Dang, Danielle D

Abstract We investigated the extent of access to Meckel's cave (MC) and the middle cranial fossa (MCF) protecting the internal carotid artery (ICA) using the retrosigmoid approach with endoscopic-assisted reverse anterior petrosectomy (EA-RAP). Five specimens were dissected using the limited and extended EA-RAP. Based on the bone removal of the internal acoustic meatus (IAM) and subarcuate fossa, exposure of the MC and ICA were statistically compared. The limited and extended EA-RAP allowed access to the medial and anterior MC (4 mm posterior to the first genu of the cavernous ICA, and 20 mm posterior to foramen rotundum [FR]). The access to the lateral MC varied with distance of 12 and 8 mm medial to the foramen ovale for the limited and extended EA-RAP, respectively. In the extended EA-RAP, the exposure of the ICA was gained by drilling with the 0-degree endoscope (3 mm) versus 45-degree endoscope (9 mm). The working distances from the midpoint of the IAM to the most medial point of the exposed ICA was 24 mm. The most lateral point of the exposed ICA varied between 0- and 45-degree endoscopes with a distance of 21 and 13 mm, respectively. A coronal plane from the posterior genu of the cavernous ICA and a sagittal plane to the common crus of the semicircular canals can define the area of MCF accessed by the EA-RAP. Drilling of the temporal bone should be carefully customized according to the patient and can be aided by endoscopic assistance for direct visualization to minimize the risk of injuries to ICA.

Abstract Introduction The transbasal approach traditionally uses a bicoronal scalp incision with bifrontal craniotomy to establish an extradural midline skull base working corridor. Depending on additional craniofacial osteotomies, this approach can expand its reach to the nasal cavity and paranasal sinuses and may be employed for the resection of particularly complex sinonasal and midline skull base tumors. Given its discrepancy in nomenclature and differences in interoperator technique, we propose a practical, operatively oriented guide for trainees performing this approach. Methods Three formalin-fixed, latex-injected specimens were dissected under microscopic magnification and endoscopic-assisted visualization. Stepwise dissections of the transcranial-transbasal approach with common modifications were performed, documented with three-dimensional photography, and supplemented with representative case applications. Results The traditional transbasal approach via bifrontal craniotomy affords wide extradural access to the anterior cranial fossa and central skull base. The addition of craniofacial osteotomies further expands access into the sinonasal cavities, clivus, and craniocervical junction. Key steps described include patient positioning, bicoronal skin incision, pericranial graft harvest, bifrontal craniotomy, orbital rim osteotomy, sphenoidotomy, bilateral ethmoidectomies, and microsurgical dissection of the sellar region. Basal superior sagittal sinus ligation and durotomy allow for intradural exposure. Reconstruction techniques are also discussed. Conclusion While the transbasal approach is rich with historical descriptions, illustrations, and modifications, its stepwise performance may be relatively unknown and unclear to younger generations of trainees. We present a comprehensive guide to optimize familiarity with the transbasal approach and its indications in the surgical anatomy laboratory, mastery of the relevant microsurgical anatomy, and simultaneous preparation for learning and participation in the operating room.