18 Midline Interhemispheric Approach The interhemispheric approach is a midline transcranial approach, which provides access through this anatomical corridor to the corpus callosum and the ventricular system. The craniotomy can be easily tailored according to the pathology and to the venous anatomy, which is one of the main limiting factor of surgical maneuverability. Callosotomy provides access to the lateral ventricle and to the third ventricle, either through the foramen of Monro or through the choroidal fissure. The approach is indicated for extra-axial tumors involving the interhemispheric fissure, as well as intra-axial lesions located in the anterior aspect of the third ventricle and lateral ventricles. • Vascular and neoplastic lesions located in the anterior aspect of the third ventricle, including lesions extending out of the third ventricle into the lateral ventricles. ◦ Tumors of the third ventricle including gliomas, ependymomas, choroid plexus papillomas, meningiomas, craniopharyngiomas. ◦ Colloid cysts. ◦ Vascular malformations. • Extra-axial tumors of the interhemispheric fissure (i.e., falx or parasagittal meningiomas). • Position: The patient is positioned supine or lateral decubitus with the head fixed with a Mayfield head holder. • Body: The body is lined horizontally. • Head: The head is flexed 15 to 30°, depending on the location of the lesion. • U-shaped unilateral incision ◦ An area of approximately 5×5 cm centered on the bregma is shaved, prepped and draped. ◦ A U-shaped horseshoe scalp incision is made with the open end of the “U” pointing laterally. ◦ Starting point: The incision starts just behind the hairline, 5 cm lateral from the midline. ◦ Course: It runs 1/3 anterior and 2/3 posterior to the coronal suture. ◦ Ending point: Incision ends the same as the starting but more posterior. • Linear ¾ Suttar or bicoronal incision ◦ Starting point: The incision starts just above the pinna. ◦ Course: It runs along the coronal suture. ◦ Ending point: Incision ends at the superior attachment of the temporal muscle controlaterally. Fig. 18.1 Skin incision (red dotted line). • Superficial temporal artery. • Auriculo-temporal nerve. • Myofascial level ◦ The myofascial level is incised according to skin incision. ◦ It is important to preserve the pericranial layer, for further reconstruction. • Muscles ◦ Although the temporal muscle is exposed by the skin incision, there is no need to incise it, thus it is preserved. • Bone exposure ◦ The bone exposure is completed when the frontal and parietal bony surface are exposed for about 5×5 cm. ◦ Antero-posterior extension of the bone exposure has to run 1/3 anterior and 2/3 posterior to the coronal suture. ◦ Lateral exposure extends up to the temporal muscle attachment on the ipsilateral side. ◦ The sagittal suture has to be exposed on the midline. Midline coronal craniotomy • Burr holes ◦ I: The first burr hole has to be placed along the midline about 2 to 3 cm anterior to the coronal suture. ◦ II: The second burr hole is made along the midline about 3 to 4 cm posterior to the coronal suture. • Cuts ◦ The first cut is made between the two burr holes, laterally in a U-shaped fashion with a lateral extension reaching the superior temporal line. ◦ The second cut is made along the sagittal sinus.
18.1 Introduction
18.2 Indications
18.3 Patient Positioning
18.4 Skin Incision (Fig. 18.1)
Abbreviations: CS = coronal suture; LE = left ear; M = midline; N = nose; RE = right ear.
18.4.1 Critical Structures
18.5 Soft Tissues Dissection
18.6 Craniotomy/Craniectomy (Figs. 18.2, 18.3)
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