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Suprasellar and paraclinoidal regions
Core Procedures
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Endoscopic endonasal suprasellar approaches
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Open transbasal subfrontal approach to anterior cranial fossa and lamina terminalis
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Anterior clinoidectomy
With the increase in the application of endoscopic endonasal surgery to the skull base, it is feasible to access midline lesions in the rostrocaudal axis extending from the cribriform plate to the inferior clivus and the foramen magnum.
The principles of standard sellar approaches both endonasally and via the use of a microscope have been extensively described in the literature. In this chapter, sellar anatomy will be covered with the emphasis on introducing the anatomical principles underlying approaches to the suprasellar region. In order to provide a comprehensive open microsurgical view of this region, pertinent anatomy for performing a transbasal subfrontal approach and anterior clinoidectomy will also be covered. The primary aim is to enable familiarization with the anatomical principles underlying these approaches.
Endoscopic endonasal approaches
Endoscopic transplanum transtuberculum approach
Indication
Variations of the endoscopic transplanum transtuberculum approach are used to access pituitary tumours with suprasellar extension, tuberculum sellae or planum meningiomas, and craniopharyngiomas.
Patient positioning
The patient is positioned supine with a Mayfield head holder being used to maintain a neutral position, or with slight head rotation towards the surgeon.
Critical anatomy and operative steps
Osseous anatomy
Understanding the anatomy of the sphenoid bone is crucial for these approaches. In Fig. 21.1 , moving from caudal to rostral, note the location of the sella, tuberculum, chiasmatic sulcus and limbus sphenoidale. The medial optico-carotid recess (MOCR) corresponds to the lateral aspect of the tuberculum, and the lateral optico-carotid recess (LOCR) represents the base of the optic strut. The chiasmatic sulcus is defined as the region from the tuberculum to the limbus sphenoidale that extends between the optic canals. The planum sphenoidale is defined as the region more distal to the limbus. The anterior root of the lesser wing of the sphenoid forms the roof of the optic canal (OC) while the posterior root or the optic strut forms the floor of the OC.
Operative approach
Extradural bony drilling
An endoscopic endonasal approach to the sella and tuberculum sellae region involves a wide bilateral sphenoidotomy, posterior ethmoidectomy and posterior septectomy ( Fig. 21.2 ). The intrasphenoidal septations are thinned down using a drill. It should be noted that these septations can lead the operator off the midline to the paraclival or clinoidal internal carotid artery (ICA). Bone overlying the sella and the chiasmatic sulcus is egg-shelled using a coarse diamond 4 mm burr ( Fig. 21.3 ). The thinned-down bone overlying the chiasmatic sulcus is gently dissected off while maintaining dural integrity. A thickened dural fold (limbus dura) overlies the limbus sphenoidale. The tuberculum strut is then carefully thinned down prior to its subsequent removal (see Fig. 21.3 ). The MOCR at the lateral end of this strut corresponds to the transition between the paraclinoidal and supraclinoidal segments of the ICA ( Fig. 21.4 ). Understanding these segments from an endonasal perspective is critical for operating safely in this region. The parasellar ICA relevant to this approach is a combination of the cavernous and paraclinoidal segments. The proximal dural ring (located at the level of the middle clinoid) marks the transition between the anterior genu of the cavernous ICA and the clinoidal segment (see Fig. 21.4 ). From caudal to rostral, the relevant anatomical relationships to note at this stage are the sella, diaphragm, superior intercavernous sinus, tuberculum, chiasmatic sulcus, limbus dura, and finally the dura of the planum. The next step represents further removal of bone to expose the planum dura (see Fig. 21.4 ). The bone overlying the OC along its medial aspect and the roof can be seen. In a standard transplanum transtuberculum approach, the limbus sphenoidale is drilled, along with further removal of the medial aspect of the anterior root of the lesser wing of the sphenoid that forms the roof of the OC (right side, see Fig. 21.4 ). This will usually mark the end of the bony drilling involved in such an exposure.
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