GAMMA-KNIFE RADIOSURGERY IN ACOUSTIC NEUROMA

Abstract

Lesions of the cerebellopontine angle (CPA) are frequent and represent 6%–10% of all intracranial tumors. Acoustic neuromas, which are also called vestibular schwannomas, along with meningiomas are the two most frequent lesions and account for approximately 85%–90% of all CPA tumors. These benign lesions involving the middle ear comprise a diverse spectrum of local manifestations within the temporal bone. Despite their usually benign histopathological characteristics, these lesions may be locally destructive. Prompt diagnosis and treatment are therefore necessary to prevent progression of audiologic, vestibular, and facial nerve dysfunction, which may also be present. Because of the surgically formidable anatomical location of these tumors, curative resection often proves challenging. Treatment options include surgical resection, stereotactic radiosurgery (SRS), hypofractionated stereotactic radiotherapy (SRT), alone or in combination. Stereotactic radiosurgery is a minimally invasive option for management of skull base tumors. Brain stereotactic radiosurgery involves the use of precisely directed closed skull single fraction (one surgical session) radiation to create a desired radiobiologic response within the target with minimal effects to surrounding structures or tissues. Stereotactic radiosurgery is associated with a high rate of local tumor control and a low risk of neurologic complications for patients with skull base tumors. Stereotactic radiosurgery can be used as an up-front treatment or as an adjuvant therapy for patients with recurrent or residual tumor after surgical resection. The superior safety efficacy of stereotactic radiosurgery over microsurgery in small- to middle-sized vestibular schwannomas is demonstrated in worldwide comparative studies. Normal motor facial nerve function and serviceable hearing are more likely to be preserved with radiosurgery as compared with microsurgery. In very large schwannomas, a combined approach with a deliberate subtotal removal with functional monitoring of the facial nerve followed by radiosurgery of the remnant dramatically reduces the risk of facial palsy as compared with radical removal. Hypofractionation of radiosurgery (stereotactic radiotherapy or multisession radiosurgery) has failed until now to demonstrate any advantage over single-dose, high-precision radiosurgery. Literature has documented the cost savings benefit of stereotactic radiosurgery versus invasive surgical procedures and the lower risk potential of bleeding, anaesthesia problems, infections, and side effects which may result in transient or permanent disabilities from open surgery. At the same time, literature has demonstrated that the risk of radiation-associated intracranial malignancy after stereotactic radiosurgery was found to be similar to the risk of developing a malignant CNS tumour in the general population of the USA and some European countries as estimated by the CBTRUS and IARC data, respectively.

Keywords

• GAMMA-KNIFE RADIOSURGERY IN ACOUSTIC NEUROMA