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ORIGINAL ARTICLE

From The: Department of Department of Anatomy Govt Medical College, Jammu, J&K-IndiaCorrespondence to : Dr. Sangeeta Gupta Associate Professor, PG Department of Anatomy, GMC, Jammu, J&K-India

Anatomic Variations In Foramen Ovale and Foramen Spinosum

AbstractAn anatomical study was conducted to observe the shapes of foramen ovale and foramen spinosumwith their anatomical variants. The foramen ovale being one of the important foramina in the middlecranial fossa, is present in the superior surface of greater wing of sphenoid bone. Foramen spinosum islocated posterolateral to foramen ovale. We studied seventeen human skulls and three sphenoid bones(i.e. total 40 foramen ovale and 40 foramen spinosum were studied, since foramen of right as well asleft sides were taken for study). They were obtained from the Post graduate Department of Anatomy,Government Medical College, Jammu. Posterior part of the greater wing of sphenoid was observed forvisualising the foramen ovale and foramen spinosum. Oval, round, almond and slit like foramen ovalewere found. The maximum number was that of oval shaped foramina followed by almond, round andslit like foramen . Moreover, bony outgrowths in the form of spines were observed in two foramenovale, and in the form of bony plate was seen in one foramen ovale. Furthermore, confluent foramenovale and spinosum was seen on left side in one skull and on right side in another skull. Double foramenspinosum was seen in one skull on right side. Absence of foramen spinosum was observed in one of theskulls on right side. Foramen ovale is of surgical importance in percutaneous trigeminal rhizotomy intrigeminal neuralgias. For surgical procedures in the middle cranial fossa, the knowledge about thevariations of these foramina should be taken into account. This data will add to the knowledge ofclinicians as well as anatomists.

KeywordsForamen Ovale, Foramen Spinosum, Skull, Trigeminal Neuralgia, Anatomical Variation

Berjina Farooq, Sangeeta Gupta, Sunanda Raina

IntroductionThe foramen ovale being one of the importantforamina in the middle cranial fossa, is present inthe superior surface of greater wing of sphenoidbone. It opens into the infratemporal fossa (1). Itgives passage to important structures i.e.mandibular nerve, the accessory meningeal artery,the lesser petrosal nerve and the emissary vein (2).It is one of the foramen of importance which ispresent between the intracranial and extracranialstructures. Venous part of foramen ovale may beseparated from other structures of the foramen bymeans of a bony spur. These spurs are locatedanteriorly and medially (3). It is usually oval in shape but its shape showsvariations when compared to rest of the foraminain the skull. It is of great significance toneurosurgeons as transcutaneous approach to skull

base is possible via it in cases of trigeminalneuralgias (4,5). A careful observation of theseforamina will be helpful in the diagnosis of thelesions present in the nasopharynx and middlecranial fossa. Neuroma of the fifth cranial nervecan lead to enlargement of the foramen ovale (6).Moreover, bony outgrowths in the form of spurs,can compress the passing mandibular nerve andhenceforth could lead to dysfunction of the musclessupplied by it (7). Foramen spinosum being a circular foramen,is present in the greater wing of the sphenoid,posterolateral to foramen ovale. It is present atroot of spine of sphenoid. It gives passage to middlemeningeal artery (8,9,10). In 0.4% of cases,foramen spinosum may be absent and in that casethe middle meningeal artery arises from ophthalmic

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artery. Moreover, foramen spinosum can be duplicatedin some cases (11).Material and MethodsThe study was conducted on seventeen human skullsand three sphenoid bones (i.e. in total on the 40 foramenovale and 40 foramen spinosum) obtained from the Postgraduate Department of Anatomy, Government MedicalCollege, Jammu. Posterior part of the greater wing ofsphenoid was observed for visualising the foramen ovaleand foramen spinosum. Their patency was checked bymeans of bristle. Skulls used for study were not damagedor broken. For each skull, general features and anatomicalvariations of the foramen ovale and spinosum werecarefully noted. Bony spur in the form of spine, tubercleor bony plate, in any foramen ovale was noticed.ResultsThe study was conducted on a total of 40 sides in 17 dryadult human skulls and three sphenoid bones. Onvisualizing the foramen ovale, it was seen that 28foramina out of 40 foramina had an oval shaped foramen(Fig 1) (Table 1), 7 foramina showed almond shapedforamen (Fig 2) (Table 1), 4 foramina showed roundshaped foramen (Fig 3) (Table 1)and 1 foramina showedslit shaped foramen (Fig 4) (Table 1). Incidences ofoval, almond, round and slit shaped foramen were 70%,18%, 10% and 2% respectively. Out of 40 sides, 2foramina showed the presence of bony spine (Fig 5)(Table 2), 1 foramina showed the presence of bony plate(Fig 6) (Table 2) and foramen with a tubercle was seenin none. Incidence of spine and bony plate were 5% and3% respectively.Confluency of foramen ovale and spinosum (Fig 7)wasseen in two skulls, in one, on the right side and in other,on the left side. Moreover, double/duplicated foramenspinosum (Fig 8) was seen on right side in one skull andabsence of foramen spinosum ( Fig 9)was also seen onthe right side in one of the skulls.Discussion

The sphenoid bone has two type of ossification centresi.e. the intramembranous and endochondral ossificationcentres which form body, lesser wings and greater wings(7). Foramen ovale shows variations in shape and sizethroughout natural life. In the 7th fetal month, the earliestformation of ring shaped foramen ovale was observedand latest it was observed at 3 years after birth (12).Foramen ovale is of significance in various invasive anddiagnostic procedures. In cases going foramygdalohippocampectomy, the electroencephalographicanalysis is done by placing electrodes at the foramenovale. It provides good neurophysiological information(13). Percutaneous biopsy of cavernous sinus tumourscan be successfully achieved through foramen ovalewhich definitely is of significance before making anymove for open surgical procedures (14). Nasopharyngealcarcinoma spreads intracranially and usually spreads viaforamen ovale (15). Anatomical variations of foramenovale are of importance in operative treatment oftrigeminal neuralgia which is performed through theopening of foramen ovale. Moreover, any stenosis orbony plate leads to reduced patency and difficulty inapproaching for surgical procedures through this route(16,17). Yanagi reported that foramen ovale in majority caseswas found to be oval in shape and furthermore they wereirregular in shape in comparison to the other foraminapresent in the sphenoid bone (12). In our study also, themajority of the foramen ovale were oval in shape(Table1)( Fig 1). There are some developmentalreasons for the variations in the shape of foramen ovale(18). Tubbs et al., in their work revealed thatpterygospinous (ligament of Civinini) and pterygoalar(ligament of Hyrtl) ligaments lead to division of foramenovale into two compartments. These ligaments couldmake transcutaneous needle placement into the foramenovale very difficult (19). Ray et al., observed in theirstudy on anatomic variations of foramen ovale that aspine was present on the margin of the foramen ovale.

Shape Right (n=20) Left(n=20) Total(n=40)Oval 17 11 28Almond 3 4 7Round 3 1 4Slit shaped 1 0 1

Bony outgrowths Right(n=20) Left(n=20) Total(n=40)Spine 0 2 2Tubercle 0 0 0Bony plate 1 0 1

Table 2. Bony Outgrowths Seen in Foramen Ovale

Table 1. Variations in Appearance of Foramen Ovale

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It was seen in 3 cases (3). In our study, we alsoappreciated two bony spines on the margins of foramenovale in two different skulls and both were present onleft side (Table 2) (Fig 5) Moreover, 1 bony plate wasalso seen on foramen ovale in our study(Table 2) (Fig6). Studies on the morphology of foramina of greaterwings of sphenoid have revealed variations in theforamen spinosum. The foramen spinosum may beabsent, when the meningeal artery arises from ophthalmicartery instead of arising from maxillary artery or incircumstances, when meningeal artery enters the cranialcavity through foramen ovale (20). Ginsberg et al., alsoobserved that the foramen spinosum may be absent whenmiddle meningeal artery follows an aberrant pathway

(21). Berge and Bergman conveyed that the foramenspinosum was found to be unilateral in (1%) skulls or(0.5%) of foramina which were examined had noevidence of assimilation with foramen ovale (22).Lindblom observed that the foramen spinosum was smalland was not present in 0.4% cases. It was observed byhim in his roentgenographic study of the vascular channelsof the skull (23). In the present study, foramen spinosumwas absent in one skull and that too on the right side(Fig 9). Lindblom and Sondheimer also reported a variant inwhich double foramen spinosum were found on the sameside of the skull. A bony bar was a partition which leadto the duplication of foramen spinosum which can bebecause of division of middle meningeal vessels before

Fig 1-3. Skull Showing Foramen Ovale of Oval Shape, Sphenoid Bone with Almond Shaped Foramen & Skull Showing Round Shaped Foramen Ovale

Fig 4-6. base of skull showing slit like foramen ovale; base of skull showing bony spine in left foramen ovale &base of skull showing bony plate in right foramen ovale

Fig 7-9. showing base of skull with confluent foramen ovale and foramen spinosum on right side;base of skull showingdouble foramen spinosum on right side & skull showing absence of foramen spinosum on right side

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entering the foramen spinosum (23,24).Our study alsorevealed a skull with double foramen spinosum on thesame side of the skull i.e. the right side. They wereseparated from each other by a thin bony margin (Fig8). Osunwoke et al., made thorough study on 87 driedhuman skulls from the southern Nigerian population andthey noticed that all skull had foramen. They were notable to find any skull with absence of foramen spinosum(25).ConclusionThe present study was conducted to provide informationregarding the foramen ovale and foramen spinosum asthe knowledge about these foramina is still scarce. Someforamen ovale present with tubercles or bony plates. Themandibular nerve passes through the foramen ovale andit is via this foramen that trigeminal rhizotomy is done.So, the patency of the foramen ovale is very importantfor this procedure. In case of stenosis of foramen ovaleas is seen in foramen with tubercles, the surgeriesprocedures are difficult. For surgical procedures in themiddle cranial fossa, the knowledge about the variationsof these foramina should be taken into account and thepresent data will suffice for that purpose. Refinedsurgical techniques in microsurgery are available forwhich the foramen spinosum acts as an identifiablelandmark. So, the knowledge about the anatomicalfeatures of foramen spinosum alongwith its variationswill enlighten the minds and will be fruitful. For medicalpractitioners this data will be of significance in dealingthe cases of trigeminal neuralgia and will aid in diagnosingvarious vascular lesions in cranial cavity. This data willadd to the knowledge of clinicians as well as anatomists.

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