The function of the carotid body is related to its role in the autonomic control of the respiratory and cardiovascular systems. It is responsible for detecting changes in the composition of arterial blood. The only other paraganglia with similar chemoreceptor function are the aortic bodies. Hypercapnia, hypoxia, or decreasing pH stimulate Type I cells to initiate an autonomic reflex which leads to increased respiratory rate and depth, sympathetic nervous system activation(increased heart rate, systemic vascular tone and blood pressure), and cerebral cortical activity. The carotid body is also stimulated by increased blood temperature and certain chemicals(cyanide and nicotine). It is this close association with respiratory drive and the sympathetic nervous system response that have prompted investigation of the carotid body's role in disease processes such as obstructive sleep apnea and sudden infant death syndrome. Although no clear conclusions can be drawn at this time, the carotid body and its response to intermittent hypoxia appear to be related to the systemic hypertension seen in OSA. It has also been shown that some SIDS children had either small carotid bodies or a decreased Type I cells(mature) to Type II cells ratio. It is hypothesized that this may attenuate the child's response to a hypoxic crisis.
The hereditary form occurs in 7-9% of cases and is more frequently multicentric(30-40%). These are seen with equal frequency in both sexes and the inheritance pattern is autosomal dominant modified by genomic imprinting. Although the allele can be passed from either parent, only those from the father will lead to the paraganglioma phenotype in the children. It is thought that this occurs because the allele is only activated during spermatogenesis and not during oogenesis. Since treatment of smaller tumors carries a much lower risk of morbidity and mortality, and because of the autosomal dominant pattern of inheritance, routine examination and screening with MRI every two years for at risk individuals older than 16 to 18 years of age is recommended (McCaffrey, 1994). This costly approach may be eliminated in the future if a reliable genetic screening test can be developed.
Although it is an invasive test, carotid angiography is by far the most useful diagnostic test for paragangliomas. This modality can establish the diagnosis, demonstrate multiple lesions, determine the size and vascularity, and evaluate the tumor blood supply. Additionally, it can be modified to include selective, controlled balloon occlusion of the internal carotid artery to evaluate the cerebral cross-flow. This information is extremely important in pre- operative planning and counselling of the patient as to the relative risk of surgery. The classic, pathognomonic finding on arteriogram is widening of the carotid bifurcation by a well-defined tumor blush("lyre sign"). It should be emphasized that angiography of both carotid systems is required to rule out bilateral tumors. MRI with gad.(tumors as small as 5 mm) and contrast CT are also effective imaging modalities in this area and are non-invasive. Biopsy, including fine needle aspiration is unnecessary, dangerous, and contra-indicated in the evaluation of paragangliomas.
Routine screening for urinary metanephrines and VMA, and serum catacholamines is probably only indicated for multiple or familial paragangliomas or in the presence of catecholamine related symptoms(Johnson, 1991). However, considering the hazards associated with operating on a previously unsuspected, metabolically active tumor, an argument can be made for obtaining these studies in all cases.
The approach is usually transcervical but occasionally a superiorly based carotid paraganglioma or one that reaches the skull base may require a skull base approach. Wide exposure is a must as is meticulous hemostasis. Early control of the proximal and distal vessels is then accomplished with vessel loops. Important neurovascular structures are identified and appropriately retracted. The tumor is then carefully dissected from the common carotid in a subadventitial plane. This dissection is carried superiorly, making every effort to protect the internal carotid. If necessary, the external carotid can be sacrificed in most cases. If the common or internal carotid is encased in tumor or damaged during resection, immediate repair/replacement should be performed. Again, the preoperative work up should indicate the likelihood of vascular involvement and give some indication as to how well the patient will tolerate temporary internal carotid compromise.
Radiotherapy, either alone or in conjunction with surgery, is a second consideration and an area of some controversy. Historically, paragangliomas were considered radioresistant. Some authors believe this is false and is based on past experience where only large, recurrent or inoperable tumors were treated with this modality. Several more recent studies indicate good responses to supervoltage radiation including some complete responses. They report only minimal acute complications(skin changes) and no long term complications. However, other studies have demonstrated persistence of disease in lesions whose growth was stabilized by radiotherapy. Most authors still recommend XRT only for very large tumors, recurrent tumors or for those patients who are poor surgical candidates(Sykes, 1986).
Balatsouras, D.G. et al. Multiple glomus tumours. J Laryn and Oto. 1992:106:538-43
Dailey, J.C. Familial multiple cervical paragangliomas: report of a kindred and review of the literature. Oto HNS 1990:102(4):382-90
Eyzaguirre, C. Neurobiology and Cell Physiology of Chemoreception. New York: Plenum Press, 1993;123-29
Handel, S.F. et al. Angiographic changes of head and neck chemodectomas following radiotherapy. Arch Oto. 1977:103:87-89
Heath, D. The human carotid body in health and disease. Journal of Pathology, 1991:164:1-8
Johnson, J.T., Parapharyngeal Space Masses: Diagnosis and Management in: Otolaryngology; Paparella, M.M., Shumrick, D.A., Gluckman, J.L., Meyerhoff, W.L. eds.; Philadelphia PA.; W.B. Saunders, 1991; 2584-5
Kairemo, K.J.A., Hopsu, E.V.M. Radioimmunodetection of Chemodectoma by In-111 labeled anti-CEA antibody. Clinical Nuclear Med. 1990:15:900-3
Kyriakos, M., Pathology of Selected Soft Tissue Tumors of the Head and Neck in: Comprehensive Management of Head and Neck Tumors; Thawley, S.E., Panje, W.R. eds.; Philadelphia PA. W.B. Saunders; 1987; 1261-4
Maves, M.D., Vascular Tumors of the Head and Neck in: Head and Neck Surgery-Otolaryngology; Bailey, B.J., Johnson, J.T., Kohut, R.I., Pillsbury, H.C., and Tardy, M.E. eds. Philadelphia PA. J.B. Lippincott, 1993, 1397-1409
McCaffrey, T.V. et al. Familial Paragangliomas of the head and neck. Arch of Oto. HNS:1994:120:1211-16
Myers, E.N., Johnson, J.T., Neoplasms in: Otolaryngology-Head and Neck Surgery; Cummings, C.W., Fredrickson, J.M., Harker, L.A., Krause, C.J., Schuller, D.E. eds.; St. Louis; Mosby Year Book; 1993; 1590-7
Saldana, M.J. et al. High altitude hypoxia and chemodectomas. Human Path. 1973:4:251-63
Sarosi, M.N., Carpenter III, R.J. Carotid body tumor with extension to skull base. Oto-HNS. 1983:91:322-26
Schild, S.E. et al. Results of radiotherapy for chemodectomas. Mayo Clinic Proceedings. 1992:67(6):537-40
Shamblin, W.R., ReMine, W.H., Sheps, S.G., et al. Carotid body tumor(chemodectoma): Clinicopathologic analysis of ninety cases. Am J Surg., 1971:122:732
Shedd, D.P. et al. Familial occurrence of carotid body tumors. Head and Neck. 1990:12(6):496-9
Sobol, S.M., Dailey, J.C. Familial multiple cervical paragangliomas:Report of a kindred and review of the literature. Oto-HNS. 1990:102:382-90
Strauss, M. et al. Malignant catecholamine-secreting carotid body paraganglioma. Otolaryngology-Head and Neck Surgery. 1983:91:315-21
Sykes, J.M., Ossoff, R.H. Paragangliomas of the Head and Neck. The Otolaryngologic Clinics of North America. Vol. 19, no. 4, Nov. 1986;755-67
Valdagni, R., Amichetti, M. Radiation therapy of carotid body tumors. Am J Clin Oncol:1990:13(1):45-48
Zbaren,P., Lehmann, W. Carotid body paraganglioma with metastases. Laryngoscope. 1985:95:450-54