Hypoglossal Nerve Schwannoma at the Carotid Bifurcation: An Unlikely Discovery

Background/Objective: Schwannoma of the hypoglossal nerve (HNS) is a rare event, with ~40 extracranial tumors identified in the literature. Most have been characterized in the parapharyngeal space or submandibular triangle. To our knowledge, prior to this report only one HNS at the bifurcation of the carotid system has been described. Symptomatology varies and can include a palpable neck mass, neck pain, dysphagia, tongue weakness, tongue fasciculation and tongue atrophy. Paramount to developing and narrowing a differential diagnosis is obtaining and carefully reviewing head and neck imaging, which often includes an MRI with contrast. These lesions are typically characterized by a smooth, encapsulated appearing mass that are relatively homogenous and enhance after contrast administration. However, as seen in our case, symptomatology and radiographic features may overlap with other lesions seen in the area, such as carotid body tumors, other paragangliomas, or schwannomas. Considering all these options helps drive work-up, and peri-operative discussion of possible outcomes/deficits with patients.

Design: Single case report.

Setting: Single tertiary academic referral center.

Participant(s): An isolated case report.

Main Outcome Measures: Case presentation.

Results: A 33 year-old Caucasian female presented to our institution for management of known multiple sclerosis. She had numerous MRI’s of the head over the past several years. During a recent study, a neck mass was identified and she was referred to both our department of the department of neurologic surgery. She presented with complaints of neck discomfort, a palpable neck mass, intermittent otalgia, and mild dysphagia. Her exam was significant only for a neck mass in level II, in the area of the carotid bifurcation. The mass was mobile in the transverse dimension, but not in the cephalocaudal. She had no sign of cranial neuropathy on complete head and neck examination including endoscopy. Review of her imaging revealed a 1.8 X 3.7 cm well-circumscribed mass at the carotid bifurcation, causing lateral splaying. The mass was heterogenously enhancing, with a “salt and pepper” appearance. She was therefore counseled that this was likely a carotid body paraganglioma and was referred to Endocrinology for functional work-up. Due to growth over time and her young age, she was counseled regarding surgical removal. Operative findings revealed a vascular, flesh-colored mass centered at the carotid bifurcation, clearly pedicled on the hypoglossal nerve and separate from the carotid system. Initial attempts at resection with nerve preservation were unsuccessful, and the mass the extirpated with a segment of nerve. Intra-operative and permanent pathology revealed schwannoma with negative proximal and distal nerve margins. She has had mild dysarthria but otherwise has done well in short-term follow-up.

Conclusions: Our case demonstrates the importance of recognizing the overlap in symptomatology and radiographic features between paragangliomas and schwannomas in the upper neck. Armed with a broad differential, we are more equipped to make management decisions in the operating room and have a greater likelihood of accurately describing possible functional outcomes/expectations for our patients. Cervical HS can be easily managed with gross-total resection.