![]() ![]() In the lateral segment of the internal auditory canal, about 3 to -4mm from the fundus, the cochlear and vestibular nerves join to form one common nerve. The vestibulocochlear nerve runs most often posteriorly to the facial nerve in the internal auditory canal. The posterior portion of the fundus is filled with a macula crista, which is a series of very small openings that the vestibular nerves pass to reach the superior and inferior semicircular canals. These two spines form three distinct osseous structures through which the facial and vestibulocochlear nerve branches can be found in a consistent pattern, represented by figure 1. The superior half is further divided into anterior and inferior segments by Bill’s bar, a vertical crest of bone named after otologist Dr. It is divided into superior and inferior segments by the transverse crest (also called the falciform crest). The fundus separates the internal auditory canal from the cochlea and vestibule which are located in close proximity. The canal narrows as it moves towards the fundus, a thin cribriform plate of bone that marks the lateral boundary of the canal. The rounded and smooth canal is on average 8.5mm (5.5 to 10.mm) in length and about 4mm in diameter. It is lined by dura and filled with spinal fluid. The canal runs through the petrous segment of the temporal bone, which is located between the inner ear and posterior cranial fossa. The internal auditory canal begins in the temporal bone within the cranial cavity at an oval-shaped opening called the porus acusticus internus. Knowledge of the anatomy and relationship of these structures plays a vital role during the evaluation and management of diseases involving the internal auditory canal. It includes the vestibulocochlear nerve (CN VIII), facial nerve (CN VII), the labyrinthine artery, and the vestibular ganglion. Fine-cut CT scanning of the internal auditory canal with contrast can detect medium-size or large tumors but are not reliable imaging techniques to detect a tumors smaller than 1 - 1.5 cm.The internal auditory canal (IAC), also referred to as the internal acoustic meatus lies in the temporal bone and exists between the inner ear and posterior cranial fossa.However, even with intravenous contrast enhancement, thin-cut CT scanning can miss tumors as large as 1.5 cm. ![]() Well-performed scanning can demonstrate tumors 1 - 2 mm in diameter.Contrast enhancement is present, but can be underwhelming, especially in larger lesions with cystic components.CT may show erosion and widening of the internal acoustic canal.On CT scan, vestibular schwannoma can be seen as an enhancing lesion in the region of the internal auditory canal with variable extension into the cerebellopontine angle.CT scan with bone windows can be of prognostic significance as the extent of widening of the internal auditory meatus and the extent of tumor growth anterior and caudal to the internal auditory meatus are predictive of postoperative hearing loss.Findings on CT scan diagnostic of acoustic neuroma include erosion and widening of the internal acoustic canal. OverviewĬT scan of the head may be diagnostic of acoustic neuroma. Associate Editor(s)-in-Chief: Simrat Sarai, M.D. ![]() Risk calculators and risk factors for Acoustic neuroma CTĮditor-In-Chief: C. Natural History, Complications and PrognosisĪmerican Roentgen Ray Society Images of Acoustic neuroma CTĪll Images X-rays Echo & Ultrasound CT Images MRIĭirections to Hospitals Treating Acoustic neuroma Differentiating Acoustic neuroma from other Diseases ![]()
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