An 8.5-year-old 17.2-kg (37.8-lb) neutered female English Springer Spaniel was referred to the Neurology and Neurosurgery Service at the Royal Veterinary College for evaluation of thoracolumbar kyphosis and lethargy of 2 days' duration. The referring veterinarian had first examined the dog 6 weeks earlier because of lethargy, and a diagnosis of pyometra was made 4 weeks later for which the dog was treated surgically. Following 2 weeks of sustained postoperative improvement, the dog began to shiver intermittently and adopted a hunched posture. Proprioceptive deficits were then noticed affecting both pelvic limbs. Rest and provision of analgesia did not improve the clinical signs, and the dog was referred for neurology consultation. At the referral examination, the dog was lethargic but responsive. Except for the neurologic examination findings, results of a complete physical examination were unremarkable.
Assessment
Anatomic diagnosis
| Problem | Rule out location |
|---|---|
| Spinal ataxia and bilateral proprioceptive deficits in the pelvic limbs | Focal or diffuse spinal cord lesion within the T3 through L3 spinal cord segments |
Likely location of one lesion
| A lesion within the T3 through L3 spinal cord segments was suspected |
Etiologic diagnosis—Diagnoses to consider for a painful, deteriorating myelopathy are intervertebral disk disease (extrusion or protrusion), vertebral malformation, neoplasm, inflammatory or infectious meningomyelitides, diskospondylitis, and paravertebral abscesses. Other progressive myelopathies such as degenerative myelopathy or myelopathies secondary to a subarachnoid diverticulum are less likely because they are not associated with pain. Myelopathies secondary to a vascular accident are usually nonpainful or static or have a more rapid clinical onset with signs of improvement over time. Finally, syringomyelia may also be considered within the differential diagnosis list, although it is not always associated with signs of pain. The diagnostic plan included clinicopathologic analyses (to help rule out inflammatory or infectious diseases) and imaging of the thoracic and lumbar portions of the vertebral column (to detect the lesion suspected of causing the myelopathy). Subsequent diagnostic procedures such as analysis of a CSF sample or biopsy of any abnormal structure would be guided by the imaging findings. Magnetic resonance imaginga was the imaging modality of choice.
Diagnostic test findings—Results of a CBC and serum biochemical analysis were unremarkable. Magnetic resonance imaging (ie, T1-weighted, T2-weighted, T1-weighted following administration of contrast medium, and short TI inversion recovery images in transverse and sagittal planes) of the thoracic and lumbar portions of the vertebral column revealed a contrast enhancing, extradural lesion at the level of the T12–13 intervertebral space extending from the paravertebral musculature into the vertebral canal causing spinal cord compression and the myelopathy associated with the T3 through L3 spinal cord segments (Figure 1). An additional lesion was visible adjacent to the left kidney; a subsequent abdominal ultrasonographic examination revealed this to be an adrenal gland mass. Given the dog's breed, the history of pyometra, and the MRI findings, a paraspinal abscess was highly suspected. Neoplastic disease processes (eg, lymphoma) were considered less likely. A hemilaminectomy was performed to allow decompression of the spinal cord, and tissue samples of the mass were collected for cytologic and histologic examinations. A mast cell tumor (MCT) was identified on the basis of results of cytologic examination of an impression smear of the tissue removed during the hemilaminectomy and subsequently confirmed via histologic examination of the tissue samples, which revealed a lack of cellular pleiomorphism and a scant mitotic activity.
Magnetic resonance images of the vertebral column at the level of the T12–13 intervertebral disk space in a dog that was evaluated because of thoracolumbar kyphosis and lethargy of 2 days' duration. A left-sided extradural lesion that compresses the spinal cord is visible. The lesion is iso- to hyperintense (compared with the spinal cord) on T2-weighted (A) and T1-weighted (B) images and is enhanced after contrast agent administration on the T1-weighted image (C).
Citation: Journal of the American Veterinary Medical Association 242, 5; 10.2460/javma.242.5.619
Magnetic resonance images of the vertebral column at the level of the T12–13 intervertebral disk space in a dog that was evaluated because of thoracolumbar kyphosis and lethargy of 2 days' duration. A left-sided extradural lesion that compresses the spinal cord is visible. The lesion is iso- to hyperintense (compared with the spinal cord) on T2-weighted (A) and T1-weighted (B) images and is enhanced after contrast agent administration on the T1-weighted image (C).
Citation: Journal of the American Veterinary Medical Association 242, 5; 10.2460/javma.242.5.619
Magnetic resonance images of the vertebral column at the level of the T12–13 intervertebral disk space in a dog that was evaluated because of thoracolumbar kyphosis and lethargy of 2 days' duration. A left-sided extradural lesion that compresses the spinal cord is visible. The lesion is iso- to hyperintense (compared with the spinal cord) on T2-weighted (A) and T1-weighted (B) images and is enhanced after contrast agent administration on the T1-weighted image (C).
Citation: Journal of the American Veterinary Medical Association 242, 5; 10.2460/javma.242.5.619
Comments
To our knowledge, spinal MCT has been previously reported for 3 dogs. In 1 of those dogs, the MCT was suspected to be a primary lesion1; for the other 2 dogs, the lesions were potentially metastases of cutaneous MCTs.2,3 For only 1 of those 3 prior cases, the diagnosis of spinal MCT was made on the basis of examination of a biopsy specimen obtained during surgery, rather than on the basis of necropsy findings. Given the unusual location of the MCT in the dog of this report, information that could be used to evaluate prognosis was limited. However, in this case, the lack of cellular pleiomorphism and scant mitotic activity in the examined tissue samples were consistent with a low grade MCT.4 Extensive staging was not performed, but there was no clinical evidence of any MCT at another site. Surgery with adjunctive chemotherapy was the treatment of choice in this case. Lomustine, vinblastine, and prednisolone have been shown to be the most active agents against MCTs.5 For the dog of this report, a rapid and marked postoperative improvement was apparent, and the dog was still doing well clinically at a 3-month follow-up examination while receiving lomustine (80 mg/m2, q 4 to 6 wk, PO). The dog did not develop any complications as a result of treatment with lomustine. This case highlights the value of preoperative or intraoperative cytologic or histologic assessment of samples from paraspinal masses. Mast cell tumor should be included in the differential diagnosis list when a paravertebral mass with extension into the vertebral canal is identified via MRI, even in the absence of clinical evidence of systemic mastocytosis.
Philips Intera 1.5T Pulsar System, Philips Medical Systems, Reigate, Surrey, England.
This feature is published in coordination with the American College of Veterinary Internal Medicine on behalf of the specialty of neurology. Contributors to this feature should contact Dr. Helen L. Simons (800-248-2862, ext 6692) for case submission forms. Submissions will be sent to Dr. Karen Kline, DVM, DACVIM, for her review, except when Dr. Kline is an author.
References
1. Moore LE, Garrett LD, Debey B, et al. Spinal mast cell tumor in a dog. J Am Anim Hosp Assoc 2002; 38: 67–70.
2. Cooper M, Bennett P, Laverty P. Metastatic mast cell tumour in a dog presenting with spinal pain. Aust Vet J 2009; 87: 157–159.
3. Tyrrell D, Davis RM. Progressive neurological signs associated with systemic mastocytosis in a dog. Aust Vet J 2001; 79: 106–108.
4. Kuipel M, Webster JD, Bailey KL, et al. Proposal of a 2-tier histologic grading system for cutaneous mast cell tumours to more accurately predict biological behaviour. Vet Pathol 2011; 48: 147–155.
5. Gieger T, Northrup N, Wall M. Clinical management of mast cell tumors in dogs. Compend Contin Educ Pract Vet 2005; 27: 56–68.
