THE OCCYPITAL DYSPLASIA IN THE PAPILLION DOG

Maciej Janeczek, Aleksander Chrószcz, Norbert Pospieszny
Department of Biostructure and Animal Physiology, Wrocław University of Environmental and Life Sciences, Poland

ABSTRACT

The dorsal notch and incomplete ossification of the occipital bone in the 8 month old puppy of Papillion dog was described. Although at occipital dysplasia, the neurological signs did not occur. On the base of the standart craniometrical measurements, the type of the skull was idnetyfied as mesocephalic. The height of dorsal notch was 5.28 mm and the foramen magnum index equals 162.54 and dysplasia index 54 in post mortem examination. The literature is a source of various opinions about dorsal notch. Some authors qualified this as anatomical variation, but others suggest the dorsal notch occurs for example in cases of occipital hypoplasia and syringomyelia.

Key words: occipital dysplasia, skull, dorsal notch, foramen magnum, Papillion.

INTRODUCTION

The morphology of the foramen magnum is important in clinical causes and comparative researches [2,6,11,13,14,20]. The malformations of the foramen magnum, the hypoplasia and dysplasia of the occipital bone can lead to neurological symptoms as convulsions, consciousnessless, ataxias and many others. The pathological shape of the foramen magnum is the element of Arnold-Chiari syndrom, described also in dogs [3,13,14]. Some authors considered, this anatomical formation is not a pathology but a morphological variation of the foramen magnum [18,19]. The height of dorsal notch in young Pekingese was not greater than that in adult dogs, in contrast in the Beagles, where tendency for larger dorsal notches occurrence in juvenile dogs is less evident [18,19]. Other authors observed the dorsal notch formation in dogs with occipital hypoplasia and syringomyelia [15,16,17]. Parker and Park [13] founded a large dorsal notch in three dogs with neurological signs. The morphology of occipital bone with incomplete ossification and the foramen magnum with the dorsal notch is described in this paper.

MATERIAL AND METHODS

The material was the skull a male Papillion in 8 month age (Fig. 1). The dog died in an accident. The skull was macerated and prepared. The height of the skull, height and width of the foramen magnum were measured. The foramen magnum index was calculated [18]. The facial lenght (Prosthion-Nasion), cranial lenght (Nasion-Inion), skull lenght (Prosthion-Inion), maximum width of neurocranium (Euryon-Euryon) and maximum zygomatic width (Zygion-Zygion) were estimated [1,9,12]. The length-length index 2, length-width index 2 and length-width index 4 and dysplasia index (dorsal notch height/normal height of the foramen magnum) were calculated. The measurment were made with electronic slide caliper SYLVAC 110-DL with the precision of 0.1 mm.

RESULTS

The foramen magnum had a hexagonal shape with a significant dorsal notch in squamous part of the occipital bone (Fig. 2). The dorsal notch was located in saggital plane and was symmetrical. The shape of the extension was rectangular. The irregular openings on the both sides of the occipital bone, dorsal from the ventral condylar fossas were observed. Above mentioned openings became wider dorsally and were limited by the squamos part of temporal bones and the squamos part of occipital bones (Fig. 2). The large temporal openings were located on the border between temporal and occipital bones (squamous suture). The value of foramen magnum index was 162.54, the dysplasia index was 54 (Table 1).

DISCUSSION

On the base of measurements, the skull was classified as mesocephalic type (Table 1). In opinion of some authors, the value of the foramen magnum index is constans in dogs and does not change according to animal age [18,19]. Onar et al. [12] described the foramen magnum index in German shepherd puppies as 92.76. He also stated, the changes of foramen magnum index with age. Simoens et al. [18] estimated the mean value of foramen index in Pekingese to 93.4. Chrószcz et al. [2] evaluated this index in American Staffordshire terriers in perinatal period as 106.82. The index calculated in this paper was much more higher, it is 162.54. Simoens et al. [18] and Watson et al. [19] observed dorsal notch in Pekingese and Beagles. The height of dorsal notch in the investigated skull was smaller than the half of total height of the foramen magnum (35.27%). Dysplasia index, calculated according to Parker and Park method, was 54, it is low limit of the 2^nd dysplasia stage. It was also occurred the incomplete ossification of the occipital bone in vermiform impression. The similar occurrence was observed by Simeons et al. [18] in young Pekingese. Watson et al. [19] and Simoens et al. [1994] on the base of acquired results stated, the dorsal notch is not a patological formation but the morphological variation. The similar results had came from observations provided by other authors [21]. Onar et al. [12] in German shepherd dogs and Chrószcz et al [2] in American Staffordshire terriers did not find the similar creations. Wielądek and Kupczyńska [10] described the dorsal notch in three Yorkshire terriers. Only one of them had a neurological signs. It means, probably dorsal notch occurred only in some breeds, especially in brachy- and mesocephalic dogs. Despite the fact that the influence of the endocrine system on the shape of the skull was proven, its influence on the foramen magnum formation were not observed [4,5]. It is believed, that occurrence of the dorsal notch may have something to do with a disproportionately larger brain due to small neurocranium in relation to the skull capacity in dogs of brachycephalic breeds. In such case an increasing pressure on occipital bone can lead to disturbances in the process of bone formation resulting in a dorsal notch [7]. Rusbridge et al. [17] stated, that the most common causes of syringomyelia is occipital bone hypoplasia. In their opinios, the smaller occipital bone reduced the volume of the caudal fossa. Thus the cerebrospinal fluid flow is obstructed by the cerebellum. This all due to the hypoplasia of the occipital bone and the syringomyleia [15,17]. Rusbridge and Knowler [16] described the dorsal notch in 10 years old Cavalier King Charles spaniel skull. The dog had a serious neurological dysfunction. The occipital dysplasia and occipital hypoplasia was observed in this dog. Authors state, the occipital dysplasia is not a clinical problem per se. They stated the hypothesis, that membrane covering the supraoccipital defect allows for a dynamic expansion and less severe obstruction CSF movement through the foramen magnum. As consequence it is possible that syringomyelia could develop more slowly, resulting in later onset signs. The dogs with occipital hypoplasia and occipital dysplasia potentially may have a milder phenotype than those with occipital hypoplasia alone. The archeozoological investigations on the iron age remains proved the dorsal notch occurrence in dogs from Yan-Yoncatepe fortress in Urartu (Anatolia) [9]. Its mean, this extension in occipital bone occurred also in early stage of dog breeding. The dogs from Urartu were military animals and they couldn't have any neurological symptoms because of the duty.

CONCLUSIONS

Although anatomically visible the dorsal notch is not synonymous with neurological symptoms, but it increases the risk of their presents (for example in injuries). Probably this anatomical formation related to small occipital bone capacity for the encephalon and it is a signum of problems with cerabrospinal fluid circulation.

ACKNOWLEDGEMENT

The authors gratefully acknowledgements the kindness for advices of professor dr hab. Vedat Onar from Istambul University, Faculty of Veterinary Medicine.

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Accepted for print: 22.02.2010

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