30 Transbasal and Extended Subfrontal Bilateral Approach • The transbasal approach is a transcranial extradural anterior approach to the midline anterior skull base, sellar region-suprasellar region, and clivus. • It is considered the workhorse for removing a variety of benign and malignant tumors of the anterior skull base. • Anterior skull base pathology extending intradurally can also be resected via this approach. • Pathology: Chordomas, chondrosarcomas, meningiomas, craniopharyngiomas, sino-nasal malignancies with cranial extension. • Pre-positioning: A spinal drain or a frontal ventriculostomy is inserted for brain relaxation. • Position: The patient is positioned supine with the head fixed in a Mayfield head holder. • Head: The head is translated up and slightly extended to allow the frontal lobes to fall away from the skull base. • The glabella must be the highest point in the surgical field. • Bifrontal curvilinear incision ◦ Starting point: Incision starts at the level of the zygoma. ◦ Course: It runs behind the hairline, preferably 2 cm posterior to the proposed edge of the craniotomy, so that the skin incision does not overlie the bony opening. ◦ Ending point: It ends at the contralateral zygoma. • Variations ◦ Bow shaped incision (yellow dotted line–Fig. 30.2) ◦ Zig-zag incision (red dotted line–Fig. 30.2) • Myofascial level (Fig. 30.3) ◦ The scalp flap along with the pericranium is reflected inferiorly over the face. ◦ The temporal fascia is sharply incised, and further dissection is carried inferiorly in an interfascial or subfascial plane to protect the branches of the facial nerve. Fig. 30.1 (A,B) Patient head positioning in a Mayfield head-holder. Fig. 30.2 (A,B) Variations in incision planning. Curvilinear incision (black solid line), bow-shaped incision (yellow dotted line), zig-zag incision (red dotted line). Fig. 30.4 Dissection of the supraorbital nerves, and craniotomy planning. ◦ The branches of the facial nerve travel through the superficial fat pad, which lies in the plane between the superficial temporal fascia and the scalp. ◦ The superficial temporal fascia and fat pad are reflected inferiorly together with the scalp. ◦ The orbital rims are exposed bilaterally, and the supraorbital nerves are mobilized out of the supraorbital notches and reflected inferiorly with the scalp (Fig. 30.4). ◦ The temporal muscle and fascia over the keyhole is sharply incised and pushed inferiorly to create space for placement of a burr hole. • Facial nerve branches. • Supraorbital nerves. • Burr holes (Fig. 30.4) ◦ One over each keyhole. ◦ One anterior to the coronal suture in a parasagittal location. • Craniotomy ◦ A unifrontal craniotomy flap is turned using a craniotome (Fig. 30.5). ◦ The dura over the superior sagittal sinus is stripped from the overlying bone using a Penfield under direct tangential view (Fig. 30.5). ◦ The craniotomy is extended to the contralateral keyhole for a bi-frontal craniotomy (Fig. 30.6). ◦ The edge of the craniotomy is kept at least 2 cm in front of the skin incision to facilitate wound healing and reduce the incidence of infection. • Orbitofrontal osteotomy ◦ With spinal fluid drainage, the dura mater of the anterior fossa is dissected from the anterior cranial base bilaterally. ◦ Similarly, the periorbit is dissected from the roof of the orbit. ◦ Osteotomy cuts are made with a reciprocating saw near the nasofrontal suture to the crista galli, and through the roof of the orbits and laterally to the orbital rims (Figs. 30.7, 30.8). ◦ An alternate smaller orbitofrontal osteotomy cut is shown with red dotted lines (Fig. 30.7).
30.1 Indications
30.2 Patient Positioning (Fig. 30.1)
30.3 Skin Incision (Fig. 30.2)
30.4 Soft Tissue Dissection
Abbreviations: FB = frontal bone; KH = keyhole; P = pericranium; SN = supraorbital nerve.
30.4.1 Critical Structures
30.5 Craniotomy
30.5.1 Bifrontal Craniotomy
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