Intratemporal Tumors of the Facial Nerve 

Updated: Mar 11, 2016
Author: Jacek Szudek, MD, PhD; Chief Editor: Arlen D Meyers, MD, MBA 

Overview

Background

The most common tumors of the peripheral nerves are neuromas, which are defined as a growths or swellings on nerves. Neuromas may arise extrinsically or intrinsically. Primary intrinsic nerve cell tumors include schwannomas, which arise from Schwann cells that support the endoneurium, as well as perineuromas, which arise from cells that line the perineurium.

Fifty percent of all neuromas are found in the head and neck region. The vestibular schwannoma, also known as the acoustic neuroma, is the most frequent type of nerve cell tumor of the head and neck. Facial neuromas are extremely rare. The vast majority of facial neuromas are benign, although malignant schwannomas have occasionally been reported. Neuromas can be located intracranially, intratemporally, or extratemporally. One series of 600 temporal bones reported a facial schwannoma incidence of 0.8%.

See the image below.

A small acoustic neuroma within the internal audit A small acoustic neuroma within the internal auditory canal is easily observed on postgadolinium MRI.

Due to their low incidence, facial nerve neuromas are often misdiagnosed. Although they manifest distinctively, clinicians may still find the diagnosis difficult to establish. Patient history is usually the most reliable indicator of the presence of a facial nerve tumor. These tumors can manifest symptomatically during the early growth phase, depending on their location. Imaging studies may not reveal a tumor as a result of their small size, resulting in misdiagnosis and further loss of facial function.

Etiology

The vast majority of intratemporal facial nerve tumors are either schwannomas or hemangiomas. Schwannomas are far more common (comprising 64% of facial nerve tumors in one retrospective series) and may arise from any point along the course of the facial nerve. These tumors tend to involve multiple facial nerve segments. Some studies report the geniculate ganglion as the most frequently involved portion of the nerve. Unlike vestibular schwannomas, no genetic locus has been implicated in the pathogenesis of facial schwannomas.[1]

Hemangiomas of the temporal bone are extremely rare benign vascular tumors and, when present, often arise in the area of the geniculate ganglion, although they may also be present in the internal auditory canal. The rich blood supply around the geniculate and the Scarpa ganglia may predispose these locations to hemangiomas. Unlike facial schwannomas, facial hemangiomas are extraneural in origin. They grow very slowly and are most commonly found in middle-aged adults. They tend to cause compressive symptoms even when very small in size.

Other tumors, which are less frequently observed, include perineuriomas and malignant schwannomas. Meningiomas intrinsic to the geniculate ganglion and in the intratemporal segment of the facial nerve have also been reported. Middle ear carcinoma can present with sudden deafness or facial nerve paralysis.

Hematogenous metastasis can also manifest with facial nerve involvement, disruption of the nerve sheath, and facial nerve paralysis. In descending order of frequency, the following are the most common sites for metastasis:

  • The intracanalicular segment

  • Mastoid segment

  • Tympanic segment

  • Labyrinthine segment

Tumors that have been shown to hematogenously metastasize to the temporal bone include breast, kidney, lung, and stomach tumors.

The facial nerve itself also provides a route for the direct spread of neoplastic disease into the temporal bone. Parotid mucoepidermoid carcinoma and squamous cell carcinoma of the skin have the ability to spread perineurally via the facial nerve into the temporal bone. Benign pleomorphic adenoma of the parotid gland that circumferentially involved an intratemporal segment of the facial nerve has also been reported.

Popular concern exists that cellular phone use is associated with head and neck or brain tumors. To date, case control studies have failed to show an association between regular cellular phone use and intratemporal facial nerve tumors. However, a causal relationship cannot be excluded completely based on current data. Most cellular phone exposure is brief, so dose response effects have been difficult to establish. Also, cellular phone technology is relatively new. As lifetime exposure increases, larger more powerful studies may show more convincing results.[2]

Pathophysiology

Most symptoms of facial nerve dysfunction due to a neoplasm are caused by compression of the nerve secondary to tumor growth. Therefore, a relatively small tumor can become symptomatic if it arises within a narrow bony canal (eg, at the labyrinthine segment), while a more proximal tumor within the cerebellopontine angle can become quite large before causing symptoms.

In addition, hemangiomas can produce facial nerve paralysis even when they are too small (several millimeters in diameter) to cause nerve compression. Some have suggested that the hemangioma shunts blood flow away from the facial nerve segment, causing local ischemia and leading to paralysis.

A study by Doshi et al of 28 patients with facial nerve schwannomas found that the tumor most frequently affected the facial nerve segment running through the internal auditory canal (19 patients, or 68%). The investigators also found that 46% of patients had multisegmental schwannomas. Hearing loss and facial weakness were the most common presentations, with the latter being most frequently linked to labyrinthine segment involvement (89%).[3]

Presentation

Intratemporal facial nerve tumors typically manifest with one ore more of the following symptoms: facial weakness, hearing loss, tinnitus, unsteadiness, vertigo, or pain.

Facial weakness

The incidence of facial weakness at the time of presentation varies in the literature from 51-86%. Slowly progressive (more than 3 wks) facial nerve paresis, often preceded by facial twitching, is a common presenting symptom. Note that over 50% of the facial nerve may be destroyed before clinical effects become apparent. Facial nerve paralysis is most often seen with intratemporal tumors that involve the labyrinthine segment. Extratemporal parotid tumors may also present with facial paralysis, especially if they are malignant. Recurrent episodes of facial nerve paralysis should alert the clinician to the diagnosis of a facial nerve tumor. Approximately 5% of facial nerve palsies are caused by facial nerve tumors.

For most clinicians, a history of facial paralysis related by a patient immediately triggers thoughts of Bell palsy, rather than facial nerve tumors. Because Bell palsy remains the most common diagnosis for a rapid-onset lower motor neuron facial palsy, several salient features should be considered.

Bell palsy is considered a diagnosis of exclusion in otolaryngology. Unfortunately, this exclusion can take quite a while to establish. Familiarity with the common presentation of Bell palsy is essential. Presentation is a sudden onset of unilateral lower motor nerve facial palsy or paresis that occurs over the course of 24-48 hours. It is frequently preceded or accompanied by periauricular paresthesias or even otalgia, traditionally without vesicles. The emerging conventional wisdom implicates herpes viruses, varicella-zoster, or herpes simplex. Infectious processes such as otitis media or Lyme disease must be excluded.

In some cases, a viral prodrome exists, which commonly manifests as an upper respiratory infection or as flulike symptoms. Dysgeusia, hyperacusis, and facial numbness are commonly experienced. Approximately 85% of patients recover facial function to House-Brackmann grade I or II over the course of the subsequent 8-12 weeks. In contrast, neoplastic processes most commonly cause a gradual paralysis, which exhibits no recovery. Onset of paralysis exceeds 48 hours, frequently occurring over the course of weeks. No recovery is detectable to the patient months following initial symptoms. Steroid responsiveness, if initially effective in modulating the degree of paralysis, eventually disappears and should not enter into decision-making.

Hearing loss

Hearing loss was found to be present in 46-69% of patients with intratemporal facial nerve tumors. This loss may be sensorineural (SNHL) or conductive (CHL) in nature, depending on the tumor location. Tumors proximal to the geniculate ganglion, in the labyrinthine segment, may present with SNHL, tinnitus, or vertigo. Tumors in the horizontal segment may present with conductive hearing losses.

Indications

See Surgical therapy.

Relevant Anatomy

See Pathophysiology.

Contraindications

See Surgical therapy.

 

Workup

Laboratory Studies

See the list below:

  • Because the diagnosis of Bell palsy is one of exclusion, the astute otolaryngologist must rule out other causes of acute progressive facial nerve paralysis. Bell palsy does typically not present with hearing loss; the absence of hearing thus should alert the clinician to further investigate the possibility of a facial nerve tumor.

  • A detailed head and neck examination should be performed, with focus on certain physical examination findings.

  • Evaluation of facial nerve status

    • Have the patient repeat facial movements; assess for subtle asymmetry.

    • Observe for involuntary facial twitching.

    • Evaluate the eyelids: Ask the patient to close the eye; attempt to lift up the eyelid with your finger. Note any asymmetry between sides.

    • Evaluate for scleral show and corneal dryness. Referral to an ophthalmologist may be necessary.

    • Consider photographs.

    • Use an objective classification scheme, such as the House-Brackmann scale, to document the extent of facial weakness or paralysis.

  • Evaluation of the external, middle, and inner ear

    • Perform pneumatic otoscopy; observe for a possible mass.

    • Tuning fork examinations should be performed. The presence of conductive or sensorineural hearing loss should be documented.

    • Consider obtaining an audiogram, especially if the history or physical findings include hearing loss.

  • Evaluation of the neck

    • Pay particular attention to the parotid region. A mass may be present.

    • A thorough neck examination for adenopathy should also be performed.

Imaging Studies

See the list below:

  • CT scanning

    • High-resolution, thin-cut CT imaging of the temporal bone is believed to be superior to MRI for visualization of bony structures.

    • High-resolution CT imaging of the temporal bone with axial and coronal views can aid in localization of tumor margins and involvement or erosion of adjacent structures.

    • A tumor along the course of the intratemporal facial nerve does not have to be very large to be symptomatic. Additionally, nonspecific enhancement of the nerve is commonly observed. Therefore, by defining the bony anatomy, CT scanning can add confirmatory or exclusionary evidence of the presence of these tumors.

    • Bony spicules within hemangiomas are also sometimes noted, which may be helpful in differentiating these lesions from schwannomas.

  • Gadolinium-enhanced MRI of the posterior fossa and temporal bones

    • MRI is the criterion standard for assessing soft tissue, such as the facial nerve. It provides specific information regarding perineural invasion and soft tissue involvement.

    • Facial nerve neuromas can arise from any facial nerve segment. Therefore, all facial nerve segments should be imaged and studied in detail.

    • This study is helpful in determining whether a larger size tumor is present. Obtaining MRI is not necessary in every case of Bell palsy because MRI results do not change the initial management. However, if a tumor is suspected, perform MRI. Note that tumors of the intratemporal facial nerve might escape MRI visualization because of their size. The most common histopathologic types (schwannoma and hemangioma) appear as enhancing lesions on T1-weighted images.

    • Radiographically distinguishing between an intracanalicular seventh nerve tumor and vestibular schwannomas is often impossible. Frequently, this rare diagnosis is made intraoperatively.

Other Tests

See the list below:

  • Audiologic testing and immittance measures

    • A pure tone audiogram should be obtained.

    • Stapedial reflexes should be performed, although they are not always reliable indicators of distal facial nerve function.

  • Electroneuronography

    • Surgical intervention for facial nerve tumors is initiated once a patient's facial nerve function has deteriorated to the point at which the expected result would be nearly equivalent to the patient's current function (ie, House-Brackmann grade III or IV).

    • Because of this, serial electroneuronography (ENog) evaluations are helpful as a quantitative measure to augment the patient's self-assessment and the physician's observations.

  • Facial nerve action potential

    • Facial nerve action potential (FNAP) is a valid method for assessing facial nerve function waveform.

    • Facial nerve schwannomas are extremely slow growing and frequently present without facial dysfunction.

  • Photography

    • Photography of resting and dynamic facial nerve function also augments the physician's serial assessment of the deteriorating facial nerve.

    • Postoperative comparison is also made possible.

Histologic Findings

The 2 most common tumors found along the course of the intratemporal facial nerve are schwannomas and hemangiomas. Schwannomas are well-circumscribed, encapsulated masses that arise from Schwann cells. They tend to splay rather than to invade the nerve fibers. Surgical removal of these tumors while sparing the nerve is possible, with better results in terms of postoperative function. They are firm gray masses that may have areas of cystic and xanthomatous change. They are characterized by bland palisading cells with slender nuclei.

The 2 classic conformations are the Antoni A and Antoni B patterns. The Antoni A pattern demonstrates elongated cells with cytoplasmic processes arranged in fascicles in areas of moderate to high cellularity with little stromal matrix; the nuclear-free zones of processes that lie between the regions of nuclear palisading are termed Verocay bodies. In the Antoni B pattern, the tumor is less cellular with a loose meshwork of cells along with microcysts and myxoid changes. Because the tumor displaces the nerve of origin as it grows, silver stains or immunostains for neurofilament proteins reveal axons that are largely excluded from the tumor. These tumors are immunoreactive to S-100. Malignant change is extremely rare, although local recurrence can occur with incomplete resection.

Hemangiomas are highly vascular lesions that consist of endothelium-lined channels. These tumors are lobulated but unencapsulated aggregates of closely packed, thin-walled capillaries, usually blood filled, and separated by scant connective tissue stroma. The lumina may be partially or completely thrombosed and organized. Rupture of vessels causes scarring and leads to the occasional hemosiderin pigment. Because of the proclivity of hemangiomas to be found near the geniculate ganglion, neuronal cell bodies and bone fragments often accompany the histologic specimen.

Of note, a histological specimen from the mastoid segment that demonstrates fibroadipose tissue without nerve tissue indicates a facial nerve pseudocyst, which is treated with surgical excision.

 

Treatment

Medical Therapy

In patients without facial dysfunction, a conservative strategy consisting of clinical and radiological observation should be considered as a treatment option. When facial nerve paralysis has developed to a House-Brackmann grade of more than III, an immediate operation is recommended to obtain a good postoperative facial functional recovery. On the other side of this debate, some experts report early schwannoma resection with facial nerve preservation. Little data have been published on the use of radiotherapy to treat facial nerve tumors.

Surgical resection of facial nerve neuromas is also indicated when a large cerebellopontine angle tumor compresses the brainstem or results in hydrocephalus. Note that brainstem compression and hydrocephalus are far more common among cases of vestibular schwannoma rather than facial nerve tumors. Other operative indications include tumor invading the inner ear or suspicion of malignancy or neurofibromatosis 1.[4]

Surgical Therapy

Surgery is the preferred therapeutic modality for advanced schwannomas and hemangiomas of the facial nerve. The surgical approach depends on the anatomic location of the tumor, the extent of the tumor, and the hearing status in both ears. Timing of surgical intervention presents a thornier dilemma.[5]

Hemangiomas, with their proclivity to arise from the geniculate ganglion, are often confined to the middle cranial fossa and can therefore be removed via a subtemporal craniotomy. If the tumor extends laterally down the labyrinthine segment or along the tympanic segment of the facial nerve, a combined approach that incorporates a postauricular mastoidectomy may be necessary. A transmastoid approach is usually preferred. Since hemangiomas are extraneural, they can, if small, be removed while sparing the facial nerve.

Surgical removal of facial nerve schwannomas is approached similarly. These tumors are more likely to extend into the cerebellopontine angle and therefore may also reach a larger size before they become symptomatic. However, often the diagnosis of facial nerve schwannoma can only be made intraoperatively during removal of what had been regarded as a vestibular schwannoma.

In a retrospective study, Lahlou et al reported that of 19 patients who underwent surgery for intratemporal facial nerve schwannomas, postoperative facial nerve function was stable or improved in 57.9% of them and became worse in 42.1% them. Most of the patients had House-Brackmann grade III facial nerve function postoperatively, with none having grade V or VI. In addition, 52.6% of patients maintained stable postoperative hearing, with 10.5% of them experiencing an improvement.[6]

In a study of 17 cases of intratemporal facial nerve schwannoma, Lu et al found that stripping surgery removed the tumor completely in all patients, while leaving the nerve intact in 12 cases (70.6%). Six of these 12 patients (50%) experienced acceptable nerve recovery.[7]

In patients with residual or recurrent intracanalicular neuromas, the translabyrinthine approach is the preferred surgical route, allowing complete tumor removal; it may also be used for exposure of the intratemporal portion of the facial nerve for a hemihypoglossal-facial nerve anastomosis when a postoperative facial palsy exists. The facial nerve is exposed in its mastoid and tympanic parts, mobilized, and transected. Then, the long nerve stump is transposed into the neck and used for an end-to-side anastomosis with the hypoglossal nerve, although end-to-end anastomosis of distal facial nerve to its proximal counterpart is preferred with the removal of an intracanalicular residual schwannoma. Neurotization of the facial muscles through a nerve graft may be used when no distal trunk of the facial nerve is available for the anastomosis.

The translabyrinthine or transpetrosal route is useful for patients without useful hearing and a facial nerve neuroma in the internal auditory canal. In patients with useful hearing, a hearing-sparing approach (eg, middle fossa approach) is used. However, the middle fossa approach involves retraction of the temporal lobe.

Clinicians should beware that, although radiation doses delivered to middle and external ear structures are unlikely to contribute to post–gamma knife surgery complications, unexpectedly high doses may be delivered to sensitive areas of the intratemporal facial nerve. Rare cases of intratemporal facial nerve tumors are reported in the stereotactic radiosurgery literature. Therefore, data available are insufficient to determine whether this treatment modality is safe.

Preoperative Details

Follow-up and appropriate timing of intervention are the key issues in managing patients with intratemporal facial nerve tumors. If a 3-mm hemangioma is discovered at the geniculate ganglion, it may be amenable to being stripped off of the nerve such that the nerve is left intact, but often, the tumors are larger. Hemangiomas insinuate between the nerve fibers, making nerve-sparing dissection difficult. Schwannomas often are tightly integrated into the nerve such that no safe surgical plane is identifiable. Thus, removal of these tumors endangers nerve integrity and function.

Because of the high likelihood that the facial nerve will be resected along with the tumor, a primary anastomosis (for smaller tumors) or a cable graft (using great auricular nerve, sural nerve, most commonly) may be required. Because the best expected functional result with these nerve repair techniques rarely exceeds a House-Brackmann grade III paresis, intervention is timed such that facial nerve function has degenerated to worse than House-Brackmann IV or so. However, intervention should not be delayed past the point where motor endplates have atrophied.

Obviously, patients need close follow-up on an outpatient basis in the surgeon's clinical practice. Patients should understand the nature of their disease and the rationale behind the timing of intervention to be better able to incorporate those considerations into the decision-making process.

Finally, the decision on how to treat these patients should be individualized and based on initial facial function, growth rate, surgical experience, and informed patient consent.

Complications

Complications of surgery for facial nerve tumors are related to the surgical approach. For craniotomies, these complications include but are not limited to cerebrospinal fistula, seizures, hydrocephalus, meningitis, and possible loss of any and all neurologic functions. Complications of mastoid or translabyrinthine approaches include hearing loss, tinnitus, vertigo, infection, and hematoma. Discuss facial paralysis with the patient, so that expectations for functional recovery are realistic. Most patients who had worse than moderate facial palsy can expect no better.