Case report of a giant cell tumor of the carotid sheath

Giant cell tumor of the soft tissue (GCTST) is a neoplasm with low malignant potential and typically affects the trunk and extremities. Herein, we present a case of a palpable right neck mass diagnosed as a GCTST of the carotid sheath in a 38-year-old woman. A review of the imaging characteristics as well as of the differential diagnoses of primary neoplasms of the carotid space is presented.


Introduction
Giant cell tumor of the soft tissue (GCTST) is an extremely rare tumor that is considered as either a giant cell variant of malignant sarcoma or a soft tissue equivalent of a giant cell tumor of bone. This sort of tumors are typically found in the extremities with the femoral bone being the most common location (80%-90%) [ 1 ,2 ]. Although they are considered to be benign, there have been reports of metastasis and local recurrence in the literature [1] . Herein, we present a case of giant cell tumor of soft tissue in the neck region that originated from the carotid sheath treated with embolization.
✩ Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. * Corresponding author.

Case report
A 38-year-old woman presented with a painless right-sided neck mass (     the patient underwent angiography and embolization of the vascular mass ( Fig. 3 ). Surgical excision of the mass was performed, and the tumor demonstrated a nodular spindle cell proliferation with scattered giant cells ( Fig. 4 A). There was no significant atypia. Immunostains were positive for CD68 in the giant cells ( Fig. 4 B). These findings supported a diagnosis of giant cell tumor of soft tissue. The patient suffered no ill effects from the procedure and is recurrence-free 30 months following excision ( Fig. 3 ).

Discussion
GCTST of the carotid sheath is scarce, this is only the second case reported in literature of this tumor in the carotid sheath. These tumors are rare and composed of multinucleated giant cells and initially, they were thought to be identical to their bony counterparts; however, recent genetic analysis of the Gly34 codon of the H3F3A gene suggests that they may be pathogenically distinct [3][4][5][6][7] . To date, approximately 71 cases of giant cell tumor of soft tissue have been reported, and they have been shown to exist on a spectrum from benign to malignant, with local recurrence being reported in between 6.2%-25% of cases [8][9][10][11][12] . Primary neoplasms of the carotid sheath typically have a narrow range of differential diagnoses that include carotid body tumors (CBTs), glomus vagale, nerve sheath tumors such as schwannomas and neurofibromas, as well as metastatic lymphadenopathy and lymphoma ( Table 2 ).
CBTs, paragangliomas located at the carotid bifurcation, can present as slow-growing, pulsatile masses and may involve cranial nerves. They typically splay the internal and external carotid arteries, and catecholamine secretion, although rare, can lead to hypertensive urgency. CBTs are associated with multiple endocrine neoplasia and von Hippel-Lindau and are the most common head and neck paraganglioma [ 13,14 ].
Glomus vagale, another possibility, refers to paragangliomas of the neck that occur along the vagus nerve and tend to arise more cephalad than CBTs. These tumors often present with vocal cord paralysis due to impairment of the recurrent laryngeal nerve. Glomus vagale is the least prevalent of the primary carotid sheath neoplasms.
Nerve sheath tumors, including schwannomas and neurofibromas, are slow-growing, usually benign tumors of peripheral nerve sheaths that can cause a paroxysmal cough that may be elicited by palpating the mass. Vagal schwannomas displace the internal jugular vein and the carotid artery. Schwannomas are typically T2-hyperintense and do not demonstrate the "salt and pepper'' signal intensity pattern on MRI. Neurofibromas may be more heterogeneous, may demonstrate central T2 hypointense (target sign), and are more likely to be central and inseparable from the nerve. Last, malignant peripheral nerve sheath tumors are often larger, more ill-defined, and painful [15] .
When considering metastatic lymphadenopathy and lymphoma as potential differential diagnosis, additional considerations should be taken into account. Metastatic disease can have varied signal intensity characteristics, while lymphoma will typically be T2-hypointense, diffusion restricting, and avidly enhancing.
Aneurysms (patent or thrombosed) and thrombosed veins may occur in this location, and signal intensity, enhancement, and flow characteristics would vary depending on the degree of thrombosis. Lesions would also be inseparable from the parent vascular structure.

Conclusion
Giant cell tumor of the soft tissue can occur in the carotid sheath and should be considered as part of the differential particularly when imaging characteristics do not follow that of other, more common carotid sheath neoplasms.

Author contributions
Junjian Huang -Initial manuscript preparation Jason Newman -Performed excisional surgery Bryan Pukenas -Performed embolization Apoorva Kotha -manuscript preparation Michael Husson -Performed pathology interpretation, manuscript preparation Linda Jane Bagley -Performed imaging interpretation and initial manuscript preparation.

Human and animal rights
Not applicable.

Patient consent
Informed consent was obtained from the patient as part of care at the University of Pennsylvania Health System.