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Carotid Paragangliomas
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Carotid Paragangliomas | ||
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Related narrative: Carotid Paragangliomas, Multiple Paragangliomas Paragangliomas are neoplasms derived from extra-adrenal neural crest derivatives (see paraganglioma discussion). They usually do not secrete catecholamines and do not produce vasomotor symptoms. Thus they do not react positively with chromaffin stain. A common presentation is as a neck mass at the carotid bifurcation. In 10% of cases there is a family history, and those patients have a higher incidence (26%) of multiple lesions (see multiple paragangliomas), and a higher chance of having a functional lesion. Only patients with vasomotor symptoms need be tested for catecholamine secretion with a 24-hour urine collection for VMA. There is a 5% chance of malignancy, which is determined by histologic evidence of local invasion. The lesions are encapsulated, firm, brown collections of epitheliod cells in highly vascular fibrous stroma. The term glomus tumor which was formerly applied to paragangliomas is a separate entity and should not be used. Pheochromocytomas are related, but more commonly secrete catecholamines. Paraganglionic tissue is closely associated with arteries and nerves and is distributed symmetrically and segmentally. The largest collection of such tissue in the neck is in the carotid body (see cervical mass at the carotid bifurcation). The carotid body is found at the carotid bifurcation and mediates chemosensory reflexes associated with changes in pH and oxygen tension in the blood. Neoplastic degeneration of the carotid body has also been called a chemodectoma. The most common presentaton (94%) of carotid body paraganglioma is as a neck mass (see differential diagnosis of neck masses). It must be differentiated from branchial cleft cysts (see branchial cleft cyst), lymph node metastases, lymphoma, tortuous carotid and carotid aneurysm. Large lesions may cause pressure symptoms such as dysphasia, cough or hoarseness. About 20% of patients experience pain. Diagnosis is based on a high index of suspicion corroborated with radiographic studies. Contrast-enhanced CT or MRI delineates the lesion and separation of the internal and external carotid arteries by the lesion. Arteriogram demonstrates bowing of the vessels (lyre sign), and demonstrates the vascularity of the lesion. Carotid body paragangliomas tend to be slow growing, and a case can be made for observing asymptomatic lesions in elderly or high-risk patients. Symptomatic patients should have the lesion excised. Pre-operative embolization to decrease vascularity has been tried in the past, but the complications of TIA and CVA outweigh the benefit. Surgery entails obtaining proximal and distal vascular control of the carotid system (see carotid endarterectomy), and subadventitial dissection of the lesion (see carotid paragangliomas). Planning for large lesions should include the possibility of harvesting saphenous vein for vascular reconstruction. The vagus, hypoglossal and spinal accessory nerves are carefully identified and preserved. References: Cummings: Otolaryngology: Head and Neck Surgery, 3rd ed., 1998, Mosby-Year Book, Inc., pp. 1722, 1727.
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