Chiari malformations and syringohydromyelia are an important disease complex in Cavalier King Charles Spaniels. Although abnormalities in caudal fossa morphology are considered major contributors to the development of this disease, limited information exists on the range of morphologies in Cavalier King Charles Spaniels and on the relationship of these to clinically evident disease. Sixty-four Cavalier King Charles Spaniels were studied. Each underwent a neurologic examination and magnetic resonance imaging of the cervical spine and brain. T2-weighted sagittal images were used to determine both the morphologic characteristics and volume of the caudal fossa in each dog. This volume was also analyzed as a percentage of total cranial cavity volume. Each attribute was correlated with neurological grade and presence of syringohydromyelia. Fifteen dogs had neurologic signs, and 59 had morphologic abnormalities of the craniocervical junction. While 27 dogs had syringohydromyelia, 13 of these were clinically normal. Cerebellar herniation and occipital dysplasia were common findings but were not associated with syringohydromyelia. Dorsal compressive lesions were noted at the first and second cervical vertebral junction. Factors associated with the presence of neurologic signs included syringohydromyelia and the ratio of caudal fossa/total cranial cavity volume; dogs with signs had significantly larger syringohydromyelia than asymptomatic dogs. Caudal fossa size was not associated with syringohydromyelia. A positive association was identified between foramen magnum size and length of cerebellar herniation. The prevalence of craniocervical junction abnormalities is high in Cavalier King Charles Spaniels. While several factors are associated with neurologic signs, occipital hypoplasia appears to be the most important factor.

Syringomyelia is an important morbidity source in Cavalier King Charles Spaniels. Although abnormal cerebrospinal fluid (CSF) flow secondary to Chiari malformations is thought to cause syringomyelia in humans, this relationship is unknown in dogs. We used phase-contrast magnetic resonance (MR) imaging to evaluate CSF flow in dogs. Fifty-nine Cavalier King Charles Spaniels were assigned a neurologic grade reflecting their neurologic status. Five normal control dogs of other breeding were imaged for comparison. The presence of syringomyelia was noted from sagittal MR images. The pattern and velocity of CSF flow were assessed using phase-contrast cine MRI at the foramen magnum, C2-C3 disc space, and within syrinxes. Flow was measured most easily with the neck flexed to mimic standing. CSF flow velocity in the dorsal aspect of the subarachnoid space at the foramen magnum was significantly higher in control dogs than Cavalier King Charles Spaniels (P = 0.035). Flow was obstructed at the foramen magnum in 41 of 59 Cavalier King Charles Spaniels. Turbulent flow and jets were associated with syringomyelia presence and severity, and CSF flow velocity at C2/3 dorsally was inversely related to the presence of syringomyelia (P = 0.0197). Peak dorsal subarachnoid space CSF flow velocity at the foramen magnum and C2-C3 were together highly predictive of syringomyelia. CSF flow can be assessed in dogs using phase-contrast cine MRI. Obstruction to flow at the foramen magnum is common in Cavalier King Charles Spaniels and CSF flow pattern and velocity are related to the presence of syringomyelia.

Lesion heterogeneity among chronically paralyzed dogs after acute, complete thoracolumbar spinal cord injury (TLSCI) is poorly described. We hypothesized that lesion severity quantified by diffusion tensor imaging (DTI) is associated with hindlimb motor function. Our objectives were to quantify lesion severity with fractional anisotropy (FA), mean diffusivity (MD), and tractography and investigate associations with motor function. Twenty-two dogs with complete TLSCI in the chronic stage were enrolled and compared with six control dogs. All underwent thoracolumbar magnetic resonance imaging (MRI) with DTI and gait analysis. FA and MD were calculated on regions of interest (ROI) at the lesion epicenter and cranial and caudal to the visible lesion on conventional MRI and in corresponding ROI in controls. Tractography was performed to detect translesional fibers. Gait was quantified using an ordinal scale (OFS). FA and MD values were compared between cases and controls, and relationships between FA, MD, presence of translesional fibers and OFS were investigated. The FA at the epicenter (median: 0.228, 0.107-0.320), cranial (median: 0.420, 0.391-0.561), and caudal to the lesion (median: 0.369, 0.265-0.513) was lower than combined ROI in controls (median: 0.602, 0.342-0.826, p < 0.0001). The MD at the epicenter (median: 2.06 × 10, 1.33-2.96 × 10) and cranially (median: 1.52 × 10, 1.03-1.87 × 10) was higher than combined ROI in controls (median: 1.28 × 10, 0.81-1.44 × 10, p ≤ 0.001). Four dogs had no translesional fibers. Median OFS was 2 (0-6). The FA at the lesion epicenter and presence of translesional fibers were associated with OFS (p ≤ 0.0299). DTI can detect degeneration and physical transection after severe TLSCI. Findings suggest DTI quantifies injury severity and suggests motor recovery in apparently complete dogs is because of supraspinal input.