Patients with VS commonly present with progressive unilateral sensorineural hearing loss and tinnitus, but can also present with SSNHL, symptoms of vestibular dysfunction, facial numbness/pain, and facial paresis. The most common pathology of the VCN in the CPA and IAC is a vestibular schwannoma (VS), a neoplasm of Schwann cells that is responsible for 5-10% of all intracranial tumors. The prevalence of AICA loops within the IAC has been reported to be between 13-40% in post-mortem dissections and 14-34% by magnetic resonance imaging (MRI). There is high variability in the course of the AICA within the CPA. A terminal artery, the labyrinthine artery is the sole blood supply of the labyrinth and an area of the brainstem and cerebellum. It gives rise to the labyrinthine (internal auditory) artery, which supplies the cochlea and vestibular system. The anterior inferior cerebellar artery (AICA) arises from the basilar artery and courses variably posterolaterally in the CPA or along the underside of the cerebellum supplying the anterior cerebellum including the flocculus, middle cerebellar peduncle, and inferolateral pons. Anterolateral to the CPA, the internal auditory canal (IAC), a bony channel situated along the posterior face of the petrous bone, transmits the facial nerve from the CPA to the temporal bone and ultimately the face, and the vestibulocochlear nerve (VCN) from the cochlea and vestibular apparatus to the brainstem. The CPA contains cranial nerves V-VIII, the superior cerebellar artery (SCA), anterior inferior cerebellar artery (AICA), and draining veins. The cerebellopontine angle (CPA) is a cerebrospinal fluid-filled, triangular space located at the junction of the lateral pons and anterior cerebellum. She was not offered radiosurgery, and she elected conservative management. There was no evidence of a schwannoma on the repeat MRI. Repeat MRI demonstrated a loop of the anterior inferior cerebellar artery (AICA) compressing the vestibulocochlear nerve within the right IAC. She was originally diagnosed with a vestibular schwannoma on magnetic resonance imaging (MRI) and was referred to our institution for Gamma Knife radiosurgery. The current report represents an attempt to understand this clinical entity as discussed in the current literature.Ĭase summary: A 77-year-old female with a long history of progressive right-sided hearing loss and episodic vertigo developed unilateral right SSNHL, tinnitus, vertigo, and disequilibrium. Underlying pathophysiologic factors surrounding microvascular compression of the vestibulocochlear nerve are poorly understood and make treatment recommendations, especially the option of microvascular decompression, difficult if not controversial. 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).We present a patient with unilateral sudden sensorineural hearing loss (SSNHL) who was found to have a vascular loop in the ipsilateral internal auditory canal (IAC), and we review the literature regarding this association. 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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