Introduction

Paragangliomas of the head and neck are rare neoplasms of neural crest cell origin. The four most common sites for paragangliomas within the head and neck are at the carotid body, the jugular foramen, in the middle ear, and along the vagus nerve. Rarely, paragangliomas have been found within the larynx, orbit, thyroid gland, nasopharynx, mandible, soft palate, face, and cheek.

Carotid body tumors account for 60% of head and neck paragangliomas and have a female predominance. As the majority of carotid body tumors are nonfunctional and do not secrete catecholamines, these tumors more commonly present as an incidental neck mass. Almost one-quarter of carotid body tumors are bilateral, and of these bilateral tumors, the majority are associated with succinate dehydrogenase (SDHx) mutations. Because of their location at the carotid bifurcation, carotid body tumors splay the internal and external carotid arteries as they grow ( Fig. 44.1 ).

(A) Axial T2-weighted and (B) sagittal-unenhanced T1-weighted images of a carotid body tumor (asterisk) with splaying of the internal carotid artery (short white arrow) and the external carotid artery (long white arrow) .

Paragangliomas arising at the jugular foramen and middle ear comprise approximately 30% of paragangliomas in the head and neck and also have a female predominance. These paragangliomas arise from three distinct bodies that are closely related to Jacobsen’s nerve (the tympanic branch of cranial nerve IX), Arnold’s nerve (the auriculotemporal branch of cranial nerve X) and the jugular bulb, respectively. Glomus tympanicum lesions arising from Jacobson’s nerve in the middle ear typically occur at the cochlear promontory and can present clinically with conductive hearing loss, pulsatile tinnitus, or as a red retrotympanic mass ( Fig. 44.2 ). Glomus jugulare tumors typically involve the medial aspect of the jugular foramen and thus can present with cranial nerve IX, X, and/or XI palsies.

Axial computed tomography in bone algorithm image (A) and axial contrast-enhanced T1-weighted MRI (B) of a glomus tympanicum (white arrow) demonstrating the typical location along the cochlear promontory and avid enhancement.

As these paragangliomas frequently involve both the middle ear and jugular foramen, the term glomus jugulotympanicum is often preferred ( Fig. 44.3 ). Demineralization or erosion of the lateral plate of the jugular foramen is diagnostic of a glomus jugulotympanicum, whereas glomus tympanicum lesions are isolated to the middle ear with an intact jugular plate. As terminology may vary by institution, it is important for the radiologist to use terms consistently and in agreement with the referring clinicians. The extent of tumor must be clearly described and well delineated, as the surgical approaches, such as a cervical and/or temporal approach, may be required depending on the extent of disease.

Axial contrast-enhanced T1-weighted images of a glomus jugulogympanicum (asterisk) with involvement of both the jugular foramen (A) and the middle ear (B).

Glomus vagale tumors comprise approximately 10% of paragangliomas and typically present as a palpable neck mass or with a lower cranial neuropathy. While most paragangliomas in the head and neck are extrinsic to the cranial nerves, glomus vagale tumors are the exception and are associated with a higher rate of cranial neuropathies. Although vagal paragangliomas are typically described as arising from two sites (the inferior or nodose ganglion and superior or jugular ganglion), they can arise elsewhere along the course of the vagus nerve. Unlike the carotid body, the paraganglia of the vagus nerve are not organized into a distinct mass but are instead spread along the perineurium, deep to the nerve sheath, or interspersed between the nerve fibers. Approximately one-third of patients with glomus vagale tumors have additional paragangliomas, and the majority of these patients have a family history suggesting a strong genetic correlation ( Fig. 44.4 ). Glomus vagale tumors are typically located within the poststyloid parapharyngeal space and result in anterior displacement of the internal and external carotid arteries and posterolateral displacement and compression of the internal jugular vein. These tumors typically occur more cranially than the carotid body tumors and more inferiorly than the skull base glomus jugulare/jugulotympanicum tumors (see Fig. 44.4 ).

Coronal STIR image in a patient with bilateral paragangliomas, including a glomus vagale on the right (long white arrow) and a carotid body tumor on the left (short white arrow) . Note that the left-sided carotid body tumor is more inferiorly located than the right-sided glomus vagale.

Rarely, paragangliomas can arise within the larynx ( Fig. 44.5 ). These can be difficult to differentiate from neuroendocrine carcinomas; however, patients with neuroendocrine carcinomas generally have elevated catecholamines, unlike the typically nonfunctional paragangliomas of the head and neck.

Contrast-enhanced axial computed tomography image in a patient with avidly enhancing bilateral carotid body tumors (black asterisks) and a laryngeal paraganglioma in the left paraglottic fat (red asterisk) .

Approximately 30% to 40% of paragangliomas are familial. The most common genetic mutation associated with paragangliomas are SDH pathway mutations, of which SDHD mutations are the most common. Other common genetic syndromes associated with paragangliomas include von Hippel-Lindau (VHL) disease and neurofibromatosis type 1 (NF1).

Histopathology, including assessment of mitoses, necrosis, and vascular invasion, remains insufficient to determine the risk of metastases from a paraganglioma. As distinguishing between benign and malignant paragangliomas is primarily based on the presence of metastatic disease, imaging plays a critical role in determining the ultimate diagnosis and staging.

Imaging

On ultrasound, paragangliomas of the head and neck are generally hypoechoic, solid, well-circumscribed tumors. Color Doppler can demonstrate the vascularity of these lesions ( Fig. 44.6 ).

Gray scale (A) and color Doppler (B) ultrasound images of a carotid body tumor, demonstrating a hypoechoic solid mass with marked internal vascularity.

Cross-sectional imaging provides additional information, particularly in characterizing lesion extent at the skull base or within the deep poststyloid parapharyngeal space, which may not be visible on ultrasound. In addition, the presence of permeative osseous destruction at the skull base in the setting of glomus jugulare or glomus jugulotympanicum is best appreciated on computed tomography (CT) images in bone algorithm ( Fig. 44.7A ). Regardless of location, paragangliomas on CT demonstrate avid enhancement (see Fig. 44.5 ).

Axial computed tomography image in bone algorithm (A) and axial T2-weighted image (B) of a glomus jugulotympanicum. Note the permeative osseous destruction of the margins of the jugular foramen in image (A, arrow ). In image (B, arrow ), the “salt and pepper” appearance typical for a paraganglioma is seen.

Magnetic resonance imaging (MRI) provides more detailed soft tissue characterization. On T1- and T2-weighted images, paragangliomas may have a characteristic “salt and pepper” appearance (see Fig. 44.7B ). On T1-weighted imaging, the salt appearance can be seen in areas of high T1 signal, due to the presence of hemorrhage. On T2-weighted images, the salt appearance can be seen in areas of T2 prolongation or hyperintensity, representing areas of slow-flow blood or hemorrhage within the lesion, depending on the stage of hemorrhage. Foci of T2 hypointensity, creating the pepper appearance, are attributable to the presence of multiple flow voids. Recently the use of dynamic contrast-enhanced MRI of the neck has been investigated to help distinguish paragangliomas from schwannomas. Paragangliomas have high peak enhancement, signal enhancement ratio, and time to maximum enhancement, whereas schwannomas have lower peak enhancement, signal enhancement ratio, and longer time to maximum enhancement.

According to Bustillo et al., indium-111 octreotide scanning has an 82% specificity and 97% sensitivity for the diagnosis of paragangliomas and can also be used to assess for recurrent or metastatic disease.

Screening may be performed in high-risk patients with a genetic predisposition. Although CT is fast and more readily available, radiation exposure (particularly in younger patients) should be avoided if possible. A recent study of a 5- to 10-minute abbreviated MRI protocol performed in carriers of the SDHx mutation—which included a rapid contrast-enhanced MR angiogram of the head and neck and postgadolinium T1-weighted sequence with fat saturation—showed no difference in the diagnostic assessment of paraganglioma compared with a full standard MRI.