MORPHOLOGICAL VARIATIONS AND MORPHOMETRIC ANALYSIS OF FORAMEN OVALE WITH ITS CLINICAL IMPLICATIONS

Address for Correspondence: B Sadananda Rao, Associate Professor, Department of Anatomy, Kamineni Academy of Medical Sciences, L B Nagar, Hyderabad, Telangana, India. Contact number: 9908892376 E-Mail: sadanand.anat@gmail.com Background: Foramen ovale (FO) plays an important role in the diagnostic and surgical procedures related to middle cranial fossa. So the knowledge on the variations, dimensions and the topographic location is must to the neurosurgeons while dealing with this region. The present study aimed at finding the anatomical variations, dimensions and the location of foramen ovale. Materials and Methods: Present study was carried out on 100 foramina ovalia using 50 dry adult human skulls of South Indian origin. The incidence of the presence of any accessory bony structure like bony plate, spine, tubercle and septa were noted. The size of the foramen ovale was measured by taking Antero-posterior length and the width. The location was determined by measuring the distance from the centre of the foramen ovale (CF) to the tubercle of root of zygoma and distance from the CF to the midline of the base of the skull bilaterally using double tipped compass and digital vernier calipers. Results: Among 50 skulls studied 4 skulls (8%) were bearing bony structures in which 2 skulls (4%) were showing the complete septum dividing the foramen ovale into two parts and in 2 skulls (4%) bony spines were observed which were partially covering the foramen ovale bilaterally. The average anteroposterior length of FO was 7.17±0.94 mm and the width was 3.75±0.69 mm. The average distance from the centre of foramen ovale to the tubercle of root of zygoma was 33.04±2.11 mm and the average distance from the centre of foramen ovale to the midline of the base of the skull was 24.26±1.68 mm. There was no significant difference between the right and left sides. Conclusion: Proper knowledge on the location, dimensions and variations of foramen ovale will be providing guidance to neurosurgeons while performing various procedures through foramen ovale.

accessory meningeal artery, lesser petrosal nerve and an emissary vein passes through the foramen ovale [1][2][3].The foramen ovale is not present in the class reptilia and was acquired in mammal during the process of evolution.The Foramen ovale (FO) is located in the greater wing of the sphenoid bone, posteriolateral to the foramen rotundum which opens into the infratemporal fossa.Mandibular nerve, the foramen is absent in some living mammals including the mammalian embryo, where the semilunar ganglion develops outside the skull and its intracranial position is secondary in ontogeny.Exit of mandibular nerve through foramen ovale is an advanced character acquired during the evolution process [4].
Knowledge on the development of foramen ovlae in humans is important to know its topography, morphology and the morphological variations.
The foramen ovale is located in the greater wing of sphenoid bone.This sphenoid bone develops from both intramembranous and endochondral ossification centers.Sphenoid consists of the body, the paired lesser wings and the greater wings.The basis sphenoid is derived mainly from presphenoid and postsphenoid centres and the postsphenoid centre is the one which is associated with the development of the greater wing of sphenoid.The first ossification centre appears for the greater wing of sphenoid by membranous ossification.The mandibular nerve becomes surrounded by cartilage to form the foramen ovale.At 22 weeks of age the foramen ovale can be seen as discrete ring shaped opening in the area of unossified cartilage that can be well recognised by 3 years after birth [5,6].The morphological variations of the foramen ovale, such that it can be occasionally covered by ossified ligaments stretching between the lateral pterygoid process and the spine of sphenoid resulting in the formation of double foramen ovale [7,8].
Foramen ovale plays an important role in many neurosurgical and diagnostic procedures related to middle cranial fossa.Electroencephalo graphic analysis of seizure by placing electrode at FO provided good neurophysiological information in candidates for selective amygdalohippocampectomy [9].100% success rate was achieved in the treatment of trigeminal neuralgia when foramen ovale was punctured with the help of radiofrequency ablation under the guidance of X-ray real time imaging [10].Foramen ovale permits biopsy of deep lesions of middle carnial fossa such as biopsy of cavernous tumors, percutaneous trigeminal rhizotomy for trigeminal neuralgia due to easy access of the gasserian ganglion through CT guided fine needle aspiration technique which is better than the open surgical biopsy or craniotomy, thus decreasing cost and patient morbidity [11][12][13][14].
The present study was carried out to provide proper knowledge on the location, dimensions and variations of foramen ovale, which will be providing guidance to neurosurgeons while performing various procedures through foramen ovale.
Present study was carried out on 100 foramina ovalia using 50 dry adult human skulls of South Indian origin.Skulls with damage at the surroundings of foramen ovale were excluded from the study.All the skulls were observed to note the presence of any accessory bony structure like bony plate, spine, tubercle and septa.The size of the FO was measured by taking Antero-posterior length and the width.The location was determined by measuring following parameters.Distance from the centre of the foramen ovale (CF) to the tubercle of root of zygoma and distance from the CF to the midline of the base of the skull was also measured bilaterally using double tipped compass and digital vernier calipers (Figure 1).Among 50 skulls studied 4 skulls (8%) were bearing bony structures around FO. 2 skulls (4%) were showing the complete septum dividing the foramen ovale into two parts (Figure 2) and in 2 skulls (4%) bony spines were observed which were partially covering the foramen ovale bilaterally (Figure 3).The average anteroposterior length of FO was 7.17±0.94mm and the width was 3.75±0.69mm.There was no significant difference in the anteroposterior length and width of foramen ovale in between the right and left sides.The average distance from the centre of foramen ovale to the tubercle of root of zygoma was 33.04±2.11mm and the average distance from the centre of foramen ovale to the midline of the base of the skull was 24.26±1.68mm.There was no significant difference between the right and left sides.

DISCUSSION
Foramen ovale is one of the important foramina situated in the greater wing of sphenoid bone through which middle cranial fossa can be approached for micro neuro surgical and diagnostic procedures without performing craniotomy.So the knowledge of anatomical variations, location and diameters of foramen ovale is essential for surgeons.
In the present study 8 % of skulls were bearing bony structures around FO among that bony tubercles were observed in 4% of cases bilaterally and complete septum dividing the foramen into 2 parts was observed in 4% cases bilaterally.Presence of bony structures around the foramen ovale may manipulate the anatomical organization of the nerves transmitted through the foramen namely mandibular and lesser petrosal nerves which often results in the lateral disposition of mandibular nerve resulting in the entrapment of its branches between bony structure and the neighbouring muscles which might lead to neuralgia [15].
The size of the foramen ovale in the present study was determined by measuring maximum anteroposterior length and maximum width.The anteroposterior length was ranging from 5.71 to 9.46mm where as width was ranging from 2.42 to 6.61mm.Narrow size of foramen ovale is a common manifestation in the clinical scenario of Paget's disease or osteopetrosis [16].The average anteroposterior length and width of FO were 7.17±0.94mm and 3.75±0.69mm respectively.Our results were coinciding with the study of Suniti Raj Mishra et al., where the mean length was 7.5mm and width was 4.2mm [17].The anteroposterior length of the present study was lesser than the study by Magi muruganet al., where it was 8.4mm [5].Karishma Ravinthar et al., reported the mean length on right side as 6.7mm and left side 5.7mm whereas width was 3.56mm on right side and 4.28mm on left side which were less when compared to the results of the present study [18].Localizing the exact position of foramen ovale is important for various surgical and diagnostic procedures.In the present study the distance from the tubercle of root of zygoma to center of FO and the distance between the midline to center of FO was considered to locate the FO.The average distance between the centre of foramen ovale to the tubercle of root of zygoma was 32.99±2.07mm on right side and 33.08±2.17

CONCLUSION
The variations observed in the present study and the data on its location and dimension is of immense value to the neurosurgeons while performing various diagnostic and surgical procedures through foramen ovale.The distance measured between the centre of foramen ovale to the tubercle of root of zygoma provides guidance to the neurosurgeons while performing trans zygomatic approach of foramen ovale to reach the middle cranial fossa.

Fig. 1 :
Fig. 1: Distance from the centre of the foramen ovale (COF) to the tubercle of root of zygoma (TOZ) and distance from the COF to the midline (ML) of the base of the skull.

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Sadananda Rao, M Yesender, B H Shiny Vinila.MORPHOLOGICAL VARIATIONS AND MORPHOMETRIC ANALYSIS OF FORAMEN OVALE WITH ITS CLINICAL IMPLICATIONS.
mm on left side which was correlating with study of Jyothsna Patil et al., where it was observed to be 32.58±1.72mmon right side and 32.75±1.76mmon left side.The average distance between the centre of FO to midline was also correlating with the Jyothsna Patil et al. [19].

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Sadananda Rao, M Yesender, B H Shiny Vinila.MORPHOLOGICAL VARIATIONS AND MORPHOMETRIC ANALYSIS OF FORAMEN OVALE WITH ITS CLINICAL IMPLICATIONS.

Table 1 :
Mean and standard deviations of the anteroposterior length and width of the foramen ovale.

Table 2 :
Showing the mean and standard deviations of the various parameters to locate the foramen ovale.

Right side Left side CF to the midline of the base of the skull 24
.28±1.55 mm 24.24±1.83mm

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Sadananda Rao, M Yesender, B H Shiny Vinila.MORPHOLOGICAL VARIATIONS AND MORPHOMETRIC ANALYSIS OF FORAMEN OVALE WITH ITS CLINICAL IMPLICATIONS.