The paper presents anatomical considerations on the pterygoalar bar and the
pterygoalar foramen of the human skull. The pterygoalar bar is a bony bridge
that stretches between the lateral pterygoid lamina and the greater wing of the
sphenoid bone, while the space under this bar is termed the pterygoalar foramen.
These structures were noted in 5 out of 70 investigated skulls. The length
of the pterygoalar bar ranged from 4 to 8 mm, while the diameter of the pterygoalar
foramen ranged from 7 to 11 mm. The presence of the pterygoalar bar is
clinically important because it may disturb access to the foramen ovale during
anaesthesia of the trigeminal nerve

Skrzat, J

Walocha, J

Środek, R

English

Via Medica Journals

Folia Morphol. Vol. 64, No. 2, pp. 92–96Copyright © 2005 Via MedicaISSN 0015–5659www.fm.viamedica.plO R I G I N A L  A R T I C L E92Address for correspondence: Dr Janusz Skrzat, Department of Anatomy, Collegium Medicum, Jagiellonian University, ul. Kopernika 12,31–034 Kraków, Poland, tel: +48 12 422 95 11, fax: +48 12 430 30 06, e-mail: jskrzat@poczta.onet.plAn anatomical study of the pterygoalar barand the pterygoalar foramenJanusz Skrzat, Jerzy Walocha, Robert ŚrodekDepartment of Anatomy, Collegium Medicum, Jagiellonian University, Kraków, Poland[Received 27 December 2004; Revised 11 February 2005; Accepted 11 February 2005]The paper presents anatomical considerations on the pterygoalar bar and thepterygoalar foramen of the human skull. The pterygoalar bar is a bony bridgethat stretches between the lateral pterygoid lamina and the greater wing of thesphenoid bone, while the space under this bar is termed the pterygoalar fora-men. These structures were noted in 5 out of 70 investigated skulls. The lengthof the pterygoalar bar ranged from 4 to 8 mm, while the diameter of the ptery-goalar foramen ranged from 7 to11 mm. The presence of the pterygoalar bar isclinically important because it may disturb access to the foramen ovale duringanaesthesia of the trigeminal nerve.Key words: pterygospinous ligament, pterygospinous foramen, foramencrotaphitico-buccinatorium, pterygoid process, sphenoid boneINTRODUCTIONThe term “pterygoalar bar” applies to bony for-mations (osseous bridges or laminae) which resultfrom ossification of the ligaments that are stretchedbetween the lateral pterygoid plate and the greaterwing of the sphenoid bone in the outer aspect ofthe skull base, running closely to the foramen ovale(Fig. 1). These structures are also known as laminaepterygospinosae, the pterygospinous process and thelimited spaces by these structures are termed theforamen pterygospinale, pterygoalar foramen or fo-ramen crotaphitico-buccinatorium [3, 4, 9, 10]. Thebony bar which projects from the posterior borderof the lateral pterygoid plate to the sphenoid spineis termed the lamina pterygospinosae and the limit-ed space above it the pterygospinous foramen.Hence, similar lamina may extend from the root ofthe lateral pterygoid plate (passing over the groovewhich runs from the foramen ovale outwards) to theinferior surface of the greater wing of the sphenoidbone, than it limits the foramen crotaphitico-bucci-natorium [3, 10].Occasionally foramen pterygospinale may trans-mit the nerves and vessels for the pterygoid mus-cles, particularly to the medial pterygoid. The fora-men crotaphitico-buccinatorium provides passage forsome of the motor fibres of the trigeminal nerve (i.e.the masseter nerve) and deep temporal nerves [1].The pterygoalar bar and pterygoalar foramen are rarecranial features but their presence may be of clinicalimportance in the event of trigeminal nerve injec-tion or anaesthesia. Little is known of the incidenceof these anatomical formations in the human popu-lation and there is only scarce information on theirmorphology in the literature [11, 12]. A completeunilateral pterygoalar bar has been found in about5% of Anatolian skulls and with greater frequencyin Negro, while the incidence of the bilateral ptery-goalar bar is very low (1%). Thus, the occurrence ofthe pterygoalar bar and foramen may very from 1%to 10% [5, 6, 8]. A similar incidence has been calcu-lated by Kapur et al. [8] for the pterygoalar foramen(foramen crotaphitico-buccinatorium, foramen ptery-gospinale).93Janusz Skrzat et al., Pterygoalar bar and pterygoalar foramen…The aim of this study was to investigate the mor-phological appearance of the pterygoalar bar and thepterygoalar foramen in the human skull and to evalu-ate their topography in the basicranium (Fig. 1).MATERIAL AND METHODExamination of the pterygoalar bar and thepterygoalar foramen was performed on 70 non-deformed dry skulls, which are housed in the De-partment of Anatomy of the Collegium Medicumof the Jagiellonian University. The examined skulls showa varied craniofacial morphology but they are notidentified with any particular populations. Thus theresults of our study do not provide information onthe incidence of the pterygoalar bar and the ptery-goalar foramen but focus on morphological con-siderations only.The external appearance of the pterygoalar barand its location towards the foramen ovale wasvisually inspected. It was recorded whether the ptery-goalar bar was unilateral or bilateral and whether itwas complete or incomplete. In addition, the lengthof the pterygoalar bar and the maximum diameterof the pterygoalar foramen were measured witha digital sliding calliper.RESULTSVisual inspection of the basicranium of the70 skulls revealed the presence of a pterygoalar bar andthe pterygoalar foramen in 5 cases. The pterygoalarbar was located medially or laterally to the foramenovale, while in one case it crossed the foramen ovale(Fig. 2). Thus, we confirm that the position of thepterygoalar bar differs towards the foramen ovaleFigure 1. Inferior (A) and lateral (B) view of the pterygoalar bar (black arrow) and the ptery-goalar foramen (white arrow); pt — lateral plate of the pterygoid process, ch — choana,sp — sphenoid bone, fm — foramen magnum.94Folia Morphol., 2005, Vol. 64, No. 2Figure 2. Position of the pterygoalar bar (ossified pterygospinous ligament — black arrow)to the foramen ovale (white arrow); A. Medial; B. Lateral; C. Across the lumen of the fora-men ovale; oc — occipital bone, te — temporal bone, pt — pterygoid process.95Janusz Skrzat et al., Pterygoalar bar and pterygoalar foramen…Table 1. Statistics for the length of the pterygoalar bar and the diameter of the pterygoalar foramen (measurements inmillimetres)Feature No. obs. Mean value Min. value Max. value Stand. dev.Length of pterygoalar bar 5 6.2 4  8 1.67Diameter of pterygoalar foramen 5 8.4 7 11 1.79and its size may vary from short and narrow bonytrabeculae to wider laminae. Hence, we noted thatthe extension of these structures had three variants.First — the bar of bone arising from the posteriorborder of the lateral pterygoid plate was longer thanthat growing from the greater wing of the sphenoidbone. Second — a short bony process of the lateralpterygoid plate unites with a longer bony extensionof the infra-temporal surface of the sphenoid bone.Third — the bony extensions contribute equally tothe formation of the entire pterygoalar bar.The complete pterygoalar bar and the pterygoalarforamen were found in both the female and the maleskulls. An incomplete pterygoalar bar was observedin one case out of all the skulls observed (Fig. 3). Wedid not find any skull with a complete bilateral ptery-goalar bar. However, one skull had a complete ptery-goalar bar on the right side and an incomplete oneon the left side. Measurements of the complete ptery-goalar bar and of the pterygoalar foramen are givenin Table 1.Figure 3. Complete and incomplete form of the pterygoalar bar (black arrow). Pterygoalar foramen indicated by white arrow; za — zygomaticarch, pt — lateral pterygoid plate.DISCUSSIONThe pterygoalar bar and the pterygoalar foramenare rarely described in anatomical literature and evenpapers on morphological variants and books of grossanatomy do not always mention of these structures[2, 4, 9, 15]. Hence, there is inconsistency in the usageof descriptive terms for osseous structures, whichare ossified ligaments of the inferior surface of thesphenoid bone and exist close to the foramen ovale.In our material we found different variants of theaccessory osseous trabeculae that exist close to theforamen ovale. They always arise from the posteriorborder of the lateral pterygoid plate but project todifferent regions of the inferior surface of the great-er wing of the sphenoid bone. If the osseous bridgeextended from posterior edge of the lateral ptery-goid plate to the sphenoid spine, it could be reco-gnised as the ossified pterygospinous ligament,which limited the foramen pterygospinale.The osseous bridge, which arose from the rootof the lateral pterygoid lamina to the infra-temporal96Folia Morphol., 2005, Vol. 64, No. 2surface of the greater wing of the sphenoid bone,limited the space termed the foramen crotaphitico--buccinatorium.In cases where the bony bridge was formed be-tween the lateral pterygoid plate and the infra-tem-poral surface of the sphenoid bone or its greater wingand was not connected to the sphenoid spine, it wasdecided to name these osseous structures “pterygoalarbars” and “the pterygoalar foramen”, respectively.Our cranial material presented a rather low inci-dence of the accessory bony bars that exist alongthe foramen ovale. We did not therefore analyseseparately the morphology of the ossified ligaments(e.g. the pterygospinous or pterygopetrosal) and thecorresponding foramina (the foramen crotaphitico-buccinatorium and pterygospinale) but they weredescribed collectively as pterygoalar bars and ptery-goalar foramina.Patnaik and colleagues discovered a pterygoalarbar arising from the upper posterior border of thelateral pterygoid plate and growing backwards andlaterally towards the greater wing of sphenoid bone.They termed the foramen thus constituted porus cro-taphitico-buccinatorius. The vertical and horizontaldiameters of this foramen were 4.7 mm and 4.45 mmrespectively [11]. In contrast, the diameters of thepterygoalar foramina of our investigated skullsranged from 7 to 11 mm.Either the caudal extension of the lateral ptery-goid plate or the entire pterygoalar bar passing lat-erally to the foramen ovale may interrupt the injec-tion of the trigeminal ganglion or mandibular nerveby blocking it [14]. In the case of anaesthesia withinthe foramen ovale, one should, in access to theseneural structures, be aware of anatomical obstaclesbecause of the possible presence of the complete orincomplete form of the pterygoalar bar. Percutane-ous procedures for the treatment of trigeminal neural-gia involve the penetration of the foramen ovale [7].This approach to the trigeminal ganglion may bedifficult when the pterygoalar bar covers the fora-men ovale. Radiological guidance is thus required tovisualise the foramen ovale and its related structures,which makes puncture easier and more precise [8].Otherwise, a higher dosage of the anaesthetic agentis recommended to influence effectively the trigem-inal nerve or its branch.Although the incidence of the pterygoalar barand the pterygoalar foramen is low in the humanpopulation, it would seem important to extend ourknowledge of the morphology and topography ofthese structures. To improve therapeutic perfor-mance medical progress currently needs more accu-rate knowledge concerning the variability of humanmorphology [13].REFERENCES1. Bergman RA, Afifi AK, Miyauchi R (2004) Illustratedencyclopedia of human anatomic variation. In: Skele-tal system: Cranium: Sphenoid Bone (unpublisheddata).2. Berry CA, Berry RJ (1967) Epigenetic variation in thehuman cranium. J Anat, 101: 361–379.3. Bochenek A, Reicher M (1990) Anatomia człowieka.PZWL, Warszawa.4. Błaszczyk B, Kaszuba A, Kochanowski J (1980) Atypi-cal foramina of the base of the skull. Folia Morphol(Warsz), 93: 201–209.5. Chouké KS (1946) On the incidence of the foramen ofCivinini and the porus crotaphitico-buccinatorius inAmerican Whites and Negroes. I. Observations on1,544 skulls. Am J Phys Anthropol, 4: 203–226.6. Chouké KS (1947) On the incidence of the foramen ofCivinini and porus crotaphitico-buccinatorius in Ame-rican Whites and Negroes. II Observations on 2,745additional skulls. Am J Phys Anthropol NS, 5: 79–86.7. Gerber AM (1994) Improved visualization of the fo-ramen ovale for percutaneous approaches to the gas-serian ganglion. Technical note. J Neurosurg, 80:156–159.8. Kapur E, Dilberovic F, Redzepagic S, Berhamovic E(2000) Variation in the lateral plate of the pterygoidprocess and the lateral subzygomatic approach to themandibular nerve. Med Arh, 54: 133–137.9. Long J (1995) Skull base and related structures. Atlasof clinical anatomy. Shattauer, Stutgart, New York.10. Łasiński W (1993) Anatomia głowy dla stomatologów.PZWL, Warszawa.11. Patnaik VVG, Singla Rajan K, Bala Sanju (2001) Bilateralpterygo-alar bar and porus crotaphitico buccinatorius— A case report. J Anat Soc India, 50: 161–162.12. Peker T, Karakose M, Anil A, Turgut HB, Gulekon N(2002) The incidence of basal sphenoid bony bridgesin dried crania and cadavers: their anthropological andclinical relevance. Eur J Morphol, 40: 171–180.13. Sañudo JR, Vázquez R, Puerta J (2003) Meaning andclinical interest of the anatomical variations in the 21stcentury. Eur J Anat, 7: 1–3.14. Stajcic Z, Stojcev Lj, Mileusnic I, Djuric-Srejic M (2002)Mandibular nerve block at the foramen ovale using re-liable landmarks: refinement of a previously describedprocedure. Int J Oral Maxillofac Surg, 31: 423–426.15. Williams PL, Bannister LH, Berry MM, Collin P, Dyson M,Dussek JE, Ferguson MWJ (2000). Gray’s anatomy.38th Ed. Churchill Livingstone, New York.

An anatomical study of the pterygoalar bar and the pterygoalar foramen

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An anatomical study of the pterygoalar bar and the pterygoalar foramen

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