New Swedish study on skull shape/SM correlation

This recent study (February 2006) postulates a definite association between the skull malformation that can lead to syringomyelia, and the steep, short back of skull that is now popular in cavaliers, also noting that SM is more prevalent in cavaliers than any other breed. You can download a pdf of the study but it is in Swedish so we need a translator!! This abstract is in English.

The relevant conclusion:

"This study showed that there is a difference in the shape of the caudal fossa between dogs with a normal head shape and small bred dogs with a steep back of the head. This indicates that occipital bone hypoplasia is related to a head shape where the back of the head is steep and that the malformation is common in these breeds."

Researchers have already been aware that the malformation does not always cause syrinxes (syringomyelia) nor symptoms even in badly affected cavaliers. If the correlation of skull shape holds up, it could indicate that breeders could begin to directly address the increasing incidence of symptomatic SM in the breed by working to alter the steep backward slope of the skull. More work yet to be done, but this is a very interesting addition to current research. The study was published in February but because it is in Swedish few were aware of it until now. If you download the paper there are a range of images in it as well that might interest those familiar with SM and ongoing research.

Perhaps clubs or breeders might consider a programme of assembling x-rays (much cheaper than MRIs!) of their dogs especially if an MRI has also been done, to start analyzing skull shapes? Note that it is *shape* (steep back of skull) and not *size* that is the relevant point in this study.

Link:

http://ex-epsilon.slu.se/archive/00000866/

Bakre skallgropens form hos hund
:
en studie av occipital hypoplasi hos hund

Spångberg, Camilla (2006) Bakre skallgropens form hos hund. Dept. of Small Animal Clinical Sciences, SLU. Examensarbete (Sveriges lantbruksuniversitet, Fakulteten för veterinärmedicin och husdjursvetenskap, Veterinärprogrammet) vol. 2006:51.

Abstract

Chiari type I malformation is a condition in humans characterized by a small posterior cranial fossa, downward herniation of the cerebellar tonsils, foramen magnum overcrowding and disturbances of cerebrospinal fluid dynamics. Syringohydromyelia is often seen in patients with Chiari type I malformation. Syringohydromyelia is characterized by fluid-filled cavities in the spinal cord. This causes damage to the nervous tissue in the spinal cord. In recent years, a condition similar to Chiari type I malformation has been recognized in dogs. It has mostly been seen in Cavalier King Charles spaniels (CKCS). The condition seen in dogs is usually called occipital bone hypoplasia.

The aim of the study was to examine whether there is a difference in the shape of the caudal fossa between CKCS, small bred dogs with a similar head shape and dogs with a normal head shape and if occipital bone hypoplasia is related to a head shape with a steep back of the head. Other aims of the study were to examine the crowding of nervous tissue in the foramen magnum in each breed group, the extent of syringohydromyelia and to what extent the malformation had caused neurological signs.

Sculls from dogs on autopsy were divided in halves and the position of the cerebellum compared to the level of the foramen magnum was studied. The degree of crowding of nervous tissue in the foramen magnum was determined. Based on this the shape of the caudal fossa was classified as normal, possible occipital bone hypoplasia or occipital bone hypoplasia. The cervical spinal cord was extracted and examined for syringohydromyelia. To determine whether the malformation had caused any neurological signs, the medical records of the patients with occipital bone hypoplasia or possible occipital bone hypoplasia were studied. In cases where the medical records not include such information, the owners of the dogs were contacted and asked if they had noted any neurological signs in their dog.

This study showed that there is a difference in the shape of the caudal fossa between dogs with a normal head shape and small bred dogs with a steep back of the head. This indicates that occipital bone hypoplasia is related to a head shape where the back of the head is steep and that the malformation is common in these breeds. The study also showed that occipital bone hypoplasia not inevitably causes syringohydromyelia. Only one of the dogs with occipital bone hypoplasia or possible bone hypoplasia had had neurological signs that with certainty were related to the malformation. This result gives further support to previous studies that have stated that occipital bone hypoplasia occurs asymptomatic.