35 Jugular Foramen Tumors

The jugular foramen (JF), sometimes referred to as the posterior foramen lacerum, is situated in the floor of the posterior fossa posterolateral to the carotid canal, between the petrous temporal bone (anterolaterally) and the occipital bone (posteromedially).1 The distance between the outer border of the jugular fossa and the apex of the mastoid process was 23 mm; between the outer border of the jugular fossa and the tympanomastoid suture, the distance was 15 mm. A degree of asymmetry of the JF is common and is attributed to variability in bone formation around the primitive posterior foramen lacerum and to unequal development of the lateral sinuses.² The JF is a complex crossroad of neurovascular structures in the skull base. Anatomical variation in the course of the nerves and vessels adds to the complexity of this area. The contents of the JF are conventionally divided into the smaller pars nervosa, situated anteromedially, and the larger pars vascularis that is posterolateral.³ The pars nervosa compartment contains the glossopharyngeal (IX) and Jacobsen nerve together with the inferior petrosal sinus, whereas the pars vascularis contains the internal jugular vein, vagus (X), spinal accessory (XI), and Arnold nerve. The IX, X, and XI nerves run through the JF in a connective tissue layer that attaches the dura matter intracranially to the pericranium extracranially.^1,2 The posterior meningeal artery also traverses the JF. This artery is usually a branch of the ascending pharyngeal artery but can also arise from the anterior inferior cerebellar artery in 8% of cases.⁴ The relationship of the JF to the deep fascial planes of the neck are extremely important as tumors and infective lesions from the neck can track along these planes to the JF.

Clinical Presentation and Investigations

Regardless of the type, JF tumors present with similar symptoms and signs. Deficits of cranial nerves IX to XII and hearing disturbances are common. By contrast, facial nerve dysfunction is rarely encountered at an early stage.⁵ The most common presenting complaint in jugular paragangliomas (PGLs) was pulsatile tinnitus whereas the most common symptom elicited was hearing loss and tinnitus. The most common nonotologic symptom was hoarseness.⁶

The differential diagnosis of JF neoplasms is made on the basis of the imaging characteristics assessed by high-resolution computed tomography (CT), magnetic resonance imaging (MRI), and four-vessel digital subtraction angiography (DSA).⁶ CT is useful for analysis of JF bony margins as well as of adjacent skull base foramina. Tumor calcification and hyperostosis are well demonstrated with this form of examination. DSA is a prerequisite in patients with extremely vascular lesions for which preoperative embolization might be appropriate. Because the skull base presents an undulating surface and is relatively thin, section thickness must be kept to a minimum (i.e., 3 mm sections on MRI and thinner axial reconstructions of the spiral CT data). Coronal images are essential because the plane of the JF approximates the axial.³ Whole-body positron emission tomography, using either 18-fluorine l-3,4-dihydroxy-phenylalanine or 18-fluoro-deoxy-D-glucose, is highly sensitive in the detection of PGLs. It can alert the clinician to previously unsuspected multifocal or metastatic disease.⁷

Molecular genetic screening for succinate dehydrogenase (SDH) subunit B, C, D SDHB, SDHC, and SDHD gene mutations is recommended for all apparently sporadic head and neck PGLs to identify the risk of inheritance. The risk for manifestation of the disease phenotype is only increased if the mutation is inherited through the paternal line. Maternal transmission does not cause tumor development.⁷

Classification of Lesions

A large number of lesions may develop or are found in the JF. They may arise intrinsically from structures normally found within the foramen or extrinsically from adjacent tissues.³ The most frequent tumors are jugular PGLs, schwannomas of the lower cranial nerves (LCNs), JF schwannomas, and JF meningiomas.⁸ Rarely, other primary malignant or benign tumors may be encountered in this anatomical region, for example, squamous cell carcinomas, chondrosarcomas, and chordomas.⁸ PGLs account for 80% of JF tumors⁹.⁵

Intrinsic Jugular Foramen Tumors

Paraganglioma

The most common JF tumor is a PGL. PGLs in the skull base are ubiquitous in their distribution and arise from paraganglia or glomus cells situated at the following sites: (1) in the adventitia of the jugular bulb beneath the floor of the middle ear, (2) in the bony walls of the tympanic canals related to the tympanic branches of the IX and X nerves, and (3) in the bone of the promontory, close to the mucosal lining of the middle ear.^3,7,10 Glomus jugular tumors are not encapsulated and tend to infiltrate connective tissue planes. They have a distinctive pattern of spread that helps to differentiate them from other intrinsic tumors in this region. Glomus jugular tumors follow the path of least resistance including mastoid air cell tracts, vascular channels, the eustachian tube, and neural foramina.2,6,9,11 Jugular PGLs can extend from the site of origin to involve the middle ear and ossicles, bony labyrinth, cerebellopontine angle (CPA), the parotid gland, the cavernous sinus and the neck.⁶ In some cases, the internal carotid artery (ICA) can also be involved resulting in stenosis of the ICA.^6,12,13 Temporal bone PGLs are classified according to the classification by Fisch and Mattox¹¹ (Table 35.1). Jugular PGLs usually begin as class C tumors that may progress to class D tumors.

Radiologically, jugular PGLs produce a characteristic “moth-eaten” pattern of bone destruction on CT of the temporal bone. The key point that differentiates jugular from tympanic PGLs is dehiscence of the jugular bulb in the hypotympanum, which is best seen in coronal bone-windowed CT sections.^3,7 MRI with gadolinium shows the characteristics of a tumor, its vascularization and extension and its relationship to neighboring structures. Tumor delineation can be improved using fat-suppression sequences. With MRI, the “salt and pepper” appearance on long repetition time (TR)/long echo time images is typical. The “pepper” component represents the multiple areas of signal void, interspersed with the “salt” component, which is seen as hyperintense foci (because of slow flow) on both long TR and short TR images. Magnetic resonance angiography or venography can help to demonstrate the type of the tumor vascularization and its local venous circulation.^3,5,7

Their most common feeding vessels arise from the ascending pharyngeal artery and supply the inferomedial tumor compartment.^3,10 The posterior auricular, stylomastoid, and occipital arteries supply the posterolateral tumor compartment. Large PGLs may derive further feeding vessels from branches of the internal maxillary, internal carotid, or even from the contralateral carotid and vertebral, via meningeal or pial arterial branches.^6,12,13 Pial artery supply indicates transdural spread.

Neural Sheath Tumors

Neural sheath tumors, such as schwannomas and neurofibromas, share a common site of development in the JF. Schwannomas of LCNs IX, X, and XI represent 3 to 4% of all intracranial schwannomas and these schwanommas are thought to arise from the ganglia of the cranial nerves IX and X that are situated close to the JF; the exact nerve of origin remains, for the most part, unknown.⁵ JF neural sheath tumors have been classified into four groups: type A, tumors primarily in the CPA with minimal enlargement of the JF; type B, tumors primarily in the JF with intracranial extension; type C, extracranial tumors with extension into the JF (and with clinical signs of XII nerve involvement); and type D, dumbbell-shaped tumors with both intra- and extracranial components.¹⁴ From the JF, tumors follow the path of least resistance and may invade the posterior fossa superiorly, the parapharyngeal space inferiorly and spread to the skull base around the JF area. Thus, dumbbell-shaped tumors have both intra- and extracranial extensions with a “passing through” component in the JF.^5,8 In nonenhanced CT images, neural sheath tumors are isodense to the brain parenchyma and are almost indistinguishable from it. After contrast, they appear as well-demarcated vascular tumors.^3,15,16 Bone-windowed images show a smoothly scalloped, well-corticated enlargement of the JF in contrast to the moth-eaten pattern that is seen with PGLs or the irregular osteolytic destructive pattern of metastases or lymphomas. All neural sheath tumors show low uniform T1-weighted intensity (usually matching that of the brain), high T2-weighted signal, and marked (or moderate) contrast enhancement.^7,17 Neural sheath tumors do not generally show internal flow voids, although flow voids may be seen at the periphery of some relatively vascular vestibular schwannomas. If in doubt, DSA will differentiate between glomus jugular and neural sheath tumors on the basis of relative vascularity.³ Other distinguishing features are the absence of vascular pedicle (s) and jugular bulb compression with neural sheath tumor.¹⁶

Table 35.1 Fisch and Mattox Classification of Temporal Bone Paragangliomas

Meningiomas

JF meningiomas are thought to arise from the arachnoid-lining cells of the jugular bulb within the jugular fossa.18 They are uncommon tumors and less than 100 cases of JF meningiomas have been documented.^18–20 They are defined as primary lesions (intrinsic lesions) when they are centered on the JF and secondary when centered in the posterior fossa with extension into the JF.¹⁹ Primary meningiomas of the JF are characterized by an invasive growth pattern with extensive skull base infiltration. Two growth patterns are recognized, centrifugal and en plaque. Centrifugal growth takes place in all directions and involves the middle ear, the jugular tubercle, hypoglossal canal, occipital condyle, and clivus. Extrinsic spread inferiorly into the nasopharynx and carotid space may be seen.³ Further spread superiorly along the intracranial dural reflections is characteristic of en plaque growth.¹⁶

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