Circularity, Solidity, Axes of a Best Fit Ellipse, Aspect Ratio, and Roundness of the Foramen Ovale

Abstract

The structure of the foramen ovale of the sphenoid bone is clinically important, particularly with regard to surgical procedures that cannulate of the foramen such as percutaneous trigeminal rhizotomy for the treatment of trigeminal neuralgia, percutaneous biopsy of parasellar lesions, and electroencephalographic analysis of the temporal lobe among patients undergoing selective amygdalohippocampectomy. Differences in the morphology of the FO have been reported to contribute to difficulties in the cannulation of the FO. However, reports regarding the structure of the FO use subjective and ambiguous descriptions of morphology including “oval”, “truly oval”, “elongated oval”, “elongated”, “semicircular”, “almond”, “round”, “rounded”, “slit”, “irregular”, “D shape”, and “pear.” Therefore, it is necessary to describe the structure of the FO with reproducible objective morphometric data. This study analyzed 169 foramina to determine normative morphometric shape descriptions of the following: area, perimeter, circularity, solidity, axes of a best fit ellipse, aspect ratio, and roundness. The shape descriptors reported herein may aid in identification and description of structural variation in FO including bony projections encroaching upon the foramina and may improve surgical approaches to transovale cannulation.

Cranial Nerve Foramina Part I: A Review of the Anatomy and Pathology of Cranial Nerve Foramina of the Anterior and Middle Fossa

“…The prevalence of the pterygospinous bar, also known as the ligament of Civinini, has been reported as 2.6 - 17%, while that of the pterygoalar bar, also known as the ligament of Hyrtl, has been reported as 2.6 - 30% [5-6]. These bars can be unilateral and/or extend additionally over the foramen spinosum [7]. …”

“…Other structures include the accessory branch of the middle meningeal artery, the lesser petrosal nerve, small emissary veins, and the middle meningeal artery [7, 10]. The venous plexus, joining the cavernous sinus to the pterygoid plexus, can also run through this path [11].…”

“…The venous plexus, joining the cavernous sinus to the pterygoid plexus, can also run through this path [11]. If we compare the cross-sectional area of the mandibular nerve, 7.8 - 14.5 mm 2 on the right and 10.4 - 16.2 mm 2 on the left [12], with that of the foramen, 16.55 mm 2 on the right and 14.39 mm 2 on the left [7], it is clear that lesions can potentially obstruct the FO.…”

Orientation of the Foramen Ovale

“…Likewise, shape descriptors such as circularity and solidity have been utilized to objectively demonstrate the shape of the FO. 39 Using data such as the aforementioned trajectory angles of cannulation and objective shape descriptor data, in conjunction with the data presented within this report, may help aid in stereotactic neurosurgical planning and transovale cannulation.…”

Angular Relationship Between the Foramen Ovale and the Trigeminal Impression

“…14 The diverse shapes of foramina ovalae have been described as “banana-like,” “triangular,” “oval,” “truly oval,” “elongated oval,” “elongated,” “semicircular,” “almond,” “round,” “rounded,” “slit,” “irregular,” “D shape,” and “pear”. 15–24 The diverse morphology of the FO may partly explain why failure to cannulate the FO has been reported to occur in as many as 8% of procedures. 25,26 Even CT paired with navigation technology has proved unsuccessful in cannulating the FO in 5.17% (9:174) of patients due to suspected variation in FO morphology.…”