Operative surgical nuances of modified extradural temporopolar approach with mini-peeling of dura propria based on cadaveric anatomical study of lateral cavernous structures

Abstract

Background: Extradural temporopolar approach (ETA) has been modified as less invasive manner and named as trans-superior orbital fissure (SOF) approach with mini-peeling technique. The present study discusses the operative nuances of this modified technique on the basis of cadaveric study of lateral cavernous structures.

Methods: In five consecutive cadaveric specimens, we performed an extradural anterior clinoidectomy with mini-peeling of the dura propria to expose the anterior clinoid process entirely. We also investigated the histological characteristics of the lateral cavernous sinus (CS) between the dura propria and periosteal dura at the SOF, foramen rotundum (FR), and foramen ovale (FO) levels, and of each trigeminal nerve division.

Results: Coronal histological examination of the lateral wall of the CS showed invagination of the dura propria and periosteal dura into the SOF. In contrast, no such invagination was observed at the levels of the FR and FO. This finding supports the technical rationale of the only skeletonization of the SOF for peeling of the dura propria but not FR. In addition, our modified ETA method needs only minimal dural incision between the SOF and FR where no cranial nerves are present.

Conclusion: Our technical modification of ETA may be recommended for surgical treatment of paraclinoid lesions to reduce the risk of intraoperative neurovascular injury.

Keywords: Anterior clinoidectomy; cavernous sinus; extradural temporopolar approach; paraclinoid lesion; skull base surgery.

Figure 1

After standard frontotemporal craniotomy, the middle fossa dura is dissected until the foramen rotundum, and superior orbital fissure are exposed (a). Skeletonization of the foramen rotundum is not needed because this junction is naturally exposed at the foramen rotundum (a, arrow). The roof of the superior orbital fissure is skeletonized and opened to expose the junction between the dura propria of the temporal lobe and the periosteal dura (b, arrowheads). The bone around the meningo-orbital band is drilled and incised to a length of 4 mm (c). Peeling of the dura propria is started from the foramen rotundum to the lateral wall of the superior orbital fissure (d). V2: Second division of the trigeminal nerve

Figure 2

The dura propria is peeled from the lateral wall of the superior orbital fissure until the anterior clinoid process is exposed epidurally (a). Drilling of the anterior clinoid process with a high-speed drill using saline irrigation is started from the lateral part of the anterior clinoid process (b). After removal of the anterior clinoid process, the clinoid segment (C3) of the internal carotid artery can be seen (c). II: Optic nerve, III: Oculomotor nerve, IV: Trochlear nerve, V1: First division of the trigeminal nerve, V2: Second division of the trigeminal nerve

Figure 3

Cavernous sinus region including the superior orbital fissure, foramen rotundum, and foramen ovale was removed en bloc (a), and embedded in paraffin (b). The dura propria, which consists of the cranial nerve perineurium, is invaginated at the level of the superior orbital fissure (c). In contrast, no such invagination was observed at the levels of the foramen rotundum (d) and foramen ovale (e). Black broken line shows the layer of the peeling. V1: First division of the trigeminal nerve, V2: Second division of the trigeminal nerve, V3: Third division of the trigeminal nerve. Scale bars = 500 μm

Figure 4

Schematic illustration of the dura propria of the temporal lobe and other anatomical structures. The junction between the dura propria and the periosteal dura was invaginated at the superior orbital fissure (a, blue broken line). Our method needs only minimal dural incision between the superior orbital fissure and foramen rotundum where no cranial nerves are present (b, blue broken line). The dura propria peeling can be performed until the anterior clinoid process is totally exposed epidurally (c). OC: Optic canal, II: Optic nerve, III: Oculomotor nerve, IV: Trochlear nerve

Figure 5

Schematic illustration of the operative techniques of extradural anterior clinoidectomy with mini-peeling of the dura propria followed by extradural temporopolar approach. During cutting of the meningo-orbital band, the tip of the micro-scissors is pointed to the exposed dura propria junction at the skeletonized superior orbital fissure (a). The dura propria incision can be limited to the dura propria between superior orbital fissure and foramen rotundum where no neurovascular structures exist (a, black broken line). The dura propria should be carefully peeled from the superior orbital fissure to preserve the sphenoparietal sinus on the peeled dura propria, which appears whitish until the anterior clinoid process is entirely exposed (b). Before drilling, the inferolateral part of the anterior clinoid process should be dissected because the extradural part of the oculomotor nerve passes there (b, arrow). After removal of the anterior clinoid process, the optic canal should be opened using a micro-punch. The clinoid segment (C3) of the internal carotid artery can be seen and the optic strut between the C3 and optic sheath is removed if necessary (c). Final operative view of the extradural temporopolar approach (d) suggests that incision of the falciform ligament and distal dural ring facilitates mobilization of the optic nerve and internal carotid artery, which contributes to a wide operative field in the infraoptic and subchiasmatic spaces without intraoperative neurovascular injury. OC: Optic canal, OS: Optic strut, II: Optic nerve, III: Oculomotor nerve, IV: Trochlear nerve, V1: First division of the trigeminal nerve, V2: Second division of the trigeminal nerve, SPS: Sphenoparietal sinus, DDR: Distal dural ring, FL: Falciform ligament, OA: Ophthalmic artery, Ach: Anterior choroidal artery