35 Once a mass is localized to the carotid space (also known as the poststyloid parapharyngeal space in the suprahyoid neck), the differential becomes narrow and relates to structures that occur within it. It contains mainly neural and vascular structures, including the structures within the carotid sheath, the carotid artery, the internal jugular vein (IJV), and the lower four cranial nerves. The sympathetic chain and phrenic nerve do not lie within the carotid sheath, but are considered within this “space.” Lymph nodes also lie in this region. Differential considerations for pathology include paragangliomas and nerve sheath tumors arising from lower cranial nerves or from the sympathetic chain. Nodal metastasis, abscess, and venous thrombosis are also differential considerations as well as an extracranial carotid artery aneurysm. Lesions such as schwannomas or paragangliomas, which arise in the carotid sheath, will be intimately related to the vessels and may involve or separate them in characteristic patterns, whereas lymph nodes generally displace the carotid and jugular vessels together. Paragangliomas are generally hypervascular and may have shunting with early draining veins. Features such as these can aid in the differentiation of these lesions (Table 35.1).
Carotid Space Masses
Paragangliomas
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