Carotid Body Tumors



Carotid Body Tumors



Adam H. Power and John W. Hallett, Jr.


Carotid body tumors are the most common form of paraganglioma in the head and neck. These tumors are difficult to resect because of impressive vascularity, arterial adherence, and local cranial nerve involvement. Stroke and cranial nerve dysfunction remain sobering risks of surgical resection. However, advances in diagnostic imaging and surgical technique have reduced perioperative complications to a reassuringly low level.


The carotid body is located in the adventitia of the common carotid artery at its bifurcation. It consists of chemoreceptors that aid in homeostasis by increasing the ventilatory rate when stimulated by hypoxia, hypercapnia, and acidosis. These tumors have an extremely high blood flow and oxygen consumption, more than either the brain or the heart. Its blood supply runs through a thin strand of adventitia, known as Meyer’s ligament, and arises from the external carotid artery (ECA) through multiple feeder vessels, with the ascending pharyngeal artery typically being the largest. The carotid body is innervated by the nerve of Hering, which originates from the afferent ganglion of the glossopharyngeal nerve.


Carotid body tumors, also known as cervical paragangliomas, chemodectomas, or glomus caroticum tumors, are of both mesodermal and neuroectodermal origin. They are generally well circumscribed, splay the carotid bifurcation, and adhere to the adventitial surface of the artery. Carotid body tumors are characteristically extremely vascular, secrete catecholamines on rare occasions, and are usually benign. When malignant, they can metastasize to local lymph nodes, liver, lung, bone, and occasionally the brain, although metastases occur in no more than 5% of cases. Carotid body tumors tend to be sporadic but are familial in 10% to 20% of cases, with succinate dehydrogenase (SDH) B, C, and D germline mutations being predominant. Familial tumors are often bilateral, occurring in a synchronous or metachronous fashion, and may be associated with other cervical paragangliomas, such as glomus vagale or jugulare tumors.


Current controversy in the diagnosis and management of carotid body tumors centers on determining if a carotid body tumor is in need of resection, the necessary preoperative tests, the role of preoperative embolization and the technical steps that will allow complete tumor resection with minimal neurovascular complications.



Clinical Presentation


Carotid body tumors usually manifest as an asymptomatic anterior neck mass. Patients commonly note the sensation of a lump in the neck, sometimes before a mass is detectable by palpation. Most patients appreciate a slow increase in the size of the mass over several years. A third of patients note some discomfort in the area of the mass, whereas a minority of patients complain of dysphagia or voice change. Carotid body tumors have been reported to be more prevalent in patients who live at high altitudes, with chronic hypoxia causing carotid body cell hyperplasia. Rarely, they produce neuroendocrine secretions causing catecholamine-related symptoms, such as headache, flushing, and diaphoresis.


Tumors that are at least 3 cm may be appreciated on physical examination as a bulging lump in the anterior triangle of the neck. The tissue is rubbery, firm, and noncompressible. The lump can be displaced laterally but not vertically, and lateral displacement results in movement of the carotid pulse in the same direction, known as Fontaine’s sign. Generally, a thrill or a bruit is not present. Cranial nerve deficits are rarely present unless the tumor is larger than 5 cm, if there is an associated cervical paraganglioma, or if the tumor is malignant.


Other causes of neck mass are commonly confused with a carotid body tumor. These causes include benign nodal inflammation or hypertrophy, metastatic cancer to a cervical node, a branchial cleft cyst, low parotid tumors, or a glomus jugulare tumor. They can be differentiated from carotid aneurysms by the pulsatile and expansile nature of an aneurysm, which is not present with a carotid body tumor.



Diagnosis


The extensive vascularity of carotid body tumors precludes percutaneous needle aspiration or incisional biopsy, and therefore the diagnosis relies heavily on radiologic imaging techniques. Color-flow carotid duplex scanning is extraordinarily accurate in detecting the presence of a carotid body tumor and coexistent atherosclerotic disease in the carotid artery. Characteristically, the tumor is localized to the carotid bifurcation as a well-defined, solid, and hypoechoic mass. With color Doppler imaging, hypervascularity with a low-resistance flow pattern is evident. The limitation of color-flow duplex ultrasonography is its inability to image the low or high neck for other paragangliomas.


Cross-sectional imaging of these tumors, in the form of either computed tomography angiography (CTA) or magnetic resonance angiography (MRA), has become the preferred diagnostic modality. CTA is an excellent method to define the size and extent of a carotid body tumor, as well as the relation of the tumor to bony landmarks in the neck, which can modify the surgical approach (Figure 1). It can also easily identify contralateral tumors and other associated paragangliomas of the neck.



CTA is especially helpful in classifying the Shamblin group of tumor (Figure 2). Shamblin’s classification divides carotid body tumors into three groups that relate to the difficulty of resection and the likelihood of local neurovascular complications. Group I tumors are small and readily resected from the carotid bifurcation. Group II are larger tumors that are densely adherent to the carotid arteries and can partially surround them. Group III tumors encase the carotid artery or adjacent nerves. MRA is also excellent at characterizing carotid body tumors, although it is more time consuming and expensive than CTA. MRA can estimate the size of the tumor and clearly delineate the adjacency and involvement of the carotid vessels. Gadolinium enhancement helps to define the arterial blood supply to the tumor and also reveals any associated atherosclerotic changes that may be present.



In the past, the classic diagnosis of a carotid body tumor was by arteriography. An arteriogram provides the image of a very vascular mass splaying the carotid bifurcation, also known as the lyre sign (Figure 3A). Standard arteriography is mainly necessary for patients who are selected for preoperative embolization of the blood supply to the tumor.


Jul 15, 2018 | Posted by in CARDIOLOGY | Comments Off on Carotid Body Tumors
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