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CHAPTER 24 Paraganglioma
Douglas J. Quint
Epidemiology
Temporal bone paragangliomas/chemodectomas are most commonly found along cranial nerves IX and X. Within the temporal bone region, they occur in the middle ear cleft on the cochlear promontory (20%) or the hypotympanum (25%) as glomus tympanicum tumors, the jugular foramen region (50%) as glomus jugulare tumors, or just below the skull base (5%) as glomus vagale tumors. Lesions involving the middle ear and jugular fossa regions are called glomus jugulotympanicum tumors. Paragangliomas are the most common primary middle ear neoplasm.
The incidence of temporal bone paragangliomas is approximately 1/million/year, and somewhat preferentially occur in middle-aged women.
When spontaneously occurring, these lesions are multiple in 5 to 10% of patients, but are multiple in up to 50% of patients in familial cases.
Clinical Features
Presenting symptoms in patients with these neoplasm are a function of the location of the tumor. Mid- dle ear lesions (glomus tympanicum tumors) can present with pulsatile tinnitus (80 to 90%) as they are vascular tumors, conductive hearing loss (50 to 60%) as ossicles can be affected, otalgia, or simply a sense of ear “fullness.” Less than 5% of these tumors are physiologically active, producing catechol- amines (norepinephrine). Middle ear paragangliomas are essentially never physiologically active. On physical examination, these lesions can be seen as a reddish vascular mass behind the anteroinferior portion of the tympanic membrane.
Pathology
All paragangliomas/chemodectomas, regardless of location, are histologically identical. They arise from embryonic neural crest cells that have differentiated into paraganglia (chemoreceptor cells). These extremely vascular, but histologically benign tumors are composed of central “chief” cells that are arranged in a typical pattern called “zellballen.” Less than 5% of these “chief” cells actively secrete catecholamines. More aggressive tumor variants can have similar histology but can only be diagnosed when metastatic lesions are present (<5% of patients).
Treatment
Preoperative endovascular embolization, surgery, or radiation therapy are potential therapies for larger lesions. Smaller lesions (which include essentially all lesions confi ned to the middle ear region) are usually treated with surgery only. Complete resection is curative.
Imaging Findings
When tumors are large, their respective site of origin can be obscure, as the jugular foramen, mid- dle ear, and petrous temporal bone regions may all be involved. Such large tumors of the temporal
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bone may simply be referred to as glomus jugulotympanicum tumors and should be characterized with computed tomography (CT) (osseous involvement) and magnetic resonance imaging (MRI) (intra- cranial and infratemporal extension; differentiating tumor from trapped middle ear or mastoid secre- tions). When confi ned to the middle ear cleft, these tumors can arise anywhere on the medial wall of the mesotympanum and hypotympanum (i.e., along the course of the tympanic branch of cranial nerve IX), not just the cochlear promontory region, and are considered glomus tympanicum tumors. Such smaller tumors can be adequately characterized with CT without the need for MRI.
CT
High-resolution (1 to 2 mm) noncontrast CT performed in the axial and coronal planes and recon- structed with a detail (bone) algorithm best delineates temporal bone structures. Sagittal reformatted images may also prove useful.
On CT scans, because of the superior spatial resolution, a small middle ear paraganglioma is best localized and delineated. CT is the only imaging modality necessary to search for small tumors on the cochlear promontory or involving only the hypotympanic region. Glomus jugulare or glomus jugulo- tympanicum tumors can enlarge the jugular foramen, erode the jugular spine, or destroy the osseous margin between the jugular foramen and the carotid canal. These lesions can frankly invade and de- stroy portions of the temporal bone. The extent of osseous destruction is best characterized with mul- tiplanar CT ( Fig. 24–1A ).
There is no role for contrast-enhanced CT imaging in these patients.
MRI
Thin-section multiplanar pre- and postcontrast T1- and T2-weighted scanning is best for delineating the overall extent of lesions, particularly when they invade the temporal bone or extend intracranially or below the temporal bone ( Fig. 24–1B, Fig. 24–2A, and Fig. 24–2B ).
Magnetic resonance is excellent for showing the typical “salt and pepper” (fl ow voids) appearance of paragangliomas (on noncontrast T1-weighted scan) when such lesions are large (usual presentation for glomus vagale, jugulare, and carotid paragangliomas), but such fl ow voids will not be seen in small middle ear lesions (glomus tympanicum paraganglioma). Paragangliomas demonstrate intermediate heterogeneous signal on T2-weighted scans. As these lesions are quite vascular, they enhance on con- trast-enhanced T1-weighted scans. Even very small temporal bone lesions can be detected on contrast- enhanced MRI scans. However, when defi nitively identifi ed as a small medial wall middle ear lesion on CT without associated osseous destruction, additional MRI is not necessary.
When a larger lesion is associated with opacifi cation of the middle ear and mastoid regions, MRI can differentiate tumor from trapped secretions. Contrast-enhanced MRI can enhance the glomus tumor, whereas contiguous trapped secretions do not enhance. Similarly, on T2-weighted scans, trapped secre- tions are hyperintense, whereas glomus tumors are heterogeneously isointense to brain ( Fig. 24–2 B ).
Other Imaging
Endovascular angiography can be performed for larger lesions so that the extent of these highly vascu- lar tumors can be assessed and preoperative embolization performed as necessary. These lesions are supplied by internal or external carotid branches depending on their locations ( Fig. 24–2 C ). MRI angi- ography is of no value when evaluating these lesions. Smaller, typical appearing purely mesotympanic paragangliomas do not require preoperative angiography.
Indium scintigraphy has been used to identify somatostatin receptors in paragangliomas, but the sensitivity of this technique for small lesions in the temporal bones remains unknown.
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Figure 24-1 A 49-year-old woman presents with right- sided pulsatile tinnitus, dizziness, loss of balance, and head- ache. (A) Axial contrast-enhanced bone window (left) and brain window (right) computed tomography (CT) scans through the right skull base demonstrate the enhancing mass involving the right cerebellomedullary cistern and the right jugular foramen region (dotted arrows), but bet- ter demonstrate the MRI (Fig. 24-1B) associated osseous destruction and the right middle ear involvement (solid arrow). Angiography confi rmed the presence of a vascu-
lar glomus jugulotympanicum tumor, which encased the right internal carotid artery at the skull base. The patient failed a balloon test occlusion and was treated with radia- tion therapy with resolution of symptoms.
(B) Axial precontrast (left) and contrast-enhanced (right) T1-weighted magnetic resonance imaging (MRI) through the right skull base region demonstrates the enhancing mass involving the right cerebellomedullary cistern and the right jugular foramen region (dotted arrows) with mini- mal extension into the right middle ear cleft (solid arrow).
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