30, 55, 61]. Radiotherapy may be useful as a palliative method for those tumours that cannot be controlled by surgical means. Local infiltration of vagal body tumours and extension into the cranial cavity represent significant problems in disease control. The rate of metastasis in in-travagal tumours is estimated at 16%, but most of these are to regional lymph nodes [14, 30].
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