The prevalence of Chiari-like malformation and Syringomyelia in several toy breeds in the Netherlands
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Chiari-like malformation (CM) is caused by herniation of the cerebellum through the foramen magnum. The herniation might be the result to the apparent mismatch in volume between the caudal brain structures and the caudal skull. This condition occurs in several toy breeds like for instance the Griffon Bruxellois, chihuahua and the Cavalier king Charles Spaniel CKCS[4,5] Syringomyelia [SM] is, defined as, a dilatation of the central canal, larger than 2 mm. This condition occurs among others in toy breeds like the Chihuahua, and the dachshund. [4,8] Until now several hypotheses have been raised addressing the pathogenesis of SM. One hypothesis is that due to the herniation of the cerebellum (Chiari-like Malformation) an abnormal cerebrospinal fluid (CSF) flow arises. The abnormal flow in turn causes a sucking effect around the spinal cord and this supposedly would lead to a dilatation of the central canal and fluid-containing cavities (syrinx) within the parenchyma of the spinal cord (myelia). Another hypothesis is that the shortening of the skull base can lead to a narrowing of the jugular foramina (JF) between the cranial base synchondroses, which in turn might cause a congestion of the major venous outflow tracts of the skull and consequently to an increase of the intracranial pressure (ICP). The stenosis of the JF and a consequential vascular compromise in this opening could contribute to venous hypertension and rising ICP. The raised ICP could further raise the CSF pulse pressure which in turn might cause CSF jets. This could be an additional pathogenetic factor for the development of SM[10,13]. In about 50 % of the Cavalier King Charles Spaniels with a herniation of the cerebellum (CM) syringomyelia occurs. In an other study 60.7% of the 56 Griffon Bruxellois had CM. SM occurred with (37.5%) and without (8.9%) CM. Most studies described the disorder with the CKCS. In this retroperspective study the prevalence of CM and SM in other brachycephalic dog breeds is investigated.