Contrast-enhanced computed tomography (CT) , magnetic resonance imaging (MRI) , and angiography are usually required for adequate diagnosis, localization, and evaluation of extension patterns of jugular foramen tumors. High-definition CT scan with thin section of temporal bone is the best resource to differentiate glomus jugulare tumors from glomus tympanicum [1]. Glomus jugulare erodes jugular fossa and glomus tympanicum occupies middle ear. Jugular paragangliomas erode bone, glomus tympanicum arises from the cochlear promontory and usually does not destroy the ossicular chain. Thin CT scans (13 mm) performed with a detailed bone algorithm and coronal reconstruction gives detailed information of cranial base bone structures, bone erosion, tumor calcification, and hyperostosis (Fig. 6.1). The bony margins of the tumor are irregularly eroded with a “mouth-eaten” pattern . It also provides information about the position of the jugular bulb and jugular foramen, and the enlargement of the canal, which usually appears as a sharp, rounded shape with sclerotic rims (bone scalloping). CT is useful in differentiated schwannomas, meningiomas, aneurysmatic bone cysts, and chondrosarcomas. Schwannomas typically promote smooth erosion of jugular foramen, paragangliomas tend to erode irregularly the margins and destroy the jugular spine and caroticojugular spine (Fig. 6.2). Meningiomas may be difficult to distinguish from schwannomas, and frequently invade the bone causing hyperostosis and calcifications (Fig. 6.3). Other bony structures of the middle ear, mastoid (facial nerve canal), internal auditory canal, and high cervical spine are adequately studied with thin CT scans.

Diagnostic MR imaging, with its multiplanar capabilities and gadolinium (Gd), is very useful to demonstrate the characteristics of tumor, its vascularization, extension, and relationship with neighboring structures. MRI is superior than CT scans in determining tumor vascularity, intracranial extension, extension along vessels, nerves and skull base structures, the presence of other tumors (multifocality and multicentricity), and relationship with brainstem. Tumor extent may be overestimated on T1WI [2]. Paragangliomas are usually hypointense on T1WI (Fig. 6.4). These highly vascularized lesions, with pronounced heterogeneous gadolinium enhancement (Fig. 6.5), present characteristic vascular flow voids patterns with “salt and pepper” characteristics (Fig. 6.6). The “pepper” component are the multiple areas of signal void and the “salt” component are hyperintense foci produced by slow flow or subacute hemorrhage on both long TR and short TR images [3]. MRI shows the vascular nature of these lesions, low signal areas characteristic of rapid arterial and venous blood flow were present in the matrix of these tumors on both T1 and T2WI. Other tumors like schwannomas have a less vascular appearance in their internal matrix [4]. Paragangliomas of jugular foramen may cause occlusion of jugular vein and sigmoid sinus, intracranial extension through an eroded jugular foramen, invasion of fallopian canal, and involvement of the internal carotid artery, middle ear, mastoid, and structures in the neck. All these extensions can be demonstrated with high field MRI. This examination method can also diagnosis the presence of a glomus vagal tumor and differentiate a glomus tympanicum from glomus jugular. Jugular foramen paragangliomas are the only tumors at the cranial base that present the “dropout” phenomenon (seen in time-intensity curves) after intravenous injection of high-dose gadolinium (0.3 mmol/kg) [5].

In non-enhanced CT images, schwannomas are isodense to the brain parenchyma. The smoothly scalloped well-corticated enlargement of the jugular foramen contrasts to the mouth-eaten pattern seen with paragangliomas [6]. Schwannomas of jugular foramen have the same characteristics as other intracranial schwannomas on MRI, are smooth contoured masses, iso-intense on T1WI, and high signal intensity on T2WI (Fig. 6.7) [7] that gradually enlarges the jugular foramen by pressure erosion and gives an expanded and scalloped but well-defined corticate margin to the jugular foramen. These tumors present moderate to significant homogenous gadolinium enhancement (Fig. 6.8). They may be cystic, with no flow void characteristic of paragangliomas and other highly vascular tumors observed. They may present a large posterior fossa mass (Fig. 6.9) and a dumbbell extension into the high cervical region. Calcifications are rarely seen and jugular foramen schwannomas do not invade the lumen of the internal jugular vein and jugular bulb. These tumors may occlude these structures by compression. Jugular foramen chondromas may also be misdiagnosed with schwannomas. These very rare tumors present homogeneous enhancement on MRI (Fig. 6.10).