CT-based morphometric predictors of feasibility for the infralabyrinthine approach to the petrous apex: a radioanatomical study.

BACKGROUND

The infralabyrinthine approach offers a direct, hearing-preserving route to the petrous apex but is limited by substantial anatomical variability.

PURPOSE: To develop a reproducible computed tomography based morphometric protocol for preoperative assessment of the infralabyrinthine approach to the petrous apex.

METHODS

This retrospective, single-centre morphometric study, conducted according to STROBE guidelines, included 40 adults with high-resolution temporal bone CT scans allowing clear delineation of infralabyrinthine landmarks. Patients with prior otologic surgery or congenital inner ear malformations were excluded. Nine bilateral anatomical distances of the infralabyrinthine corridor were bilaterally measured in the Pöschl plane. Intra- and interobserver reproducibility were assessed with Lin's concordance coefficient, while correlations were tested with Spearman's. 3D modelling and surgical videos illustrated findings.

RESULTS

Among 80 ears, 34 (42.5%) had at least one direct limiting measurement (≤3 mm), and 65 (81.25%) when including indirect projections. The most restrictive distances involved the jugular bulb's proximity to inner ear structures. In contrast, distances between the facial nerve and the dura of the posterior cerebral fossa, the internal auditory meatus and the jugular bulb, the cochlea and the dura of the posterior cerebral fossa, and the internal carotid artery and the internal auditory meatus rarely showed such limitations.

CONCLUSIONS

Preoperative CT morphometry allows reproducible assessment of infralabyrinthine access to the petrous apex. Key distances, especially between the jugular bulb and inner ear structures, can guide surgical feasibility. This approach may enhance planning, navigation, and patient safety.