Etiology

In general, for tumors of the skull base, neck and spine, diagnosis can best be determined by plain radiographs and CT to delineate the extent of bony involvement; by MRI for the extent of soft tissue involvement, which may include cranial nerve or spinal cord compression, as well as enhancement patterns and signal characteristics; and finally by biopsy for definitive histopathological diagnosis. Angiography can demonstrate the pattern and extent of vascularity and provide presurgical identification of the relationship of the tumor blood supply to that of the surrounding structures, cranial nerves, and spinal cord. For an adequate assessment of tumor vascularity, several things must be considered. For glomus tumors of the skull base and neck, specific imaging of the external carotid artery must be done, as this is the most common blood supply. For tumors of the spine, the segmental arteries on both sides must be catheterized at least two levels above and below the level of the tumor. For tumors of the cervical region, the vertebral arteries, external carotid arteries, thyrocervical and costocervical trunks, and the supreme intercostal arteries must also be catheterized and studied. In the lumbosacral area, both iliac arteries and the median sacral artery must be catheterized and studied. Radiographic identification of each of the six specific tumors will be discussed below within each subsection.

Glomus Tumors

Glomus tumors, which are part of the paraganglioma family of tumors, are rare hypervascular tumors that typically occur in three areas: the middle ear (glomus tympanicum), jugular foramen (glomus jugulare), and skull base (glomus vagale). These tumors are thought to arise from chemoreceptor organs derived from the neural crest. Glomus jugulare tumors are thought to originate from the chief cells of the paraganglia, or glomus bodies, located within the jugular bulb adventitia. Other locations occur when the tumor is associated with either the auricular branch of the vagus nerve (glomus vagale) or the tympanic branch of the glossopharyngeal nerve (glomus tympanicum). Glomus tumors are found most commonly in women during the fifth and sixth decades and have an estimated annual incidence of 1 in 1.3 million people. Although most glomus tumors are thought to be sporadic, familial inheritance (autosomal dominant and incomplete penetrance) does occur in 25%–50% of cases. Tumors develop almost exclusively in the children of disease-gene-carrying males. Due to the tumors’ slow-growing nature, the clinical presentation is often indolent and delayed. The most common presentations are usually related to the location of the tumor, that is, conductive hearing loss and pulsatile tinnitus for glomus tympanicum, jugular foramen syndrome (paresis of cranial nerves IX-XI) for glomus jugulare, and hoarseness and dysphagia for glomus vagale.

All common imaging modalities may show changes related to the location of the glomus tumor. Plain X-rays may show asymmetric sizes of the middle ear or jugular foramen. CT scans of the skull base will usually demonstrate the extent of bone thinning or bone erosion around the mass lesion. MR images are classically described as having a “salt and pepper” appearance, as the imaging characteristics involve heterogeneous signal intensity on both T1- and T2-weighted sequences with and without contrast.

Hemangioblastomas

Hemangioblastomas are histologically benign tumors located predominantly in the posterior fossa and the cervicothoracic spinal cord. These tumors are composed of densely packed capillaries with intervening stroma and may be confused histopathologically with renal cell carcinoma. Hemangioblastomas compose approximately 2% of spinal cord tumors and are associated with von Hippel Lindau (VHL) disease in approximately 20% of the cases. These lesions often present as a mural nodule with a large cystic component, which may manifest with pain, sensory disturbance, and myelopathy. In cases of VHL, it is important to note that not all lesions necessarily progress. Consequently, strong consideration for treatment should be reserved for symptomatic lesions.

These lesions are most often characterized with MRI. T1-weighted MRI demonstrates an isointense nodule that enhances brightly with gadolinium contrast; T2 may demonstrate vascularity in the form of flow voids and/or an associated cyst or syrinx. Angiographically, a well-circumscribed, hypervascular mass is usually associated with a single feeding artery that arises from one of the posterior spinal arteries, although deep intramedullary lesions may also receive blood from the sulcocommissural branches of the anterior spinal artery. Hemangioblastomas opacify in the arterial phase and drain quickly but can be differentiated from AVMs by the absence of arteriovenous shunting.