Radiologic evaluation of the jugular foramen. Anatomy, vascular variants, anomalies, and tumors.

The jugular foramen varies considerably in size and shape, along with the jugular vein. The foramen is traversed by several vessels and nerves. CT, in various section planes, demonstrates the bone anatomy optimally, whereas MR (including MR angiography) reveals the vascular and soft tissue structures to best advantage. A diverse group of vascular anomalies originate in the foramen and adjacent carotid canal that must be differentiated from tumors. The most common tumor within the jugular foramen is the hypervascular glomus jugulare tumor followed by neurogenic tumors, predominantly the schwannoma. Less common lesions comprise meningioma, hemangiopericytoma, chondrosarcoma, and plasmacytoma. Metastases and malignant tumors arising in adjacent anatomic structures (nasopharynx, parotid, and temporal bone), in advanced stages, may spread to the jugular foramen. Endolymphatic sac tumors arise at the posterior medial aspect of the petrous bone and frequently extend to the jugular foramen. Irregular lytic bone destruction, with enlargement and hypervascularity, demonstrated by CT and MR imaging, are characteristic for glomus jugulare tumors. Benign tumors, most commonly the jugular foramen schwannoma, display an enlarged jugular foramen with well-defined bone margins.