History
A 5-year-old 36-kg (79-lb) neutered male German Shepherd Dog was evaluated because of a 3-week history of progressive urinary incontinence and signs of lumbosacral pain.
Neurologic examination revealed mild proprioceptive ataxia and mild postural reaction deficits in the pelvic limbs. Muscle bulk and muscle tone appeared normal in all 4 limbs, and segmental spinal refexes were intact. Mild discomfort was detected on palpation of the lumbosacral vertebral column. Physical examination findings were otherwise unremarkable. Because of signs of lumbosacral pain and urinary incontinence, neuroanatomic localization was consistent with a lesion of spinal cord segments L4 through S3; however, because no spinal reflex abnormalities were detected, a lesion localized to spinal cord segments T3 through L3 could not be excluded.
The dog was anesthetized for MRI of the lumbosacral vertebral column (Figure 1).
Midsagittal (A), right parasagittal (B), and transverse (C) T2-weighted MRI images and transverse fat suppression precontrast (D) and postcontrast (E) T1-weighted MRI images of the lumbosacral vertebral column of a 5-year-old 36-kg (79-lb) neutered male German Shepherd Dog that was evaluated because of a 3-week history of progressive urinary incontinence and signs of lumbosacral pain. A neuroanatomic lesion was localized to spinal cord segments L4 through S3. Transverse images (C, D, and E) were obtained at the level of the dotted line in the midsagittal (A) image. In all images, cranial (A and B) or right (C, D, and E) is to the left.
Citation: Journal of the American Veterinary Medical Association 253, 8; 10.2460/javma.253.8.987
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
A 1.5-T magnet was used to perform MRI of the lumbosacral vertebral column. Sagittal and transverse T2-weighted images were obtained. Transverse T1-weighted and T1-weighted fat suppression images were obtained before and after IV administration of gadopentate dimeglumine (0.1 mmol/kg [0.045 mmol/lb]).
On the MRI images, multiple extradural rounded well-marginated cystic structures are observed in the left-dorsolateral and right-dorsolateral aspects of the vertebral canal over the caudal third of L7. The cystic structures are compressing the conus medullaris and the L7, sacral, and coccygeal nerve roots. These structures appear intimately related with the L7-S1 articular process joints. The right-dorsolateral cystic structure is bilobed with the larger lobe measuring 9 × 8 × 6 mm and the smaller lobe measuring 7 × 6 × 5 mm, whereas the left-dorsolateral lesion is not bilobed and measures 11 × 9 × 6 mm. The content of the lesions is isointense to CSF on T2-weighted and on T1-weighted sequences. The walls of the lesions are isointense to adjacent muscle tissue on T2- and T1-weighted sequences, and there is marked contrast enhancement on T1-weighted fat suppression images (Figure 2). There is subtle spondylolisthesis of L7 with S1 and mild disk degeneration with the presence of a nuclear cleft.
Same MRI images as in Figure 1. Signal intensity in all sequences is compared with that of CSF. Multiple extradural rounded well-marginated cystic structures are evident within the vertebral canal over the caudal third of L7 and centered at the level of the L7-S1 articular process joints. The lesion on the right is bilobed. Notice the subtle step malalignment (ie, spondylolisthesis) of L7 with S1 and mild central degeneration of the L7-S1 disk. The content of the structures is isointense on T2-weighted (arrows; A, B, and C) and T1-weighted fat suppression images (arrows; D). After IV administration of gadopentate dimeglumine, a thin contrast-enhancing rim of the structures is evident (arrowheads; E), but the content of the structures does not have enhancement. Notice the L7 nerve roots (stars; C).
Citation: Journal of the American Veterinary Medical Association 253, 8; 10.2460/javma.253.8.987
The thin-walled fluid-filled structures were considered consistent with multiple and lobulated extradural cysts. Because of their close proximity with the L7-S1 articular process joints, extradural synovial cysts were suspected. The differential diagnosis included ganglion cysts and, less likely in view of the bilateral origin and the lack of aggressive changes, neoplasia such as myxosarcoma or synovial cell sarcoma.
Treatment and Outcome
The patient underwent a dorsal laminectomy at the L7-S1 level. Intraoperative evaluation revealed 3 fluid-filled structures in the vertebral canal causing lateromedial displacement and compression of the cauda equina. All cysts were laterally attached to the L7-S1 articular process joints.
Gentle fine-needle aspiration of the fluid inside the cavities revealed translucent and viscous fluid, consistent with synovial fluid. Cytologic analysis of the fluid aspirate revealed a nucleated cell count of 3 × 109 cells/L with 5% lymphocytes and 95% large mononuclear cells (mainly macrophages).
The cysts were bluntly dissected from the lateral aspect of the vertebral canal, and the cauda equina was decompressed. Histologic assessment confirmed the presence of a cystic lesion. The cyst wall was composed of moderately cellular fibrous tissue comprising plump fibroblasts and collagen. The cyst was lined by a single layer of flattened cells, in rare instances polygonal, with scant eosinophilic cytoplasm. Immunohistochemical investigations indicated that the cells lining the cysts were positive for vimentin, a marker for mesenchymal cells, and negative for cytokeratin and CD31, markers for epithelial and endothelial cells, respectively. Within the lumen of the cyst there was accumulation of moderate amounts of pale eosinophilic finely flocculent alcianophilic material. Overall histologic findings were consistent with fluid-filled cysts; morphological and immunohistochemical features of the cells lining the cysts were consistent with synovial elements, supporting the diagnosis of synovial cysts.
The dog was urinating in a controlled manner and appeared comfortable 4 days following surgery. One month after surgery, the urinary incontinence had completely resolved, and the signs of lumbosacral pain and proprioceptive deficits could not be elicited on neurologic examination.
Comments
In the present report, the MRI characteristics of the cysts within the vertebral canal (ie, well-demarcated, extradural, thin-walled, fluid-filled cavities) were consistent with previous reports of intraspinal cysts.1,2 Differentiation between different cyst types cannot be made with diagnostic imaging. The histopathologic features of the excised tissue of the dog of the present report were consistent with synovial cysts.1 Nonmeningeal extradural cysts are thought to develop secondary to degenerative changes in the vertebral column, most commonly arising from periarticular joint tissue or, more rarely, from the ligaments of the vertebral canal and the intervertebral disks. Extradural or juxtafacet cysts can be classified as either ganglion cysts, resulting from mucinous degeneration of periarticular connective tissue, or synovial cysts, which are typically lined by a flattened layer of synovial cells, as in the case described in the present report. Extradural cysts have been found in the caudal cervical region, thoracolumbar area, and lumbosacral junction of dogs.3,4 These have mostly been reported for large-breed dogs, but, to our knowledge, lumbosacral extradural synovial and ganglion cysts have only been described in German Shepherd Dogs.2,5,6 German Shepherd Dogs are reported to be predisposed to degenerative lumbosacral disease, possibly the result of breed-related anatomic variation of the lumbosacral articular process joint orientation.
In the case described in the present report, subtle spondylolisthesis of L7 with S1 and mild disk degeneration could have been indicative of lumbosacral instability. Underlying dynamic instability may have been the inciting cause of synovial cysts formation resulting from increased articular process joint motion and subsequent inflammation. Unfortunately, no dynamic imaging was performed to confirm instability as the underlying cause for cyst formation.
One peculiarity of the cysts described in the present report was their origin from the articular process joints on both sides of the vertebral column, and on 1 side, the cyst was bilobed. Multiple and lobulated ganglion cysts have previously been described in the lumbosacral vertebral column of a German Shepherd Dog.2
In previous reports,3,4 extradural cysts have resulted in slowly progressive clinical signs compatible with myelopathy but occasionally the extradural cysts were clinically silent. Most dogs with a lumbosacral cyst have signs of lumbosacral pain or neurologic deficits localized to spinal cord segments L4 through S3. For the dog of the present report, the main reason for veterinary evaluation was urinary incontinence.
Surgical resection is the treatment of choice for extradural cysts, with good to excellent outcomes in dogs with cysts in the lumbosacral vertebral column.5 However, this was, to our knowledge, the first description of resolution of urinary incontinence after resection of multiple, bilobed lumbosacral synovial cysts. The positive outcome for the dog of the present report may have been related to the short history of urinary incontinence.
Synovial cysts originating from the articular process joints should be considered in the differential diagnosis for cauda equina syndrome in German Shepherd Dogs with intraspinal fluid-filled lobulated lesions.
References
1. Sale CS, Smith KC. Extradural spinal juxtafacet (synovial) cysts in three dogs. J Small Anim Pract 2007;48:116–119.
2. Webb AA, Pharr JW, Lew LJ, et al. MR imaging findings in a dog with lumbar ganglion cysts. Vet Radiol Ultrasound 2001;42:9–13.
3. Dickinson PJ, Sturges BK, Berry WL, et al. Extradural spinal synovial cysts in nine dogs. J Small Anim Pract 2001;42:502–509.
4. Perez B, Rollan E, Ramiro, et al. Intraspinal synovial cyst in a dog. J Am Anim Hosp Assoc 2000;36:235–238.
5. Schmökel H, Rapp M. Lameness caused by an extradural lumbosacral foraminal synovial cyst in three German Shepherd Dogs. Vet Comp Orthop Traumatol 2016;29:83–88.
6. Forterre F, Kaiser S, Garner M, et al. Synovial cysts associated with cauda equina syndrome in two dogs. Vet Surg 2006;35:30–33.
