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Pcdiatr Neurosurg 19 9 1-9 2 :17:17 5 -18 1

Skull Base in Trigonocephaly L. Genitori, S. Cavalheiro, G. Lena, C. Dollo, M. Choux Department of Pediatric Neurosurgery, Hopital dcsenfants LaTimone. Marseille. France

Key Words. Craniosynostosis • Trigonocephaly • Nasion-pterional angle ■Clino-pterional angle • Bipterional distance • Nasion-clinoid distance • CT, three-dimensional Abstract. The authors present aspects of the skull base in trigonocephalic children. Different patterns on clinical an­ thropometric investigation, bidimensional computer tomography (CT) scan and three-dimensional (3D) CT scan were studied. We present a series of 27 cases of trigonocephaly operated on in the department of pediatric neurosurgery at the Hopital des enfants La Timone in Marseille since 1975. The skull base base been studied with CT scan in 12 pa­ tients and in 5 a 3D CT reconstruction was performed. A control series of 27 children without synostosis has been stud­ ied with the same patterns. We have analyzed in 3D. the volume of the anterior fossa related to the orbital volume, the permeability of basal sutures and the spatial orientation of petrous, sphenoid and zygomatic bones. An analysis of na­ soethmoidal complex was performed in relation with hypotelorism. CT scan allows the study of the opening of orbital, nasion-pterional angles and the clinopterional angles, as well as nasion-clinoidal and bipterional distances. A comput­ erized analysis of these data compared with normal skull base permits a new approach lo these malformations and the necessity for subdivision of trigonocephaly.

Trigonocephaly describes a triangular-shaped had with a prominent frontal crest (fig. 1). In such instances, ocular hypotelorism and deficient lateral supraorbital rims may result from a premature synostosis of the metopic suture [1-8]. This hypotelorism is accompanied by an elevation of both lateral canthal angles and the lateral eyebrow por­ tion 131. The resulting facial expression has been de­ scribed as a ‘startled raccoon’ [9, 10]. Trigonocephalic patterns have been described as an autosomal dominant inheritance trail [II. 121and may be associated with other malformations such as hypoplasia of the forebrain [2, 13, 14]. The metopic suture can be identified until the 3rd year of life when it becomes completely obliterated. However in 10% of adults it persists throught life [I5-17|. It is cur­ rently thought that premature metopic fusion occurs as an intrauterine event [18]. Virchow |8| believed that craniosynostosis was the pri­ mary event and that associated cranial base malformations

Fig. 1.3D CT. Triangular-shaped head.

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Fig. 2. 3D CT skull base, a Nasion-pierional angle: b Biorbital external opening angle, e N-C = Nasion-clinoid distance: P-P = biptcrional distance, d Interorbital distance.

Patients and Methods From 1975 to 1990. we operated on 341 children with craniofacial anomalies and craniosynostosis and 27 fulfilled the clinical and radiographic criteria for trigonocephaly. All of the cases were studied by clin­ ical anthropometry. Bidimensional CT scan was performed in 12 cases allowing studies of nasion-pterional. clinopterional (fig. 2a). opening

orbital angle and biorbital external opening angles (fig. 2b). The nasion-clinoid and bipterional distances (fig. 2c) were measured according to the parameters of Oi and Matsumoto |5|. The interorbital distance is considered to be the maximum distance between the medial walls of the bony orbits measured at the junction between the posterior lacrimal crest and the frontolacrimal suture (fig. 2d). CT with 3D reconstruction was performed in 5 cases and the anteri­ or and median fossa volumes as well as the peculiar zygomatic and pe­ trosal bone orientations and all basal sutures and other associated syn­ ostosis were studied. Clinical Anthropometric Pattern

The available literature does not provide normal standards for Med­ iterranean measurements and consequently 27 normal children have been studied with the same criteria for comparison with the trigonoce­ phalic patients. The median age of these children was 7 months and CT scan was performed during a hospitalization for benign head trauma or minor spinal malformations. Anthropometric distances measured on the

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were secondary. However. Moss [19] theorized that the skull base malformation was the primary anomaly and that the abnormal sutural obliteration was a secondary event. We present a study concerning the skull base in 27 trigonocephalic children studied by X ray. computer to­ mography (CT) scan and thre-dimensional (3D) CT re­ construction.


Skull Base in Trigonocephaly

vault were compared with basal distances analyzed on bidimensional CT scan. Basal and orbital angles were measured in accord with crite­ ria reported by Oi and Matsumoto [5). In children with metopic synos­ tosis. these data were analzyed by the authors for a follow-up in out pa­ tient clinics. 1 month. 6 months and I year after the surgical procedure.

Results Time, months

Fig. 3. Age at the time of diagnosis (27 cases).

Table 1. Clinical anthropometric patterns (cm) Distance


Trigonocephaly (med¡an )

Nasion-lambda Nasion-bregma Bitragal Medial intercanthal

28-34 9-14 27-33 2-2.7

27 10.2 29 2.3

Table 2. Basal skull angles Angles



Nasionpterional Clinopterional Opening orbital Biorbital external

115° 142° 51° 81°

105° 137.7° 50° 91.5°

Table 3. Basal skull median distances (cm) Distances



Bipterional Nasion-clinoid Interorbital

8.9 5.3 2

8.04 6.28 1.6

Table 4. Basal suture synostosis Suture

Number of cases

Metopic Frontozygomatic Sphenofrontal Coronal basal Sphenozygomatic Frontoethmoidal Sphenotemporal Lambdoid

in all cases 4 3 3 2 2 i i

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The incidence of trigonocephaly in our instituilion was 7.9%; 18 children were male and 9 were female (2:1). The age distribution shows a relative peak incidence between 2 and 4 months (fig. 3). Twenty-three children were neu­ rological ly intact, 3 presented a moderate mental delay and I child with chromosomal abnormalities was severe­ ly disabled. Syndromic conditions were observed in 7 pa­ tients: 3 Carpenter's syndrome. 2 Crouzon’s syndrome and 1 Noonan’s syndrome. One child presented with com­ plex cardiac anomalies. The most frequently employed measurements were the anthropometric distances. Para­ doxically in trigonocephaly no significant difference was found between the two groups, (table I). Nasion-pterional angle and bipterional distance were diminished in 14/17 (82%) of the cases. The clinopterional angle was diminished in 10/17 (39%) and in all cases it was invariably associated with a decrease in nasion-pte­ rional angle. The mean value of the external biorbital angle had increased by 10° and consequently each open­ ing orbital angle decreased by 1° (table 2). The mean decrease in the interorbital distance was 4 mm. When the nasion-pterional angle was normal, the interorbital distance was normal too. The nasion-clinoid distance was increased in 9/17 (53%) of the cases (table 3). All the cases that exhibited a decrease in the clinopterional angle had other associated basal synostosis. No alteration was verified in the orbital volume (aver­ age 13 cm3) and ocular volume (average 7.5 cm'). The an­ terior fossa volume was decreased in 9/17 (53%) of the cases and was associated with a hypoplasic nasoethmoid­ al complex. Owing to the compensatory growth the tem­ poral fossa volume was increased in every case and veri­ fied on all the 3D studies (fig. 4a). A backward position of the zygomatic bone was always present (fig. 4b). We had also I case where an anterior displacement of the petrous bone was associated with a lambdoidal synostosis (fig. 5). The analysis of basal sutures showed a metopic synos­ tosis in every case. In 4 cases the frontozygomatic suture was obliterated; 3 had a synostosis of the sphenofrontal and coronal basal sutures. In 2 cases sphenozygomatic and frontoethmoidal sutures were prematurely closed (table 4).




Fig. 5. 3D CT. Anterior displacement of the petrous bones associat­ ed to a lambdoidal synostosis.

In figure 6 an example is given of preoperative 3D CT in a 6-month-old boy with anomaly in axis of all basal bones and an 8-month postoperative 3D CT showing total remodelling of the anterior part of the skull.

Discussion Premature closure of the metopic suture is a rare form of eraniosynostosis. In our surgical experience of 341 craniosynostosis its incidence was 7%. First described by Welker [ 14) in 1862, trigonocephaly was classified in two categories: the simple or isolated and the complex asso­ ciated with other malformations.

The cranial sutures have three functions during the vault’s physiological development: (1) to ensure bone growth at the suture margins, that is a stimulus for a bio­ physical separation of bones as an increasing brain mass result, (2) to maintain cranial flexibility, and (3) to mod­ ulate neurocranial growth [6. 20-22]. The growth of anterior cranial fossa is completed earli­ er than that of the middle and posterior cranial fossae [231. Their postnatal growth depends primarily on the displace­ ment between the frontal sphenoidal, and ethmoidal bones that occurs in the sphenofrontal and sphenoethmoidal su­ tures. These sutures grow very rapidly in the first years of life bit stop growing around the 7th year. The middle cra­ nial fossa continues to grow for several years afterwards. The anterior fossa represents 39.4% of the newborn skull base, and by the age of 3 months it is 40.5%. The nasionclinoid distance will grow until the complete formation of frontal and sphenoidal sinuses [15. 16. 21.24—271. Virchow [81stated that the cranial deformity found in subjects with premature craniosynostosis could be ex­ plained by growth inhibition at right angles to the fused suture, with compensatory overexpansion of the cranium at patent sutural sites accommodating normal growth of the brain. Since then, this concept of dysplastic and com­ pensatory growth has been shown to involve not only the calvaria, but all the region of the craniofacial complex in patients with different types of craniosynostosis [23. 24. 28]. However, a few cases of skull base alteration have been described in this pathology. A literature review of skull base patterns in trigonoce­ phaly indicates shortening of the frontal bones, hypotelorism. inward angulations of orbits, abnormal tilled sphe-

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Fig. 4. 3D CT. a Compensatory growth of the temporal fossa, b Backward position of zygomatic bone.

noid wing, sharp anterior of the forehead, with an abnor­ mal kyphosis of the skull base as the main trigonocephaly features. The medial walls of the orbit are thickened and rise unusually high, so that the roof of the orbits are high­ est medially and tilted inferolaterally. The medial walls of the orbit are usually parallel but may sometimes converge superiorly 119. 29).The 3D CT allows a better analysis of structural and morphological aspects of each component of basal skull and their relationships. The wrong position of zygomatic bone in relation with closure of sphenozygo­ matic and frontozygomatic sutures is well demonstrated with 3D CT reconstruction. In 3/5 of patients affected by trigonocephaly the anteri­ or fossa volume was diminished, and the temporal fossa compensatory volume was increased in all cases. The normal Mediterranean nasion-pterional angle (mean 115°) was 5° larger than the Japanese normal nasi­ on-pterional angle (110-100°) [5]. The mean of nasionpterional angle in trigonocephalic patients was 105°. The trigonocephalic clinopterional angle was lowered. 137.7° (normal 142°). These results differ from Oi and Matsumoto 15 1findings. They could not find any significant clinop­ terional angle difference between normal children and trigonocephalic patients.


Fig. 6. 3D CT. a, I) Skull base and vault before surgical treatment with major anomalies in axis of bones, e, d Postoperative result (8 months) with normal nasion-pterional and clinopterional angles and normal position of zygomatic bone.

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Skull Buse in Trigonocephaly



Tabic 5. Major anomalies in trigonocephalic basal skull Increase in nasion-clinoid distance Decrease in bipterional distance Decrease in IOD Increase in biorbital external opening angle Decrease in nasion-pterional angle Increase in clinopterional angle Backward position of zygomatic bone IOD = Interorbital distance.

identified three groups: a group with metopic synostosis with only a ridge in medial frontal region without any other bone malformation: a group with malformation of the nasoethmoidal complex and an anomaly in the interor­ bital distance; and a group of children with a complex malformation occurring in the axes of bones requiring at surgery a total remodelling of anterior and median part of the skull. References 1 Anderson FM: Treatment of coronal and metopic synostosis: 107 cases. Neurosurgery 1981:X: 143-149. 2 Currarino G. Silverman FN: Orbital hypotelorism. arhincnccphaiy and trigonocephaly. Radiology 1960:74:206-217. 3 Delashaw JB. Parsing JA. Park TS. et al: Surgical approaches for the correction of metopic synostosis. Neurosurgery 1986:19:228-234. 4 Dominguez R. Oh KS. Bender T. Girdany BR: Uncomplicated trigonocephaly. A radiographic affirmation of conservative therapy. Radiology 1981:140:681-688. 5 Oi S. Malsumolo S: Trigonocephaly (metopic synostosis). Clinical, surgical and anatomical concepts. Childs Nerv Syst 1987:3: 259-265. 6 Persson KM. Roy WA. Persing JA Rodeheaver GT. et al: Craniofa­ cial growth following experimental craniosynostosis and cranietomy in rabbits. J Neurosurg 1979;50:187-197. 7 Shillito J. Matson D: Craniosynostosis: A review of 519 surgical pa­ tients. Pediatrics 1968:41:829-853. 8 Virchow R: Obcrden Cretinismus. namentlich in Franken, und tiber pathologische Schadelformen. Verh Phys Med Gesamte Würzburg 1851 ;2:230-256. 9 David JD. Poswillo D. Simpson D: Craniosynostosis - Causes. Nat­ ural History and Management. Berlin. Springer. 1982. pp 133-140. 10 Fernbach SK. Naidich TP: Radiological evaluation of craniosynos­ tosis; in Cohen M (ed): Craniosynostosis. Diagnosis. Evaluation and Management. New York. Raven Press. 1986. pp 191-214. 11 Frydman M. Kausehanksy A. Elian E: Trigonocephaly: A new fa­ milial syndrome. Am J Med Genet 1984:18:55-59. 12 Hunter AGVV. Rudd Nl.. Hoffman IIJ: Trigonocephaly and associat­ ed minor anomalies in mother and son. J Med Genet 1976: 13:77-79.

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The fusion of both clinopterion-nasion lines results in a lozenge form. This trigonocephalic basal lozenge is earacterized by decreased nasion-pterional and clinopterional angles, associated with larger nasion-clinoid distance and smaller bipterional distance. We encountered this peculiar trigonocephalic lozenge in 9/17 (53%) of our patients. In 9/17 patients the nasion-clinoid distance was in­ creased. suggesting anterior fossa sagittal elongation of the anterior fossa. This distance was significantly in­ creased in those cases associated with a small bipterional distance. The external biorbital angle mean value was larger than 10° when compared with the normal popula­ tion. This result is related to the wrong position of the ex­ ternal orbital walls, which remain posteriorly with conse­ quent orbital varus. Dhellemmes et al. 130J postulated that sphenoidal me­ senchymal dysplasia was responsible for the orbital dysmorphism. Ocular and orbital volumes showed no alter­ ations. The interorbital distance mean value was dimin­ ished by 4 mm in relation with the normal population. 3D CT scan analysis of the nasoethmoidal complex allowed a differentiation between true malformations, which are ex­ ceptional in trigonocephaly, and ethmoidal sinuses short­ ening secondary to orbital malposition. It is still uncertain which is the responsible suture for anterior fossa sagittal overgrowth in trigonocephaly. Using 3D CT it was pos­ sible to demonstrate a frontozygomatic synostosis (4 cases), sphenofrontal and coronal basal synostosis (3 cases), a sphenozygomatic and frontoethmoidal synosto­ sis (2 cases) and a sphcnotemporal synostosis (1 case). It is possible that closure of these sutures occurred after the anterior fossa elongation, and the closure of metopic su­ ture is in relation with the anterior basal skull elongation. Anderson (11demonstrated that in 6 out of 11 cases me­ topic suture closure, sphenoethmoidal and frontoethmoi­ dal sutures appeared to be obliterated early. Associated with the premature closure of the metopic suture, there are alterations in the skull base, however, whether these variations are primary or secondary is un­ known. Moss [19] suggested that the dura and the falx ce­ rebri are important regulators of suture growth in that they transmit tensile messages from the basicranium to the cra­ nial sutures. The possibility that trigonocephaly can occur in the presence of an open metopic suture has been men­ tioned [2], according to Moss’s theory. In every one of our cases the closure of metopic suture was always demon­ strated. In conclusion, we suggest a nosographic classification of the trigonocephalic skull in relation with basal suture synostosis and consequent bone deformation (table 5). We

Skull Base In Trigonocephaly

13 Probst I P: The Prosencephalies. Morphology. Neuroradiologieal Appearances and Differential Diagnosis. Berlin. Springer. 1979. pp 29-34. 14 Welker II: Untersuchungen über Wachsthum und Bau des mensch­ lichen Schädels. Leipzig. Engelmann. 1862: cited in rcf. 7. 15 Furuya Y. Edwards MSB. Alpers CE. et al: Computerized tomogra­ phy of cranial sutures. I. Comparison of suture anatomy in children and adults. J Ncurosurg 1984;61:53-58. 16 Furuya Y. Edwards MSB. Alpers CE. et al: Computerized tomogra­ phy of cranial sutures. 2. Abnormalities of sutures and skull defor­ mity in craniosynoslosis. J Ncurosurg 1984:61:59-70. 17 Hansman CF: Growth of interorbital distance and skull thickness as observed in roentgcnographic measurements. Radiology 1966:86: 87-96. 18 ScarloGB. Tomaccini D: Trigonocephaly. Some clinical and surgi­ cal features. Acta Neurol Belg 1980:80:137-143. 19 Moss ML: Functional anatomy of cranial synostosis. Childs Brain 1975:1:22-33. 20 Albright AL. Byrd RP: Suture pathology in craniosynoslosis. J Neurosurg 1981:54:384-387. 21 Hoytc DA: Mechanisms of growth in the cranial vault and base. J


24 Marsh JL. Schwartz H: The surgical correction of coronal and metopic craniosynoslosis. J Ncurosurg 1983:59:245-251. 25 Rune B. Selvik G. Kreiborg S, et al: Motion of bones and volume changes in the neurocranium after craniectomy in Crouzon's dis­ ease. A roentgen stereometric study. J Neurosurg 1979;50:494-498. 26 Vannier MW. Marsh JL, Warren JO: Three dimensional CT recon­ struction images for craniofacial surgical planning and evaluation. Radiology 1984:150:179-184. 27 Vencs JL. Burdi A: Proposed role of the orbitosphenoid in craniofa­ cial dysostosis. Concepts Pediatr Neurosurg 1985:5:12 6 -135. 28 Nappen DL. Kokich UG: Experimental craniosynoslosis in growing rabbits. The role of periosteum. J Neurosurg 1983:58:101-108. 29 Riemenschncider PA: Trigonocephaly. Radiology 1957:68: 863-865. 30 Dhellemmes P. Pellerin Ph. Lejeune JP. cl al: Surgical treatment of trigonocephaly. Experience with 30 cases. Childs Ncrv Syst 1986: 2:228-232.

Dent Res 1971:50(suppl): 1447-1461.

Editorial Comment The relationship o f trigonocephaly to metopic craniosynostosis is one o f the most important concepts in any discussion o f the pathophysiology o f craniosynostosis. The authors report a thorough anthropometric analysis o f the skull base changes found in trigonocephaly. These data are obtained from CT and three-dimensional CT ra­ diographs o f children with this condition. The study de­ fines and clarifies the extensive changes in the skull base associated with this abnormality o f head shape. The authors o f this excellent study state clearly that their purpose is not to discern whether or not the skull base abnormalities represent the primary defect or wheth­ er it is the metopic craniosynostosis which was found in all o f their patients. This question is very important in spe­ cific relation to trigonocephaly since uniquely among the alleged craniosynostotic syndromes, trigonocephaly is not a progressive disease. There are clearly patients with

L. Genitori Department of Pediatric Neurosurgery Hôpital des enfants La Timone F-13005 Marseille (France)

minor ridging o f the metopic sutural area who do not need surgical intervention even though the ridge is present from birth. The authors point out that this may be a clearly de­ finable subset who are spared the pervasive changes in the skull base. Moss I author's ref 19/has shown that the skull base changes in trigonocephaly clearly predate the synos­ tosis and Persson et al. ¡author's ref. 6/ have shown that restraint o f skull growth locally can lead to secondary su­ tural synostosis which is indistinguishable from primary craniosynoslosis. The authors are to be commendedfo r this thorough and informative work. It is an excellent model fo r the anthro­ pometric assessment o f skull base changes using contem­ porary imaging studies. It would certainly be interesting to obtain follow-up data following the treatment o f this condition to document the changes in the skull base which have resulted from surgical intervention or the effect of growth. Harold L. Rekate, MD

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22 Ortiz MH. Brodic AG: On the growth of the human head from birth to the third month of life. Anal Rec 1949;103:311-332. 23 Ford EHR: Growth of the human cranial base. Am J Orthod 1958:44:498-506.

Skull base in trigonocephaly.

The authors present aspects of the skull base in trigonocephalic children. Different patterns on clinical anthropometric investigation, bidimensional ...
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