Evaluation of the Relationship Between the Internal Acoustic Canal Anatomy and Loops of the Anterior Inferior Cerebellar Artery Using 3-Tesla Magnetic Resonance Imaging

Background: Anatomical variations in vascular structures are frequently encountered. In the cerebellopontine region, anatomical variations, especially variations in the anterior inferior cerebellar artery (AICA) in relation to cranial nerves passing through the internal acoustic canal (IAC), are common. Magnetic resonance imaging (MRI) provides detailed information for the evaluation of the cerebellopontine region and the IAC anatomy. Objectives: This study aimed to examine the relationship between the IAC anatomy and AICA loop variations and to investigate the frequency of anatomical variations and its correlation with demographic variables. Patients and Methods: In this study, 253 patients (age > 18 years), who underwent 3-Tesla MRI of the temporal bone between July 2019 and December 2019, were retrospectively evaluated. The exclusion criteria were images of poor diagnostic quality due to technical or patient-related reasons and the presence of a localized tumor that could disrupt the IAC. Four patients were excluded from the study because they had tumors related to IAC. The AICA variations were categorized according to the Chavda classification. The IAC size, canal diameter, canal length, and meatus width were measured, and the canals were characterized as cylindrical, funnel-shaped, and bud-shaped. Results: A total of 249 patients were included in this study. The Chavda type I vascular loop was the most common type on both sides. The mean size measurements of IACs were significantly higher in the group of vascular loops compared to the group without vascular loops. The presence of a vascular loop was significantly more common in funnel- and bud-shaped IACs compared to cylindrical IAC. Also, there was a negative correlation between the patient’s age and all IAC dimensions. Conclusion: The results of the present study showed that the AICA loop variations were closely related to the size and shape of the IAC.

Incomplete Partition type I: Radiological Evaluation of the Temporal Bone

Objective: Incomplete partition type I is an uncommon congenital anomaly of the inner ear, characterized by typical cystic cochleovestibular appearance. Incomplete partition type I was firstly defined as cystic cochlea and vestibule without large vestibular aqueduct; however, large vestibular aqueduct and/or enlarged endolymphatic duct could rarely be seen in incomplete partition type I anomaly. Correct diagnosis of the type of cochlear malformation and differentiation of incomplete partition type I is necessary for patient management and surgical approach. Our aim was to document the temporal bone imaging findings in a series of patients with incomplete partition type I. Materials and Methods: CT (n=85) and/or MRI (n=80) examinations of 99 ears in 59 incomplete partition type I patients were retrospectively evaluated. All structures of the otic capsule were retrospectively assessed. The appearances of cochlea and vestibule, vestibular aqueduct/endolymphatic duct, semicircular canals were qualitatively evaluated by an experienced neuroradiologist. The vertical dimension of vestibular aqueduct and/or endolymphatic duct (from the point where the duct arises from the vestibule) was measured on CT/MRI. Anterior-posterior diameter of the internal acoustic canal and the diameter of cochlear aperture were measured on CT. The cochleovestibular nerves were evaluated on sagittal-oblique high T2-weighted imaging. Results: All 99 ears had defective partition with unpartitioned cochlear basal turn and absent interscalar septae, separated but cystic cochlea. The vestibule was enlarged in all ears except one. Semicircular canals were usually dysplastic (92.9%). A total of 35 incomplete partition type I ears (35.3%) had large vestibular aqueduct and/or enlarged endolymphatic duct. Internal acoustic canal was wide in 21% of ears. Cochlear aperture was wide in 5.9% of ears. Cochlear nerve was either hypoplastic or aplastic in about a quarter of incomplete partition type I ears. Conclusion: In up to one-third of incomplete partition type I patients, an associated large vestibular aqueduct /endolymphatic duct could be seen accompanying typical inner ear findings. Although the cochlear nerves are normal in the majority of cases, auditory brainstem implantation may be necessary in certain cases of incomplete partition type I anomaly.

The cranial nerves

There are 12 pairs of cranial nerves that are individually named and numbered using Roman numerals. Only some cranial nerves are mixed in function, i.e. they carry both sensory and motor fibres; others are purely sensory or motor and some may also carry pre- or post-ganglionic parasympathetic fibres. They pass through foramina in the base of the skull and are the olfactory (through cribriform plate to the nasal cavity), optic (through the optic foramen to the eye), oculomotor (through the cavernous sinus and superior orbital fissure to supply the eye), trochlear (as per oculomotor), trigeminal (three main branches that pass through the superior orbital fissure, foramen rotundum and foramen ovale, respectively), abducens (as per oculomotor), facial (through stylomastoid foramen to supply muscles of facial expression), vestibulocochlear (through the internal acoustic canal to control balance and hearing), glossopharyngeal, vagus, accessory (all pass through the jugular foramen) and hypoglossal (through the hypoglossal canal to control movements of the tongue) nerves.

Developmentally anomalous cerebellar encephalocele arising within the cerebellopontine angle and extending into the adjacent skull base in a pediatric patient

Lesions of the cerebellopontine angle (CPA) in young children are rare, with the most common being arachnoid cysts and epidermoid inclusion cysts. The authors report a case of an encephalocele containing heterotopic cerebellar tissue arising from the right middle cerebellar peduncle and filling the right internal acoustic canal in a 2-year-old female patient. Her initial presentation included a focal left 6th nerve palsy. Magnetic resonance imaging was suggestive of a high-grade tumor of the right CPA. The lesion was removed via a retrosigmoid approach, and histopathologic analysis revealed heterotopic atrophic cerebellar tissue. This report is the first description of a heterotopic cerebellar encephalocele within the CPA and temporal skull base of a pediatric patient.

Anatomical Limits of the Endoscopic Contralateral Transmaxillary Approach to the Petrous Apex and Petroclival Region

Objectives This study aimed to establish the anatomical landmarks for performing a contralateral transmaxillary approach (CTM) to the petrous apex (PA) and petroclival region (PCR), and to compare CTM with a purely endoscopic endonasal approach (EEA). Design EEA and CTM to the PA and PCR were performed bilaterally in eight human anatomical specimens. Surgical techniques and anatomical landmarks were described, and EEA was compared with CTM with respect to ability to reach the contralateral internal acoustic canal (IAC). Computed tomographic scans of 25 cadaveric heads were analyzed and the “angle” and “reach” of CTM and EEA were measured. Results Entry to the PA via a medial approach was limited by (1) abducens nerve superiorly, (2) internal carotid artery (ICA) laterally, and (3) petroclival synchondrosis inferiorly (Gardner's triangle). With CTM, it was possible to reach the contralateral IAC bilaterally in all specimens dissected, without dissection of the ipsilateral ICAs, pterygopalatine fossae, and Eustachian tubes. Without CTM, reaching the contralateral IAC was possible only if: (1) angled endoscopes and instruments were employed or (2) the pterygopalatine fossa was dissected with mobilization of the ICA and resection of the Eustachian tube. The average “angle” and “reach” advantages for CTM were 25.6-degree greater angle of approach behind the petrous ICA and 1.4-cm more lateral reach. Conclusion The techniques and anatomical landmarks for CTM to the PA and PCR are described. Compared with a purely EEA, the CTM provides significant “angle” and “reach” advantages for the PA and PCR.