Craniometric Analysis of the Hindbrain and Craniocervical Junction of Chihuahua, Affenpinscher and Cavalier King Charles Spaniel Dogs With and Without Syringomyelia Secondary to Chiari-Like Malformation.

Susan P Knowler,Tarja S Jokinen,Roberto M La Ragione,Angus K Mcfadyen,Clare Rusbridge,Anna-Mariam Kiviranta,Carlos E Ambrósio

doi:10.1371/journal.pone.0169898

Susan P Knowler, Tarja S Jokinen + Show 5 more

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https://doi.org/10.1371/journal.pone.0169898

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Abstract

ObjectivesTo characterize and compare the phenotypic variables of the hindbrain and craniocervical junction associated with syringomyelia (SM) in the Chihuahua, Affenpinscher and Cavalier King Charles Spaniel (CKCS).MethodAnalysis of 273 T1-weighted mid-sagittal DICOM sequences of the hindbrain and craniocervical junction from 99 Chihuahuas, 42 Affenpinschers and 132 CKCSs. The study compared 22 morphometric features (11 lines, eight angles and three ratios) of dogs with and without SM using refined techniques based on previous studies of the Griffon Bruxellois (GB) using Discriminant Function Analysis and ANOVA with post-hoc corrections.ResultsThe analysis identified 14/22 significant traits for SM in the three dog breeds, five of which were identical to those reported for the GB and suggest inclusion of a common aetiology. One ratio, caudal fossa height to the length of the skull base extended to an imaginary point of alignment between the atlas and supraoccipital bones, was common to all three breeds (p values 0.029 to <0.001). Associated with SM were a reduced occipital crest and two acute changes in angulation i) ‘sphenoid flexure’ at the spheno-occipital synchondrosis ii) ‘cervical flexure’ at the foramen magnum allied with medulla oblongata elevation. Comparing dogs with and without SM, each breed had a unique trait: Chihuahua had a smaller angle between the dens, atlas and basioccipital bone (p value < 0.001); Affenpinschers had a smaller distance from atlas to dens (p value 0.009); CKCS had a shorter distance between the spheno-occipital synchondrosis and atlas (p value 0.007).ConclusionThe selected morphometries successfully characterised conformational changes in the brain and craniocervical junction that might form the basis of a diagnostic tool for all breeds. The severity of SM involved a spectrum of abnormalities, incurred by changes in both angulation and size that could alter neural parenchyma compliance and/or impede cerebrospinal fluid channels.

Highlights

Syringomyelia (SM) secondary to Chiari-like malformation (CM) is diagnosed increasingly in toy breed dogs [1]
The analysis identified 14/22 significant traits for SM in the three dog breeds, five of which were identical to those reported for the Griffon Bruxellois (GB) and suggest inclusion of a common aetiology
Caudal fossa height to the length of the skull base extended to an imaginary point of alignment between the atlas and supraoccipital bones, was common to all three breeds (p values 0.029 to

Summary

Introduction

Syringomyelia (SM) secondary to Chiari-like malformation (CM) is diagnosed increasingly in toy breed dogs [1] Since both of these conditions can be accompanied by pain and /or neurological deficits [2,3,4], there are associated welfare concerns and a desire to reduce the disease prevalence in predisposed breeds [5]. CM, sometimes referred to as caudal occipital malformation syndrome (COMS), is a complex developmental abnormality of the skull and craniocervical junction. It is usually defined as a mismatch between size of the brain and the caudal fossa leading to cerebellar and brainstem herniation [6,7,8]. The mismatch of the skull and brain, like its human equivalent Chiari type I and O malformation (CM1 and CM0) [11], disrupts the cerebrospinal fluid (CSF) flow dynamics which may be progressive over time [12,13,14] with resultant CSF-like fluid cavitation in the spinal cord known as SM [15, 16]

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