Difficult Decisions in Head and Neck Oncologic Surgery by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030151232
Publisher: Springer International Publishing

Vagal Schwannoma

Introduction

Schwannomas arising from the vagus nerve are rare. They may arise from the intracranial section or the extracranial section of the nerve.

Pure intracranial vagal schwannomas with no connection with the jugular foramen are extremely unusual with only six reported cases [37–39]. Intracranial schwannomas are typically located in the Jugular foramen and are classified into three types: Type A tumor, with primary intracranial involvement and minimal extension into the jugular foramen; Type B tumor, primary involvement of the jugular foramen with or without an intracranial component; Type C tumor, primarily extracranial with minimal extension into the jugular foramen. Most symptoms are not localized to the vagus nerve but tend to mimic those of an acoustic neuroma with decreasing hearing, vertigo and ataxia being the most common presentations. Occasionally, neurogenic hypertension consequent to hyperstimulation of the vagus nerve has been noted [37].

Extracranial Cervical Schwannoma arising from the vagus nerve presents as a benign nerve tumor in the parapharyngeal space. It typically occurs in adulthood and affects both genders equally. MR and FNAC are the evaluation methods of choice. On CT images, vagal schwannomas appear as well-defined masses, usually of higher attenuation than muscle on contrast-enhanced images. MR evaluation typically shows masses of intermediate signal on T1-weighted images and increased signal intensity on T2-weighted images with smooth, well-delineated margins and a homogeneous overall appearance (Fig. 17.2). Vagal schwannomas splay the common or internal carotid artery from the jugular vein, whereas schwannomas of the cervical sympathetic chain tend to push both the carotid artery and IJV anteriorly [40]. Glomus tumors may be reliably differentiated from Schwannomas by their vascularity, the salt and pepper appearance on MR consequent to its multiple vascular channels, and by the intense uptake on a DOTANOC Scan [25, 41–43]. Diffusion weighted MR imaging may further aid in this differentiation [7]. Current radiological sophistication can confirm the diagnosis with a fair degree of certainty and the same may be further supported by FNAC. Additionally, radiological assessment of the nerve of origin serves to prognosticate the risks of surgery. Associated malignancy or malignant transformation in Schwannomas is extremely rare.

Fig. 17.2Vagal Schwannoma—T1W Contrast MR (a) Axial sections, showing the hypointense lesion on left side separating the ICA and IJV. (b) Coronal sections, showing the same homogenous mass with fusiform tapering edges continuous with the X Cranial nerve and splaying the ICA and IJV

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