Facial Nerve Schwannoma Extending to Jugular Foramen: A Case Report

Abstract

Facial nerve schwannoma (FNS) is a benign, slow-growing schwannoma that originates from Schwann cells. Facial nerve schwannoma is the most common tumor of the facial nerve but rare and only accounts for 0.15% to 0.8% of intracranial neurinomas. It may be manifested as asymmetric hearing loss, facial palsy, and hemifacial spasm. A 56-year-old woman was transferred to our department, because of pain behind the right ear and spasm of the right lateral muscle for more than 2 years and pulsatile tinnitus for half a year. Based on the preoperative medical history, physical signs, and auxiliary examination, it was diagnosed with jugular foramen (JF) space-occupying lesion. We removed the tumor through the infratemporal fossa type A approach and found that the tumor originated from the facial nerve. After the tumor resection, sural nerve transplantation was performed. The patient demonstrated postoperative facial palsy (House-Brackman grade VI) and was smoothly discharged after good recovery. Facial nerve schwannoma rarely invades the JF, and the most common tumor in the JF is the glomus jugular tumor, followed by the posterior cranial schwannoma. They have common symptoms, making it difficult to obtain a correct diagnosis. Clinical data, medical history, and auxiliary examinations should be carefully analyzed to avoid misdiagnosis or mistreatment. Infratemporal fossa type A approach is an effective method for treating FNS of JF.

Introduction

A 56-year-old woman presented with pain in the tip of the mastoid behind the right ear and right lateral muscle spasm for more than 2 years, and pulsatile tinnitus for half a year. Two years ago, the patient developed pain in the right mastoid region, accompanied by intermittent right facial spasm which lasted for about 10 seconds each time. Half a year ago, she developed right-sided pulsatile tinnitus, which was obvious in the right supine position. When pressing the tip of her right mastoid, she felt hearing loss in the right ear, accompanied by a sense of ear blockage, which could be relieved after release. On physical examination, forehead wrinkling, eye closure, and nasolabial fold depth were normal and symmetric functions. The posterior wall of the right external auditory canal was protruded, with the tympanic membrane unseen and the mastoid tender. Computed tomography (CT) of the temporal bone showed that the posterior wall of the external auditory canal was destructed by a lesion of soft tissue mainly located in the jugular foramen (JF), and that the bony plates of the sigmoid sinus and the posterior inferior wall of the tympanic cavity and the base of the styloid process were also damaged (Figure 1). On magnetic resonance imaging (MRI), they presented with equal signal in T1-weighted image (T1WI; Figure 2A), high in T2-weighted image (T2WI; Figure 2B), and marked contrast enhancement (Figure 2C and D). The tumor was removed through the infratemporal fossa type A approach (IFTA) with blind sac closure of the external auditory canal, closure of Eustachian tube, and abdominal fat obliteration.

Figure 1.

Axial (A) and coronal (B) computed tomography revealed the destruction of the posterior wall of the external auditory canal by a lesion of soft tissue density mainly located in the jugular foramen and also destruction of the bony plates of the sigmoid sinus and the posterior inferior wall of the tympanic cavity and of the base of the styloid process.

Figure 2.

Magnetic resonance imaging showed an equal signal in T1-weighted image (T1WI) (A), high in T2-weighted image (T2WI) (B) and marked contrast enhancement without “salt-and-pepper” appearance (C-D).

During the operation, we found that the tumor invaded the JF (Figure 3A) and involved the conical segment, vertical segment, part of the temporal segment of the facial nerve, jugular bulb, adjacent sigmoid sinus, and part of the internal carotid artery. The sternocleidomastoid muscle was cutoff at the attachment of the mastoid process. The posterior abdomen of the digastric muscle was cutoff at the crest of the digastric muscle. The internal jugular vein and internal and external jugular arteries were dissected. The internal jugular vein was ligated at the level of the transverse process of the atlas. The unclear boundary between the tumor and the facial nerve made it unable to separate the whole facial nerve sheath and nerve bundle, so the diseased tissue was cutoff at the horizontal segment of the facial nerve and the main trunk of the mastoid foramen. The bone groove was ground above the anterior wall of the external auditory canal, above the geniculate ganglion and below the stylomastoid foramen. The facial nerve was grafted with 10-cm sural nerve and placed in the bone groove (Figure 3B). The Eustachian tube was closed and the abdominal fat was taken to fill the surgery-left cavity. The patient was discharged smoothly after operation, and there were no other complications, except for facial paralysis (House-Brackman [H-B] grade VI). Facial nerve schwannoma (FNS) was confirmed in postoperative pathological report.

Figure 3.

During the operation, a reddish mass (arrow) protruded from the mastoid process into the jugular foramen (A). The facial nerve was grafted with 10-cm sural nerve (arrow) and placed in the bone groove (B).

Discussion

Schwannoma is the most common neoplasm arising from the facial nerve and can occur anywhere along the nerves. The geniculate ganglion is the most involved part, followed by cerebellopontine angle and internal auditory canal; geniculate ganglion; or tympanic, mastoid, and intraparotid segments. ¹ The size and location of the tumor decide the patient’s symptoms, including facial nerve paresis or paralysis, hearing loss, tinnitus, pain and vestibular symptoms, all nonspecific. ² The JF, a complex bony canal, transmits vessels and nerves (such as jugular bulb, internal jugular artery and vein, and posterior cranial nerve) from the posterior cranial fossa, through the skull base, and into the carotid space. ³ The most common tumor in the JF is hypervascular glomus jugular tumor, followed by posterior cranial neurilemmoma and meningioma. Most JF schwannomas (90%) originate from glossopharyngeal or vagus nerves. ⁴ The most common symptoms are pulsatile tinnitus, conductive hearing loss, and hoarseness. Facial nerve schwannoma at the JF share similar presentations with posterior cranial neurilemmoma or glomus jugular tumor. Therefore, adequate preoperative assessment is needed for differential diagnosis. In this case, the patient presented with hemifacial spasm and pulsatile tinnitus. In case of a tumor in the facial nerve canal, even a small one, the symptoms of facial nerve paralysis appear earlier and are more serious due to the narrow space of canal. ⁵ But if the enlarged tumor grows around the defect part of the facial nerve canal, and the symptoms of facial nerve paralysis may not appear early. When the tumor is located in the parotid gland without bone canal restriction, the symptoms of facial nerve paralysis generally appear late and are mild. ⁶ In this case, the tumor was located in the JF, and there was no facial paralysis before operation, which is consistent with the explanation of the literature. The possible mechanisms underlying pulsatile tinnitus include turbulences of blood flow, secondary symptoms of vascular stenosis, and increased blood flow, which can be caused by tumor involving jugular vein bulb. Differential diagnosis based on the patient’s symptoms seems difficult, yet, preoperative imaging examination can help to localize the tumor and provide qualitative and differential diagnosis.

Imaging examination showed that this case conformed to the general characteristics of schwannoma: expansive destruction of temporal bone on CT rather than lytic. ⁷ On MRI, it showed low signal intensity on T1WI and high signal intensity on T2WI without flow void effect. This case was differentiated from glomus jugular tumor. On CT, glomus jugular is tumor presents a “moth-eaten” pattern destruction of the temporal bone, which is strongly and inhomogeneously enhanced with contrast medium. On MRI, its vascularity is manifested by obvious flow voids, resulting in the typical “salt-and-pepper” appearance.

The optimal treatment strategy for FNS remains controversial. Some scholars have reported that conservative treatment may be a choice for patients with few symptoms, small lesions, and no brainstem compression, due to the slow growth of the tumor (2.0 mm/years). ⁸ Although some others believe that surgical resection is appropriate and should be performed promptly after diagnosis. ⁹ Tumor growth can cause local nerve degeneration and regeneration, leading to unsatisfactory functional and cosmetic results after nerve reconstruction. Stereotactic radiotherapy is also an alternative treatment, but it is mostly used in patients with small tumors and facial nerve function graded as H-B Grade I-III. ¹⁰ For patients with poor facial nerve function (H-B Grade IV-VI), mass enlargement with compression symptoms or failure of stereotactic radiotherapy, complete tumor removal with nerve sacrifice followed by great auricular or sural nerve grafting is recommended. ¹¹ However, H-B Grade III is the best that could be achieved after facial nerve anastomosis. ¹² In this case, the patient suffered no obvious preoperative facial paralysis, but her life quality was seriously affected by pulsatile tinnitus. The tumor was large enough to invade the JF area. Surgical resection was considered because conservative treatment could further destroy the skull base, and the symptoms of cranial nerve compression might appear.

According to the preoperative evaluation of the location and involvement of the tumor by CT and MRI of the temporal bone, we chose IFTA for the following reasons: (1) FNS invading the JF was rare. Although preoperative auxiliary examination showed no characteristic changes in glomus jugular tumor, the possibility could not be completely excluded. (2) The tumor invaded part of the jugular bulb and there was a risk of massive bleeding after tumor resection.

Infratemporal fossa type A approach described by Fisch focuses on JF and is accepted as an established method for tumor treatment in this region. This approach affords excellent exposure of the infralabyrinthine region as well as the middle ear and the neurovascular structures in the neck. ¹³ If the jugular bulb ruptures, the internal jugular vein can be ligated to control the bleeding. Because the jugular bulb was invaded by tumor in this case, internal jugular vein was ligated at the level of the transverse process of the atlas and the tumor was resected en bloc. Since the tumor involved the pyramidal segment, vertical segment, and part of the external temporal segment of the facial nerve, which had no obvious boundary with the facial nerve, it was difficult to remove the tumor completely and maintain the integrity of the facial nerve. Hence, we resected the facial nerve from the geniculate ganglion to the extratemporal segment, with a sural nerve interposition graft repair. The sural nerve could meet the repair of facial nerve defect of any length because a long length of it could be harvested. Studies have shown that nerve function recovery after facial nerve reconstruction depends on the severity of nerve injury and the interval between nerve injury and operation. ¹¹ More severe facial nerve injury (less functional nerve fibers) is associated with poorer postoperative recovery. The postoperative recovery of facial nerve injury within one year was significantly better than that of more than one year. ¹⁴ The patient in this case is being followed up after the operation, and the local tumor control and facial nerve function are being observed.