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220 Expanded Anterior Petrosectomy Through the Transcranial Middle Fossa and Extended Endoscopic Transphenoidal-Transclival Approaches: Qualitative and Quantitative Anatomic Analysis.

INTRODUCTION
Petroclival tumors and ventrolateral lesions of the pons present a unique surgical challenge. We aimed to provide qualitative and quantitative anatomic analyses of anterior petrous apicectomy through the transcranial middle fossa (TMF) and the extended endoscopic transphenoidal-transclival (EETT) approaches.


METHODS
Ten cadaveric silicon-injected cadaver heads were used for this study. The petrous apex and the clivus were drilled extradurally through both middle fossa and endonasal approaches. Using in situ and frameless stereotactic navigation points, we described and compared consistent data points collected from both approaches to calculate and compare their respective working areas, volumes of bone removed, approach angles and surgical freedom.


RESULTS
Mean exposed TMF area was 21.03 ± 3.46 cm, providing a 44.71 ± 4.13° working angle to the brainstem between cranial nerves (CNs) V and VI. Kawase rhomboid area measured 1.76 ± 0.34 cm. Mean volume of bone removed at the petrous apex was 1.20 ± 0.12 cm. GSPN-V3 and petroclival angles were 73.8° ± 8.55° and 70.07 ± 4.7°, respectively. Surgical freedom on the lateral brainstem was higher at a point halfway between CNs V and VI at the center of the rhomboid compared with the midline at the basilar sulcus (P < .01). Following clivectomy and petrous apicectomy through the EETT approach, area exposed was 5.29 ± 0.66 cm. Its boundaries were: CN V anterosuperiorly, anterior wall of the internal acoustic canal posteroinferiorly, carotid genu at the foramen lacerum anterolaterally, and clivus medially. Two subareas were defined and measured. One corresponded to the petrous apex, the other to the clivus. They measured 1.05 ± 0.44 cm and 4.25 ± 0.44 cm, respectively. There was no statistically significant difference in surgical freedom at the foramen lacerum and the midpoint basilar sulcus when approaching from either nostril (P > .05). At the petrous apex, volume of bone removed and area exposed were significantly larger for TMF approach (P < .001).


CONCLUSION
Expanded transclival anterior petrosectomy through the TMF approach provides an adequate corridor to lesions in the upper ventrolateral pons. EETT approach better fits midline lesions not extending laterally beyond CN VI and the C3 carotid when evaluating normal anatomical parameters.