A 52-year-old man presented after a fall with a questionable history of loss of consciousness. Urine toxicology was positive for cocaine. A trauma imaging work-up revealed a nondisplaced occipital fracture, bilateral frontal parenchymal hemorrhages, and possible subarachnoid hemorrhage. An incidental finding was identified on a computed tomography angiogram (CTA) of the neck (Figure 1).
Enhancing carotid space mass
Carotid body paraganglioma
Glomus vagale paraganglioma
Carotid space schwannoma
The carotid space extends from the aortic arch to the skull base and traverses the suprahyoid and infrahyoid neck to enter the anterior mediastinum. Structures normally contained within the carotid space include the carotid artery, internal jugular vein, sympathetic plexus, vagus nerve, lymph nodes, and the congenital remnants of the second branchial cleft—all of which may lead to pathology. An enhancing mass in the carotid sheath located between the carotid artery and the internal jugular vein excludes a lymph node, which is typically found lateral to these vessels rather than between them. Brachial cleft cysts are classically cystic and nonenhancing structures. An enhancing lesion, therefore, is more suggestive of a mass arising from one of the neural structures. In this case, the most likely differential considerations include paragangliomas (e.g., carotid body tumors and glomus vagale tumors), as well as vagal nerve schwannoma. Imaging distinction between paragangliomas and nerve sheath tumors is important, since biopsy of highly vascular paragangliomas is not typically recommended.
Carotid body tumors (CBTs) are the most common head and neck paragangliomas. They are highly vascular lesions derived from neural crest cells located at the carotid bifurcation. They feature characteristic splaying of the internal and external carotid arteries (ICA and ECA, respectively), described as the lyre sign.1 Though CBTs are usually asymptomatic, they can present as slow-growing, pulsatile rounded neck masses anterior to the sternocleidomastoid at the angle of the mandible at the level of the hyoid bone. Involvement of the cranial nerves that travel through the carotid sheath (the glossopharyngeal, vagus, accessory, and hypoglossal nerves) can lead to associated signs and symptoms including dysphagia, hoarseness and shoulder drop.2 Catecholamine-secreting CBTs are rare but may be related to chronic hypoxia in some patients.
On contrast-enhanced CT, the carotid body tumor appears as an avidly enhancing hypervascular mass at the carotid bifurcation with splaying of the ECA anteriorly and ICA posteriorly. Dynamic enhancement is rapid compared to nerve sheath tumors. CTA demonstrates the relationship of the mass to the carotid arteries, while MRI is considered the best diagnostic modality for CBTs, better delineating the mass from surrounding soft tissue. MRI can detect tumors as small as 0.8 cm; tumors over 2 cm may demonstrate serpentine or punctate vascular flow voids (“pepper”) on T2 MR sequences, corresponding with vascular structures.3 The ascending pharyngeal artery is the typical arterial feeder. Arteriovenous shunting may be seen on angiography.
Surgical excision is the treatment of choice with preoperative embolization of larger lesions. Preoperative angiography can provide a vascular roadmap for the surgeon, allow embolization for prophylactic hemostasis, and aid in the evaluation of collaterals. Surgical outcome is related to the Shamblin classification of CBTs, which predicts tumor resectability and vascular morbidity. MRI findings can be used to predict the Shamblin surgical classification by noting the degree of contact of the tumor relative to the ICA with regard to < 180°, between 180° and 270°, and > 270°; additionally, vascular splaying > 90° indicates a less easily resectable tumor.4
Carotid body tumors (CBTs) may be associated with multiple syndromes, both familial and sporadic, including the paraganglioma syndromes, multiple endocrine neoplasia syndromes (MEN), and von Hippel-Lindau syndrome.5 Approximately 5%-10% of CBTs are bilateral, especially when in conjunction with an inherited syndrome. Imaging surveillance with MR is recommended in cases of familial disease.
Glomus vagale tumors are paragangliomas that occur along the path of the vagus nerve and are the least common of the head and neck paragangliomas. The key distinction between glomus vagale tumors and carotid body tumors is their relative location in the neck, with glomus vagale tumors arising slightly more cephalad. They often present as a painless mass behind the carotid arteries and nearly half of patients demonstrate vocal cord paralysis.2
Contrast-enhanced CT demonstrates an intensely vascular, enhancing mass displacing the ICA and ECA anteriorly and the internal jugular vein posteriorly. As with CBTs, conventional angiography may reveal arterial feeders from the ECA, particularly from the ascending pharyngeal artery. However, as with CBTs, MRI is considered the most important imaging modality, similarly demonstrating high signal intensity with multiple flow voids on T2.2
Schwannomas are slow-growing, usually benign tumors that arise from the Schwann cells of peripheral nerve sheaths. Unlike neurofibromas, they are intimately associated with their nerve origin. In contrast to paragangliomas, which have a higher prevalence in women, schwannomas do not show any sex predilection.2 Vagal nerve schwannomas may be difficult to discern from paragangliomas, as they can arise in similar locations with similar presentations. Hoarseness is the most common symptom, but in some cases, a paroxysmal cough may be elicited by palpating the mass—a clinical sign unique to vagal schwannomas.2
MRI is of greatest value in evaluating the relationship between the tumor and the carotid artery and jugular vein. Such a distinction is critical in discerning vagal schwannomas from the similarly appearing schwannomas of the sympathetic chain. Vagal schwannomas displace the internal jugular vein (IJV) laterally and the carotid artery medially, whereas schwannomas from the cervical sympathetic chain displace both the carotid and IJV without separating them.2 The characteristic neovascularity and “salt and pepper” pattern of hyperintense tumor with foci of hemorrhage (salt) with hypointense flow voids (pepper) typical of paragangliomas are absent in schwannomas.2
Carotid body tumor
When presented with an enhancing carotid space mass, imaging is the primary diagnostic work-up, since biopsy of a highly vascular tumor is not recommended. Contrast-enhanced CT readily identifies an enhancing neck mass; the pattern of vascular displacement or splaying may suggest a particular diagnosis. MRI is the modality of choice, however, in differentiating paragangliomas, which often demonstrate the characteristic “salt and pepper” appearance when large, from nerve sheath tumors. The presence or absence of neovascularity and vascular shunting is also helpful. Knowledge of these imaging characteristics is critical to render an accurate diagnosis and guide appropriate management for a patient with an enhancing carotid space mass.
Enhancing Carotid Space Mass. J Am Osteopath Coll Radiol.