26 Anterolateral Skull Base: Anatomy, Surgical Technique, and Nuances

Iype Cherian, Hira Burhan, Eugenio Cerezo, Juan Lopez, Ahmed Al Jradi, Vinod Felix, Sunil Munakomi, Pramod Chaudhary, Prakash Kafle, Vignesh S., Jagadish Thingujam, and Sudeep Shrestha

The brain is like a tube which is folded in the sagittal and axial manner. The most important structures that a skull base surgeon desires to operate upon are situated within these folds. A pterional approach with sylvian dissection helps in unfolding the brain to a certain extent,1 in an oblique fashion; however, this maneuver limits the surgeon to only one surgical window. Maneuvers to unlock the brain in the sagittal and axial planes give an excellent exposure to the skull base.

To unlock the brain in a sagittal fashion, one needs to remove as much of sphenoid ridge as possible. To unlock the temporal lobe in an axial fashion, one needs to detach the temporal lobe from the cavernous sinus in an extradural fashion, thus opening the curve. Adding a sylvian dissection to the abovesaid maneuvers greatly improves the basal exposure by opening up the brain in a lateral oblique fashion.

26.2 Extended Skin Incision and Craniotomy

An extended skin incision is carried out to expose the frontotemporal, orbitobasal, and middle fossa. This skin excision is an extension of the routine pterional approach ( Fig. 26.1a). A layer-by-layer dissection allows removal of subcutaneous tissue, and the temporalis muscle is retracted to expose the bony structures underneath ( Fig. 26.1b, c). A keyhole is drilled across the lateral margin of the sphenoid as close to frontal bone as possible ( Fig. 26.1d) and craniotomy is performed to prevent any interference with the retracted temporalis muscle (Fig. 26.2).

Fig. 26.1Skin incision: (a) Extended incision for frontotemporal, orbitobasal, and middle fossa exposure; must be an extension of the incision in the routine pterional approach. Dissection performed in layers. (b) Subcutaneous fat dissection of the temporoparietal muscle layer. (c) Separation of temporal muscle fascia from muscle fibers in the zygomatic arch before its exposure. (d) Exposure of the zygomatic arch (ZF), temporal bone (T), and frontal bone (F); the circle indicates the point where the keyhole for the craniotomy is made. Drill across the lateral surface of the greater wing of the sphenoid bone as close to the frontal process as possible.

Fig. 26.2Craniotomy: For exposure of the floor or the temporal base, groove is drilled to prevent interference with retracted temporal muscle. After drilling, a craniotomy is done.

26.3 Orbitomeningeal Band Dissection

Once the dura is exposed, the sphenoid ridge and the temporal bone are drilled as much as possible to provide an optimal view of skull base (Fig. 26.3). The orbitomeningeal band (OMB) is at the junction of basi-frontal and temporal lobe and is the lateral aspect of superior orbital fissure (Fig. 26.4). Dissecting the OMB under high magnification enables one to get into a plane where the frontal lobe dura can be dissected off the anterior clinoid and the temporal dura can be dissected off the true cavernous membrane of the cavernous sinus. This uncovers the clinoid for easier anterior clinoidectomy and displaces the temporal lobe laterally in an extradural fashion, thus enabling axial unlocking.²

Fig. 26.3Sagittal unlocking: (a) Exposure of the dura. The temporal lobe (T), frontal lobe (F), orbitomeningeal band (OMB), and sphenoid ridge can be seen. (b) The sphenoid ridge and temporal bone are drilled for optimal view of the skull base.

Fig. 26.4Dissection of orbitomeningeal band (OMB): (a) Exposure of anterolateral approach; the OMB, maxillary branch of the trigeminal nerve (V2), temporal bone (T), and frontal bone (F) can be seen. (b) Identifying the OMB at the lateral edge of the superior orbital fissure and maxillary (V2) and mandibular (V3) branch of the trigeminal nerve. (c) Sharp cutting of the OMB under high magnification (arrow). (d) Exposure after complete dissection of the OMB. (e) After dissection of the OMB, the ophthalmic (V1) and maxillary (V2) branch of the trigeminal nerve can be seen, and oculomotor (CN3) and trochlear (CN4) nerves followed through the cavernous sinus (CS).

26.4 Pericavernous Dissection Techniques

Once the true cavernous membrane plane is reached by accurate dissection of the OMB, one can follow sharp dissection to maintain a pericavernous plane. At the level of V2 and below, this plane is absent, but the interdural plane may be maintained, thereby decreasing the bleeding. In cases of bleeding, fibrin glue and Surgicel are useful. Using this technique, once the dissection is extended behind V3, and the middle meningeal artery is coagulated and divided, the greater superficial petrosal nerve (GSPN) can be seen as a dural band rather than a nerve.

Following dissection of the OMB in the right plane, the basi-frontal dura can be sharply dissected off the anterior clinoid to completely uncover it (Fig. 26.5 and Fig. 26.6). This makes anterior clinoidectomy easier and safe. Orbital roof removal to uncover the extradural optic nerve can also be combined along with the dural cutting and sectioning of the distal dural band. This allows mobilization of the carotid and increase space while dealing with aneurysms of this region.³

Fig. 26.5Anterior clinoidectomy: (a) Anterior clinoid process (ACP) is drilled very carefully due to its close relationship with adjacent neurovascular structures. (b) Careful removal of the ACP. The optic nerve (CN2) lies medially and internal carotid artery laterally. (c) The membrane and anterior petroclinoid fold are opened. Structures visible: Optic nerve (CN2), internal carotid artery (ICA), oculomotor nerve (CN3), trochlear nerve (CN4), and ophthalmic and maxillary branches of the trigeminal nerve (V1–V2).

Related posts:

The Microsurgical Transoral Approach Eyebrow Supraorbital Approach for Skull Base Lesions Transbasal/Transcranial Microsurgical Approaches to Anterior Fossa Meningiomas Microsurgical Anatomy of the Orbit Cranio-Orbit-Zygomatic (COZ) Approach Pretemporal Approach

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