Microvasculature of the Middle Fossa Floor as Potential Landmarks for Middle Fossa Approaches: An Anatomical Study

Background: Microvasculature of the structures of the middle ear plays an important role in the preservation of their optimum functions. Advancement in the endoscopic equipment allowed better visualization of these tiny vessels. Visualization of these vessels during middle fossa approaches not only help in protection of the structures supplied by these vessels, but also can be used as landmarks to structures viewable in the middle fossa floor, namely, the arcuate eminence (AE), great superficial petrosal nerve (GSPN), geniculate ganglion (GG), and cochlea (Co).

Objective: To identify and describe the microvasculature visualized on the floor of the middle fossa from an endoscopic view via the lateral transorbital approach (LTO) and microscopic view via the extended middle fossa approach (EMF) and the possibility of their use as new landmarks.

Methods: Five Latex-injected heads (10 sides) were dissected. LTO approach was performed first with the aid of 0o and 30o rod-lens endoscopes with the drilling of the greater sphenoid wing to get access to the middle fossa as described previously, followed by the EMF approach with the aid of the microscope. AE, GSPN, GG, and Co were identified. The microvasculature, namely, the superior tympanic artery (STA), superficial petrosal artery (SPA), subarcuate fossa artery (SFA), and common cochlear artery (CCA) were also identified. The length of these vessels was measured. Origin, course, and relation to the surrounding structures were described.

Results: The STA, SPA, SFA, and CCA were identified in all specimens. In 70% of the specimens, the STA was predominant, while in 30%, the SPA and STA arose as a distinct branch from middle meningeal artery. In all specimens, the STA and the SFA arteries functioned as a reliable and constant landmark running to the arcuate eminence; the CCA to the cochlea and the SPA to the GSPN. We found that the GG receives blood supply in 60% of specimens from the STA while in 40% from the STA. In all specimens, a branch from the STA led the AE; this branch usually crosses some bony prominences in the middle fossa floor but always ends 1 to 0.5 mm before the AE. The CCA was identified during unroofing the IAC and was possible to follow it 0.5 mm close the cochlea which marks the limit of the petrosectomy close to the medial aspect of Co. The SFA led to the AE in the posterior wall of the ICA in all specimens. AICA loop inside the IAC was identified in 20% of the specimens and in these cases, the labyrinthine artery arose from the top of the loop and CCA was pushed anteriorly with the point of entry to the cochlea maintained.

Conclusion: The enhanced and close visualization of the microvasculature on the floor of the middle fossa following the advancement in endoscopic equipment made possible to identify small vessels not easily visualized before. These tiny vessels may play as landmarks to essential structures in middle fossa approaches, and their preservation is vital to achieving better functional outcomes.

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