Veterinary Record (2013) doi: 10.1136/vr.101082
T. A. Shaw, I. M. McGonnell, C. J. Driver, C. Rusbridge, H. A. Volk
T. A. Shaw, BVetMed, MRCVS C. J. Driver, BSc, BVetMed (Hons), MVetMed, DipECVN, MRCVS H. A. Volk, PhD, DipECVN, PGCAP, FHEA, MRCVS Department of Veterinary Clinical Sciences, Royal Veterinary College, Hatfield AL9 7TA, UKI. M. McGonnell, PhD Department of Veterinary Basic Sciences, The Royal Veterinary College, Royal College Street, London, UK
C. Rusbridge, BVMS, PhD, DipECVN, MRCVS Goddard Veterinary Group, Stone Lion Veterinary Hospital, London, UK
Email for correspondence: hvolk@rvc.ac.uk .
A retrospective study of Mri scans of CKCS, other small breed dogs (SB) and labradors (lD) was performed. Methods for selecting individuals, performing scans, con- structing 3D models of intracranial structures and partitioning the cerebral spinal fluid (CCF )and its contents are described in our previous study (Shaw and others 2012). However, in the present study, we partitioned the CCF into three compartments (pars rostralis, pars media and pars caudalis) for volumetric analysis. These parts were chosen to represent the volumes bounded by the occipital bones (pars caudalis), squamous portion of the temporal bone (pars media) and tentorium cerebelli (pars rostralis). The volumes were expressed as percentages of the total skull volume (the sum of the volumes of the CCF and the rostroten- torial compartment). Hindbrain volume (defined as the volume of parenchyma in the CCF) was expressed as a percentage of the overall brain volume (the sum of CCF parenchyma volume and rostrotento- rial parenchyma volume). Subjects were divided into the following groups: 38 SB, 26 lD and 45 CKCS. SM is thought to be a late onset disease, and in order to distinguish dogs that develop SM later in life from dogs that are unlikely to ever develop the condition, two further subgroups were selected from the individuals in the CKCS group.
The results revealed important differences in the relationship between hindbrain volume and CCF morphology in CKCS, pars rostralis volume was more sensitive than pars caudalis volume to variation in hindbrain volume (coef: pars rostralis 0.41±0.077 (P<0.0001), pars caudalis 0.105±0.073 (P=0.1538)). Conversely, in lD and SB, pars rostralis volume was less sensitive than pars caudalis volume to variation in hindbrain volume (pars rostralis coef: SB 0.13±0.065 (P=0.0519), lD 0.13±0.085 (P=0.1578), pars caudalis coef: SB 0.44±0.099 (P<0.0001), lD 0.59±0.18 (P=0.0027). These findings suggest that SB and lD compensate for variations in hindbrain volume by modifying the growth of the occipital skull, whereas in CKCS, occipital bone development is insensitive to changes in hindbrain volume. We infer from these results that increased hindbrain volume in CKCS causes the tentorium cerebelli to compensate by bulging in a rostral direction. a similar phenomenon, an increase in the angle of the tentorium, has been widely reported in humans with Chiari malformation 1
Email for correspondence: hvolk@rvc.ac.uk .
A retrospective study of Mri scans of CKCS, other small breed dogs (SB) and labradors (lD) was performed. Methods for selecting individuals, performing scans, con- structing 3D models of intracranial structures and partitioning the cerebral spinal fluid (CCF )and its contents are described in our previous study (Shaw and others 2012). However, in the present study, we partitioned the CCF into three compartments (pars rostralis, pars media and pars caudalis) for volumetric analysis. These parts were chosen to represent the volumes bounded by the occipital bones (pars caudalis), squamous portion of the temporal bone (pars media) and tentorium cerebelli (pars rostralis). The volumes were expressed as percentages of the total skull volume (the sum of the volumes of the CCF and the rostroten- torial compartment). Hindbrain volume (defined as the volume of parenchyma in the CCF) was expressed as a percentage of the overall brain volume (the sum of CCF parenchyma volume and rostrotento- rial parenchyma volume). Subjects were divided into the following groups: 38 SB, 26 lD and 45 CKCS. SM is thought to be a late onset disease, and in order to distinguish dogs that develop SM later in life from dogs that are unlikely to ever develop the condition, two further subgroups were selected from the individuals in the CKCS group.
The results revealed important differences in the relationship between hindbrain volume and CCF morphology in CKCS, pars rostralis volume was more sensitive than pars caudalis volume to variation in hindbrain volume (coef: pars rostralis 0.41±0.077 (P<0.0001), pars caudalis 0.105±0.073 (P=0.1538)). Conversely, in lD and SB, pars rostralis volume was less sensitive than pars caudalis volume to variation in hindbrain volume (pars rostralis coef: SB 0.13±0.065 (P=0.0519), lD 0.13±0.085 (P=0.1578), pars caudalis coef: SB 0.44±0.099 (P<0.0001), lD 0.59±0.18 (P=0.0027). These findings suggest that SB and lD compensate for variations in hindbrain volume by modifying the growth of the occipital skull, whereas in CKCS, occipital bone development is insensitive to changes in hindbrain volume. We infer from these results that increased hindbrain volume in CKCS causes the tentorium cerebelli to compensate by bulging in a rostral direction. a similar phenomenon, an increase in the angle of the tentorium, has been widely reported in humans with Chiari malformation 1
The data support the hypothesis that CM/SM in CKCS is a multifactorial disease process governed by the effects of increased hind-brain volume and impaired occipital bone development. The present authors recently reported that CM/SM is linked to increased cerebellar volume (Shaw and others 2012). in view of this, the aetiopathogenesis of CM/SM may equivocally be mediated by conditions independently affecting the developing occipital bones and cerebellum, or by dysregulation of a signalling mechanism coordinating the growth of the developing hindbrain and occipital skull.
