Acoustic Neuroma: The Fully Endoscopic Removal of Acoustic Neuromas
To remove these tumors, surgeons have traditionally relied on one of two common approaches. The most frequently used procedure, the Translabyrinthine approach, involves several surgeons from different disciplines such as Otolaryngology and Neurosurgery who drill through the mastoid bone behind the external ear and through the labyrinth and inner ear mechanism to access the tumor. For smaller tumors, the "retrosigmoid" or" sub-occipital" approach offers the possibility of saving some hearing. Instead of going through the mastoid bone, surgeons make a large incision behind the ear, open the skull behind the mastoid bone, push the brain aside, and take the tumor out.
At the Skull Base Institute, our surgeons have developed a fully endoscopic approach. Instead of drilling through the mastoid bone or cutting a large opening in the skull, our surgeons make a burr hole the size of a dime behind the mastoid. From this point, thin, flexible and precise endoscopic instruments are inserted - slipping them between the brain and skull to the site of the tumor.
The entire procedure is performed using minimally invasive techniques and allows, in most cases, patients to be discharged within 48 hours. This is mainly attributed to the fact that the brain is not manipulated, retracted or pushed resulting in lower complication rates and faster recovery times.
Over the past five years, hundreds of patients have successfully undergone a minimally invasive fully endoscopic resection of their acoustic neuroma.
Tumors as small as 6mm and as large as 6cm have been resected by this innovative technique. Although we routinely used to perform the translabyrinthine and suboccipital approaches in the past, we have not reverted to those "open" procedures and anticipate further evolutions in the endoscopic approach to acoustic neuromas. Continuous neurophysiologic monitoring of the facial nerve, the hearing and the brainstem is routinely performed during these procedures in order to avoid any cranial nerve or neurologic deficits.
More specifically, the rates of facial nerve paralysis, CSF leakage, hearing loss, neurologic injury such as strokes and cerebellar contusions have all plummeted. Finally, there are no exclusion criteria for the endoscopic technique such as tumor size or patient age. Any patient who is a candidate for an open approach such as either the translabyrinthine approach or the suboccipital approach can be a candidate for this minimally invasive endoscopic approach and can benefit from this cutting edge technology, lower complication rates and shorter hospitalization stay.
Overview
Vestibular schwannoma (VS)- incorrectly but more commonly known as acoustic neuroma or neurinoma- is a benign (non-cancerous) tissue growth resulting from an overproliferation of "schwann cells" constituting the eighth cranial nerve sheath. The eighth cranial nerve-also known as the acoustic nerve or the vestibulocochlear nerve- has two distinct parts, one part associated with transmitting sound and the other sending balance information to the brain from the inner ear. The eighth cranial nerve lies adjacent to the seventh cranial nerve (facial nerve), as they both pass through a bony canal called the internal auditory canal (IAC). The facial nerve provides motion of the muscles of facial expression. This canal is approximately 2 cm long and it is at this site that acoustic neuromas originate from the sheath surrounding the eighth nerve.
Acoustic neuromas are reported to occur in all races and they account for 6 to 10% of all primary intracranial tumors and for approximately 70 to 90% of all cerebellopontine angle (CPA) (the cerbellopontine angle is the area or "angle" between the cerebellum and the brainstem) tumors. Most commonly acoustic neuromas occur during the fourth and fifth decades of life and are about two times more common in females than in males.
Causes
The cause is unknown. Although there is an inherited condition called neurofibromatosis type 2 (NF-2) which can lead to bilateral acoustic neuroma formation in some children, most acoustic neuromas occur spontaneously and manifest in adulthood without any evidence of an inheritable pattern.
Symptoms
Acoustic neuromas usually grow slowly over a period of years. They expand in size at their site of origin and ultimately displace normal brain tissue. The brain is not invaded by the tumor, but the tumor pushes the brain as it enlarges. The slowly enlarging tumor protrudes from the internal auditory canal into an anatomically complex area at the base of the skull, the cerebellopontine angle.
Symptoms and signs associated with acoustic neuromas have been well known for over 150 years and are due to direct tumor compression. Acoustic neuromas are commonly associated with gradual (over months or years) hearing loss indicating damage to the cochlear nerve. They may manifest with other symptoms and signs depending on the site of origin and the growth pattern of the tumor; including tinnitus, vertigo, cerebellar dysfunction, cranial nerve dysfunction, and secondary obstructive hydrocephalus.
These tumors can reach a remarkable size causing severe compression of the brain stem, the cerebellum and the surrounding cranial nerves such as the seventh (facial) or fifth (trigeminal) nerves, they can induce bony changes with invasion of the surrounding pneumatic cells and marrow spaces and may lead to a life threatening condition.
Bilateral schwannomas are rare and usually an expression of neurofibromatosis type 2 (NF-2). Neurofibromatosis type 1 (NF-1) or von Recklinghausen's disease, is a separate genetic disease resembling NF-2, and in extremely rare occasions can manifest with an acoustic neuroma.
Diagnosis
Initially, following careful history and physical examination, patients usually undergo a thorough ear examination, hearing test (audiogram) and in some cases an auditory brainstem response test is performed which measures the passage of sound information from the ear through various locations in the brain.
The diagnosis of an acoustic neuroma has changed considerably during the last years as MRI has become the standard in assessing patients with possible acoustic neuromas. Computerized tomography (CT) was previously used as a reliable method for detection and assessment of acoustic neuromas.
Treatment
Treatment options include observation, surgical removal and radiotherapy (Conventional and Gamma Knife); which option is best depends upon the size of the tumor and the age and general health of the patient. The two important considerations in treatment are preservation of serviceable hearing and facial nerve function.
Prognosis
The prognosis for someone with a unilateral acoustic neuroma is usually quite good provided the tumor is diagnosed early and appropriate treatment is instituted.
In spite of the fact that an acoustic neuroma is a benign tumor, it can still be fatal if left untreated. As these tumors continue to grow they run out of space inside the small canal that links the inner ear to the brain, and begin to grow into the skull cavity and compress the brain tissue, including the brain stem which has vital functions such as regulating heart rate, breathing and blood pressure.
The prognosis can be poorer for those with NF-2 who have an increased risk of bilateral acoustic neuromas and other tumors.
