Petrous Slope: Quantifying the Exposure of Trautmann's Triangle

Introduction: Trautmann’s triangle is an area of dura exposed via a retrolabyrinthine presigmoid approach, and represents a transpetrosal surgical corridor to the posterior fossa that will preserve hearing.¹ Given that this operating space is subject to anatomical constraints, i.e., a high-riding jugular bulb or a short labyrinth-sigmoid distance, a quantitative radiologic measure could be used in preoperative planning to determine if additional bone removal is necessary. The authors hypothesize that an increased angle between the sigmoid sinus and petroclival fissure – the ‘petrous slope’ – would provide the largest area of Trautmann’s triangle to be exposed via a retrolabyrinthine presigmoid approach.

Methods: 30 thin-cut head CTs were randomly selected from those performed at our institution in the prior 12 months, excluding scans with any temporal bone pathology. Axial and coronal cuts of both sides of each scan were examined for distance from jugular bulb to petrous ridge, distance from posterior semicircular canal (PSCC) to sigmoid sinus, and the ‘petrous slope’ defined as the angle between the sigmoid sinus and the petroclival fissure at the level of the internal auditory canal (IAC). Aeration of the temporal bone was measured at level of sigmoid sinus and at the labyrinth by previously described methods.²

Results: We found no significant difference between the left and right sides for any of the 5 measurements taken. The average jugular bulb-petrous ridge distance was 16.7 mm (range 9.5–18.0 mm). The average sigmoid sinus-PSCC distance was 11.1 mm (range 6.26–10.9 mm). The average angle of the petrous slope was 152.7° (range 119.3–177.0°). There was no statistically significant correlation between the petrous slope and the jugular bulb-petrous ridge or sigmoid sinus-PSCC measurements. Increasing temporal bone aeration by either metric did not show any trend with measurements of the petrous slope.

Conclusions: In exposing Trautmann's triangle via a posterior petrosectomy, one faces challenges related to the close proximity of several critical structures. By using jugular bulb-petrous ridge distance and sigmoid sinus-PSCC distance as proxies for Trautmann’s triangle, the surgeon can use preoperative imaging to determine if adjunct approaches are necessary for the desired exposure. In particular, the petrous slope delineates the anterior limit of visualizing the petroclival region in the context of a posterior pestrosectomy. The range of values for this easy-to-define, highly reproducible measurement suggests that further anatomic and radiographic study can yield relationships between critical structures to assist in designing individualized surgical approaches for each patient and their respective anatomy and pathology.

Referenzen

References

1 Tubbs RS, Griessenauer C, Loukas M, Ansari SF, Fritsch MH, Cohen-Gadol AA. Trautmann’s triangle anatomy with application to posterior transpetrosal and other related skull base procedures. Clin Anat 2014;27(7):994–998

2 Han SJ, Song MH, Kim J, Lee WS, Lee HK. Classification of temporal bone pneumatization based on sigmoid sinus using computed tomography. Clin Radiol 2007;62(11):1110–1118