Skull Base Tumor and Other CPA Tumors Treatment & Management

Diuretic therapy may provide symptomatic relief in a minority of patients with arachnoid cysts. Otherwise, options for management of lesions in the cerebellopontine angle (CPA) include observation with serial imaging, radiation therapy, or surgery. Chemotherapy is an option only for occasional malignant lesions. Therapeutic embolization for vascular tumors has had limited success.

A study by Tan et al indicated that patients with small vestibular schwannomas can be managed with a watch, wait, and rescan approach, with 67.3% of these individuals not exhibiting growth over a 5-year period. The report found that if serial scanning reveals that small tumors have grown by over 2 mm, radiotherapy can provide good tumor control, with such management controlling 95% of these cases in the study. The investigators also determined that microsurgical excision by the translabyrinthine route resulted in a radiologically clear resection in 93% of individuals with larger vestibular schwannomas (over 20 mm in size). ^[6]

Surgical approaches vary depending on the pathologic entity, as well as the size and involvement of adjacent structures. Although complete excision is planned for most cases, the intimate involvement of surrounding structures may impose unwarranted morbidity if complete excision is attempted. Meningiomas are excised completely more readily than epidermoids, whereas adequate therapy for arachnoid cysts is drainage. ^[1]

Standard approaches to the CPA include the translabyrinthine, suboccipital (retrosigmoid), or middle fossa craniotomies (see Skull Base, Acoustic Neuroma (Vestibular Schwannoma)). The choice of approach is based on specific location and hearing status. Occasionally, these craniotomies can be combined or performed in addition to an infratemporal fossa dissection for larger tumors. ^[7]

See the list below:

• Neurotologic evaluation

  • Obtain a patient history as it relates to presenting symptoms.

  • Perform a complete physical examination including cranial nerve and cerebellar testing.

• Audiologic testing

  • Testing most commonly reveals high-frequency sensorineural loss.

  • Flat mid- and low-frequency sensorineural losses have been described.

  • Speech discrimination is usually diminished out of proportion to degree of loss on affected side.

  • Little relationship exists between severity of hearing loss and size of lesion.

  • Conductive loss occurs with middle ear involvement of facial nerve schwannomas or paragangliomas.

• Auditory-evoked brainstem response (eg, ABR, BAER)

  • Abnormal I-V interpeak latencies, a significant interaural latency difference for wave V, and poor waveform morphologic characteristics are suggestive of retrocochlear pathology on ABR.

  • Preoperative assessment is required when hearing preservation surgery is to be attempted.

• Vestibular testing

  • Testing may be helpful in patients presenting with vestibular symptoms.

  • Abnormal electronystagmography (ENG) findings may result from direct compression of the vestibular nerve, brain stem, or cerebellum.

  • Localizing specific vestibular nerve involvement based on laboratory vestibular testing alone is unlikely.

• Radiographic imaging: Plain radiography has virtually no role in the diagnosis of these lesions.

• CT scanning: Bone algorithms can help delineate bony involvement and destruction. CT scanning helps determine the location of jugular bulb.

• Contrast MRI of the head and internal auditory canals

  • This is the criterion standard for diagnosis.

  • Perform magnetic resonance angiography (MRA) or magnetic resonance venography (MRV) on patients with suspected vascular lesions as a screening technique.

  • Angiography prior to embolization is the criterion standard in assessing the vascular tributaries to various tumor types.

• Ventricular shunting or drainage: This is considered for large tumors.

See the list below:

• Use neuroanesthetic techniques with continuous blood pressure monitoring.

• Positioning of patient is based on approach to be used.

• Administer perioperative prophylactic antibiotics for 24 hours.

• Use applicable cranial nerve monitoring techniques (eg, intraoperative ABR, facial and lower cranial nerve monitoring).

• Obtain proximal control of the internal carotid artery and internal jugular vein in the neck in patients with lesions with involvement of these vessels.

• Consider the administration of mannitol and/or diuretics before craniotomy.

• Stereotactic operative techniques can be used for selected lesions.

• Meticulously wax temporal bone air cells.

• Seal off the eustachian tube if the middle ear is opened.

• Attempt watertight closure of the dura and/or skin.

See the list below:

• Continuous intensive care unit monitoring with frequent neurologic checks is imperative in the immediate postoperative period.

• Maintain meticulous eye care when facial nerve function is compromised.

• Appropriately manage comorbid medical conditions.

• Institute speech and physical therapy as soon as possible.

See the list below:

• Guidelines for follow-up care depend on the type of lesion and morbidity.

• Typically, an enhanced MRI is obtained 6 months to 1 year after surgery and at variable periods thereafter.

• Malignant lesions require more frequent follow-up care.

Contemporary surgical and anesthetic techniques have minimized morbidity for these lesions. Careful preoperative assessment and control of comorbid conditions can further diminish the risks of complication. Complications from these procedures can include the following:

• Permanent hearing impairment or complete hearing loss on the operative side

• Temporary or permanent facial paralysis ^{[8, 9]}

• Exposure keratitis or corneal ulcer

• Ipsilateral facial hypesthesia

• Lower cranial nerve deficits (eg, dysphagia, hoarseness, aspiration)

• CSF leak (eg, otorrhea, rhinorrhea)

• Infection (eg, wound, meningitis, intracranial abscess

• Intraoperative hemorrhage

• Hematoma

• Seizures

• Stroke

A retrospective study by Shew et al suggested that the chance of CSF fistula following CPA tumor resection is greater in patients with isolated petrous apex (PA) pneumatization. The investigators found the rates of CSF leak and CSF rhinorrhea to be 25.0% and 15.0%, respectively, in patients with PA pneumatization who underwent resection, compared with 13.7% and 5.9%, respectively, in resection patients without pneumatization. ^[10]

The outcome and prognosis for cure from surgical resection depends on the histology, size, and location of the tumor and the approach chosen. Cessation of tumor growth from primary radiation also depends on the specific factors listed above. Expected facial palsy rates are high for primary facial schwannomas. The effect on quality of life from facial nerve palsy is quite significant. Results also depend on the experience and skills of the surgeon.

In a study of 34 patients who underwent surgery for CPA meningiomas, Agarwal et al found that the rate of permanent cranial nerve deficits was significantly greater in patients with tumors of more than 3 cm in size than in those with smaller meningiomas (45.5% vs 5.9%, respectively). It was also found that deficits of the lower cranial nerves occurred only in patients whose tumors extended into the jugular foramen. No association was found between tumor extension into the internal acoustic canal and either postoperative complications or cranial nerve deficits. Among all patients, 5.9% suffered postoperative facial nerve palsy. ^[11]

Further advances in surgical techniques and radiotherapy are being made. Endoscopic surgical techniques in the cerebellopontine angle (CPA) have improved visualization of the tumor and adjacent structures. Stereotactic methods have improved accuracy of the delivery of microsurgical dissection and radiation therapy, thus minimizing damage to adjacent tissue. New radiation delivery protocols, although incompletely followed up, show some promise as primary or adjuvant therapy of some of these lesions.