CASE 18266 Published on 18.08.2023

Carotid Space Cranial Nerve Schwannoma: A rule-out diagnosis

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Gian Marco Frigerio1,2, Caterina Giannitto1,2, Giorgia Carnicelli1,2, Stefano Lusi1,2, Federica Fici1,2

1. Department of Biomedical Sciences, Humanitas University, Pieve Emanuele- Milan, Italy
2. Department of Radiology, IRCCS Humanitas Research Hospital, Rozzano-Milan, Italy

Patient

55 years, female

Categories
Area of Interest Head and neck ; Imaging Technique CT, MR
Clinical History

A 55-year-old-woman, who presented with a slowly enlarging, non-painful right neck mass, without other associated symptoms. She had neither relevant pathologies nor other palpable mass lesions.

Imaging Findings

Initial CECT revealed a well-circumscribed, low-density carotid space fusiform mass with a faint internal enhancement that increases in the late-phase contrast. External and internal carotid arteries were bowed over anteromedially by the encapsulated mass, whereas the internal jugular vein was stretched posteriorly. The lesion displayed the parapharyngeal space fat anteriorly and posterior belly of digastric muscle laterally, thereby locating at the oropharyngeal level. Further, MR showed no inner high-velocity flow voids on T1WI, conspicuous hyperintensity on T2WI and patchy enhancement on T1WI C+FS.

Discussion

Background

Carotid Spaces Cranial Nerve Schwannomas are rare benign encapsulated tumours of Schwann cells that wrap around their parent nerve. Although all the final four cranial nerves could be involved, vagal schwannomas are the most common. Neurofibromatosis type 2 could be associated.

Clinical Perspective

Typically, the patients are middle-aged old with an asymptomatic palpable cervical mass. If present, symptoms are nonspecific and due to local mass effect rather than dysfunction of the nerve they arise from (exceedingly rarer), such as dysphagia, hoarseness, sore throat, and sleep apnoea. Moreover, clinical symptoms more common with neurofibromas than schwannomas.

Imaging Perspective

CECT is often the 1st exam of evaluation followed by MR. CECT is useful for depicting vascularisation and bone and vascular relation but is quite unsatisfactory in the delineation of the internal structure. At the same time MR image is often degraded by swallowing, coughing and breathing. Therefore, in selected compliant patients, it’s possible to renounce CECT in favor of MR, adding 4D time resolve MR sequence for the vascular study.
The cranial nerve schwannoma presents as ovoid to fusiform enhancing mass displacing carotid artery anteromedially and jugular vein posteriorly (the displacement,
without separation, of both carotid arteries and internal jugular vein, is typical of sympathetic chain schwannoma).

Since they are masses of the carotid space, they displace the parapharyngeal fat anteriorly. When they are located at the nasopharyngeal level, the anterolaterally displacement of the styloid process is typical, whereas the lateral displacement of the posterior belly of the digastric it’s an important clue for the oropharyngeal schwannoma. On MR, the best diagnostic clue is the lack of high-velocity flow voids in T1WI that differentiate them from the glomus vagale paraganglioma. Moreover, if large, intramural cysts may be present. Quite heterogeneous enhancement is typical of schwannoma. The exact cranial nerve involved is not certainly identifiable at imaging [1,2,3]. In this case, at surgery was evident the involvement of the descendent branch of the hypoglossal nerve (XII nc).

Outcome

Gross total resection of the mass with the preservation of the parent nerve is the treatment of choice. This strategy is not free of postoperative complications such as hoarseness and/or swallowing difficulties, therefore, watch-and-wait is a frequently followed strategy as patients tend to be asymptomatic [4].

Teaching Points

When approaching a carotid space mass, always look for the displacement pattern of the surrounding structures, for the presence or not of the high-velocity flow voids on T1WI (to differentiate paragangliomas from schwannomas), and for the target sign on T2WI (to differentiate neurofibromas from schwannomas).

Differential Diagnosis List
Carotid Space Cranial Nerve Schwannoma
Carotid Body Paraganglioma
Glomus Vagale Paraganglioma
Carotid Space Neurofibroma
Sympathetic Schwannoma
Final Diagnosis
Carotid Space Cranial Nerve Schwannoma
Case information
URL: https://www.eurorad.org/case/18266
DOI: 10.35100/eurorad/case.18266
ISSN: 1563-4086
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