The Infralabyrinthine Route to the Petrous Apex: A Comparison of the Extradural Infralabyrinthine and Retrosigmoid Intradural Inframeatal Approaches

Background: The extradural infralabyrinthine approach (ILA) is often preferred in patients with lesions of the petrous apex and serviceable hearing. Recently, the retrosigmoid intradural inframeatal approach (RIIA) was described as a viable alternative with successful results. Since the ILA and the RIIA share the same surgical corridor, we compare both techniques anatomically.

Methods: Three adult cadaveric heads (6 sides) injected with colored latex underwent RIIA and ILA approaches to study the neurovascular structures and surgical landmarks. Dimension of the access window, area of exposure, angle of view, and depth of field were measured and analyzed.

Results: The average vertical dimensions and areas of exposure for the ILA and RIIA were 6.56 mm and 7.07 mm, and 63.77 mm² and 51.95 mm², respectively. The horizontal dimensions were similar in both approaches. After detachment and slight retraction of the jugular bulb, the vertical dimensions of the ILA further increased to 10.86 mm (range: 7.49–14.23 mm) and the area of exposure increased to 86.40 mm² (range: 58.81–114 mm²). The depth of the surgical field at the petrous apex in the RIIA (mean: 48 mm) was deeper than that of the ILA (mean: 41.7 mm) and the angle of view was directed toward the internal carotid artery.

Conclusion: The extradural ILA provides a larger area of exposure compared with the RIIA in normal anatomical specimens. The ILA to the petrous apex is a time-consuming and technically demanding approach but the RIIA requires cerebellar retraction and places the endolymphatic sac at risk of injury.