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Internal auditory canal segments12/29/2023 Image 5: AICA traveling between and partially separated the nervus intermedius and facial nerve proper. Image 4: AICA traveling between and partially separated the nervus intermedius and facial nerve proper. Image 3: AICA traveling below the CN VII/VIII complex. Image 2: AICA and the CN VII/VIII complex traveling in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. Image 1: AICA (anterior inferior cerebellar artery) and the cranial nerve (CN) VII/VIII complex traveling in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. No statistical significance was found between sides.Īnterior inferior cerebellar artery in relation to porus acusticus and cranial nerve VII/VIII complex Although a trend was seen with male specimens having arteries that more commonly rested at or within the porus acusticus, this did not reach statistical significance. Five arteries (10%) traveled below the CN VII/VIII complex (Figure 1, image 3), six (12%) traveled posterior to the nerve complex (Figure 1, image 6), four (8%) formed a semicircle around the upper half of the nerve complex (Figure 1, image 8), and two (4%) traveled between and partially separated the nervus intermedius and facial nerve proper (Figure 1, images 4-5). In regard to relationships between the AICA and the nerves of the facial/vestibulocochlear complex, 33 arteries (66%) traveled in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves (Figure 1, images 1-2, 7, 9). Of these vessels that approached the porus, eight (29%) were medial to it (Figure 1, images 3, 7-9), 17 (61%) were at the porus (Figure 1, images 1-2, 4-5), and three (10%) extended through the porus and into the internal acoustic meatus (Figure 1, image 6). A loop of the AICA was found to protrude toward the porus acusticus on 28 sides (56%). Surgeons should consider these with approaches to the cerebellopontine angle.Īn AICA was identified on all sides. Although the relationship between the AICA and porus acusticus and AICA and the nerves of the CN VII/VIII complex are variable, based on our findings, some themes exist. Our study found that the majority of AICA will travel in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. Five arteries (10%) traveled below the CN VII/VIII complex, six (12%) traveled posterior to the nerve complex, four (8%) formed a semi-circle around the upper half of the nerve complex, and two (4%) traveled between and partially separated the nervus intermedius and facial nerve proper. In regard to relationships between the AICA and the nerves of the facial/vestibulocochlear complex, 33 arteries (66%) traveled in a plane between the facial/nervus intermedius nerves and the cochlear and vestibular nerves. Twenty-five (50 sides) fresh adult cadavers underwent dissection of the cerebellopontine angle in the supine position. The formation of arterial loops inside or outside of the internal auditory meatus (IAM) can cause abutment or compression of CN VII and CN VIII. AICA compression of the facial-vestibulocochlear nerve complex can lead to various clinical presentations, including hemifacial spasm (HFS), tinnitus, and hemiataxia. The anterior inferior cerebellar artery (AICA) has variable branches producing vascular loops that can compress the facial cranial nerve (CN) VII and vestibulocochlear (CN VIII) nerves. The narrowest part of the external auditory canal is called the isthmus and lies at the junction of the cartilaginous and bony portions of the canal 5.Vascular loops in the cerebellopontine angle (CPA) and their relationship to cranial nerves have been used to explain neurological symptoms. A normal variant defect in the anteroinferior aspect of the osseous part of the canal that connects with the temporomandibular joint is known as the foramen tympanicum (foramen of Huschke). The skin of this inner part is directly applied to periosteum, with no subcutaneous tissue present. The roof and upper part of the posterior wall arise from the squamous part of the temporal bone 4. The anterior wall, floor, and lower part of the posterior wall arise from the tympanic part of the temporal bone 3,4. The medial two-thirds is surrounded by bone. Defects in the cartilaginous part of the canal, which allow transmission of infection and malignancy, are known as fissures of Santorini. The lateral one-third is bounded by a fibrocartilaginous tube continuous with the auricle 3. The external auditory canal is typically 2.5 cm in length and is S-shaped. As the term external auditory meatus is variably used to refer to the canal itself or the porus acusticus externus (the round lateral opening), it may be better to use the term external auditory canal rather than meatus to avoid potential confusion.
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