Background
Cerebellopontine angle (CPA) tumors are the most common neoplasms in the posterior fossa, accounting for 5-10% of intracranial tumors. Most CPA tumors are benign, with over 85% being vestibular schwannomas (acoustic neuromas), lipomas, vascular malformations, and hemangiomas. The most frequent nonacoustic CPA tumors are meningiomas, epidermoids (primary cholesteatomas), and facial or lower cranial nerve schwannomas. Primary malignancies or metastatic lesions account for less than 2% of neoplasms in the CPA.
History of the Procedure
Early in the 20th century, CPA lesions were difficult to diagnose and rarely completely excised. Indeed, the mortality rate for operative intervention in the posterior fossa approached 50%. However, revolutionary advances in neuroradiologic imaging and surgical techniques and approaches have made these lesions almost uniformly treatable with acceptable morbidity and very low rates of mortality. Surgical intervention remains the most definitive means for complete tumor removal for most of these lesions. Radiation therapy has gained popularity to arrest tumor growth with specific tumor types and is also an option for patients who are unwilling or medically unable to undergo surgery.
Problem
The density of vital neurologic structures in the posterior fossa requires careful assessment and treatment planning to avoid unnecessary morbidity and mortality.
Etiology
A study by Berkowitz et al found a tendency for patients diagnosed with vestibular schwannoma to be white, aged 50-60 years, and in a professional occupation, but there seemed to be no specific sex preference in the disease. A strong association appeared to exist between hay fever and vestibular schwannoma, while tobacco use seemed to have an inverse relationship to the likelihood of developing the condition.[1]
Indications
Because of the location of these tumors within the cerebellopontine angle (CPA) and the significant number of closely associated vital neurologic structures, the risk of complications from cranial nerve damage and brainstem compression increases with delays in diagnosis and treatment. Patient age and medical condition, specific tumor growth rate, and pathologic behavior are taken into account when recommending a mode of therapy. Surgical resection is considered for any patient in good medical condition with a benign or malignant lesion in the CPA if the boundaries of the tumor are resectable with minimal risk to the local neurologic structures. Surgical resection renders the greatest chance for complete tumor eradication of the vast majority of CPA lesions. Occasionally, planned partial resection is considered in patients with extensive tumors associated with increased intracranial pressure.
A study by Goebel and Mehdorn indicated that untreated CPA tumors can lead to neurocognitive impairment. The investigators found that out of 45 patients with an untreated CPA tumor, including 27 with a vestibular schwannoma and 18 with a meningioma, 69% demonstrated neurocognitive problems, with attention and visuomotor speed impairment revealed in 62% of cases. Visuoconstruction was affected in 44% of patients. Clinically relevant depression and/or anxiety was reported by approximately one third of individuals in the study, while 48% stated that they suffered from high fatigue levels.[2]
Relevant Anatomy
See the Pathophysiology section.
Contraindications
Although patient age and medical condition, specific tumor growth rate, and pathologic behavior are taken into account when recommending a mode of therapy, surgical resection is considered for any patient in good medical condition with a benign or malignant lesion in the cerebellopontine angle (CPA) if the boundaries of the tumor are resectable with minimal risk to the local neurologic structures. Occasionally, complete resection is impossible because of the intimate involvement of surrounding structures, which may impose unwarranted morbidity if complete excision is attempted, and planned partial resection is considered.
Medical Therapy
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.
Surgical Therapy
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.[4]
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.[5]
Complications
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[6, 7]
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.[8]
Outcome and Prognosis
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.[9]
Future and Controversies
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.
Author
Jack A Shohet, MD, President, Shohet Ear Associates Medical Group, Inc; Clinical Professor, Department of Otolaryngology-Head and Neck Surgery, University of California, Irvine, School of Medicine
Disclosure: Medical Advisory Board Member, consultant for: Envoy Medical.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Gerard J Gianoli, MD, Clinical Associate Professor, Departments of Otolaryngology-Head and Neck Surgery and Pediatrics, Tulane University School of Medicine; President, The Ear and Balance Institute; Board of Directors, Ponchartrain Surgery Center
Disclosure: Nothing to disclose.
Chief Editor
Arlen D Meyers, MD, MBA, Professor of Otolaryngology, Dentistry, and Engineering, University of Colorado School of Medicine
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Cerescan;RxRevu;Cliexa;The Physicians Edge;Sync-n-Scale;mCharts<br/>Received income in an amount equal to or greater than $250 from: The Physicians Edge, Cliexa<br/> Received stock from RxRevu; Received ownership interest from Cerescan for consulting; .
Acknowledgements
Douglas D Backous, MD Director of Listen for Life Center, Department of Otolaryngology-Head and Neck Surgery, Virginia Mason Medical Center
Douglas D Backous, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American Auditory Society, American College of Surgeons, American Laryngological Rhinological and Otological Society, American Medical Association, Association for Research in Otolaryngology, North American Skull Base Society, Society for Neuroscience, and Washington State Medical Association
Disclosure: Nothing to disclose.
