Lateral Transorbital versus Extended Middle Fossa Approach to the Petrous Apex: A Comparative Anatomical Study

Background: Transorbital approaches to challenging anatomic structures within the skull base have recently gained significant interest. Indeed, a recent publication described the feasibility of the transorbital approach to the petrous apex, the middle fossa floor and even to the posterior fossa. Choosing the appropriate approach to lesions in these areas is multifactorial dependent on the location of the lesion, location of adjacent critical structures, and surgical training.

Objective: This anatomical study aimed to compare the surgical accessibility of the petrous apex between the lateral transorbital (LTO) approach and the classic extended middle fossa (EMF) approach by quantifying the surgical freedom, angle of attack, and the distances to important landmarks viewable with both approaches.

Materials and Methods: Five colored latex-injected cadaveric heads (10 sides) were utilized in this study. On the right side, the LTO approach was performed first followed by the middle fossa approach. The opposite sequence was performed on the left side. The endoscopic LTO approach was accomplished with the aid of 0 and 30 degrees rod-lens endoscopes. First, the lateral orbital rim was removed. Drilling of the greater wing of the sphenoid permitted access to the middle fossa. The EMF approach was accomplished with the aid of the microscope. For this purpose, a 5 × 5 cm craniotomy was performed with the anterior two-thirds of the bony flap anterior to a line extending from the external auditory canal. Surgical freedom and angle of attack were measured using the Neuronavigation system. Landmarks used for measurements included the Arcuate eminence, Geniculate ganglion, Cochlea, greater superficial petrosal nerve (GSPN), trigeminal impression, and medial and lateral parts of the internal auditory canal (IAC).

Results: The LTO approach provided more surgical freedom to the GSPN, the porous acoustics, and the trigeminal impression compared with EMF approach; however, the EMF showed more surgical freedom to the arcuate eminence and geniculate ganglion. It was also noted that was easier to separate the two layers of dura via transorbital approach in comparison to the middle fossa approach. Direct identification of the greater superficial petrosal nerve was accomplished via an anterior to posterior direction with a favorable angle of view using the endoscope for better preservation of GSPN in comparison to the posterior to an anterior fashion of dissection in the EMF approach. Unroofing of IAC and Cochlea was more favorable with the LTO approach because of a better vertical angle of attack.

Conclusion: In general, we believe that the LTO approach allows more surgical freedom, especially in the vertical plane, and better visualization with minimal retraction of the temporal lobe to reach medially located structures; however, situated laterally structures made the EMF approach more favorable. It is important to emphasize that the clinical applicability of LTO approach still needs to be approved, but the EMF approach is already established.

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No conflict of interest has been declared by the author(s).