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Paraganglioma
44 Paraganglioma
44
Katherine L. Reinshagen, Hillary R. Kelly
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). 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.
A
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. 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
B
Figure 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).
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B
Figure 44.2. 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.
A
B
Figure 44.3. Axial contrast-enhanced T1-weighted images of a glomus jugulogympanicum (asterisk) with involvement of both the jugular foramen (A) and the middle ear (B).
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). 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. 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). 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). 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
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Figure 44.5. 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). Figure 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.
A
B
Figure 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.
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.
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A
B
Figure 44.7. 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.
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.
TEMPORAL EVOLUTION AND TREATMENT Adjacent structures in the head and neck can become involved as paragangliomas increase in size. As carotid body tumors grow, these can envelope the adjacent carotid arteries. This is reflected in the Shamblin surgical classification, which helps to predict surgical morbidity. Shamblin class 1 lesions are located at the carotid bifurcation, Shamblin class 2 lesions are adherent to or partially surrounding the internal and external carotid arteries, and Shamblin class 3 lesions encase one or both of the internal and external carotid arteries. Carotid body tumors can become so large that distinguishing them from glomus vagale tumors can be difficult. Progression of permeative osseous destruction can be a helpful clue in assessing skull base masses and differentiating a glomus jugulare or glomus jugulotympanicum from other skull base masses (Fig. 44.8). Surgery with preoperative endovascular embolization is commonly used to mitigate the increased risk of intraoperative hemorrhage. Because of their high vascularity, glomus jugulare tumors often undergo preoperative embolization when surgery is considered. However, although preoperative embolization is typically successful and can decrease overall tumor vascularity by as much as 90%, there have been reported increased incidents of cranial nerve palsy associated with the embolization procedure. Although there is no general consensus for the use of preoperative
endovascular embolization for carotid body tumors, a recent meta-analysis has shown that the use of embolization decreases operative time and blood loss in carotid body tumor resections. For the management of carotid body tumors, surgery is considered the preferred and definitive treatment. Management of glomus jugulotympanicum and glomus vagale tumors is more challenging owing to the increased risk of cranial nerve palsy following surgery. The incidence of cranial nerve palsies of glomus jugulotympanicum and glomus vagale tumors can range from 22% to 100% and tumor recurrence occurs in 3% to 20%. In addition, skull base surgery for glomus jugulare tumors has additional risks, including leak of cerebrospinal fluid and meningitis. Owing to the morbidity of skull base surgery for these tumors, radiation therapy, including fractional external beam radiation (or more recently CyberKnife), can also be considered. Postoperative and posttreatment imaging is standard to assess for residual or recurrent tumor and can be done with CT, MRI, or both. Expected postradiation changes include decreases in tumor size (Fig. 44.9) and heterogeneity of contrast enhancement. The lack of interval growth is also reassuring in the postradiation setting (Fig. 44.10). Although less common in the head and neck, functional catecholamine-secreting tumors are best treated with surgery, owing to poor functional control following radiation therapy.
MIMICS AND DIFFERENTIAL DIAGNOSIS Glomus Vagale and Carotid Body Tumor Mimics Sympathetic chain or vagal schwannomas can sometimes be mistaken for glomus vagale tumors. These tend to be less avidly enhancing and have been demonstrated to have longer times to peak enhancement as compared with paragangliomas. Flow voids are typically absent in schwannomas and are a helpful distinguishing feature (Fig. 44.11). In addition, cystic change is more commonly seen in schwannomas.
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A
B
C
D
E Figure 44.8. (A–E) Temporal progression from 2006 to 2011 in a patient with a glomus jugulare with permeative osseous erosion (black arrow). There was continued progression of tumor into the middle ear in 2008 (white arrow), consistent with a glomus jugulotympanicum.
A
B
Figure 44.9. Before radiation therapy, 2011 (A), and after radiation therapy, 2012 (B), contrast-enhanced axial computed tomography images of a glomus jugulotympanicum (asterisk) demonstrating decreased bulk of the enhancing soft tissue component in the left posterior fossa.
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B
Figure 44.10. Before radiation therapy (A) and after radiation therapy (B) contrast-enhanced axial computed tomography images of a glomus vagale (asterisk) with no interval growth over 1 year.
A
C
B
D
Figure 44.11. Axial T2-weighted (A and B) and axial T1-weighted postcontrast (B and D) images of a sympathetic chain schwannoma (asterisk) and a vagal schwannoma (white arrow). Note the absence of flow voids on the T2-weighted images as well as the T2 hyperintense nonenhancing cystic change (C and D) in keeping with schwannomas.
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A
B
Figure 44.12. (A–B) Contrast-enhanced axial computed tomography images demonstrate an opacity in the middle ear cavity (white arrow) overlying the cochlear promontory; this is similar in appearance to a glomus tympanicum but is contiguous with the internal carotid artery and is therefore an aberrant internal carotid artery.
Figure 44.13. Coronal computed tomography image in bone algorithm demonstrates a dehiscent jugular bulb extending into the middle ear cavity (white arrow), with opacification of the round window niche. Note the smooth osseous margin (black arrow), which would be atypical for a glomus jugulare/jugulotympanicum.
Since the sympathetic chain is medial and travels along the posterior aspect of the internal carotid artery, sympathetic chain schwannomas tend to be medial to the vessels of the carotid sheath and displace the internal carotid artery anteriorly or anterolaterally. Vagal schwannomas tend to grow between the internal carotid artery and internal jugular vein, and splay these vessels apart, displacing the internal carotid artery anteromedially and the internal jugular vein posterolaterally. The pattern of vascular displacement can sometimes be misleading, particularly when lesions become larger. Using a combination of location and enhancement characteristics is helpful.
Glomus Tympanicum Mimics Vascular abnormalities within the middle ear can sometimes be mistaken for glomus tympanicum lesions clinically and radiographically, including an aberrant internal carotid artery with or without a persistent stapedial artery (Fig. 44.12), jugular dehiscence
(Fig. 44.13), a jugular diverticulum, or a high-riding jugular bulb. Other mimics on imaging can include rarer lesions such as a middle ear adenoma or congenital cholesteatoma, although these lesions do not tend to have the typical red hue on clinical examination.
Glomus Jugulare Mimics Lesions at the skull base can sometimes mimic a glomus jugulare. These include vascular variants such as the high-riding or dehiscent jugular bulb or diverticulum, which tend to have smooth osseous borders (see Fig. 44.13); metastatic lesions, which can have a destructive appearance; or meningiomas, which tend to cause hyperostosis of the surrounding bone (Fig. 44.14). The degree of enhancement is not as helpful in distinguishing between these lesions, as meningiomas and metastases can also be hypervascular. However, meningiomas typically demonstrate characteristic “dural tails” (see Fig. 44.14).
Figure 44.14. Meningioma. A large avidly enhancing mass is seen in the left poststyloid parapharyngeal space on the coronal postcontrast T1-weighted image. There is extension intracranially with enhancing dural tails (white arrows).
SUGGESTED READINGS
Anil G, Tan TY. Imaging characteristics of schwannoma of the cervical sympathetic chain: a review of 12 cases. AJNR Am J Neuroradiol. 2010;31(8):1408–1412. Bustillo A, Telischi F, Weed D, et al. Octreotide scintigraphy in the head and neck. Laryngoscope. 2004;114(3):434–440.
Capatina C, Ntali G, Karavitaki N, et al. The management of head and neck paragangliomas. Endocr Relat Cancer. 2013;20:R291–R305. Gaddikeri S, Hippe DS, Anzai Y. Dynamic contrast-enhanced MRI in the evaluation of carotid space paraganglioma versus schwannoma. J Neuroimaging. 2016;26(6):618–625. Gaynor BG, Elhammady MS, Jethanamest D, et al. Incidence of cranial nerve palsy after preoperative embolization of glomus jugulare tumors using Onyx. J Neurosurg. 2014;120(2):377–381. Gravel G, Niccoli P, Rohmer V, et al. The value of a rapid contrast-enhanced angio-MRI protocol in the detection of head and neck paragangliomas in SDHx mutations carriers: a retrospective study on behalf of the PGL.EVA investigators. Eur Radiol. 2016;26(6):1696–1704. Griauzde J, Srinivasan A. Imaging of vascular lesions of the head and neck. Radiol Clin North Am. 2015;53(1):197–213. Hu K, Persky MS. Treatment of head and neck paragangliomas. Cancer Control. 2016;23(3):228–241. Jackson RS, Myhill JA, Padhya TA, et al. The effects of preoperative embolization on carotid body paraganglioma surgery: a systematic review and meta-analysis. Otolaryngol Head Neck Surg. 2015;153(6):943–950. Marchetti M, Pinzi V, Tramacere I, et al. Radiosurgery for paragangliomas of the head and neck: another step for the validation of a treatment paradigm. World Neurosurg. 2017;98:281–287. Myssiorek D, Rinaldo A, Barnes L, et al. Laryngeal paraganglioma: an updated critical review. Acta Otolaryngol. 2004;124(9):995–999. Olsen WL, Dillon WP, Kelly WM, et al. MR imaging of paragangliomas. AJR Am J Roentgenol. 1987;148:201–204. Rao AB, Koeller KK, Adair CF. From the archives of AFIP. Paragangliomas of the head and neck: radiologic-pathologic correlation. Armed Forces Institute of Pathology. Radiographics. 1999;19(6):1605–1632. Sargar K. Parapharyngeal neck schwannomas with unusual vascular displacement. Case Rep Med. 2013;2013:563019. van den Ber R. Imaging and management of head and neck paragangliomas. Eur Radiol. 2005;15(7):1310–1318. Williams MD, Tischler AS. Update from the 4th edition of the World Health Organization Classification of Head and Neck Tumors: paragangliomas. Head Neck Pathol. 2017;Feb 28, [Epub ahead of print]. Woolen S, Gemmete JJ. Paragangliomas of the head and neck. Neuroimaging Clin N Am. 2016;26(2):259–278. Zhou X, Jiang S, Li H. A case of laryngeal paraganglioma and literature review. Int J Clin Exp Med. 2015;8(9):16934–16936.
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Katherine L. Reinshagen, Hillary R. Kelly
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). 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.
A
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. 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
B
Figure 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).
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A
B
Figure 44.2. 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.
A
B
Figure 44.3. Axial contrast-enhanced T1-weighted images of a glomus jugulogympanicum (asterisk) with involvement of both the jugular foramen (A) and the middle ear (B).
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). 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. 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). 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). 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
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Figure 44.5. 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). Figure 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.
A
B
Figure 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.
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.
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PART Iii Tumors
A
B
Figure 44.7. 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.
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.
TEMPORAL EVOLUTION AND TREATMENT Adjacent structures in the head and neck can become involved as paragangliomas increase in size. As carotid body tumors grow, these can envelope the adjacent carotid arteries. This is reflected in the Shamblin surgical classification, which helps to predict surgical morbidity. Shamblin class 1 lesions are located at the carotid bifurcation, Shamblin class 2 lesions are adherent to or partially surrounding the internal and external carotid arteries, and Shamblin class 3 lesions encase one or both of the internal and external carotid arteries. Carotid body tumors can become so large that distinguishing them from glomus vagale tumors can be difficult. Progression of permeative osseous destruction can be a helpful clue in assessing skull base masses and differentiating a glomus jugulare or glomus jugulotympanicum from other skull base masses (Fig. 44.8). Surgery with preoperative endovascular embolization is commonly used to mitigate the increased risk of intraoperative hemorrhage. Because of their high vascularity, glomus jugulare tumors often undergo preoperative embolization when surgery is considered. However, although preoperative embolization is typically successful and can decrease overall tumor vascularity by as much as 90%, there have been reported increased incidents of cranial nerve palsy associated with the embolization procedure. Although there is no general consensus for the use of preoperative
endovascular embolization for carotid body tumors, a recent meta-analysis has shown that the use of embolization decreases operative time and blood loss in carotid body tumor resections. For the management of carotid body tumors, surgery is considered the preferred and definitive treatment. Management of glomus jugulotympanicum and glomus vagale tumors is more challenging owing to the increased risk of cranial nerve palsy following surgery. The incidence of cranial nerve palsies of glomus jugulotympanicum and glomus vagale tumors can range from 22% to 100% and tumor recurrence occurs in 3% to 20%. In addition, skull base surgery for glomus jugulare tumors has additional risks, including leak of cerebrospinal fluid and meningitis. Owing to the morbidity of skull base surgery for these tumors, radiation therapy, including fractional external beam radiation (or more recently CyberKnife), can also be considered. Postoperative and posttreatment imaging is standard to assess for residual or recurrent tumor and can be done with CT, MRI, or both. Expected postradiation changes include decreases in tumor size (Fig. 44.9) and heterogeneity of contrast enhancement. The lack of interval growth is also reassuring in the postradiation setting (Fig. 44.10). Although less common in the head and neck, functional catecholamine-secreting tumors are best treated with surgery, owing to poor functional control following radiation therapy.
MIMICS AND DIFFERENTIAL DIAGNOSIS Glomus Vagale and Carotid Body Tumor Mimics Sympathetic chain or vagal schwannomas can sometimes be mistaken for glomus vagale tumors. These tend to be less avidly enhancing and have been demonstrated to have longer times to peak enhancement as compared with paragangliomas. Flow voids are typically absent in schwannomas and are a helpful distinguishing feature (Fig. 44.11). In addition, cystic change is more commonly seen in schwannomas.
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A
B
C
D
E Figure 44.8. (A–E) Temporal progression from 2006 to 2011 in a patient with a glomus jugulare with permeative osseous erosion (black arrow). There was continued progression of tumor into the middle ear in 2008 (white arrow), consistent with a glomus jugulotympanicum.
A
B
Figure 44.9. Before radiation therapy, 2011 (A), and after radiation therapy, 2012 (B), contrast-enhanced axial computed tomography images of a glomus jugulotympanicum (asterisk) demonstrating decreased bulk of the enhancing soft tissue component in the left posterior fossa.
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B
Figure 44.10. Before radiation therapy (A) and after radiation therapy (B) contrast-enhanced axial computed tomography images of a glomus vagale (asterisk) with no interval growth over 1 year.
A
C
B
D
Figure 44.11. Axial T2-weighted (A and B) and axial T1-weighted postcontrast (B and D) images of a sympathetic chain schwannoma (asterisk) and a vagal schwannoma (white arrow). Note the absence of flow voids on the T2-weighted images as well as the T2 hyperintense nonenhancing cystic change (C and D) in keeping with schwannomas.
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A
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Figure 44.12. (A–B) Contrast-enhanced axial computed tomography images demonstrate an opacity in the middle ear cavity (white arrow) overlying the cochlear promontory; this is similar in appearance to a glomus tympanicum but is contiguous with the internal carotid artery and is therefore an aberrant internal carotid artery.
Figure 44.13. Coronal computed tomography image in bone algorithm demonstrates a dehiscent jugular bulb extending into the middle ear cavity (white arrow), with opacification of the round window niche. Note the smooth osseous margin (black arrow), which would be atypical for a glomus jugulare/jugulotympanicum.
Since the sympathetic chain is medial and travels along the posterior aspect of the internal carotid artery, sympathetic chain schwannomas tend to be medial to the vessels of the carotid sheath and displace the internal carotid artery anteriorly or anterolaterally. Vagal schwannomas tend to grow between the internal carotid artery and internal jugular vein, and splay these vessels apart, displacing the internal carotid artery anteromedially and the internal jugular vein posterolaterally. The pattern of vascular displacement can sometimes be misleading, particularly when lesions become larger. Using a combination of location and enhancement characteristics is helpful.
Glomus Tympanicum Mimics Vascular abnormalities within the middle ear can sometimes be mistaken for glomus tympanicum lesions clinically and radiographically, including an aberrant internal carotid artery with or without a persistent stapedial artery (Fig. 44.12), jugular dehiscence
(Fig. 44.13), a jugular diverticulum, or a high-riding jugular bulb. Other mimics on imaging can include rarer lesions such as a middle ear adenoma or congenital cholesteatoma, although these lesions do not tend to have the typical red hue on clinical examination.
Glomus Jugulare Mimics Lesions at the skull base can sometimes mimic a glomus jugulare. These include vascular variants such as the high-riding or dehiscent jugular bulb or diverticulum, which tend to have smooth osseous borders (see Fig. 44.13); metastatic lesions, which can have a destructive appearance; or meningiomas, which tend to cause hyperostosis of the surrounding bone (Fig. 44.14). The degree of enhancement is not as helpful in distinguishing between these lesions, as meningiomas and metastases can also be hypervascular. However, meningiomas typically demonstrate characteristic “dural tails” (see Fig. 44.14).
Figure 44.14. Meningioma. A large avidly enhancing mass is seen in the left poststyloid parapharyngeal space on the coronal postcontrast T1-weighted image. There is extension intracranially with enhancing dural tails (white arrows).
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