Maxillary Strut Anatomy and Implications for a Transpterygoid Approach to the Middle Fossa

Introduction: Endoscopic endonasal approaches (EEA) offer surgical access to middle fossa structures including Meckel’s cave and medial temporal lobe without the need for brain retraction. The anteromedial triangle of the middle fossa, bounded by the ophthalmic (V1) and maxillary (V2) branches of the trigeminal nerve and a line between the superior orbital fissure (SOF) and foramen rotundum (FR), can act as a corridor to the sphenoid sinus from a lateral approach, or to the temporal lobe from an EEA. While one study has looked specifically at the maxillary strut (MS) in the context of EEA,¹ the authors sought to establish a radiographic method to quantify the increased exposure of temporal lobe offered by drilling out the MS during a transpterygoid approach. In addition, they looked for correlations between MS height, FR position relative to midline, and pneumatization of the sphenoid sinus (SS), as each has implications for surgical planning.

Methods: Fifty-four thin-cut head CTs were randomly selected from those performed at our institution in the prior 18 months, excluding scans with nasal or sinus surgery or pathology. Coronal cuts of both hemisinuses on each scan were examined for distance from FR at its widest cross-section to SOF, representing the height of the maxillary strut; the distance from FR to the midline; and pneumatization of SS as described by previous methods.²

Results: There was no significant difference between the left and right hemisinuses for any of the 3 metrics applied. The average height of the maxillary strut was 3.0 mm (range: 0.9–7.8 mm). The average distance from FR to the midline was 18.5 mm (range: 15.1–23.0 mm). The most common SS pneumatization pattern was prerotundum for the right hemisinuses, consistent with the prior study;² however, this did not hold true for the left hemisinuses. There was no correlation between maxillary strut height with either FR-to-midline distance or SS pneumatization. Increasing SS pneumatization displayed a slight trend toward increased FR-to-midline distance on both sides but did not reach statistical significance.

Conclusion: The anteromedial triangle represents a surgical window to the middle fossa via a transpterygoid approach, and maxillary strut removal may improve exposure. In examining the radiographic characteristics of the MS and surrounding structures, the authors found some concordance with previous studies, but also identified some differences. Notably, the average radiographic MS height measured on CT was significantly different than that measured in EEA cadaver dissections: 3.0 mm vs 10.1 mm respectively.³ Further radiographic study, as well as correlation with anatomic measurements, can help define a proxy for MS height that, in combination with other radiographic features, can help tailor the surgical approach.