The angular trajectory of the vestibular aqueduct: evaluation using photon-counting CT

The angular trajectory of the vestibular aqueduct (ATVA) has been proposed as a radiographic marker for developmental endotypes of Menière's disease. Current ATVA measurements rely on software-based proxies because the proximal vestibular aqueduct is often below the spatial resolution of conventional CT. Photon-counting CT (PCCT) may allow direct visualization of the proximal trajectory and enable patient-specific ATVA measurement. In this retrospective study, PCCT temporal bone scans from 64 patients (128 ears) were analyzed, and ATVA was measured directly by two independent readers, alongside additional VA morphometric parameters. The mean ATVA (106.9° ± 11.7°) was consistent with previously reported values, suggesting that PCCT can approximate established measurements without relying on geometric proxies. However, reproducibility was poor: interobserver agreement for ATVA was low (ICC = 0.24), and intra-observer agreement varied markedly between readers (ICC = 0.80 vs. 0.27). This variability can be related to subjective line placement, the curved anatomy of the VA, and the need to integrate information across multiple image slices. In contrast, midpoint VA diameter measurements, particularly in the Pöschl plane, demonstrated moderate to good reproducibility. Methodological standardization, such as the use of individualized oblique reconstructions or minimum intensity projections, may improve the reliability of ATVA measurements. Alternatively, other surrogate markers, such as the retrolabyrinthine bone thickness, may provide superior reproducibility while maintaining clinical relevance for endotype differentiation. Overall, despite enabling direct visualization, the current PCCT-based ATVA assessment is limited by poor reproducibility and requires methodological refinement for routine clinical implementation. KEY POINTS: •Question Photon-counting CT can directly assess the angular trajectory of the vestibular aqueduct for Menière's disease endotyping, avoiding software-based proxies used as conventional CT cannot resolve its proximal anatomy. •Findings Photon-counting CT showed a mean ATVA of 106,9°, comparable to values previously reported in the literature, but with poor inter-reader agreement. •Critical relevance statement Photon-counting CT enables direct patient-specific assessment of the angular trajectory of the vestibular aqueduct and may support clinically meaningful endotype categorization in Menière's disease.