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Journal of the Anatomical Society of India

Duplication of optic canal in adult Japanese human skulls

Author(s): Mandavi Singh

Vol. 54, No. 2 (2005-07 - 2005-12)

Mandavi Singh
Institute of Medical Sciences, Banaras Hindu University
Varanasi-221 005, India

Abstract: Adult human Japanese skulls (435) were observed for the presence of duplicated optic canals from the
collection of bones stored in the Laboratory of Anatomy and Embryology, Department of Anatomy, Hokkaido University
School of Medicine, Sapporo, Japan with a database of attributes including age at death and sex. It includes 380 men and
55 women, the age at death ranged from 30 to 81 years. Duplicate optic canals were found in 13 skulls. Bilaterally
duplicated canals were found in 7 skulls out of which 5 skulls belonged to males and 2 skulls belonged to females.
Unilaterally duplicated optic canals were observed in 6 specimens out of which 4 skulls belonged to males and 2 skulls
belonged to females.

Key word: Skulls, duplication, optic Canals.

Materials and Methods

A total of 435 dry adult Japanese human skulls of known sex and age were observed for the presence of duplicated optic canal in Department of Anatomy, Hokkaido University School of Medicine, Sapporo, Japan.

Patency of both the canals main as well as accessory was confirmed by observation. The position of accessory optic canal in continuity with the groove for internal carotid artery was observed and confirmed and such accessory canals were taken into account for observation. The diameter and length of the two optic canals were not measured.

Results

On observation, 13 skulls (2.98%) showed duplication of optic canals out of which 9 skulls (2.34%) belonged to males and 4 skulls (7.2%) belonged to females. Bilateral duplication of the canal was observed in 7 skulls (1.66%), unilateral left sided duplication was observed in 4 skulls (0.92%) and right sided duplication was observed in 2 skulls only. (Fig. 1,2)

In male specimen, duplication of optic canal was observed in 9 skulls (2.34%) out of which in 5 skulls (1.3%) it was bilateral, in 3 skulls (0.78%) it was on the left side and in one specimen (0.26) it was on the right side. In female specimen, this duplication was observed in 4 skulls (7.2%) out of which in 2 skulls (3.6%) it was bilateral, in one skull (1.8%) it was on the left side and in one skull (1.8%) it was on the right side. (Table-1)

Table I: Duplicated Optic Canal

Sex Total No.of Skulls Total Duplicated Optic Canal Bilateral Duplicated Optic Canal Left Duplicated Optic Canal Right Duplicated Optic Canal Age (Years)
Total 435 13 (4%) 7 (1.6%) 4 (0.9%) 2 (0.45%) 30-81
Male 380 9 (2.34%) 5 (1.3%) 3 (0.78%) 1 (0.26%) 30-78
Female 55 4 (7.2%) 2 (3.6%) 1 (1.8%) 1 (1.8%) 50-81

In the present study duplication of optic canal was observed from 30 to 81 years. In case of males, the observed age ranged from 30 to 70 years and in females it ranged from 50 to 81 years. Duplication of the optic canal in the specimen of unknown sex and age was not taken into account.

In each duplicated optic canal, the main canal was in the usual position and the accessory canal, variable in size, but smaller than the main canal was inferolateral to it in position, (Fig 1,2) as also reported by Choudhry et al. (1988). The two canals were situated nearly parallel to each other with intervening wall of variable thickness and length. In all these duplicated canals, the oval cranial end of the main canal was continuous with the anterolateral end of chaismatic
sulcus. The accompanying accessory canal, on its cranial end was continuous with the anterior end of the sulcus for the internal carotid artery. In all the skulls studied with duplicated optic canals, the lateral wall of the accessory canal was shorter than its medial wall which formed lateral wall of the main canal. None of these skulls showed any evidence of excessive bone formation.

Discussion

In adult specimens of unknown sex and age, 2 bilaterally duplicated and one unilaterally duplicated optic canals have been reported by Choudhry et al. (1988, 1999). Keyes (1935) reported the presence of duplicated optic canals in 36 (1.64%) cases out of 2187 skulls examined, whereas in the present study it was observed in 13 (2.9%) specimen out of 435 skulls examined, which is higher in percentage. Sexwise, inmales it is present bilaterally in 5 skulls (1.3%), on left side in 3 skulls (0.78%) and right side in one skull (0.26%) out of 380 specimens. In case of females bilateral duplication was observed in two specimen(3.6%), on left side in one specimen (1.8%) and right side in one specimen (1.8%) out of 55 specimens. Since the number of female skulls was much less than the number of male skulls, no comparable statistical analysis can be presented between the two sexes.

Although, in the present study the age of the skulls examined varied between 30 to 81 years, duplicated optic canals have also been reported in newborns by White (1924) and in a 21 months old male child by Warwick (1951). Further, the skulls where duplicated optic canals were observed, did not show any sign of excessive bone formation. So, excessive formation may not be attributed as a cause for duplication of optic canal. Looking at the vast range of age (newborn to 81 years), it can only be said that the reason for the duplication of optic canal may be the increased space between the optic nerve and the ophthalmic artery where presence of connective tissue gave way to ossification during the period of normal ossification of that region of skull. So, it may be considered as a normal variation of optic canal where the normal anatomical relationship of the optic nerve and ophthalmic artery is maintained and they become responsible for the formation of main canal and the accessory canal respectively, the ossification of the intervening space occupied by connective tissue being responsible for the development of separating septum.

Duplicated optic canal of right side

Fig. 1: Duplicated optic canal of right side.

Bilaterally duplicated ooptic canal

Fig. 2: Bilaterally duplicated optic canal.

Although, in the present study the age of the skulls examined varied between 30 to 81 years, duplicated optic canals have also been reported in newborns by White (1924) and in a 21 months old male child by Warwick (1951). Further, the skulls where duplicated optic canals were observed, did not show any sign of excessive bone formation. So, excessive formation may not be attributed as a cause for duplication of optic canal. Looking at the vast range of age (newborn to 81 years), it can only be said that the reason for the duplication of optic canal may be the increased space between the optic nerve and the ophthalmic artery where presence of connective tissue gave way to ossification during the period of normal ossification of that region of skull. So, it may be considered as a normal variation of optic canal where the normal anatomical relationship of the optic nerve and ophthalmic artery is maintained and they become responsible for the formation of main canal and the accessory canal respectively, the ossification of the intervening space occupied by connective tissue being responsible for the development of separating septum.

References

  1. Choudhry R, Choudhry S, Anand C. Duplication of Human Skulls. J Anat 1988; 159; 113; 113-116.
  2. Choudhry R, Anand M, Choudhry S. Morphologic and imaging studies of duplicate optic canals in dry adult human skulls. Surg Radiol Anat. 1999; 21(3):201-205.
  3. Keyes JEL. Observations on four thousand optic foramina. Albrecht V. Graefes Archiv für opthalmologie 1935; 13, 538-568.
  4. Le-Double AF, Traite' des Variations des Os du Crane de l'Homme Paris : Vigot Fre'res. 1935; 1903 pp. 372
  5. Warwick R. A juvenile skull exhibiting duplication of optic canals and division of superior orbital fissure. J Anat. 1951; 85, 289-291.
  6. White LE An anatomic and x-ray study of optic canal. Boston Med. Surg J 1942; 189, 741-748.
  7. Whithall SE (1932). The Anatomy of human orbit 2nd ed. London : Oxford University Press, London; 1932; pp 53 and 313.
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