Subfrontal or transbasal approach

Lesion of the anterior skull base  include variety of pathologies such as trauma, SCF fistulas, tumors (including the ones from invading from nasopahryngs), metastases, infections etc.
The subfrontal/transbasal approach provides wide access to the anterior skull base and paranasal sinuses.

The pathologies 
·    Meningioma (suprasellar/olfactory groove)
·    Craniopharyngeoma
·    Chordoma
·    Chondrosarcoma
·    Germinoma
·    Esthesioneruroblastoma
·    Osteoma
·    Mucocele
·    Trauma
·    Adenoid cyctic carcinoma
·    Nasal carcinoma
·    Orbital tumors
·    Congenital Deformity

Fig. 2 Skin incision – superior view
The curvilinear skin incision is made just behind the hairline, extending no more than 2,5 cm below the superior temporal line.

Fig. 3 Keep the dissection in the loose areaolar tissue between galea and pericranium (intraoperative image)

Fig. 4 Cadaveric dissection presenting the dissection in the loose areaolar tissue betweengaleaand pericranium.

Fig. 5 Do not extend the dissection to the supraorbital rim in order not to compromise the flap blood supply.

Fig. 6 Under-mining the posterior part of the incision provides additional pericranial flap length.

Fig. 7 On this image flap incision boundaries are presented with black dots.

Fig. 8 -2 Pericranium flap – final view. Because the frontal sinuses are generously opened in this approach, this flap is used to prevent CSF leaks, as well as to reconstruct the anterior cranial fossa.

Fig. 9 The supra-orbital and supra-trochlear nerves could lie in a sulcus or a separate bony channel. These nerves need to be mobilized in order to reflect further down the skin flap.

Fig. 10. In this graphic the boundaries of the frontal craniotomy and fronto-nasal osteotomy are presented. This technique is performed in 2 separate steps

Fig. 12 Frontal craniotomy –steps (intraoperative image). A shaft is drilled over the superior sagittal sinus. Using a high speed craniotome a bone flap is developed as shown in the graphic. Use the B8 straight attachment (without the footplate) drill bit, in order to cut any bony septae in the frontal sinus.

Fig. 13 Split bone graft technique which could be used for later reconstruction of the orbit or anterior cranial fossa.

Fig. 14. Removal of the posterior wall of the frontal sinus with high-speed drill. If there is a large posterior wall this can be taken out in a large piece and used as bone graft.

Fig. 15. If there is a large posterior wall this can be taken out in a large piece and used as bone graft.

Fig. 16 The posterior wall of the frontal sinus as a separate bone graft.

Fig. 17 In the following figures the fronto-nasal osteotomy is presented. The supraorbital rim cut is medial to the supraorbital notch. Use brain spatulas to protect the globes.

Fig.18 Fronto-nasal osteotomy could be performed with oscillating saw or B8 straight attachment trough the fronto-nasal suture.

Fig. 19 Fronto-nasal bone flap final view.

Fig. 20 Removal of the fronto-nasal bone flap increases the angle of vision and leads to decreased brain retraction. The two naso-frontal ducts are visible, as well as crista gali and superior sagittal sinus.

Fig 21. Exposure achieved with bifrontal (light red area) and extended subfrontal approach (light blue area). Note the significant brain retraction needed to reach deep structures and the lines of vision (1 and 2 red lines) with the reduced amount of brain retraction provided with the extended subfrontal approach.

Fig 22. Opening the dura and Falx sectioning.

Fig. 23 Cutting the superior sagital sinus (SSS) and falx. This manoeuver allows for the visualization of the frontal base.

Fig. 24 Intradural olfactory nerve could be identified after elevation of the frontal lobes.

Fig 26. Lateral dissection exposes the ICA and ACA (A1)

Fig 27. Fenestration of lamina terminalis and exposure of the third ventricle.

Fig 28. Structures beyond the frontal skull base

Fig 29. Cribrectomy

Fig 30. Cutting the asal septum

Fig 31. Removal of the mucosa of Sphemoid sinus

Fig 32. Exposure of the rostrum and sphenoid ostia

Fig 33. The sphenoid sinus is opened and the septum is visualized

Fig 35. Carotid artery prominence in the sphenoid sinus prominence and supraclinoidal part as well as nad optic nerve are exposed.

Fig 37-1. Next step

Fig 38. Reconstruction of the anterior fossa floor after cribrectomy with a titanium mesh