Variation in the Size of the Cerebellopontine Angle in Adults: Implications for the Management of CPA Tumors

Introduction: Tumor size is a critical factor in managing vestibular schwannomas (VS), influencing decisions between conservative management, microsurgical resection, and radiotherapy. Traditionally, tumor size has been measured using linear methods, particularly focusing on the extrameatal component due to its role in brainstem compression and neurological complications. However, the impact of a tumor is also influenced by the size of the cerebellopontine angle (CPA) in which it resides. A small tumor in a confined CPA may cause significant brainstem compression, while a larger tumor in a spacious CPA may not. Despite its potential significance, CPA size has been underexplored in the literature. This study investigates the variability of CPA sizes and its implications for brainstem compression in VS patients.

Methods: A retrospective analysis was conducted on 25 adult MRI scans from a tertiary care center, focusing on the internal auditory meatus. CPA areas were measured bilaterally using axial T2-weighted FIESTA sequences at the level of the lateral semicircular canal. Exclusion criteria included patients with known VS or other CPA lesions. Four independent reviewers conducted the measurements, and inter-observer variability was assessed.

Results: The study cohort had an average age of 55.04 years, height of 163.18 cm, and weight of 69.88 kg. Comparative analysis of CPA area measurements revealed no significant difference between the left (187.36 ± 56.28 mm²) and right sides (181.34 ± 68.01 mm²; p = 0.738). Correlation analysis showed weak associations between CPA area and demographic variables, with a modest positive correlation with age (r = 0.132) and slight negative correlations with height (r = −0.074) and weight (r = −0.188).

Discussion: This study highlights the variability in CPA sizes among adults and the limited correlation between CPA size and demographic factors. While tumor size is a crucial consideration in treatment planning, especially regarding brainstem compression, these findings suggest that CPA volume should also be considered. Current classification systems that focus solely on tumor size may not adequately account for the potential impact of brainstem compression, particularly in smaller CPAs.

Conclusion: This study is the first to assess the role of CPA size in VS management. The results suggest that relying solely on linear tumor measurements may be insufficient for effective treatment planning. Incorporating CPA volume and brainstem compression assessments into clinical guidelines could improve the accuracy of predicting neurological outcomes and inform better treatment decisions for VS patients.

Publication History

Article published online:
07 February 2025