Maximizing Lateral Extension of Endoscopic Endonasal Approaches to the Posteromedial Anterior Cranial Fossa: An Anatomical Study

Introduction: The main limitation of endoscopic endonasal approaches (EEAs) to the posteromedial anterior cranial fossa (ACF) is extension lateral to the optic canals. No study, however, details how lateral a lesion needs to extend before an EEA is not effective. In this study, we quantify how lateral one can reach over the optic canal using an EEA through surgically oriented, anatomical dissections. Further, we propose technical nuances to safely maximize lateral extension.

Methods: On 20 sides of 10 formalin-fixed specimens, endoscopic endonasal transplanum approaches were performed using 0- and 30-degree angled endoscopes. Subsequently, the bone superior to the optic canal was drilled as lateral as possible, both at the levels of the sphenoid limbus and the annulus of Zinn. The lateral-most portion of ACF dura accessed at these levels was marked and its distances from the midline and the lateral aspect of optic canal were measured. These measurements were taken at the level of the limbus sphenoidale and annulus of Zinn. Next, to further extend our lateral drilling, we removed the posterior portion of the lamina papyracea (LP) and continued drilling the bone superior to the optic canal until maximal lateral drilling was performed. We then marked the new lateral-most portion of ACF dura accessed and repeated the same measurements. All measurements were made with a rigid ruler. Key steps of our dissection were 3D-photo documented on illustrative specimens and depicted in a cadaveric dissection video.

Results: At the level of the limbus sphenoidale, the dura lateral to the lateral margin of the optic canal was accessed in 50% of specimens prior to removing the LP and 100% of specimens after removing the LP. At the level of the limbus sphenoidale, the lateral-most portion of ACF dura accessed was 14.2 and 19.5 mm lateral to midline before and after removing the LP, respectively. At the level of the limbus sphenoidale, the lateral-most portion of ACF dura accessed was 0.7 and 6.0 mm lateral to the lateral margin of the optic canal before and after removing the LP, respectively. At the level of the annulus of Zinn, the dura lateral to the lateral margin of the optic canal was accessed in 30% of specimens prior to removing the LP and 100% of specimens after removing the LP. At the level of the annulus of Zinn the lateral-most portion of ACF dura accessed was 16.1 mm and 23.6 mm lateral to midline before and after removing the LP, respectively. At the level of the annulus of Zinn, the lateral-most portion of ACF dura accessed was 0.1 mm medial and 7.4 mm lateral to the lateral margin of the optic canal before and after removing the LP, respectively.

Conclusion: Through surgically oriented anatomical dissections, we demonstrate that removal of the LP may facilitate lateral drilling of the ACF at the level of the limbus sphenoidale and annulus of Zinn. Using this technique, consistent access to ACF dura lateral to the lateral limit of the OC can be afforded.

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Artikel online veröffentlicht:
07. Februar 2025