Vestibular schwannomas (VS) are benign, extra-axial, encapsulated, Schwann cell derived neoplasms of the vestibular part of the eighth cranial nerve. Although some earlier reports indicated that the superior vestibular nerve is the more common origin of VS, recent studies suggest otherwise. that the most common origin for VS are the nerve sheath of the inferior vestibular nerve, and less frequently the superior vestibular nerve13. Eighth cranial nerve schwannomas represent 90% of all intracranial nerve sheath tumors14. VS account for approximately 6–8% of intracranial tumors in adults and are the most common tumor in the cerebellopontine angle (CPA) ranging between 80% and 95%15,16,17,18, followed by meningiomas ranging between 5% and 10% and epidermoid tumors ranging between 4% and 7%19,20. An occipital headache attributable to the tumor is a late finding with 20% of patients with tumors between 1 and 3 cm, with 40% of patients with tumors larger than 3 cm verifying this symptom. There are two types of VS; sporadic and familial. The sporadic form of VS is commonly seen in adults and is very rare in pediatric patients. The familial form of VS is most commonly seen in patients with neurofibromatosis type 2 (NF2), and is usually bilateral.
Various terminologies have been used to define the VS pathology, with “Acoustic Neuroma” the most common. Prior terminology has caused confusion regarding the origin, biological behavior, and natural history of VS. This confusion is now resolved by using the correct name of “Vestibular Schwannoma” (VS) to define this pathology. “Vestibular” clearly indicates the origin of the tumor as from the vestibular nerve, while “schwannoma” indicates that Schwann cells are the cell of origin. In 1777, anatomist Eduard Sandifort was the first to recognize the VS as an acoustic neuroma at autopsy. It was observed as a fixed and rigid tumor adjacent to the cochlear nerve with extension into the internal acoustic canal (IAC) and that caused compression on the brainstem21. From that time to the early twentieth century, acoustic neuromas were used to the define all tumors located in the CPA. The first attempt to remove a VS in the CPA via the transcranial route was under taken by Von Bergmann in 1890. The patient did not survive the surgery and histopathology confirmed a VS22. In 1894, Charles Balance performed the first successful removal of the CPA tumor at two separate stages23.
In 1936, Cushing introduced a new surgical technique. This consisted of a “T-shape” skin incision that included a horizontal incision between both mastoid notches, and a vertical incision from the midline to the middle level of the cervical spine. After this extensive skin incision, Cushing performed a large bilateral posterior fossa craniectomy that exposed both CPAs laterally, the corticomedullary junction and the cisterna magna inferiorly, and the venous sinuses superiorly. Cushing’s novel approach allowed a wider surgical working area, provided cerebellar relax Action through CSF drainage from the cisterna magna, and mobilization of the cere Bellum and the brainstem. Thus, neuro-vascular structures became more mobile and were less affected by surgical maneuvers. Dandy modified Cushing’s technique, and hypothesized that total resection of the tumor would decrease the rates of recurrence and increase the long-term survival24. He performed more aggressive internal debulking to create free space and created a cleavage plane to pull the tumor capsule away from surrounding structures for circumferential dissection. Finding this unacceptably high, Cushing endorsed internal debulking of VS without removing the capsule and reported a mortality rate of 10% to 15%, though this increased to 54% at 5 years secondary to tumor recurrence1,2. Dandy further refined VS surgery with intratumoral decompression followed by extracapsular dissection with an operative mortality rate of 10.9% in 1941. Not long after, using a similar technique, Horrax and Poppen reported a 5-year mortality rate of 12.7%1. In 1913, using finger dissection, some of the earliest case series of VS removal reported operative mortality rates between 67% and 84%1,2,4.
While mortality rates declined, morbidity rates remained high due to cranial nerve injury, particularly of the facial nerve. Although the first successful gross total resection of a VS with preservation of the facial nerve was reported by Cairns in 19311, it could not be accomplished on a routine basis; it was not until the microsurgical revolution led by House, Hitselberger, Kurze, and Yasargil in the 1960s1,2 and the introduction of intraoperative EMG monitoring in 19795 that facial nerve preservation became routinely achievable. Currently, rates of mortality are less than1%6, and facial nerve dysfunction rates are between 3% and 43%, depending on tumor size7.
Even with these advances, sometimes the surgeon and patient must choose between complete tumor resection and risk of permanent facial nerve dysfunction. Factors that influence this are tumor size, the degree to which the nerve fibers are spread out by the tumor, and the location of the facial nerve relative to the tumor5,8,9.
Dandy also reported the first surgical series of VS in which the tumors were removed gross totally24. In 1905, Victor Horsley performed a gross total resection of a VS that unfortunately resulted in severe postoperative brain ischemia25. In 1949, Horrax and Poppen reported mortality rate of 10.8% in patients with VS after gross total resection26.
Advances in microneurosurgical techniques due to new instruments, imaging systems, skull base techniques and neurophysiological monitoring have improved outcome parameters from just survival, to address quality of life and cosmetic results that include preservation of the facial nerve and hearing.
Vestibular schwannomas constitute 6% of all intracranial neoplasms16. and are the most common benign lesions of the IAC and CPA cistern constituting between 60% and 90% of the entire lesions seen in this area27,28. VS are most commonly diagnosed in adults, and the median age of diagnosis is ranging between 52 and 55 years in different studies29. According to recent population-based studies, the overall incidence of VS is 9–13 cases per million persons per year30,31.
This translates to about 3000 cases per year within the United States, a number that is consistent with clinical experience. However, these population-based studies likely underestimate the incidence, since in the pre and early magnetic resonance imaging (MRI) era, diagnostic cross Sectional imaging capable of detecting small lesions was unavailable or uncommonly performed. Contemporary MRI technology is faster and less expensive than previously, and is capable of detecting small lesions. Recent reports have documented the capability to identify small lesion without the use of paramagnetic contrast material32,33. Thus, it is expected that with this more sensitive diagnostic imaging, the incidence of VS, asymptomatic or symptomatic, will increase. Indeed, Anderson and colleagues found that a rate of asymptomatic VS was 0.7% per 10,000 MRI images obtained for reasons other than assessing for CPA lesions34. Stangerup and colleagues reported that when assessing 30 years of data from a national population sample size, tumor size decreased from ~3 cm in the 1970s to ~1 cm in the mid 2000s35. Additionally, there was no lesions discovered in the 1970s that were limited to the IAC, but by the mid-2000s, 33% of lesions discovered were restricted to the IAC35. Historical estimates for VS based on autopsy have placed the prevelance at 2.6%36. Through further review and reclassification of previous studies, the VS incidence was decreased to ~0.8% by the mid twentieth century37.
In our view, this is due to technical advances in diagnostic radiology, widespread use of radiological imaging methods, growing medical awareness, and knowledge about VS that facilitates timely diagnosis.
The clinical manifestations of VSs depend on both the size of the lesion and its location relative to surrounding neurovascular structures. Schwannomas can arise from other nerves in the region and present with similar symptoms but these are uncommon. These nerves originate from the lateral aspect of the brainstem, traverse the cerebellopontine angle (CPA) cistern and the internal acoustic canal (IAC) of the temporal bone and terminate in the inner ear where they provide innervation of the vestibular end organs.
The subarachnoid cisterns are areas of expanded subarachnoid space between the central nervous system structures and bony confines of the cranial vault. There are two cisterns that are of primary importance to vestibular schwannoma treatment: the CPA and prepontine (PP) cisterns. The CPA cistern is an expansion of the sub arachnoid space between the lateral lobe of the cerebellum, cerebellar peduncles, and lateral pons medially and the temporal bone laterally. The PP cistern is an expansion of the subarachnoid space between the ventrolateral and ventral pons and the temporal and clival bone. The CPA and PP cisterns are contiguous, though bands of arachnoid mater can create separate cerebrospinal fluid (CSF) compartments. It is through these spaces that the vasculature and cranial nerves of the posterior cranial fossa course to their destinations11,12.
Within the modiolus are numerous bony channels called Rosenthal’s canals, which are adjacent to the Scala tympani and contain the spiral ganglia. The afferent branches of the cochlear nerve originate between the hair cells and the spiral ganglia. These nerve endings pierce the organ of Corti through multiple small openings called the habenula perforata. It is at this most distal location where Schwann cell myelination terminates. The afferent branches then run from the spiral ganglia through multiple small openings at the distal IAC called “the cribriform plate.” Just proximal to Scarpa’s ganglia and just distal to the cribriform plate is the Schwann-glial cell junction of the coch-lear division of the eighth cranial nerve11.
The bony vestibule, located between the cochlea and three semicircular canals, contains the utricle and saccule. The ampullated ends of the semicircular canals open into the utricle. The saccule communicates with the Scala media of the cochlea via the ductus reunion’s. Two small ducts, one each from the saccule and utricle, unite to form the endolymphatic duct. As its name implies, this endolymph-containing duct is also part of the membranous labyrinth, and is housed within the bony vestibular aqueduct. The afferent nerve fibers traveling from the vestibular hair cells of the semicircular canals, utricle, and saccule pierce the cribriform plate of the distal IAC enroute to the Scarpa ganglia within the IAC. Unlike the cochlear division, the Schwann-glial cell junction of the vestibular divisions is at the Scarpa ganglia.6 With this anatomy in mind, it is helpful to refer to the revised Kennedy classification system in order to describe tumor locations12.
When designing and conducting this systematic review we followed the PRISMA guidelines for systematic reviews .
1.2. Search strategy
A literature search was completed of Pub Med, EMBASE, Medline, Library Genesis, Until May 2020 databases for relevant articles. The search terms were vestibular schwannoma and Brain Tumor ( nervus acusticus ) and terms related to Comprehensive Management of Vestibular Schwannoma and related issues. The first author reviewed titles and/or abstracts of displayed articles and determined relevance to the review. Full text copies of relevant articles were obtained. Reference lists were screened for identification of other relevant articles. Two known systematic reviews of measurement in Brain Tumor and skull base surgery populations were screened for relevant articles. Only articles written in English were included in this review. Any year of publication was included as restricted by each database’s availability.
1.3. Inclusion criteria
Studies were included in the review if they: included only participants with a diagnosis of vestibular schwannoma; used a pro- spective design which involved initial measurement in inpatient care (acute hospital or subacute rehabilitation setting); involved a physical performance measure that related. A physical performance measure was defined as any measure that required the Survivors of medical treatments and surgical treatments were generally defined to present the topic.
1.4. Data extraction
Information about the study design, setting, participants and results were extracted by the first author and checked by the second author. Authors were contacted where there was information missing. A recent consensus statement indicated that any statistical measure of change, including looking at the difference be- tween before and after measures could be used to measure responsiveness . Consequently if any statis- tical measure of change was used the article was included in this review.
1.5. Assessing risk of bias
The risk of bias was evaluated for each study using the recent consensus statement regarding design of responsiveness studies as a guideline . In particular we examined each studies sample size and the method used to select participants.