Elsevier

Surgical Neurology

Volume 62, Issue 3, September 2004, Pages 268-274
Surgical Neurology

Anatomy
Transethmoidal approach to the optic canal: Surgical and radiological microanatomy

https://doi.org/10.1016/j.surneu.2004.01.022Get rights and content

Abstract

Background

The purpose of the study is to describe anatomic topographic landmarks for transethmoidal approach to optic canal for optic nerve decompression. The study focuses on microsurgical/radiologic anatomies and their relationships in the region of the optic canal and orbit.

Methods

Human optic canal and related anatomic structures were studied in orbits of 6 formalin preserved adult human cadavers. In addition, anatomic measurements were made with digital vernier caliper on the orbits of 25 adult human skulls. The relation between ethmoidal and sinus was assessed with computed tomography (CT) scan in 25 living human heads needing cranial CT scan for any reason.

Results

The suture on the conjunction of frontal, maxilla, and lacrimal bones with a location in medial side of the orbit was accepted as a landmark. When the measurements were taken from this landmark, the distances to supraorbital margin were: right(R): 16.76 ± 2.62 mm, left (L): 17.10 ± 1.97 mm, and to infraorbital margin were R: 20.18 ± 3.24 mm, L: 18.94 ± 2.19 mm. The distances to the anterior ethmoidal foramen were R: 19.66 ± 3.96 mm, L: 19.11 ± 2.84 mm, and to the posterior ethmoidal foramen were R: 32.01 ± 2.90 mm, L: 32.62 ± 3.33 mm. Mean distance between the anterior and posterior ethmoidal foramen were R: 12.55 ± 3.4 mm, L: 13.51 ± 4.2 mm. The posterior ethmoidal foramen and optic ring were separated only by the mean distances of R: 5.34 ± 2.81 mm, L: 4.9 ± 3.35 mm.

The distance from the suture to the distal (orbital) opening of the optic canal was R: 37.35 ± 2.73 mm, L: 37.52 ± 3.47 mm and to proximal (intracranial) opening of the canal were R: 49.52 ± 2.62 mm, L: 50.94 ± 3.35 mm. The average widths of proximal (intracranial) canal measured were R: 7.43 ± 1.95 mm, L: 7.38 ± 2.01 mm and those of distal canal (orbital) were R: 5.12 ± 1.1 mm, L: 4.95 ± 1.32 mm. The mean lengths of the optic canal were R: 11.19 ± 2.68 mm, L: 12.42 ± 3.38 mm.

In radiologic examinations, the mean numbers of anterior group ethmoidal cells were R: 7, L: 6 and those of posterior group ethmoidal cells were R: 4, L: 3. The results of CT demonstrated 7 (14%) Onodi or sphenoethmoidal cells in 50 orbits of living humans.

Conclusion

The examination of radiologic anatomy in addition to microanatomy can significantly contribute to preoperative and postoperative evaluation of the patients.

Section snippets

Materials and methods

Twelve orbits of adult cadaver fixed in formalin were dissected, and anatomic measurements were made on the orbits in 25 adult human skulls. An assessment has been made on the orbits in 25 living human heads to find out the relation among optic canal, ethmoidal and sphenoid sinus. The relations among optic canal, ethmoidal, and sphenoid sinus were investigated with computed tomography (CT) scan in 25 living human heads. Surgical and radiologic anatomic images were obtained in cadaver studies

Anatomic results

Orbital walls have seven bones. Orbital opening is somewhat quadrangular; its supraorbital margin formed entirely by the frontal bone. The lateral margin is largely the frontal process of the zygomatic bone; infraorbital margin is zygomatic bone laterally and maxilla medially. The medial margin is formed above by the frontal bone, below by the lacrimal crest of the maxillary frontal process [15].

Frontal, maxilla, and lacrimal bones are combined with fronto-maxillo-lacrimal suture on medial

Discussion

Issues like compression of the optic nerve, precise pathogenesis and the best treatment remain controversial [20]. Various mechanisms of an injury may play a role in damage to the optic nerve. Direct fractures of the optic canal may be seen with bony fragment injury or transecting the optic nerve [7]. Other mechanisms of injury include intraneural edema, hematoma, and shearing injury to the microvasculature, altered cerebrospinal fluid circulation, and interruption of direct axoplasmic

Conclusion

A comprehensive knowledge of microanatomy and radiologic anatomy will contribute to the effective use of transethmoidal approach. Preoperative orbit CT scans performed with thin slices are very important in revealing the relation between optic canal, optic nerve, ethmoidal and sphenoidal sinuses structures, the existence of Onodi cell, and the location and grade of the compression. The assessment of relation between significant vascular and neural structures and morphologic measurements of bone

Acknowledgements

We are grateful to Isıl Özkoçak, M.D. for editing the draft. We are also grateful to Haluk Erdem, M.D., and artist Erdem Yücel for the excellent artwork.

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