Cervical spondylomyelopathy, commonly known as wobbler syndrome, affects the cervical vertebral column of dogs and is the result of compression of the spinal cord or nerve roots.1,2 It is primarily a disease of large and giant breeds,3–7 and Doberman Pinschers and Great Danes are more commonly affected than other breeds.1,3–8 Small-breed dogs are rarely affected, accounting for < 5% of reported cases of CSM.4,9,10 There are 2 recognized forms of CSM, which may occur separately or in conjunction. Disk-associated CSM causes spinal cord compression secondary to protrusion of intervertebral disks and generally occurs in large breeds, typically Doberman Pinschers.11 Osseous-associated CSM usually affects giant breeds, particularly Great Danes,1 with lateral or dorsolateral compression of the spinal cord mainly from osseous proliferation of the articular processes.12–14
Although the pathophysiology of CSM has not been completely elucidated, it is believed to involve static and dynamic factors.1,2 The dynamic component is associated with the effect that physiologic movement of the neck has on spinal cord compression.15 The most important static component is stenosis of the vertebral canal, which is often considered to be a relative stenosis in Doberman Pinschers2 and an absolute stenosis in Great Danes.16 Relative stenosis itself does not result in clinical signs, but it may predispose dogs to develop clinical signs of spinal cord compression in the presence of space-occupying conditions.2,17 On the other hand, absolute stenosis refers to an abnormally narrowed vertebral canal that is directly responsible for spinal cord compression.17
Results of an osteological study18 of dogs indicate that, when adjusted for body size, the vertebral canal height and width of large-breed dogs are smaller than those of small-breed dogs, which suggests that large-breed dogs have less space available for the spinal cord if the size of the spinal cord also varies proportionally. For example, the percentage of the vertebral canal occupied by the spinal cord at C7 in Doberman Pinschers with CSM is greater than that for hound dogs of equivalent size.19 Relative and absolute stenosis of the vertebral canal have been reported in Doberman Pinschers and Great Danes with CSM, respectively.11,16 To our knowledge, the size of the vertebral canal and spinal cord of Doberman Pinschers and Great Danes relative to that of small-breed dogs has not been investigated. Given the high prevalence of CSM in large- and giant-breed dogs and its scarcity in small-breed dogs,3–10 it seems possible that the percentage of the vertebral canal occupied by the spinal cord may be a factor in disease development and could provide an indirect estimate of the extent of vertebral canal stenosis.
The objective of the study reported here was to compare the percentage of the C3-C7 vertebral canal occupied by the spinal cord in small-breed dogs with that in Doberman Pinschers and Great Danes with and without CSM. Our hypothesis was that the percentage of the C3-C7 vertebral canal occupied by the spinal cord in Doberman Pinschers and Great Danes would be greater than that in small-breed dogs.
Materials and Methods
Animals
The medical record database for the radiology service at the Veterinary Medical Center of The Ohio State University was searched to identify records for Doberman Pinschers, Great Danes, and small-breed dogs (body weight, < 15 kg) that underwent an MRI examination of the cervical vertebral region between January 2005 and February 2015. Dogs with a complete medical record and both sagittal and transverse T2-weighted MRI images of the cervical vertebral column from C3 to C7 available for review were eligible for study inclusion. Small-breed dogs also had to be free of extensive abnormalities that could affect the diameter of the spinal cord (eg, myelitis or syringohydromyelia) to be included in the study. Dogs with localized changes such as an isolated intervertebral disk extrusion were included in the study, with the areas of spinal cord compression excluded from analysis on an individual basis. Dogs with space-occupying lesions, spinal cord hyperintensity that spanned > 1 intervertebral space, or diffuse changes in the spinal cord parenchyma (eg, syringohydromyelia, meningomyelitis, or neoplasia) were excluded from the study. The study population was separated into 5 groups (small-breed dogs, Doberman Pinschers with and without CSM, and Great Danes with and without CSM) for analysis. Cervical spondylomyelopathy was diagnosed on the basis of clinical and MRI findings. The Doberman Pinschers and Great Danes evaluated in the study were involved in other prospective studies.11,14,20
MRI
All dogs were positioned in dorsal recumbency for MRI examination. Images were obtained with either a 1.5- or 3.0-T MRI scanner, with varying protocols. For each study dog, DICOM image processing softwarea was used to acquire measurements from C3 to C7 on sagittal and transverse T2-weighted images. All measurements were obtained by the same investigator (MADB), who was unaware of each dog's clinical status. Measurements were repeated after 20 days for 3 randomly selected dogs from each of the 5 groups (n = 15 dogs) to calculate intraobserver agreement.
For transverse images, the respective areas of the spinal cord and vertebral canal were determined at the most cranial and caudal aspect of each vertebral body from C3 to C7 (Figure 1). The limits of the vertebral canal were considered to be the hypointense cortical bone dorsally and laterally and the vertebral body ventrally. When the dorsal lamina was not present in an image, the most solid hypointense border between the epidural fat and surrounding soft tissue was considered the dorsal limit of the vertebral canal; the hypointense cortical bone was then followed laterally to the level of the articular facets where it crossed the intervertebral foramina toward the dorsal aspect of the vertebral body (Figure 2). The limits of the spinal cord were delineated as the most solid transition from hypointense spinal cord to hyperintense CSF. Area (cm2) was then given automatically by the software for the delineated selection. For each location (cranial and caudal edge of each vertebra from C3 to C7), the vertebral canal and spinal cord areas were determined from the same image. The percentage of the vertebral canal occupied by the spinal cord was calculated by dividing the spinal cord area by the corresponding vertebral canal area, then multiplying the quotient by 100%.
Representative sagittal T2-weighted MRI image of the cervical region of a Great Dane that depicts the locations where the respective areas of the vertebral canal and spinal cord were measured at the cranial (A) and caudal (B) aspects of each vertebra from C3 to C7 on transverse T2-weighted MRI images.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.83
Representative transverse T2-weighted MRI image obtained at the cranial aspect of C5 of a Great Dane on which the limits used to measure the respective areas of the vertebral canal (A) and spinal cord (B) are depicted.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.83
The respective heights of the vertebral canal and spinal cord were measured at the same location on each vertebra from C3 to C7 on a midline sagittal image obtained at the level where the spinal cord had the largest diameter. Vertebral canal height was measured perpendicular to the spinal cord at the cranial and caudal aspect of each vertebra (Figure 3) and was delimited as the most cranial or caudal edge of the dorsal lamina to the corresponding craniodorsal or caudodorsal edge of the vertebral body. Ventral and dorsal limits of the spinal cord were determined by the innermost solid hyperintense line that represented the subarachnoid space filled with CSF. At each location, the percentage of the vertebral canal height occupied by the spinal cord height was calculated by dividing the height of the spinal cord by the corresponding height of the vertebral canal, then multiplying the quotient by 100%.
Representative sagittal T2-weighted MRI image of the cervical region of a Great Dane that depicts the locations where the respective heights of the vertebral canal and spinal cord were measured at the cranial (A) and caudal (B) aspects of each vertebra from C3 to C7.
Citation: American Journal of Veterinary Research 79, 1; 10.2460/ajvr.79.1.83
Statistical analysis
Intraobserver reliability was assessed by calculation of the intraclass correlation between the 2 sets of measurements obtained for a subset of 15 dogs (3 randomly selected dogs from each of the 5 groups).
The mean area and height of the vertebral canal and spinal cord at the cranial and caudal edges of each vertebra from C3 to C7 were calculated for each of the 5 groups of dogs (small-breed dogs, Doberman Pinschers with and without CSM, and Great Danes with and without CSM). Data were assessed by means of a Shapiro-Wilk test and determined to be normally distributed. Mean percentages were compared among the 5 groups by use of a 1-factor multivariate ANOVA in which the response variables were the corresponding measurements and group was the predictive variable. Pairwise comparisons between the groups were performed with the Tukey multiple comparison test. All analyses were performed with a commercially available statistical software program,b and values of P ≤ 0.05 were considered significant.
Results
Dogs
The study population consisted of 30 small-breed dogs, 15 clinically normal Doberman Pinschers, 15 Doberman Pinschers with CSM, 15 clinically normal Great Danes, and 15 Great Danes with CSM. The small-breed dogs included 12 females and 18 males and had a mean ± SD age of 6.9 ± 3.1 years (range, 1 to 12 years) and weight of 9.3 ± 3.5 kg (range, 2.7 to 14.7 kg). Breeds represented in the small-breed group included Pug (n = 6), Beagle (5), Cavalier King Charles Spaniel (3), Toy Poodle (3), Boston Terrier (2), Pomeranian (2), and Chihuahua, Lhasa Apso, Miniature Schnauzer, Pekingese, Pembroke Welsh Corgi, Shih Tzu, Toy Fox Terrier, Wire Fox Terrier, and Yorkshire Terrier (1 each). All dogs in the small-breed group underwent MRI examination because of neurologic disorders. Abnormalities of the cervical vertebral column identified on MRI images included intervertebral disk protrusion or extrusion (n = 23) and C6 fracture (1). The remaining 6 dogs did not have any cervical abnormalities identified; 1 dog had a brain tumor and a definitive diagnosis was not achieved for the other 5 dogs.
The clinically normal Doberman Pinschers included 8 females and 7 males and had a mean ± SD age of 4.3 ± 1.8 years (range, 2 to 8 years) and weight of 36.7 ± 6.8 kg (range, 26 to 52 kg). The Doberman Pinschers with CSM included 7 females and 8 males and had a mean ± SD age of 6.3 ± 2.4 years (range, 3 to 12 years) and weight of 35.0 ± 5.9 kg (range, 26.3 to 50.8 kg). The clinically normal Great Danes included 6 females and 9 males and had a mean ± SD age of 2.6 ± 1.3 years (range, 1 to 6.5 years) and weight of 52.7 ± 9.4 kg (range, 40.5 to 73.0 kg). The Great Danes with CSM included 2 females and 13 males and had a mean ± SD age of 3.9 ± 2.1 years (range, 1 to 7.3 years) and weight of 57.8 ± 8.9 kg (range, 42 to 79.3 kg).
Vertebral canal and spinal cord measurements
Intraclass correlation was > 0.8 for all variables of interest, which indicated that there was a high degree of reliability between the 2 sets of measurements obtained by the same investigator.21 Intraclass correlation was lowest for vertebral canal height (0.8839) and highest for spinal cord area (0.9486).
A total of 1,694 sagittal (height) and 1,574 transverse (area) measurements were obtained from C3 to C7. For the small-breed group, 53 sagittal images and 56 transverse images were discarded because of localized changes, such as spinal cord compression caused by intervertebral disk protrusion or extrusion. In general, for clinical patients (ie, small-breed dogs), sagittal images were obtained of the entire cervical vertebral column, but transverse images were obtained only for the region of clinical interest. Consequently, transverse images for some of the locations of interest for the dogs of small-breed group were unavailable for review including the cranial edge of C3 (n = 6 dogs), caudal edge of C3 (5), cranial edge of C4 (7), caudal edge of C4 (3), cranial edge of C5 (3), caudal edge of C5 (3), cranial edge of C6 (3), caudal edge of C6 (6), cranial edge of C7 (6), and caudal edge of C7 (15). Transverse images of all locations of interest were obtained for all dogs in the other 4 groups.
In general, the mean percentage of the vertebral canal area occupied by the spinal cord was lowest for Great Danes and highest for small-breed dogs and was greater for Doberman Pinschers than for Great Danes (Table 1; Supplementary Figure S1, available at http://avmajournals.avma.org/doi/suppl/10.2460/ajvr.79.1.83). At approximately half of the locations measured, the mean percentage of the vertebral canal area occupied by the spinal cord did not differ significantly between Doberman Pinschers and small-breed dogs. Conversely, the mean percentage of vertebral canal height occupied by the spinal cord for Great Danes was generally greater than that for Doberman Pinschers (Table 2; Supplementary Figure S2, available at http://avmajournals.avma.org/doi/suppl/10.2460/ajvr.79.1.83) but usually did not differ significantly from that for small-breed dogs. Overall, neither the mean percentage of vertebral canal area nor height differed significantly between Doberman Pinschers with and without CSM or between Great Danes with and without CSM.
Mean ± SD (range) percentage of the vertebral canal area occupied by the spinal cord at the cranial and caudal edges of each vertebra from C3 to C7 for each of 5 groups of dogs (small-breed dogs [body weight, < 15 kg; n = 30], Doberman Pinschers with [15] and without [15] CSM, and Great Danes with [15] and without [15] CSM).
| Vertebra | Location | Small-breed dogs | Doberman Pinschers with CSM | Clinically normal Doberman Pinschers | Great Danes with CSM | Clinically normal Great Danes |
|---|---|---|---|---|---|---|
| C3 | Cranial edge | 31.6 ± 8a (19–52) | 25.4 ± 5.5b (17–33) | 26.9 ± 2.4ab (24–33) | 18.7 ± 4c (15–32) | 16.5 ± 2.5c (15–25) |
| Caudal edge | 36.5 ± 6.7a (21–45) | 26.3 ± 6.2b (16–40) | 28.6 ± 5.6b (17–35) | 18.4 ± 5.3c (10–28) | 18.2 ± 2.7c (12–21) | |
| C4 | Cranial edge | 34.9 ± 7.5a (22–51) | 28.1 ± 5.2a (18–38) | 30 ± 43a (21–39) | 17.9 ± 3.2c (13–25) | 17.1 ± 2.9c (14–25) |
| Caudal edge | 36.6 ± 6.8a (23–46) | 27.6 ± 5.8b (18–39) | 29.5 ± 4.0ab (23–35) | 18.3 ± 2.5c (14–22) | 19.8 ± 2.6c (15–25) | |
| C5 | Cranial edge | 38.9 ± 6.1a (25–51) | 28.9 ± 5.1a (18–36) | 29.9 ± 2.2a (25–33) | 20.8 ± 8.2c (13–48) | 19.6 ± 1.8c (16–23) |
| Caudal edge | 37 ± 6.5a (26–53) | 27.5 ± 6a (19–40) | 28.5 ± 3.9a (21–35) | 19.4 ± 5.3c (15–35) | 19.4 ± 2.5c (15–24) | |
| C6 | Cranial edge | 38.1 ± 6.8a (24–49) | 34.1 ± 5a (18–33) | 37.4 ± 2.2a (27–34) | 19.3 ± 4.3c (9–25) | 20.8 ± 1.7c (16–23) |
| Caudal edge | 37.5 ± 7.2a (24–52) | 25.9 ± 8.2a (21–47) | 30.2 ± 6.2a (28–48) | 17.6 ± 4.1c (14–26) | 19.7 ± 2.8c (17–25) | |
| C7 | Cranial edge | 38.8 ± 7.5a (25–48) | 28.7 ± 4b (16–29) | 35.7 ± 3.9a (18–30) | 19.8 ± 2.4c (13–21) | 21.5 ± 2.3c (12–20) |
| Caudal edge | 32.9 ± 5.1a (27–47) | 20.9 ± 6.1b (18–40) | 23.4 ± 6b (28–47) | 16.5 ± 3.9c (11–26) | 15.3 ± 2.6c (17–27) |
All dogs underwent MRI examination of the cervical vertebral column by the radiology service of the Veterinary Medical Center of The Ohio State University between January 2005 and February 2015. Doberman Pinschers and Great Danes with and without CSM were evaluated as part of other prospective studies.11,14,20 All small-breed dogs were clinical patients with neurologic abnormalities and had to be free of extensive abnormalities that could affect the diameter of the spinal cord (eg, myelitis or syringohydromyelia), space-occupying lesions of the vertebral canal, and spinal cord hyperintensity that spanned > 1 intervertebral space to be included in the study. At each location, the vertebral canal area and spinal cord area were measured on the same transverse T2-weighted MRI image. The percentage of the vertebral canal area occupied by the spinal cord was calculated by dividing the vertebral canal area by the corresponding vertebral canal area, then multiplying the quotient by 100%.
Within a row, values with different letters differ significantly (P < 0.001).
Mean ± SD (range) percentage of the vertebral canal height occupied by the spinal cord at the cranial and caudal edges of each vertebra from C3 to C7 for the dogs of Table 1.
| Vertebra | Location | Small-breed dogs | Doberman Pinschers with CSM | Clinically normal Doberman Pinschers | Great Danes with CSM | Clinically normal Great Danes |
|---|---|---|---|---|---|---|
| C3 | Cranial edge | 52.1 ± 7.9* (39–69) | 47 ± 5.4* (34–55) | 48.7 ± 4.4* (35–54) | 49 ± 6.6* (43–66) | 51.5 ± 5* (42–61) |
| Caudal edge | 51.4 ± 7.7a (42–68) | 46.6 ± 5.9a,b (34–55) | 43.9 ± 5.6b (41–63) | 50.6 ± 5.1a (42–61) | 49.7 ± 7.3a,b (45–71) | |
| C4 | Cranial edge | 52.4 ± 7.9a† (41–7.1) | 46.7 ± 3.8b† (41–53) | 46.3 ± 3.9b† (39–52) | 52.6 ± 7.7a† (43–69) | 53.1 ± 4.6a† (46–61) |
| Caudal edge | 52.1 ± 8.1a,b (41–68) | 45.3 ± 4.9b (38–57) | 46.1 ± 6.2b (38–56) | 53.7 ± 5.7a (43–61) | 54.4 ± 4.6a (45–60) | |
| C5 | Cranial edge | 56.4 ± 7.5a,b‡ (40–70) | 47.5 ± 4.6b‡ (40–5.9) | 47.7 ± 3.8b‡ (40–55) | 55 ± 57a† (42–60) | 55.2 ± 3.3a† (50–62) |
| Caudal edge | 55.1 ± 8.3a (44–71) | 47.1 ± 5.8b (37–57) | 47.1 ± 4.9b (38–58) | 55.5 ± 6.8a (42–68) | 55 ± 4.6a (46–64) | |
| C6 | Cranial edge | 55.4 ± 8.3a (45–70) | 49.4 ± 4.2b (41–58) | 49.9 ± 3.5b (42–55) | 55.1 ± 4.6a (42–61) | 55.7 ± 3.8a (49–61) |
| Caudal edge | 55.4 ± 8.4a (41–71) | 49.6 ± 4b (42–55) | 47.1 ± 4.4b (40–56) | 54.3 ± 5.2a (44–62) | 54.5 ± 4.2a (49–64) | |
| C7 | Cranial edge | 55 ± 7a,b§ (41–66) | 46.7 ± 6.1b§ (34–52) | 49.2 ± 5.8a,b§ (34–53) | 52.8 ± 5.1a§ (38–62) | 52.9 ± 5.8a§ (41–60) |
| Caudal edge | 52 ± 6.2a,b (43–65) | 44 ± 5b (37–53) | 43.1 ± 4.1b (40–55) | 51.2 ± 6a (43–64) | 51.9 ± 4.5a (42–60) |
At each location, the vertebral canal height and spinal cord height were measured on the same sagittal T2-weighted MRI image. The percentage of the vertebral canal height occupied by the spinal cord was calculated by dividing the vertebral height by the corresponding spinal cord height, then multiplying the quotient by 100%. Mean percentages were compared among groups with 1-factor multivariate ANOVA, and pairwise comparisons among groups were performed with the Tukey multiple comparison test.
P = 0.1509
P = 0.0004
P = 0.0001
P = 0.0023.
See Table 1 for remainder of key.
Discussion
In the present study, the percentage of the vertebral canal area and height occupied by the spinal cord at the cranial and caudal aspects of each vertebra from C3 to C7 was compared among small-breed dogs (body weight, < 15 kg), Doberman Pinschers with and without CSM, and Great Danes with and without CSM. The primary purpose for the study reported here was to determine whether the spinal cord of Doberman Pinschers and Great Danes (2 dog breeds that commonly develop CSM) occupies a greater proportion of the vertebral canal than the spinal cord of small-breed dogs (ie, dogs that rarely develop CSM). Given that vertebral canal stenosis is considered a contributing factor to the development of CSM, we hypothesized that the percentage of the C3-C7 vertebral canal occupied by the spinal cord in Doberman Pinschers and Great Danes would be greater than that in small-breed dogs. However, results indicated that the mean percentage of the C3-C7 vertebral canal occupied by the spinal cord was greatest for small-breed dogs and did not differ between dogs of the same breed that did and did not have CSM. Thus, the percentage of the vertebral canal occupied by the spinal cord, although positively associated with the extent of vertebral canal stenosis, may not have a primary role in the pathogenesis of CSM.
In human patients with cervical spondylotic myelopathy (the equivalent of CSM in dogs), absolute or relative stenosis of the vertebral canal is considered the main static factor that contributes to the development of clinical signs.22 Stenosis of the cervical vertebral canal is also believed to play a role in the pathogenesis of CSM in dogs,1,2 either as the primary cause of compression of neural structures in absolute stenosis16 or as a contributing factor in relative stenosis,2 where a stenotic canal results in less space available for the spinal cord, which predisposes the spinal cord to compression.17 Therefore, we expected that the percentage of the vertebral canal occupied by the spinal cord for dogs of breeds predisposed to developing CSM would be greater than that for dogs of breeds that rarely develop CSM, thereby making them more sensitive to relative or absolute stenosis of the vertebral canal. However, our results did not support that supposition. In fact, the mean percentage of the vertebral canal area occupied by the spinal cord for both clinically normal and CSM-affected Great Danes was significantly lower than that for Doberman Pinschers with and without CSM and small-breed dogs, which suggested that of the dogs evaluated, Great Danes had the greatest amount of vertebral canal space available for the spinal cord.
Overall, the mean percentage of the vertebral canal area occupied by the spinal cord for Doberman Pinschers with and without CSM was greater than that of Great Danes. Moreover, the mean percentage of the vertebral canal area occupied by the spinal cord did not differ between small-breed dogs and Doberman Pinschers with CSM at the cranial edge of C4, cranial and caudal edges of both C5 and C6, or between small-breed dogs and clinically normal Doberman Pinschers at all locations evaluated except the caudal edges of C3 and C7. Results of another study23 involving CT evaluation of the cervical vertebral canal and spinal cord morphometry in clinically normal dogs indicate that German Shepherd Dogs have more vertebral canal space available for the spinal cord than do small-breed dogs, which may suggest that, relative to their size, Doberman Pinschers have less space available for the spinal cord than other large-breed dogs. In yet another study,19 Doberman Pinschers had less space available for the spinal cord than English Foxhounds at all investigated sites (C5 to C7), although that difference was significant only between Doberman Pinschers with CSM and English Foxhounds at C7.
Absolute12–14 and relative11 stenosis have been observed in dogs with CSM1 as well as clinically normal Dobermans19 and Great Danes.13,14 However, the fact that the percentage of the vertebral canal area occupied by the spinal cord was generally lowest for Great Danes and the overall lack of a significant difference in that measurement between the Doberman Pinschers and small-breed dogs of the present study suggested that vertebral canal stenosis alone may not have a primary role in the pathogenesis of CSM. It is possible that the biomechanical behavior of the vertebral canal and spinal cord are more directly involved with the development of clinical signs of CSM than is a stenotic vertebral canal.
Results of a cadaveric study15 of large-breed dogs with and without degenerative disk disease indicate that the diameter of the caudal portion (C4 through C7) of the cervical vertebral canal, which was defined as the vertebral foramina and soft tissue components, decreases significantly during extension and may cause dynamic spinal cord compression and clinical signs when associated with vertebral canal stenosis. However, given that the spinal cord occupied a smaller percentage of the vertebral canal in Great Danes and the mean percentage of the vertebral canal occupied by the spinal cord was similar between Doberman Pinschers and small-breed dogs in the present study, further investigation of the biomechanics of the vertebral canal and spinal cord in dogs with CSM is necessary to elucidate a possible relationship between stenosis of the vertebral canal and dynamic compression of the spinal cord as it pertains to clinical signs of the disease.
The overall difference in the percentage of the vertebral canal occupied by the spinal cord among dogs of different sizes also suggests that Doberman Pinschers and Great Danes have a proportionately smaller spinal cord, compared with dogs of other breeds because the height and width of their cervical vertebral canal is decreased relative to their body size.18 This apparent decrease in spinal cord size may be a consequence of necessary adaptations, such as a decrease in vertebral canal diameter owing to an increase in pedicle width necessary for a greater loading capacity.18
In the present study, the mean percentage of vertebral area occupied by the spinal cord did not differ significantly between Great Danes with and without CSM or between Doberman Pinschers with and without CSM, except for the mean percentage at the cranial edge of C7, which was unexpectedly greater in clinically normal Doberman Pinschers. Prior to this study, the percentage of vertebral canal area occupied by the spinal cord in Great Danes had not been reported; however, the results of this study were consistent with findings of other studies in which the percentage of the vertebral canal occupied by the spinal cord did not differ between Doberman Pinschers with and without CSM at C2 to C711 or C5 to C7.19 Dogs with CSM may have a smaller spinal cord than clinically normal dogs, possibly because of atrophy or Wallerian degeneration,11,19 which, in conjunction with an overall stenotic vertebral canal,16 might have prevented us from identifying a significant difference in the percentage of the vertebral canal occupied by the spinal cord between dogs with and without CSM. However, that proposed mechanism conflicts with our subjective impression that dogs with CSM have less space available for the spinal cord than clinically normal dogs. Interestingly, in another study,24 there was no correlation between the subjective assessment of vertebral canal stenosis and the percentage of space occupied by the spinal cord at the intervertebral spaces of the cranial portion of the thoracic vertebral column of large- and giant-breed dogs.
The mean percentage of vertebral canal height occupied by the spinal cord for Great Danes was generally significantly greater than that for Doberman Pinschers but did not differ significantly from that for small-breed dogs at any of the locations evaluated in this study. That finding appears to disagree with the results of another study25 in which larger dogs were reported to have more space available for the spinal cord than small dogs as determined by measurement of the mid-vertebral occupancy of the vertebral canal by the spinal cord at T4, T9, and L3 on sagittal MRI images. Breeds were not reported for the dogs of that study.25 A myelographic study26 of the cranial portion of the cervical vertebral column likewise indicated that the space available for the spinal cord was greater in large-breed dogs, compared with that in small-breed dogs, although the large-breed dogs in that study consisted primarily of German Shepherd Dogs and Rottweilers. In a study18 of purebred dogs of breeds predisposed to compression of the cervical spinal cord, the mean vertebral canal diameter was smallest for Great Danes and greatest for Rottweilers; therefore, differences in the amount of space available for the spinal cord should be expected among dogs of specific breeds, even when dogs of those breeds are of similar size.
Previous studies in which the proportion of the cervical vertebral canal occupied by the spinal cord was measured involved evaluation of myelographic images,26 which have limited detail that adversely affects accuracy of measurements, or transverse MRI images.11,16,19 However, none of those studies11,16,19,26 compared that measurement among dogs of breeds with varying sizes. In 1 study23 that involved evaluation of transverse CT-myelographic images, the size of the spinal cord and vertebral canal were compared between 8 clinically normal small-breed dogs (2 Shih Tzus, 2 Miniature Schnauzers, and 4 mixed-breed dogs) and only 4 German Shepherd Dogs.
Limitations of the present study were primarily associated with its retrospective nature, such as the small number of small-breed dogs of various breeds evaluated and the fact that all of those dogs had neurologic abnormalities. For the small-breed dogs, the angle used to obtain transverse images was not standardized, and transverse images were routinely obtained only for regions of the cervical vertebral column that were likely to have abnormalities, which limited the number of images available for review for that group. A prospective study would be necessary to increase the study population. Such a study should use standardized MRI protocols and include clinically normal small-breed dogs of sufficient numbers to allow analysis by breed, along with other large- and giant-breed dogs with and without CSM for comparisons by body type and size.
Results of the present study indicated that the mean percentage of the C3-C7 vertebral canal area occupied by the spinal cord was greater for small-breed dogs (body weight, < 15 kg), compared with that for Doberman Pinschers and Great Danes, and was lowest for Great Danes. This suggested that the percentage of the vertebral canal occupied by the spinal cord, although positively associated with the extent of vertebral canal stenosis, may not have a primary role in the pathogenesis of CSM. It is possible that the biomechanical behavior of the vertebral canal and its relationship with the spinal cord is more directly involved with the development of clinical signs of CSM than is a stenotic vertebral canal, and motion of the cervical vertebral column may differ on the basis of the breed or size of the dog. Further research is necessary to investigate biomechanical differences in the cervical vertebral column among various breeds of dogs, particularly breeds that are and are not commonly affected by CSM.
Acknowledgments
Dr. Bonelli received a scholarship grant from the Coordination for the Improvement of Higher Education Personnel (CAPES), Brazil.
The authors declare that there were no conflicts of interest.
Presented in abstract form at the 28th Annual Symposium of European Society of Veterinary Neurology and European College of Veterinary Neurology, Amsterdam, The Netherlands, September 2015.
The authors thank Dr. Steven Naber for assistance with the statistical analysis and Paula Martin-Vaquero for assistance with manuscript preparation.
ABBREVIATIONS
| CSM | Cervical spondylomyelopathy |
Footnotes
ClearCanvas Workstation, version 7.0, Synaptive Medical Inc, Toronto, ON, Canada.
SAS, SAS Institute Inc, Cary, NC.
References
1. da Costa RC. Cervical spondylomyelopathy (wobbler syndrome) in dogs. Vet Clin North Am Small Anim Pract 2010; 40: 881–913.
2. De Decker S, da Costa RC, Volk HA, et al. Current insights and controversies in the pathogenesis and diagnosis of disc-associated cervical spondylomyelopathy in dogs. Vet Rec 2012; 171: 531–537.
3. Lipsitz D, Levitski RE, Chauvet AE, et al. Magnetic resonance imaging features of cervical stenotic myelopathy in 21 dogs. Vet Radiol Ultrasound 2001; 42: 20–27.
4. da Costa RC, Parent JM, Holmberg DL, et al. Outcome of medical and surgical treatment in dogs with cervical spondylomyelopathy: 104 cases (1988–2004). J Am Vet Med Assoc 2008; 233: 1284–1290.
5. da Costa RC, Echandi RL, Beauchamp D. Computed tomography myelographic findings in dogs with cervical spondylomyelopathy. Vet Radiol Ultrasound 2012; 53: 64–70.
6. Murthy VD, Gaitero L, Monteith G. Clinical and magnetic resonance imaging (MRI) findings in 26 dogs with canine osseous-associated cervical spondylomyelopathy. Can Vet J 2014; 55: 169–174.
7. Gasper JA, Rylander H, Stenglein JL, et al. Osseous-associated cervical spondylomyelopathy in dogs: 27 cases (2000–2012). J Am Vet Med Assoc 2014; 244: 1309–1318.
8. Platt SR, da Costa RC. Cervical spine. In: Tobias K, Johnston S, eds. Veterinary surgery: small animal. Philadelphia: Elsevier Saunders, 2012;410–448.
9. De Risio L, Muñana K, Murray M, et al. Dorsal laminectomy for caudal cervical spondylomyelopathy: postoperative recovery and long-term follow-up in 20 dogs. Vet Surg 2002; 31: 418–427.
10. Harris KP, Saveraid TC, Rodenas S. Dorsolateral spinal cord compression at the C2–C3 junction in two Cavalier King Charles Spaniels. Vet Rec 2011;169:416.
11. da Costa RC, Parent JM, Partlow G, et al. Morphologic and morphometric magnetic resonance imaging features of Doberman Pinschers with and without clinical signs of cervical spondylomyelopathy. Am J Vet Res 2006; 67: 1601–1612.
12. Gutierrez-Quintana R, Penderis J. MRI features of cervical articular process degenerative joint disease in Great Dane dogs with cervical spondylomyelopathy. Vet Radiol Ultrasound 2012; 53: 304–311.
13. Martin-Vaquero P, da Costa RC. Evaluation of traditional and novel radiographic vertebral ratios in Great Danes with versus without cervical spondylomyelopathy. Vet Radiol Ultrasound 2014; 55: 488–495.
14. Martin-Vaquero P, da Costa RC. Magnetic resonance imaging features of Great Danes with and without clinical signs of cervical spondylomyelopathy. J Am Vet Med Assoc 2014; 245: 393–400.
15. Ramos RM, da Costa RC, Oliveira AL, et al. Effects of flexion and extension on the diameter of the caudal cervical vertebral canal in dogs. Vet Surg 2015; 44: 459–466.
16. Martin-Vaquero P, da Costa RC, Lima CG. Cervical spondylomyelopathy in Great Danes: a magnetic resonance imaging morphometric study. Vet J 2014; 201: 64–71.
17. Bailey CS, Morgan JP. Congenital spinal malformations. Vet Clin North Am Small Anim Pract 1992; 22: 985–1015.
18. Breit S, Künzel W. Osteological features in pure-bred dogs predisposing to cervical spinal cord compression. J Anat 2001; 199: 527–537.
19. De Decker S, Gielen IM, Duchateau L, et al. Morphometric dimensions of the caudal cervical vertebral column in clinically normal Doberman Pinschers, English Foxhounds and Doberman Pinschers with clinical signs of disk-associated cervical spondylomyelopathy. Vet J 2012; 191: 52–57.
20. Foss K, da Costa RC, Rajala-Schuttz PJ, et al. Force plate gait analysis in Doberman Pinschers with and without cervical spondylomyelopathy (Erratum published in J Vet Intern Med 2013;27:424). J Vet Intern Med 2013; 27: 106–111.
21. Shrout PE. Measurement reliability and agreement in psychiatry. Stat Methods Med Res 1998; 7: 301–317.
22. Lebl DR, Hughes A, Cammisa FP Jr, et al. Cervical spondylotic myelopathy: pathophysiology, clinical presentation, and treatment. HSS J 2011; 7: 170–178.
23. Seo E, Choi J, Choi M, et al. Computed tomographic evaluation of cervical vertebral canal and spinal cord morphometry in normal dogs. J Vet Sci 2014; 15: 187–193.
24. Johnson P, De Risio L, Sparkes A, et al. Clinical, morphologic, and morphometric features of cranial thoracic spinal stenosis in large and giant breed dogs. Vet Radiol Ultrasound 2012; 53: 524–534.
25. Hecht S, Huerta MM, Reed RB. Magnetic resonance imaging (MRI) spinal cord and canal measurements in normal dogs. Anat Histol Embryol 2014; 43: 36–41.
26. Fourie SL, Kirberger RM. Relationship of cervical spinal cord diameter to vertebral dimensions: a radiographic study of normal dogs. Vet Radiol Ultrasound 1999; 40: 137–143.
