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A New Internal Acoustic Canal Anomaly, Fused Single Internal Acoustic Canal: A Case Report
Melih Akşamoğlu1, Nuray Bayar Muluk2, Mehmet Hamdi Şahan1
1Department of Radiology, Gaziantep University Faculty of Medicine, Gaziantep, Türkiye.
Insights
This case report details a rare fused internal auditory canal (IAC) anomaly in an infant with bilateral deafness, hypotonia, and epilepsy. This finding represents the first documented instance of a fused IAC in medical literature.
Area of Science:
- Neurology
- Otolaryngology
- Radiology
Background:
- The internal auditory canal (IAC) is crucial for connecting the inner ear to the posterior cranial fossa.
- Anomalies of the IAC can lead to significant neurological and auditory deficits.
- Bilateral deafness, hypotonia, and epilepsy are complex conditions that can be associated with central nervous system abnormalities.
Purpose of the Study:
- To report a unique case of a fused internal auditory canal (IAC) anomaly.
- To describe the associated clinical and imaging findings in an infant.
- To highlight this as the first reported case of its kind in the literature.
Main Methods:
- Case report of an 8-month-old patient.
- Evaluation included clinical examination, Electroencephalography (EEG), temporal bone computed tomography (CT), and magnetic resonance imaging (MRI).
- Analysis of IAC morphology, inner ear structures, and cranial nerve appearance.
Main Results:
- The patient presented with hypotonia, epilepsy, and severe bilateral sensorineural hearing loss.
- CT revealed a fused IAC at the midline, bifurcating distally, with medially positioned inner ear structures and cochlear hypoplasia type III.
- MRI demonstrated a paired appearance of the VIII cranial nerve proximally, diverging at the IAC entrance, with indistinct cochlear nerves.
Conclusions:
- This is the first reported case of a fused internal auditory canal (IAC).
- The anomaly was associated with significant neurological and auditory impairments, including bilateral deafness and epilepsy.
- Detailed imaging is essential for characterizing rare IAC malformations and understanding their clinical implications.
Abstract:
The internal auditory canal (IAC) connects the inner ear to the posterior cranial fossa. In this case report, the authors presented an 8-month-old patient with an IAC anomaly and bilateral deafness. The patient has hypotonia and epilepsy, and there is multifocal epileptiform activity on Electroencephalography (EEG). Severe (total) sensorineural hearing loss was detected bilaterally. Temporal bone computed tomography showed that the internal acoustic canal is localized as a single entity at the midline and bifurcates into right and left branches approximately ~4 mm beyond. Following branching, the diameter of each IAC measures approximately ~2 mm. On both sides, inner ear structures are located more medially than normal, positioned close to the midline and each other. Both cochleae undergo approximately 1.5 turns, classified as cochlear hypoplasia type III according to Sennaroğlu and Bajin's classification. Magnetic resonance imaging showed that in the anterior aspect of the pons, extending from the midline to the internal acoustic canal, a paired appearance, resembling a couple, of the VIII cranial nerve is observed in close proximity to each other. The pair of the VIII nerve seems to diverge at the entrance of the internal acoustic canal, and immediately thereafter, they bifurcate into branches believed to belong to the superior and inferior vestibular nerves on both sides, but the cochlear nerve cannot be discerned. To the best of current knowledge, this is the first case in the literature as fused IAC.
