Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Bifrontal Transbasal Approach, Surgical Principles, and Illustrative Cases

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.

Keywords: anterior cranial fossa; bifrontal; central skull base; step-by-step; trainee; transbasal; tumor.

Fig. 1

Step by step of the transbasal approach. ( A–F ) Without supraorbital bar removal, ( G–H ) with additional removal of the orbital bar. ( A ) Bicoronal skin incision modifications behind the hairline. ( B ) Pericranium flap harvested beyond skin incision for reconstruction. ( C ) Interfacial dissection—a cut between the superficial and the deep layer of the temporal fascia, preserving the frontal branches of the facial nerve. ( D ) Exposure of the supraorbital and supratrochlear nerves if the orbital bar removal is intended. ( E ) Bifrontal craniotomy, burr holes placed. ( F ) Dural exposure after bifrontal craniotomy. ( G ) Possible extensions of osteotomies to include the orbital bar. For a limited 2-piece transbasal, one can include an osteotomy on the red dashed lines on the frontonasal suture and just medial to the supraorbital nerve exit. For an extended transbasal approach, the osteotomies should follow the red dashed lines on the nasofrontal suture and the more lateral ones, just lateral to the frontozygomatic suture. H. Exposure after removal of the orbital bar with the extended transbasal.

Fig. 2

Intradural dissection. ( A ) Detail showing the crista galli divided and the posterior wall of the frontal sinus, which should be drilled. Its mucosa should be exenterated to prevent later complications (e.g., mucocele). ( B ) Exposure after drilling the posterior wall of the frontal sinus. ( C ) The dura mater is opened in a linear fashion, parallel to the orbital bar axis. The superior sagittal sinus is ligated inferiorly. ( D ) Intradural view with the bifrontal craniotomy. The olfactory nerve was released from the frontal lobe surface, to preserve olfaction. We can see the planum sphenoidale, followed by the limbus sphenoidale, anterior clinoid and internal carotid artery. ( E ) On this closer look, we can see the pituitary stalk, anterior and middle cerebral artery, optic nerve and optic chiasm, and the beginning of lamina terminalis. ( F ) On this interhemispheric perspective, we can see the lamina terminalis open, allowing access to the intraventricular area.

Fig. 3

Endoscopic-assisted pictures through the craniotomy. ( A ) Endoscopic picture of the olfactory nerves and the falx cerebri. ( B ) Here, we can see the lamina terminalis, the anterior cerebral artery and the anterior communicating artery (ACoA). ( C ) The infundibular recess, anterior to the ACoA. ( D ) In this detail, we can see the opening toward the third ventricle. ( E ) Intraventricular view, mammillary bodies on the floor of the third ventricle. ( F ) Thalami, massa intermedia, posterior wall of the third ventricle. ( G ) Choroid plexus along the choroidal fissure. ( H ) In this detail, we can see the foramen of Monro.

Fig. 4

Nasal cavity access. ( A ) The olfactory nerves, cribriform plate, falx insertion. ( B ) The limits of the osteotomy toward the nose are traced within the dura—lamina papyracea ( medial orbital wall ), posterior wall of the frontal sinus, planum sphenoidale. Dura is cut and the remaining flap flipped. ( C ) Drilling of the anterior fossa floor proceeds. Ethmoidal arteries are coagulated and cut. ( D ) The nose cavity is open. ( E ) Superior turbinate is removed. ( F ) Nasoseptal or an extended nasoseptal flap is harvested. The middle turbinate is removed. ( G ) Covering of the defect with the extended nasoseptal flap. ( H ) Multilayer closure. The frontal sinus is occluded with fat harvested from the abdomen, the dural defect is closed with a fascia lata graft, and the pericranial flap is folded covering the skull base.

Fig. 5

Illustrative cases superior row—Case 1, olfactory groove meningioma. Preoperative ( A ) coronal, ( B ) sagittal T1-gadolinium, showing a large homogeneous enhancing lesion, lobulated, in the olfactory groove, suggesting a meningioma ( yellow arrow head ). Postoperative ( C ) coronal, ( D ) sagittal, T1-gadolinium showing no residual lesion. Inferior row—Case 2, hypothalamic cavernous malformation. Preoperative ( E ) axial, ( F ) coronal flair MRI of the bleeding of the cavernous malformation on the topography of the hypothalamus (retrochiasmatic and retroinfundibular) ( red arrow head ). Long-term follow-up ( G ) axial, ( H ) coronal T1-gadolinium MRI images with no residual lesion.

Fig. 6

Main modifications of the transbasal approach. ( A ) Limited bifrontal transbasal craniotomy, removal of the central part of the orbital bar only. ( B ) Extended transbasal, with removal of the supraorbital bar. ( C ) Extensive transbasal, removal of the supraorbital and the lateral orbital rim.