Magnetic resonance image findings in pug dogs with thoracolumbar myelopathy and concurrent caudal articular process dysplasia

Abstract

Background: A retrospective case series study was undertaken to describe the magnetic resonance imaging (MRI) findings in Pug dogs with thoracolumbar myelopathy and concurrent caudal articular process (CAP) dysplasia. Electronic clinical records were searched for Pug dogs who underwent MRI for the investigation of a T3-L3 spinal cord segment disease with subsequent confirmation of CAP dysplasia with computed tomography between January 2013 and June 2017. Clinical parameters age, gender, neuter status, body weight, urinary or faecal incontinence, severity and duration of clinical signs were recorded. MRI abnormalities were described. Univariable non-parametric tests investigated the association between the clinical parameters and evidence of extra- or intra-dural spinal cord compression on MRI.

Results: 18 Pug dogs were included. The median age was 106 months with median duration of clinical signs 5 months. All presented with variable severity of spastic paraparesis and ataxia; 50% suffered urinary/faecal incontinence. In all cases, MRI revealed a focal increase in T2-weighted signal intensity within the spinal cord at an intervertebral level where bilateral CAP dysplasia was present; this was bilateral aplasia in all but one case, which had one aplastic and one severely hypoplastic CAP. MRI lesions were associated with spinal cord compression in all but one case; intervertebral disc protrusion resulted in extra-dural compression in 10 (56%) cases; intra-dural compression was associated with a suspected arachnoid diverticulum in 4 (22%) cases and suspected pia-arachnoid fibrosis in 3 cases (17%). There was no association between clinical parameters and a diagnosis of intra-dural vs extra-dural compression. CAP dysplasia occurred at multiple levels in the T10-13 region with bilateral aplasia at T11-12 most often associated with corresponding spinal cord lesions on MRI.

Conclusions: All Pugs dogs in this study were presented for chronic progressive ambulatory paraparesis; incontinence was commonly reported. Although intervertebral disc disease was the most common radiologic diagnosis, intra-dural compression associated with arachnoid diverticulae/fibrosis was also common. Bilateral CAP aplasia was present in all but one Pug dog at the level of MRI detectable spinal cord lesions. A causal relationship between CAP dysplasia and causes of thoracolumbar myelopathy is speculated but is not confirmed by this study.

Keywords: Facet dysplasia; MRI; Pug dogs; Vertebral malformation.

Fig. 1

Magnetic resonance imaging of the thoracolumbar spine of case no. 6, displaying extra-dural spinal cord compression associated with T11–12 disc protrusion and concurrent bilateral T11 caudal articular process aplasia. From left to right; T2-weighted mid sagittal of thoracolumbar spine, T2-weighted transverse at the affected level T11–12 (transverse level marked with a dashed line), three-dimensional reconstruction of thoracolumbar junction on CT (T11–12 marked with dashed line; the normal articular processes of T12 are highlighted with an arrow head). There is a marked focal increase in T2-weighted signal within the spinal cord despite only mild ventral extra-dural spinal cord compression (arrowed on transverse image)

Fig. 2

Magnetic resonance imaging of the thoracolumbar spine of case no. 8 (top row) and 14 (bottom row) who display intra-dural spinal cord compression. From left to right; a = T2-weighted sagittal MRI, b = T2-weighted transverse MRI, c = CISS sequence reconstructed in sagittal plane, d = CISS sequence reconstructed in dorsal plane. In case 8, intra-dural spinal cord compression appears to be associated with an expansion of the dorsal arachnoid space, consistent with spinal arachnoid diverticula. CISS imaging highlights this CSF accumulation without apparent attachment of the dura to the pia (dashed line). In case 14, in a transverse plane (lower row image b) the spinal cord appears to develop a ‘stellate’ appearance with multiple hypo-intense bands that cross the arachnoid space (highlighted with short arrows on image b). At the corresponding level on CISS imaging (lower row, images c and d, dashed line) the hypo-intense bands appear lateral to the compressed spinal cord (level marked with dashed line) with an appearance reminiscent of the original description of ‘constrictive myelopathy’ [4]

Fig. 3

Magnetic resonance imaging and computed tomography of the thoracolumbar spine of case no. 13, which does not clearly display spinal cord compression. Top row left to right; sagittal T2-weighted image of the thoracolumbar spine, transverse T2-weighted image at the level of the spinal cord lesion at T11–12 (corresponding to dashed line labelled 1). Bottom row left to right; transverse computed tomography slice at affected level T11–12 (corresponding to dashed line labelled 1) displaying concurrent bilateral caudal articular process dysplasia (left-sided hypoplasia, arrowed, right-sided aplasia, arrow-head), transverse computed tomography slice at unaffected level T12–13 (corresponding to dashed line labelled 2) displaying unilateral (right-sided; arrow-head) caudal articular process aplasia

Fig. 4

Magnetic resonance imaging and computed tomography of the thoracolumbar spine of case no. 18. a = T2-weighted sagittal MRI, b = T2-weighted transverse MRI at affected level T11–12 (corresponding to dashed line from image a), c = sagittal reconstruction of CT centred on T11–12, d = Three-dimensional reconstruction of CT viewed from a dorsolateral aspect. There is extra-dural spinal cord compression due to T11–12 intervertebral disc protrusion (images a and b). The vertebral column adopts a kyphotic appearance with marked narrowing of the T11–12 intervertebral disc space, with apposing vertebral end-plate sclerosis, ventral spondylosis deformans and slight retrolisthesis (image c; arrowed). There is bilateral aplasia of the caudal articular processes of T11 with an increase in the distance between the dorsal laminae of T11 and T12 (image d; asterisk)