Paraganglioma: Carotid Body Tumor

Extra-adrenal paragangliomas are neoplasms of the paraganglia located within the paravertebral sympathetic and parasympathetic chains. Thus paragangliomas may arise anywhere along these tracts and common sites of occurrence include abdomen, retroperitoneum, chest and mediastinum and various head and neck locations such as jugulotympanic membrane, orbit, nasopharynx, larynx, vagal body and carotid body. Recent literature suggests a molecular basis for the development of some paragangliomas, i.e. germline mutations. Six genes have been identified and are thought to contribute to the development of pheochromocytoma/paraganglioma. These include RET, VHL, NF1 and SDH subunits SDHB, SDHC, and SDHD. SDHD and SDHB mutations account for a significant percentage of head and neck paragangliomas. It is well know that paragangliomas may be hereditary and may be part of genetic syndromes such as Von Hippel-Lindau syndrome, neurofibromatosis type I (von Recklinghausen disease), MEN 2A and MEN 2B. When features of these more commonly known syndromes are not present, many familial cases, often associated with the above mentioned germline mutations, go unrecognized. In the head and neck region the normal paraganglia are associated with the parasympathetic nervous system and paragangliomas arising from these parasympathetic sites account for up to 70% of extra-adrenal paragangliomas. The most common site is the carotid body. Carotid body paragangliomas arise at the bifurcation of the internal and external carotid arteries and have classic radiographic features. Carotid body paragangliomas are vascular lesions, and this is reflected in their imaging appearance. These lesions splay apart the internal (ICA) and external carotid arteries (ECA), and as it enlarges, it will encase, but not narrow the ICA and ECA. Upon contrast administration the lesions avidly enhance reflecting their vascular nature. Flow voids from the numerous vessels are typically seen on MR imaging, and this finding is part of the classic ‘‘salt and pepper’’ imaging appearance of these lesions seen on T2 weighted images. The ‘‘pepper’’ refers to the low signal flow voids, and the ‘‘salt’’ refers to high signal foci of hemorrhage and/or slow flow. The lesions tend to be isointense relative to muscle on T1 weighted imaging and hyperintense on T2. Avid enhancement is seen on postcontrast imaging (Fig. 1a, b). Cather angiography and CT angiography reveal a hypervascular mass (Fig. 2) with enlarged feeding arteries (typically the ascending pharyngeal or ascending cervical artery), intense tumor blush and early draining veins. Indium-111 octreotide, which is a somatostatin analog, is nuclear medicine imaging study that is useful in the evaluation of paragangliomas, since these are neuroendocrine neoplasms that have surface receptors for somatostatin. A focal area of early intense radiotracer uptake will be seen in the region of the paraganglioma (Fig. 3), and is sensitive for detecting tumors greater than 1.5 cm. Octreotide scanning is useful for detecting the presence of multicentric or metastatic J. A. Wieneke (&) Division of Otorhinolaryngic-ENT Pathology, Armed Forces Institute of Pathology, Room G066-09, 6800 16th Street, N.W., Washington, DC 20306-6000, USA e-mail: [email protected]