Intratemporal Tumors of the Facial Nerve Workup

• 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.

• 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.

• 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.

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.