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 th...
