Anatomic Considerations of Microvascular Free Tissue Reconstruction of Clival Defects: Expanding the Algorithm for Skull Base Reconstruction in Endoscopic Endonasal Surgery

Objective: To describe anatomical considerations of endoscopic endonasal inset of radial forearm free tissue transfer (RFFTT) of clival defects and its clinical relevance in reconstruction of ESBS defects.

Materials and Methods: Full transclival defects averaging 17.2 cm² were dissected in four cadaveric specimens. A RFFTT model was used to characterize reconstruction technique and flap inset. Bilateral neck explorations were performed for identification of recipient vessels. Descriptive measures for pedicle orientation, pedicle length, and recipient vessel intraluminal diameter were obtained.

Results: Mean facial artery intraluminal diameter was significantly smaller on the right (2.1 ± 0.3 mm) compared with the left (2.5 ± 0.0 mm) (p = 0.02). There was no difference between mean facial vein intraluminal diameter on the right (2.8 ± 0.6 mm) compared with the left (2.5 ± 0.4 mm). Bilateral anterior and lateral maxillotomies preserving the zygomaticomaxillary buttresses and endoscopic medial maxillectomies were prepared as corridors for flap passage. For tunneling of the pedicle to the facial vessels, premasseteric space tunnels were created. In all specimens, the RFFTT was folded lengthwise and introduced via the anterior maxillotomy and passed through the medial maxillectomy. Through an endoscopic endonasal approach, the RFFTT pedicle was oriented cranially with the remainder of the flap placed against clival defect. The mean pedicle length required for anastomosis from the skull base to the neck was 13.2 ± 0.5 cm on the right and 13.1 ± 0.4 cm on the left.

Conclusion: Anatomical characterization of RFFTT repair of clival defects is critical in developing a roadmap for the reconstructive surgeon as part of team-based approach to endoscopic endonasal surgery. The primary options for reconstruction of ESBS defects include multilayer fascial grafts, vascularized pedicled flaps, and locoregional flaps, notably the temporoparietal fascial and extracranial pericranial flap. With a greater understanding of the anatomical factors related to successful preoperative planning of free flap design and inset, microvascular free tissue transfer may be added to the reconstruction ladder for ESBS defects.