Anatomic Considerations of Microvascular Free Tissue Transfer in Endoscopic Endonasal Skull Base Surgery.

 Though microvascular free tissue transfer is well established for open skull base reconstruction, normative data regarding flap design and inset after endoscopic endonasal skull base surgery (ESBS) is lacking. We aim to describe anatomical considerations of endoscopic endonasal inset of free tissue transfer of transclival (TC) and anterior cranial base resection (ACBR) defects.  Radial forearm free tissue transfer (RFFTT) model.  Six cadaveric specimens.  Pedicle orientation, pedicle length, and recipient vessel intraluminal diameter.  TC and ACBR defects averaged 17.2 and 11.7 cm , respectively. Anterior and lateral maxillotomies and endoscopic medial maxillectomies were prepared as corridors for flap and pedicle passage. Premasseteric space tunnels were created for pedicle tunneling to recipient facial vessels. For TC defects, the RFFTT pedicle was oriented cranially with the flap placed against the clival defect (mean pedicle length 13.1 ± 0.6 cm). For ACBR defects, the RFFTT pedicle was examined in three orientations with respect to anterior-posterior axis of the RFFTT: anteriorly, posteriorly, and laterally. Lateral orientation offered the shortest average pedicle length required for anastomosis in the neck (11.6 ± 1.29 cm), followed by posterior (13.4 ± 0.7cm) and anterior orientations (14.4 ± 1.1cm) (  < 0.00001, analysis of variance).  In ACBR reconstruction using RFFTT, our data suggests lateral pedicle orientation shortens the length required to safely anastomose facial vessels and protects the frontal sinus outflow anteriorly while limiting pedicle exposure through a maxillary corridor within the nasal cavity. With greater understanding of anatomical factors related to successful preoperative flap planning, free tissue transfer may be added to the ESBS reconstruction ladder.