REVIEW

Wormian Bones: A ReviewSHARATH S. BELLARY,1 ASHLEY STEINBERG,1 NADINE MIRZAYAN,1 MICHELLE SHIRAK,1

R. SHANE TUBBS,2 AARON A. COHEN-GADOL,3 AND MARIOS LOUKAS1*1Department of Anatomical Sciences, School of Medicine, St George’s University, Grenada, West Indies

2Children’s Hospital, Pediatric Neurosurgery, Birmingham, Alabama3Clarian Neuroscience, Goodman Campbell Brain and Spine, Indiana University Department of Neurological

Surgery, Indianapolis, Indiana

Wormian bones are abnormal ossicles that develop from extra ossificationcenters within the cranium. They are most frequently located in the lambdoidsuture or the coronal suture, and have been seen in the fontanelles, particu-larly the posterior fontanelle. It is unclear at this time exactly how or why theyare formed, although genetic as well as environmental factors have been pro-posed. Their initial formation is thought to be caused by a degree of duralstrain and increased sutural width. These conditions can result from mechani-cally induced stress due to intentional deformation like that practiced in ancientcultures, premature sutural closure, or from reduced skull ossification as seenin metabolic bone diseases. The cause of the malformation can have an influ-ence on the number and location of Wormian bones. Clinically, Wormian bonesare used as markers in the diagnoses of many autosomal dominant genetic dis-orders, namely, craniosynostosis and osteogenesis imperfecta. Clin. Anat.26:922–927, 2013. VC 2013 Wiley Periodicals, Inc.

Key words: craniosynostosis; osteogenesis imperfecta; bones; head; anatomy

INTRODUCTION

The human skull is composed of several bones thatfuse together after birth. The bones of the skull canbe divided into the viscerocranium and the neurocra-nium. The viscerocranium consists of the bones thatmake up the bones of the face and pharyngealarches; and the neurocranium consists of the bonesprotecting the brain and sensory organs (Schoenwolfet al., 2009). The calvaria of the skull consists primarilyof large flat bones separated by bony sutures. At theposterior aspect of the skull, the lambdoid suture andthe transverse occipital suture form the border betweenthe two parietal bones, the occipital bone, and theinterparietal (Incal) bone when present (Standringet al., 2008). The interparietal bone might be consid-ered a Wormian bone of the lambda. These sutures arethe most likely location to find Wormian bones (Jeantyet al., 2000; Sanchez-Lara et al., 2007).

Wormian, or supernumerary bones, result from theformation of abnormal ossification centers in the cra-nium that develop in addition to those seen normally.Thomas Bartholin coined the term “Wormian” bonesin honor of the Dutch anatomist Olaus Wormius(Debierre, 1890; LeDouble 1903; Huehne 1912;

Aichel, 1913; Broili, 1917; Wegner. 1959; Kadanoff,1964; Shapiro and Robinson, 1976; Parker, 2009).More recently, Bellamy in 1842 described this varia-tion in two mummified Peruvian skulls (Kadanoff,1964). Bellamy’s observations were confirmed byothers, though it was initially believed this anomalyonly occurred in Incan populations (Shapiro and Rob-inson, 1976). The consequence of these irregular ossi-fication centers is the formation of islands of isolatedbones in various locations in the skull.

Wormian bones are normally seen unilaterally andare more frequently located on the right side of theskull (Jeanty et al., 2000; Sanchez-Lara et al., 2007).About 50% of Wormian bones arise along the

*Correspondence to: Marios Loukas, M.D., Ph.D., Professor andChair, Department of Anatomical Sciences, St. George’s Univer-sity, School of Medicine, Grenada, West Indies. E-mail:mloukas@sgu.edu

Received 7 August 2010; Revised 20 March 2013; Accepted 28March 2013

Published online 20 August 2013 in Wiley Online Library(wileyonlinelibrary.com). DOI: 10.1002/ca.22262

VVC 2013 Wiley Periodicals, Inc.

Clinical Anatomy 26:922–927 (2013)

lambdoidal suture and about 25% arise along the cor-onal suture (Jeanty et al., 2000). Other locationsinclude the bregma, lambda, and pterion (epiteric)and squamosal, sagittal, lambdoid, and occipitomas-toid sutures (Figs. 1–7). The prevalence of the loca-tion within the fontanelles occurs in the followingorder: asterion, posterior, anterior, and orbital fonta-nelle. Wormian bones are found in �8–15% of thepopulation; most cases are reported in the Chinesepopulation at a prevalence of 80.32% (Jeanty et al.,

2000; Sanchez-Lara et al., 2007; Parker, 2009). Thereare some studies that claim males are affected morethan females; while others have concluded that there isno significant difference between the sexes (Sanchez-Lara et al., 2000; Jeanty et al., 2007; Parker, 2009).

CLINICAL SIGNIFICANCE

Wormian bones have pathological and diagnosticimplications. They can be important indicators in

Fig. 1. In this specimen a squamosal type of Wor-mian bone is demonstrated. This type of Wormian bone istypically located at the squamosal suture. [Color figurecan be viewed in the online issue, which is available atwileyonlinelibrary.com.]

Fig. 2. In this specimen there are two Wormianbones located at the lambdoid suture. [Color figure canbe viewed in the online issue, which is available atwileyonlinelibrary.com.]

Fig. 3. In this specimen the Wormian bone is locatedat the lambda. [Color figure can be viewed in the onlineissue, which is available at wileyonlinelibrary.com.]

Fig. 4. In this specimen the Wormian bones arelocated at the mastoid suture. [Color figure can be viewedin the online issue, which is available atwileyonlinelibrary.com.]

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revealing seemingly silent disorders (Kaplan et al.,1991). Certain attributes such as number, order ofarrangement, and size of these bones are all consider-able factors when differentiating Wormian bones asnormal variants from pathology (Cremin et al., 1982).There are certain criteria that must be met in orderfor the presence of Wormian bones to be regarded aspathologically significant. First, there must be morethan ten in number. Next, the bones must be arranged

in a general mosaic-type pattern. Second, their sizemust be larger than 6 mm by 4 mm (Cremin et al.,1982). There is considerable pathology found to beassociated with the formation of Wormian bones.These conditions include: pyknodysostosis, osteogen-esis imperfecta, rickets (healing phase), kinky hairsyndrome, cleidocranial dysplasia, hypothyroidism,hypophosphatasia, otopalatodigital syndrome, Hadju-Cheney (Primary acro-osteolysis) pachydermoperios-tosis, and Down syndrome (Cremin et al., 1982;Sanchez-Lara et al., 2007; Parker, 2009; Semleret al., 2010). Wormian bones occur more frequently inconditions like hydrocephalus where the increasedcranial volume and subsequent increased intracranialpressure and forces cause the sutures to spread out;other pathologies where Wormian bones are oftenseen include cleidocranial dysplasia (Aschoff et al.,1999; Sanchez-Lara et al., 2007; Parker, 2009;Semler et al., 2010). In diseases with decreased skullossification, this causes cranial sutures and fonta-nelles to be wider and for the skull to remain in amalleable state for a longer period of time (Sanchez-Lara et al., 2007).

ENVIRONMENT VERSUS GENETICS

There are disparities in the literature regarding thedegree to which the formation and frequency of Wor-mian bones can be attributed to environmental orgenetic influences (Goto et al., 2004; Sanchez-Laraet al., 2007; Barberini et al., 2008). It is theorizedthat the genetic expression of this so-called discretetrait may not display a direct “gene character” rela-tionship, but rather may be under the control of anadditive polygenic complex (Goto et al., 2004; Bar-berini et al., 2008). Others theorize that the pheno-typic state of Wormian bones is influenced by theenvironmental conditions they are exposed to at

Fig. 5. In this specimen the Wormian bone is locatedat the pterion, specifically, at the junction of the coronaland squamosal sutures. This type of Wormian bone is alsocalled epiteric. [Color figure can be viewed in the onlineissue, which is available at wileyonlinelibrary.com.]

Fig. 6. In this specimen there are two Wormianbones. The first one is located at the sagittal suture. Thesecond one is located at the lambda and occupies a por-tion of the right and left lambdoid sutures. This type ofWormian bone is also called the interparietal (Incal) bone.[Color figure can be viewed in the online issue, which isavailable at wileyonlinelibrary.com.]

Fig. 7. In this specimen the Wormian bone is locatedat the pterion. However, in this specimen the Wormianbone is located lateral to the coronal and squamosalsutures. [Color figure can be viewed in the online issue,which is available at wileyonlinelibrary.com.]

924 Bellary et al.

different developmental thresholds (Sanchez-Laraet al., 2007). Environmental factors, such as artificialcranial manipulations, are thought to play a significantrole in the number of Wormian bones within an indi-vidual cranium. Adding to this theory, some studiesraise the idea of epigenicity in the Wormian bone trait(Barberini et al., 2008). As opposed to normal Mende-lian inheritance of traits, epigenetic traits are alsoaffected by environmental factors. Therefore, withregards to Wormian bones, various degrees of stresscan impact their formation and prevalence. It is possi-ble that the cranium may have some amount ofgenetic susceptibility to the formation of Wormianbones and varying degrees of environmental influencedetermine the degree to which the bones form.Nevertheless, the cranial vault normally can handleconsiderable amounts of stress without substantialrearrangement of its structure. This becomes impor-tant when one considers how the environment hasaffected the craniofacial pattern that exists throughouthuman evolution (Barberini et al., 2008).

Recent studies have shown that Wormian boneslocated posteriorly have more of an environmentalfactor associated with them than anterior Wormianbones (Sanchez-Lara et al., 2007). One example thatshows how the environment might impact Wormianbone development is seen in the Chinese populationwhere the prevalence is the highest. It has been notedthat the Chinese have a longer tradition of supineinfant sleep positioning than western society. Thissupine positioning puts constant pressure on the occi-pital area causing variations in dural tension and ulti-mately expanding the posterior sutures (Grahamet al., 2005). A common consequence of this expan-sion is brachycephalic deformation of the skull, whichis characterized by a shorter front to back diameter ofthe skull due to a premature closure of the coronalsuture. This causes a wider cranial base and fore-shortened wider face (Sanchez-Lara et al., 2007).

MECHANICAL STRESS: INTENTIONALVERSUS PATHOLOGICAL

Intentional cranial deformation was a normal prac-tice in a number of ancient cultures. Both the popula-tions of Northwest Pacific Coast Native Americans andMayans from Chichen-Itza, Mexico (1200 to 1500 BC)practiced anteroposterior cranial deformation. Anthro-pologic research has shown that most Wormian bonesdevelop in anteroposterior deformed crania. Non-deformed crania were shown to have a lower preva-lence, and circumferentially deformed crania werefound to have the fewest number of Wormian bones(Anton et al., 1992). It was hypothesized that thesmall number of Wormian bones seen in circumferen-tial deformation was because of the equal distributionof compression forces on the sutures, creating insuffi-cient space and conditions for Wormian bones to de-velop. Comparatively, the larger number of Wormianbones seen in anteroposterior deformation may bedue to increased tension and subsequent spreading ofthe sutures. Moreover, in comparing anteroposteriorcranial deformation to non-deformed crania,

anteroposterior deformation displayed increased Wor-mian bone formation along the lambdoid suture (Bar-berini et al., 2008). It has also been demonstratedthat the type and frequency of Wormian bones had apositive correlation to the degree of deformation(Sanchez-Lara et al., 2007).

Another example of an intentional stress misshap-ing the skull that supports both the environmentaland genetic theories in the formation of Wormianbones was the use of cradle boards among pre-his-toric and historic southwestern pueblo Indians (el-Naj-jar et al., 1985). The pressure placed on the skullduring this cradle board deformation may impede nor-mal bone ossification and growth. Wormian bonesconsequentially form to fill in the spaces between thesutures (el-Najjar et al., 1985). Studies on theseskulls have shown that those with asymmetrical de-formation have significantly greater numbers of Wor-mian bones on the side subject to the deformation.This finding does not reveal an overall increase in theincidence of Wormian bone formation, but only of theper side number on the affected side. This reveals thepossibility that these infants may have had some sortof genetic predisposition to the actual development ofthe Wormian bone because the stress to the skullswas only a factor in an increased number of Wormianbones (el-Najjar et al., 1985). Other studies on South-western Native Americans have shown no significantdifference in incidence of these bones when compar-ing mechanically deformed and non-deformed skulls.This further supports the proposition that purposefuldeformation does not result in a greater incidence,but may have considerable influence on the overallnumber of Wormian bones (Barberini et al., 2008).

CRANIOSYNOSTOSIS

Recent studies have shown an increased frequencyof Wormian bones associated with craniosynostosis.Craniosynostosis is a condition characterized by pre-mature fusion of cranial sutures. The studies suggestthat the type of craniosynostosis present is associatedwith the number of Wormian bones. Furthermore, ithas been demonstrated that Wormian bones developin relation to the specific site where the synostosisbegins. In cases of unilateral synostoses, such thatoccur along the coronal or lambdoid sutures, anincreased frequency of Wormian bones have beenseen on the contralateral sides. In cases of midlinesynostoses, which initiate along metopic or sagittalsutures, Wormian bones form along the midline of thecranium (Sanchez-Lara et al., 2007).

Craniosynostosis is a cause of early closure of thefontanelles in infancy because of the effects of earlyfusion of the sutures. The early fusion results inabnormal dural strain in the area of the opposing fon-tanelle. This strain can result in the formation of bonyislands in the membranous portion of the fontanelle. Astudy to this effect demonstrated that Wormian bonesmay occupy the anterior fontanel in at least 4% of thecases of isolated sagittal craniosynostosis, which canlead to the appearance of a closed fontanelle (Agrawalet al., 2006). The investigators, however, were almostcertain that this is an underestimation of the true

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incidence of Wormian bones of the anterior fontanellein children with isolated sagittal craniosynostosis.

It is controversial whether the development of Wor-mian bones is influenced by genetic or environmentalfactors. However, studies on anterior fontanelle clo-sure in craniosynostosis propose that the develop-ment of Wormian bones in the anterior fontanelle mayhave a certain degree of genetic basis. If this is true itwould suggest that patients with Wormian bones inthe anterior fontanelle may have a genetic predisposi-tion in association with co-morbid sagittal craniosyn-ostosis (Agrawal et al., 2006).

OSTEOGENESIS IMPERFECTA

Wormian bones are extremely relevant in manybone dysplasias including osteogenesis imperfecta.They have become important in the clinical diagnosisof osteogenesis imperfecta due to the fact that theirpresence is commonly used as an indicator of someunderlying genetic disorder (Semler et al., 2010). Thisis because when there is a bone dysplasia such asosteogenesis imperfecta, skull growth is impairedearly in development, resulting in the formation ofthese irregular bones (Cremin et al., 1982).

Osteogenesis imperfecta is a genetic disorder thatgenerally occurs due to a mutation in one out of twogenes encoding for Type I collagen (Semler et al.,2010). The phenotypic presentation involvesextremely fragile bones and deformations in the os-seous structuring of the skull and spine. In addition,osteogenesis imperfecta can cause a gradual defor-mation of the bones of the skull base known as abasilar abnormality (Kovero et al., 2006). A basilarabnormality forms because in osteogenesis imper-fecta patients, the soft bones of the skull cannot sus-tain the normal weight of the skull and brain. Basilarabnormalities are most prevalent in Type III osteo-genesis imperfecta and least prevalent in Type I. Astudy by Kovero et al. (2006) showed that Wormianbones were observed in 44% of patients with Type Iosteogenesis imperfecta, 80% of patients with TypeIII osteogenesis imperfecta, 90% of patients withType IV osteogenesis imperfecta, and none of thecontrols. Another study by Cremin et al. (1982)revealed that Wormian bones were present in 89% ofpatients with osteogenesis imperfecta. Research wasalso done on members of a South African familyacross three generations. The members of the familyin the study all suffered from a disease known asdentinogenesis imperfect. The disease is character-ized by yellow-brown colored teeth that easily frac-ture because of the underlying abnormality of dentinin addition to the blue sclera commonly seen inosteogenesis imperfecta. This disorder is thought tobe inherited either as an isolated autosomal dominantcondition, or as a syndromic component associatedwith osteogenesis imperfecta. Each of the nine casesinvestigated from the South African family wereshown to have Wormian bones (Beighton, 1981).From the above studies, it is apparent that the pres-ence of Wormian bones is significant in the disorderof osteogenesis imperfecta. Although their presence

is not pathognomonic of osteogenesis imperfecta, itmay warrant further investigation of such disordersinvolving defective osteogenesis.

CONCLUSIONS

Wormian bones are thought to form in connectionwith increased dural strain from mechanical force aswell as increased sutural width. Additionally, geneticdefects involving bone formation may be relevant. Itremains controversial as to what affects the frequencyand incidence of Wormian bone formation; howevervarious theories exist that support both genetic andenvironmental influences. Mechanical deformation ofthe cranium, an environmental factor (whether inten-tional or pathological), has been shown to have aneffect on the number and placement of Wormianbones, but not the incidence. Other studies haveshown that anterior fontanelle Wormian bone occur-rence may have a genetic basis. Because Wormianbones are consistently seen in a number of autosomaldominant genetic disorders such as craniosynostosisand osteogenesis imperfecta, they have been includedin the diagnostic criteria as useful markers of thesedisorders.

ACKNOWLEDGMENT

Thanks to the reviewers and their suggestions forimproving our paper.

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