Trans-Frontal-Sinus Subcranial Approach

29 Trans-Frontal-Sinus Subcranial Approach

Nicola Boari, Filippo Gagliardi, Alfio Spina, and Pietro Mortini

29.1 Introduction

The trans-frontal-sinus subcranial approach is well suited for the treatment of tumors of the median anterior skull base. This technique provides early devascularization of the tumor by division of the ethmoidal arteries, direct tumor access from the base, atraumatic frontal lobes decompression, broad exposure of sphenoid and ethmoidal sinuses. It also provides good visual exposure for the dissection of the optic nerves and anterior cerebral arteries, and affords access to a pedicled pericranial flap for dural reconstruction.

29.2 Indications

• Olfactory grove and planum sphenoidale meningiomas.

• Tuberculum sellae and diaphragma sellae meningiomas.

• Giant pituitary adenomas.

• Clival chordomas.

• Esthesioneuroblastomas.

• Malignancy of the anterior skull base – sinonasal tumors.

29.3 Patient Positioning

• Position: The patient is positioned supine with the head fixed to a horseshoe head holder.

• Body: The body is placed in neutral position with the trunk elevated 30° to increase venous backflow and the legs elevated at the level of the heart.

• Head: The head is in neutral position, elevated 15° and extended 20° with the vertex kept downward.

• Anti-decubitus devices: Rolls are placed under the knees.

• The zygoma has to be the highest point in the surgical field.

29.4 Skin Incision

• Coronal incision (See Chapters 6 and 7)

◦ Starting point: Incision starts 1 cm anterior and above the tragus.

◦ Run: Incision line should stay behind the hairline.

◦ Ending point: It ends 1 cm anterior and above the tragus of the contralateral side.

29.4.1 Critical Structures

• Superficial temporal artery.

• Facial nerve.

29.5 Soft Tissues Dissection (Fig. 29.1)

• Myofascial level

◦ A subgaleal dissection posterior to the coronal plane of the incision may be performed to maximize the length of the pericranial flap.

◦ The pericranial flap is then gently elevated from the cranial vault from posterior to anterior.

Fig. 29.1 Frontonasal osteotomy. The osteotomy of the anterior wall of the frontal sinus is performed using an oscillating saw (dotted lines).
Abbreviations: FB = frontal bone; FSAW = frontal sinus anterior wall; PC = pericranium; PO = periorbit; SON = supraorbital nerve; TM = temporal muscle; ZP = zygomatic process.

• Muscles

◦ Temporal fascia and muscle are not detached from the temporal fossa.

• Bone exposure

◦ The scalp is raised forward to expose the supraorbital ridge bilaterally and the nasal process of the frontal bone up to the fronto-naso-maxillary suture in the midline.

◦ The periorbit is detached from the superior and medial wall of the orbit on both sides.

• Supraorbital nerve and artery

◦ They can be freed from the supraorbital notch bilaterally to avoid traction on the orbital contents.

29.5.1 Critical Structures

• Supraorbital nerve and artery.

• Periorbit.

• Lacrimal gland.

29.6 Osteotomy (Fig. 29.2)

An osteotomy of the anterior wall of the frontal sinus, including the upper medial aspect of the superior orbital rims is performed with a reciprocating saw.

• Cuts

◦ I: The first cut is made at the nasofrontal suture on the axial plane down the medial orbital wall and along the nasomaxillary grooves just anterior to the lacrimal crest.

◦ II and III: Two symmetric cuts are made medial to the supraorbital notch vertically on the sagittal plane.

◦ IV: A horizontal cut is made on the axial plane across the frontal bones, connecting the previous two, at a level corresponding to the superior limit of the frontal sinus.

29.7 Anterior Skull Base Exposure

• The anterior wall of the sinus is lifted after fracturing the frontal intersinus septa with a chisel.

• Intersinus septa are removed with a rongeur. The mucosa lining the anterior and posterior walls of the sinus is resected (Fig. 29.3).

• Posterior sinus wall is thinned using a diamond drill and piecemeal removed using a Kerrison punch.

• Frontal dura is dissected from the apex and lateral surfaces of the crista galli, which is detached from the ethmoidal cribriform plate, and removed.

• Dissection in a subperiorbital plane along the medial wall of the orbit is performed to identify the anterior and posterior ethmoidal arteries, which are coagulated and divided bilaterally (Fig. 29.4).

• The falx with the origin of the superior sagittal sinus are coagulated and cut.

• Bone from the medial orbital walls is removed and the ethmoid can be drilled to obtain access to the nasal and sphenoethmoidal cavities and to the upper clivus.

• Drilling of the planum sphenoidalis up to the tuberculum sellae can be accomplished (Fig. 29.5).

• The medial optic canals can be unroofed bilaterally to perform an extradural optic nerves and chiasm decompression.