Anatomical aspects of optic nerve decompression in transcranial and transsphenoidal approach

Abstract

Purpose

The proximal portion of the optic nerve is quite prone to injury at the entrance of the optic foramen by tumoral or traumatic pathologies. As a result, it is important to show which way and which part we can effectively and safely decompress the pathologies affecting the optic nerves. In this study, we compared the decompression of the proximal segment of the optic canal Likewise, we investigated the anatomy and histopathology of the opticocarotid region from below and above.

Materials and methods

A total of 30 adult sellar and parasellar samples were extracted from human cadavers. Anatomical dissection and histological examination were performed from transcranial and transsphenoidal ways. The walls of the proximal optic canal were evaluated with an operating microscope and endoscope. The relationship between the optic canal, the internal carotid artery, and the optic nerve were qualitatively and quantitatively examined.

Results

Similar rates of circular optic canal decompression were achieved by each approach; however, by means of decompression, the transsphenoidal approach was superior for the inferior and medial portions of the optic nerve and transcranial approach was superior for the superior and lateral portions and also more appropriate for optic nerve mobilization.

Conclusion

This is one of the first studies to reveal the ways of the decompression of the proximal optic canal by transcranial and transsphenoidal approaches. According to this study, the medial and inferior proximal portions of the optic nerves are histologically more prone to injury caused by traction or compression. Transcranial or transsphenoidal approach should be preferred according to the location of the pathology and anatomical and histological characteristics of this region.

Introduction

Sellar and parasellar tumors, sphenoid sinus and posterior ethmoidal sinus lesions, maxillofacial traumas, vascular pathologies and inflammatory processes can affect the optic canal and the optic nerve (Chen et al., 2007, Maurer et al., 1999, Taha et al., 2011). Optic nerve decompression is used for these pathologies, leading to optic nerve damage (Cascone et al., 2012, Feldon, 2007, Maurer et al., 1999, Pletcher and Metson, 2007, Taha et al., 2011, Tan et al., 2007).

Transethmoidal optic nerve decompression was first described by Sewell in 1926, and an intracranial approach was reported as early as 1922 by Dandy as Maurer mentioned (Maurer et al., 1999). The optic canal consists of four walls, including the following: 1) superior wall, anterior or superior root of lesser wing; 2) inferior wall, optic strut, namely, posterior root of lesser wing; 3) medial wall, the body of sphenoid bone; and 4) lateral wall, the anterior clinoid process (Onofrey et al., 2007).

Optic nerve decompression can be performed for the superior, lateral, inferior and medial walls of the optic canal (Al-Mefty et al., 1998, Evans et al., 2000, Locatelli et al., 2011, Yılmazlar et al., 2012). The dural sheath of the proximal part of the optic nerve is tightly bound with the periosteum of the lesser wing; therefore, its strict adherence to the optic nerve is most vulnerable to injury in the optic foramen entrance (Yılmazlar et al., 2012).

Optic nerve decompression can be performed by unroofing the optic canal by a transcranial approach. This approach is particularly suitable for intracranial pathologies extending to the optic canal (Yılmazlar et al., 2012). Following unroofing the optic canal, anterior clinoidectomy is performed in to decompress the optic canal laterally. Decompressed optic nerve length can be increased two-fold by anterior clinoidectomy (Evans et al., 2000).

Transcranial approaches may pose some problems for the pathologies which affect the optic nerve inferiorly, whereas the transsphenoidal approach is more suitable for pathologies affecting the optic canal inferiorly and medially (Yılmazlar et al., 2012). With the introduction of functional endoscopic sinus surgery since 1980s, endoscopic techniques have been developed (Steinsapir and Goldberg, 2011, Zada et al., 2010).

In this study, the limits of optic nerve decompression were compared using a microsurgical transcranial approach and an endoscopic transsphenoidal approach. The anatomic and histological details of the region and the anatomic landmarks were investigated during the transcranial and transsphenoidal approach. Also, the anatomical relations of the proximal part of the optic canal, the surgical importance of anatomic landmarks and the availability of mobilization of the optic nerve were examined.