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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 11  |  Issue : 2  |  Page : 90-95

Foramen ovale and associated accessory foramina: A computerized tomography study to determine morphometry and analyze gender and age differences


1 Associate Professor, Department of Anatomy, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
2 Professor, Department of Anatomy, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
3 Phase III MBBS Student, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
4 Professor and Head, Department of Anatomy, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
5 Professor and Head, Department of Dentistry, All India Institute of Medical Sciences, Raebareli, Uttar Pradesh, India

Date of Submission11-Jan-2022
Date of Decision13-Mar-2022
Date of Acceptance24-Mar-2022
Date of Web Publication26-May-2022

Correspondence Address:
Eti Sthapak
House No. 4/11, Old Campus, SGPGIMS, Raebareli Road, Lucknow, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NJCA.NJCA_14_22

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  Abstract 


Background: The mandibular nerve exits the cranial cavity by traversing through the foramen ovale (FO) which is located in the greater wing of sphenoid, posterolateral to foramen rotundum. This foramen also provides an entry portal to the accessory middle meningeal artery and helps exit the lesser petrosal nerve apart from the emissary veins. Tumors and masses in infratemporal region require an accurate and precise morphometry of FO, before planning any surgical procedure. The aim of this study is to record and analyze the metric and nonmetric data and compares the morphometry of FO with gender and age. Methodology: Type of study – Retrospective observational study. The sample size was 200 computerized tomography head axial section scans without any disease which might alter the anatomy of foramen, from picture archiving and communication system. Bilateral foraminal parameters were obtained with the help of computer-assisted software. Results: The mean length, breadth, distance from mid-sagittal plane, and size of FO in males were 7.75 ± 1.16, 3.98 ± 0.91, 21.40 ± 1.75, and 30.94 ± 8.79, and in females, measurements were 6.90 ± 0.78, 3.57 ± 1.04, 20.36 ± 1.62, and 24.86 ± 9.08, respectively. Septation was observed in 2% of cases and the most common shape observed was oval (84%). Totally 26% of accessory foramina were observed. Conclusion: Significant gender differences were seen in the morphometry in all the four parameters. A significant difference with age was seen only with distance of foramen from midsagittal plane. Variations in morphometry and shapes of the FO may affect clinical and diagnostic procedures.

Keywords: Computerized tomography, foramen ovale, gender difference, mandibular nerve, retrospective study


How to cite this article:
Sthapak E, Pasricha N, Singh A, Bhatnagar R, Bedi RS. Foramen ovale and associated accessory foramina: A computerized tomography study to determine morphometry and analyze gender and age differences. Natl J Clin Anat 2022;11:90-5

How to cite this URL:
Sthapak E, Pasricha N, Singh A, Bhatnagar R, Bedi RS. Foramen ovale and associated accessory foramina: A computerized tomography study to determine morphometry and analyze gender and age differences. Natl J Clin Anat [serial online] 2022 [cited 2022 Nov 30];11:90-5. Available from: http://www.njca.info/text.asp?2022/11/2/90/346070




  Introduction Top


The mandibular nerve (MN) exits the cranial cavity by traversing through the foramen ovale (FO), located in greater wing of sphenoid, posterolateral to foramen rotundum. Accessory middle meningeal artery, lesser petrosal nerve, and emissary veins pass from this foramen.[1] Since FO is located at a transition between intracranial and extracranial structures, it is an important site for various surgical and diagnostic procedures, especially important to anthropologists, forensic scientists, and neurosurgeons.[2],[3],[4],[5],[6] In the past, the morphometry of FO has been studied on dry skulls, mainly as a data resource for racial and gender identification.[7],[8],[9],[10] Considering the precise planning required for surgical procedures in the treatment of tumors and masses in the infratemporal region, the aim of the present study was to record and analyze metric and nonmetric data of FO and to compare the morphometry with gender and age.


  Materials and Methods Top


Type of study: Retrospective observational

The waiver of the ethical consent for the research protocol was approved by the Institute Ethics Committee vide letter number 563/RMLIMS/2019 dated May 3, 2019. This was a STS-ICMR approved project, conducted from April 2019 to July 2019 using a picture archiving and communication system in the department of radiology Dr Ram Manohar Lohia Institute of medical Sciences, Lucknow.

Sample size

Sample consisted of two hundred (110 males and 90 females) computerized tomography(CT) head axial sections from picture archiving & communication system (PACS). Bilateral foraminal parameters were obtained using computer-assisted software.

Sample size calculation

Considering the average breadth of FO 4.20 ± 0.87 and relative precision 2.5% (i.e., 0.12) at 95% level of confidence limits, a sample size of 200 was obtained.[11]

Inclusion criteria

CT head without any radiologically observable abnormalities such as fracture, tumor, and congenital abnormality.[12]

Exclusion criteria

  1. CT images of patients below 1 year of age because of the difficulty in discerning some structures in very small skulls[12]
  2. Radiologically observable abnormalities such as tumor, fracture, and congenital anomaly involving skull base[12]
  3. Low-quality scans.


Parameters studied

Variations in location, shape, size, symmetry, septation, presence or absence of FO, and frequency of occurrence of accessory foramina were observed by two observers and mean of values taken to remove observational bias.

Following morphometric parameters of FO were measured (mm).[11]

  • Length – Line was drawn between the distal points in the anterior and posterior wall and measured
  • Breadth – Line (perpendicular to length) was drawn between the points in medial and lateral wall and measured
  • Distance from mid-sagittal plane (MSP) – The medial-most point of the medial wall was marked and a perpendicular was drawn to the MSP
  • Size of foramen for the purpose of comparison has been taken as product of its length and breadth.


Statistical tests applied

One-way ANOVA, unpaired t-test, and paired t-test.


  Results Top


Two hundred CT scans studied with the age range of 1–80 years; out of which, 110 (55%) were male and 90 (45%) were female.

FO was observed on the posteromedial aspect of greater wing of the sphenoid bone. The foramen was oblique and directed anterolaterally. The mean ± standard deviation in mm of all the parameters of the right and left sides are shown in [Table 1].
Table 1: Comparative morphometry of the right and left sides

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The only a significant difference observed between the left and right sides was for distance from MSP (P = 0.038 and 0.003 for males and females, respectively).

Significant difference is seen between males and females for all the four parameters of FO which were of higher value in males: length P < 0.001, breadth P = 0.004, size P < 0.001, and distance from MSP P < 0.001.

A significant difference with age was seen only with the distance of the foramen from midsagittal plane, which increased with age in both males and females (P = 0.007 and 0.046, respectively). The comparative age-related morphometry is shown in [Table 2].
Table 2: Comparative age-related morphometry

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Shapes

Oval (84%), almond (12.5%), round (1%), slit-like (2%), and irregular (0.5%) [Figure 1] and [Figure 2]. In 0.5%, it was open posteromedially [Figure 3].
Figure 1: Axial CT scan showing oval and almond shape foramen ovale (black arrow)

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Figure 2: Axial CT scan showing slit-like foramen ovale (black arrow)

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Figure 3: Axial CT head showing partial absent of medial wall of FO (black arrow)

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Septation

Septation was observed in 2% of cases [Figure 4].
Figure 4: Axial CT scans showing septation and Accessory foramen (anteromedial to the FO) (black arrow)

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Accessory foramina or foramen venosum

Foramen venosum or foramen of vesalius was seen bilaterally in 5% of cases and unilaterally in 16% of cases of the CT head studied. It was located mostly anteromedially [Figure 4] and [Figure 5] to the FO, and in one case each, it was anterolateral [Figure 6] and posterolateral [Figure 7]. This foramen is best seen in axial planes and connects the middle cranial fossa to the scaphoid fossa.
Figure 5: Axial CT scans showing Accessory foramen (anteromedial to the FO) (black arrow)

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Figure 6: Axial CT scan showing accessory foramen (anterolateral to foramen ovale) (black arrow)

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Figure 7: Axial CT scan showing accessory foramen (posterolateral to foramen ovale) (black arrow)

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  Discussion Top


The base of the skull is traversed by important neurovascular structures, through some consistent and accessory foramina. The three consistent foramina in the greater wing of sphenoid are FO, spinosum, and rotundum. FO lies close to the upper end of the posterior margin of the lateral pterygoid plate, medial to foramen spinosum, and lateral to foramen lacerum.[1] The most important structure traversing; it is the MN. In lesions of MN, the FO provides ease of access for microvascular decompression by percutaneous trigeminal rhizotomy. Thus, in cases of “Tic douloureux,” there is a need for the determination of its exact morphometry and variations in shape and septation.[2] We observed a dearth of literature which documents the CT determined morphometric details of FO and their correlation with age and gender because these are important parameters required by surgeons and clinicians before operating on patients requiring radiological correlation.[13],[14],[15]

The length (anteroposterior) and breadth (transverse) parameters of our study were comparable with those measured in the past by Berlis et al. and Sankaran et al.[5],[11] We did not observe statistically significant difference in the major and minor axis of FO with age and side. These observations were similar to the studies done previously.[5],[16],[17],[18],[19] The only statistically significant difference observed was in the distance from midsagittal plane with side. The mean range of major and minor axis of FO varies from 7.67 to 5 and 6 to 2.65 (mm), respectively, as given in [Table 3].
Table 3: Comparison of parameters of foramen ovale of the present study with previous studies

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Measurements of FO are specific for each population and might also differ in the same population being influenced by sample size, methodology, and method of statistical analysis.

In the present study, the mean length, breadth, distance from midsagittal plane, and size in males were more than females, and the differences were statistically significant. These results agree with the study done by Li et al., the only CT study available in the literature, which documents gender differences.[20] The bilateral comparison shows a slight asymmetry in the distance from MSP only. With age, the only significant difference was seen in distance from MSP.

Past studies have compared the cross-sectional area of the MN, with that of the foramen, documenting a very less difference between the two, implicating that lesions in the nerve can potentially obstruct the FO.[16],[21] This mandates a correct morphometric analysis.

Developmental reasons may cause variations in the shapes of FO. The variety of shapes observed and compared with the past studies is shown in [Table 4].[14],[22],[23],[24],[25]
Table 4: Comparison of shape of foramen ovale

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Primitive variants of FO observed in the present study such as absent medial wall, septation, and in one case, unilateral tubular or slit-like opening of FO can be explained on the basis of development and evolutionary aspect. FO develops from primitive foramen lacerum medius, which is an opening between basisphenoid and perotic capsule. It is variably subdivided into different mammals. In lower mammals, FO and spinosum coalesce in the foramen lacerum medius. In higher mammals, FO presents as a shallow groove which deepens into a notch and ultimately becomes a foramen by ingrowth of bone around the nerve. In the new world monkey, FO may be found as a deep groove, notch, or incomplete foramen.[26] Differences in the morphology may lead to surgical difficulty and as described by Natrajan can cause difficulty in cannulation.[27]

Septation was observed in 2% of cases in our study. As with other foramina, ossification can divide into two separate compartments: a full division has been reported in 2.8% of cases and a partial division in 12.8% of cases.[8]

Foramen venosum or foramen vesalius is not observed frequently. We observed accessory foramen venosum bilaterally in 5% of cases and unilaterally in 16% of cases (totally in 26% cases). According to Wood-Jone's foramen Vesalius in its classical form is confined to man, present anteromedially to the FO.[28] This is best seen in axial plane, connecting the middle cranial fossa to the scaphoid fossa. It transmits an emissary vein from the cavernous sinus to the pterygoid plexus, and on occasion, the accessory meningeal branch of the internal maxillary artery.[1] This vein exits the skull base through the FO if the foramen Vesalius is absent. In previous studies, the occurrence of this foramen was varied, depending on the study. In Sankaran et al., it was present in only 25% of the studied skulls.[5] In Ginsberg et al., it was seen unilaterally in 80% of cases.[12] In Berlis et al., it was seen bilaterally in 15% of the population.[11] The knowledge of the presence of accessory foramen and its relation with FO is important for neurosurgeons. Surgical approach through FO should be carefully performed to avoid puncture of accessory foramen because of considerable occurrence of the accessory foramen.[29]

Strength

This study is done in a particular group of population where the morphometry of foramina is done in respect of age and gender, none of the previous studies included the age and gender as a parameters.

Recommendation

3D reconstruction of the foramina will help in better delineation of foramina.

Limitation of study

The sample size is less because CT images are stratified as per the age in four different groups.


  Conclusion Top


A comprehensive knowledge of the anatomy of FO is of paramount importance for accurate interpretation of pathology, planning of surgical procedures in the infratemporal fossa. A thorough knowledge of the normal anatomy of the FO and variations may help in diagnosis and management of neuralgia, nerve compression diseases and for novel microsurgical techniques. While undergoing invasive procedures, such as microvascular decompression by percutaneous biopsy of cavernous sinus tumors, or for CT-guided transfacial fine-needle aspiration technique through the FO, the normative data provided by a CT-based study like ours is more valid than one obtained from dry skulls.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Zdilla MJ, Hatfield SA, McLean KA, Cyrus LM, Laslo JM, Lambert HW. Circularity, solidity, axes of a best fit ellipse, aspect ratio, and roundness of the foramen ovale: A morphometric analysis with neurosurgical considerations. J Craniofac Surg 2016;27:222-8.  Back to cited text no. 21
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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