- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, USA
- Department of Neurobiology and Anatomy, West Virginia University School of Medicine, Robert C. Byrd Health Sciences Center, Morgantown, West Virginia, USA
Matthew J. Zdilla
Department of Neurobiology and Anatomy, West Virginia University School of Medicine, Robert C. Byrd Health Sciences Center, Morgantown, West Virginia, USA
DOI:10.4103/2152-7806.150456Copyright: © 2015 Zdilla MJ. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Zdilla MJ, Cyrus LM, Lambert HW. Carotico-clinoid foramina and a double optic canal: A case report with neurosurgical implications. Surg Neurol Int 30-Jan-2015;6:13
How to cite this URL: Zdilla MJ, Cyrus LM, Lambert HW. Carotico-clinoid foramina and a double optic canal: A case report with neurosurgical implications. Surg Neurol Int 30-Jan-2015;6:13. Available from: http://sni.wpengine.com/surgicalint_articles/carotico%e2%80%91clinoid-foramina-double-optic-canal-case-report-neurosurgical-implications/
Background:The lesser wing of the sphenoid is a clinically important structure, particularly with regard to its anatomical relationship with neurovascular structures including the optic nerve, ophthalmic artery, and internal carotid artery. Anterior clinoidectomy, a neurosurgical procedure utilized to access paraclinoid aneurysms and neoplasms, is often complicated by the presence of anatomical variants including the carotico-clinoid foramen and the accessory optic canal.
Case Description:A rare case report is presented documenting the simultaneous occurrence of bilateral carotico-clinoid foramina and a unilateral accessory optic canal.
Conclusion:The presence of an accessory optic canal may be misconstrued as a carotico-clinoid foramen or pneumatization of the anterior clinoid process, lesser sphenoidal wing, or optic strut. The case report documents two clinically important variant structures occurring ipsilaterally, each with the potential to masquerade as the other radiographically and present complications to both neurosurgeons and radiologists. Knowledge of the unique combination of anatomical variants presented in this report may prevent adverse surgical events during anterior clinoidectomy procedures including hemorrhage of the ophthalmic artery or internal carotid artery and subsequent vision loss or death.
Keywords: Anterior clinoidectomy, internal carotid artery, ophthalmic artery, ophthalmic foramen, optic foramen, paraclinoid aneurysm
The lesser wing of the sphenoid is an important bony structure implicated in a variety of neurosurgical procedures including management of space occupying lesions such as aneurysms and neoplasms in the paraclinoid region.[
The ICA gives rise to the OphA, which travels through the optic canal alongside the optic nerve to reach the eye. Within the optic canal, the OphA most often travels inferolateral to the optic nerve (in 40.2% of individuals) [
A normal sphenoid bone with regional anatomy of the lesser wing of the sphenoid emphasized. (a) View of a normal sphenoid from the right and posterior. (Green box indicates the region of interest, which has been enlarged to produce Figure
Sphenoid bone with carotico-clinoid foramina and a double optic canal with regional anatomy of the lesser wing of the sphenoid emphasized. (a) View of the variant sphenoid from the right and posterior. (Green box indicates the region of interest, which has been enlarged to produce Figure
Reports have noted that the presence of the CCF causes morphological changes to the ICA in almost all cases.[
The lesser wing of the sphenoid may also possess another clinically remarkable finding – a ‘double optic canal’ variant which consists of the optic canal and an ‘accessory optic canal’ (AOC) [
Examination of an isolated sphenoid bone dry specimen from an individual of undetermined sex and age, held in the anatomy collection at West Liberty University, led to the observation of bilateral CCF in addition to a unilateral AOC within the left optic strut. The left optic strut of the sphenoid bone served as both the anterior boundary of the left-sided CCF as well as the bony structure encompassing the AOC [Figures
(a) Cranial view of the left lesser wing of the sphenoid. (ACP: Anterior clinoid process; OS: Optic strut (formed by the BP: Bony plate and MB: Main body); OCCL: Ossified carotico-clinoid ligament; OC: Optic canal; AOC: Accessory optic canal; CCF: Carotico-clinoid foramen) (b) A modified Rhese projection radiograph of the sphenoid, which corresponds with
Mensuration of the AOC and CCF was accomplished via macro photography. A scale with line markers located at each millimeter was placed flush with, and adjacent to, each structure to be measured. A macro photograph was then taken with a 50× optical zoom camera (Canon PowerShot SX 50 HS, 12.1 Megapixel). The photographs were then analyzed via ImageJ (National Institutes of Health) software by using the scale as a reference for pixel calibration.
The widest diameter of the cranial end of the left-sided optic canal was 5.1 mm, the minimum diameter of the cranial end of the canal measured 3.5 mm. The AOC was circular and had a diameter of 1.4 mm. The main optic canal was separated from the AOC by a thin bony septum located superomedial to the main body of the optic strut, and measured 0.3 mm at its width between the foramina [Figures
The sphenoid was also positioned on an angle, with the aid of a ring stand, in order to capture a modified Rhese projection. After positioning the sphenoid, digital radiographs were taken with an intraoral X-ray system (Gendex GX-770 with a GXS-700 size 2 sensor, 70 kVp, 7 mA, 6 impulse exposure time). The radiograph had remarkable radiolucency inferior to the AOC within the main body of the optic strut [
The presence of bilateral CCF has been reported at a frequency ranging from 2.5% to 18%[
Clinical significance of the carotico-clinoid foramen
Removal of the ACP is often necessary to expose the cavernous sinus and access the clinoid segment of the ICA for management of aneurysms and tumors within the paraclinoid region.[
Clinical significance of the accessory optic canal
The CCF is formed largely by the ACP. The optic strut, too, is attached to the ACP and is therefore also a structure of concern with regard to surgical procedures involving the ACP. As noted by Lee et al., the optic strut is often detached along with the ACP from the lesser wing of the sphenoid to: (i) Facilitate access of the cavernous sinus or posterior orbit, and (ii) prevent a scenario in which a remaining optic strut causes injury to the optic nerve or ICA during surgery.[
Neurosurgeons and radiologists should be aware of the potential simultaneous ipsilateral occurrence of a CCF and AOC. Knowledge of the unique combination of anatomical variants presented in this report may prevent adverse surgical events during anterior clinoidectomy including hemorrhage of the ophthalmic artery or ICA and subsequent vision loss or death.
Research was supported by funding from the WV Research Challenge Fund [HEPC.dsr.14.13] and a West Liberty University Faculty Development Grant. The authors would like to thank Michele Sweeney, MSDH, Professor of Dental Hygiene, Sarah Whitaker Glass School of Dental Hygiene, West Liberty University for facilitating the radiography within this report.
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