![]() Of the tumors involving the vestibular nerve, they occurred roughly equally in the superior and inferior divisions as well as their common trunk. Twenty-one tumors clearly arose lateral to the glial-schwannian junction, whereas only 3 were located in the medial one third. Of those 40, 4 arose from the cochlear nerve and 36 from the vestibular nerve. 10Īlthough commonly described in the literature as arising from the glial-schwannian junction, a systematic review of archival temporal bone collections by Roosli et al showed 40 tumors within the internal auditory canal, and 10 intralabyrinthine. Instead, they originate from Schwann cells, 11 and they can occur anywhere lateral to the glial-schwannian junction. Historically known as acoustic neuromas, these tumors have been demonstrated not to involve the acoustic (cochlear) nerve in most cases, nor to be of neuroglial origin. In addition, factors predicting growth or requirement of intervention were initial size at diagnosis and disequilibrium. 9 A study performed by Hunter et al found 40.8% of tumors demonstrated a growth of >2 mm during a median observation period of 23 months. Although there was a large variation in the frequency of tumor enlargement over time (15 to 85%), the overall frequency of tumor growth was 46%, whereas the frequency of tumor regression was 8%. 8 Natural historyĪ systematic review on the natural history of VS performed by Yoshimoto et al showed a growth rate of 1.2 mm/year. 7 Hearing loss can be evaluated on audiometry however, audiometry results do not necessarily correlate with lesion site or tumor size. Major symptoms included facial numbness (paresthesia), hypoesthesia and pain. Trigeminal nerve disturbances occurred in 17%. Vestibular nerve dysfunction was present in 61% of patients, with a common finding of imbalance. In a study of 1000 patients, Matthies et al found symptomatic cochlear nerve involvement in 95% of patients with two major symptoms present: hearing loss and tinnitus. This paper will review the clinical presentation, natural history, and pathology of vestibular schwannomas, as well as discuss the cystic subtypes and provide an overview of imaging diagnosis and measurement techniques. ![]() 5 Genetic studies have demonstrated loss of both wild-type copies in the NF2 tumor suppressor gene as a common finding in sporadic VS as well NF2. NF2 is a rare autosomal dominant multiple neoplasia syndrome, occurring due to mutations in the NF2 gene located on chromosome 22q12, coding for the tumor suppressor Merlin. 4 The remainder predominantly occur in neurofibromatosis type 2 (NF2) one of the diagnostic criteria for which is bilateral VS. 1,2,3 The sporadic form of VS makes up > 90% of cases there is no predominance for the left or right side. From here three bundles emerge: superior and inferior division of the vestibular nerve and the nerve from the posterior semicircular canal (see article: vestibulocochlear nerve (CN VIII) for further details).Vestibular schwannomas (VS) are benign tumors of the nerve sheath and the most common tumor in the cerebellopontine angle, accounting for 6-8% of all intracranial tumors and 80% of cerebellopontine angle (CPA) tumors, with an estimated prevalence of 0.02% and mean age of diagnosis at 58 years. In addition to the three nerves which enter it, it also contains the vestibular ganglion ( ganglion of Scarpa). See mnemonic for the position of the nerves in the IAC. Inferior: cochlear nerve and inferior vestibular nerve (IVN) the cochlear nerve is situated anteriorly Superior: facial nerve and superior vestibular nerve (SVN) the facial nerve is anterior to the SVN and is separated from it laterally by Bill's bar, a vertical ridge of bone This horizontal ridge divides the canal into superior and inferior portions: Their position is most constant in the lateral portion of the meatus which is anatomically divided by the falciform crest. Superior vestibular nerve (component of CN VIII) Inferior vestibular nerve (component of CN VIII) Nervus intermedius (sensory component of CN VII)įacial motor root (motor component of CN VII) There are five nerves that run through the IAC: Labyrinthine artery (usually a branch of the AICA or basilar artery) The canal narrows laterally, and the lateral boundary is the fundus, where the canal splits into three distinct openings, one of which is the facial nerve canal. The margins of the opening are smooth and rounded, and the canal is short (1 cm), running laterally to the bone. The opening of the IAC, the porus acusticus internus, is located within the cranial cavity, near the posterior surface of the temporal bone.
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