Incidentaloma or Problem? Cerebellopontine Angle Arachnoid Cysts in Pediatric Patients

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Introduction: Arachnoid cysts (AC) are intracranial, benign, and often incidentally identified CSF-filled sacs. In the past, case reports have associated AC to cranial nerve (CN) VII and VIII symptoms such as sensorineural hearing loss, vestibular symptoms, facial paresis/spasm, and headaches. There are isolated reports using surgical intervention to rectify hearing deficits or other symptoms. Despite these reports, literature demonstrating a clear link to reported symptomatology and an understanding of their natural history is lacking. We present a case example that inspired an investigation into the possible association of AC in the cerebellopontine angle (CPA) with sensorineural hearing loss (SNHL) based on distortion of the CN VIII complex via mass effect. Methods: A single-institution, retrospective chart review was conducted between 2010 and 2024 including pediatric patients with AC and a history of audiologic evaluation. From this cohort, nineteen patients were identified with posterior fossa AC involving the CPA. Cyst characteristics including size/volume, cisternal and internal auditory canal (IAC) length, IAC diameter, and cochlear aperture were collected. Cysts were categorized as with or without contact with CN VIII complex; any nerve distortion was calculated as the perpendicular distance from the expected path at the midcisternal segment. Information regarding SNHL and other symptoms were tabulated. Descriptive statistics and linear regression analysis were performed. Results: Out of 227 total patients with AC and audiometric evaluation, 19 (8.4%) patients were identified with posterior fossa AC in the CPA. The average age was 8.1 years. 11/19 (58%) patients had contact/displacement of CN VIII complex in the CPA, while 8/19 (42%) did not. Interestingly, there was no significant difference in maximum linear dimension and estimated spheroid volume of the groups with and without distortion of CN VIII complex (median dimension: 2.50 vs. 2.05 cm, p = 0.2809) and (median volume: 3.285 vs. 1.523 cm 3 , p = 0.0506), respectively. Of the group with AC contacting with the CN VIII complex, 4/11 (36%) patients had isolated ipsilateral asymmetric SNHL not better explained by other pathology; however, this was not statistically significant when compared to those without CN VIII displacement (0/8 patients, p = 0.0549). We were unable to find any association between degrees of CN VIII displacement, involvement of the root entry zone, cyst growth, or FLAIR changes in CN VIII complex with the presence of ipsilateral asymmetric SNHL. Conclusion: AC in the CPA is an uncommon and often incidental abnormality. Contact/displacement of CN VIII complex by AC may portend development of ipsilateral asymmetric SNHL, though this was not statistically significant in our cohort. An expanded investigation is necessary to elucidate associations or predictive factors between AC and SNHL. Publication History Article published online: 07 February 2025 © 2025. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany

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