History
A 7-month-old neutered male Boxer was evaluated because of a 5-day history of signs of neck pain that were unresponsive to medical treatment with carprofen, methocarbamol, and tramadol. No abnormalities had been detected on radiography of the cervical portion of the vertebral column, thorax, and abdomen. The history did not include any known incidents of trauma. The dog had not traveled out of New Jersey and was current on vaccinations.
On the basis of a lack of response to treatment, the dog was referred; body temperature, heart rate, and respiratory rate were within reference range. Except for signs of neck pain, no abnormalities were found on physical and neurologic examination. With flexion and extension of the neck, the dog would vocalize. No abnormalities were detected on CBC, serum biochemical analysis, and 3-view thoracic radiography. Magnetic resonance imaging of the cervical portion of the vertebral column and caudal portion of the cranial fossa was performed (Figure 1).
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Diagnostic Imaging Findings and Interpretation
Chemical fat saturation T1-weighted sequences were obtained after IV administration of gadopentetate dimegluminea (0.1 mmol/kg [0.045 mmol/lb]). On T1-weighted chemical fat saturation MRI images, a left-sided lesion is evident ventral to the vertebral column (C2 and C3) and dorsal to the esophagus between the longus colli and longus capitis muscles (Figure 2). The lesion is hypointense, compared with the cervical musculature, with a thin rim of peripheral contrast enhancement (hyperintensity). Also, diffuse, poorly defined enhancement is evident along fascial planes between the longus colli muscle, longus capitis muscle, and esophagus in the cervical region and the rectus capitis ventralis and lateralis muscles ventral to the basioccipital bone. Additionally, enhancement of the meninges covering the medulla oblongata and cerebellum and cranial cervical portion of the spinal cord to the level of the midbody of C2 is evident. On a sagittal T2-weighted MRI image of the same area, the lesion appears hyperintense, loculated, and well delineated (Figure 3).
The MRI findings were consistent with a fluid-filled cavitary lesion and secondary inflammation of the cervical muscles in the ventral aspect of the neck. The differential diagnosis for a fluid-filled cavitary lesion in the paraspinal muscles includes abscess formation alone or secondary to a foreign body, sterile necrosis, neoplasia with secondary necrosis, or a hematoma.1 The meningeal enhancement was thought to represent secondary extension resulting in meningitis.
Treatment and Outcome
Following MRI, a sample of CSF was obtained from the cerebellomedullary cistern for analysis. Cerebrospinal fluid analysis findings were consistent with meningitis. Grossly, the CSF appeared straw colored, turbid, and viscous. Cerebrospinal fluid analysis revealed neutrophilic pleocytosis (total nucleated cell count, 21,038 cells/μL; reference range, < 5 cells/μL), an increase in RBC count (990 RBCs/μL; reference range, 0 RBCs/μL), and a high protein concentration (466 mg/dL; reference range, < 25 mg/dL). Cytologically, the leukocyte differential count was composed of 95% nondegenerative to pyknotic neutrophils, 2% small lymphocytes, and 3% large mononuclear cells.
Exploratory surgery of the ventral aspect of the neck was performed. A large, firm mass containing grossly purulent material was identified and removed. Foreign material was not observed. An active drainage system was placed in the surgical site for 48 hours. Cytologic examination of the purulent material revealed degenerative neutrophils with intracellular bacteria. Aerobic and anaerobic culture failed to grow any bacteria. Findings on histologic examination of the lesion were consistent with an acute necrotizing cellulitis and myositis. Forty-eight hours after surgery, the dog had no signs of pain and was discharged from the hospital; oral administration of an antimicrobial was prescribed.
Comments
Differential diagnoses for signs of neck pain in dogs include meningitis (infectious and noninfectious etiologies), diskospondylitis, vertebral malformations, intervertebral disk disease, neoplasia, and trauma. Similar imaging findings as for the dog of the present report have been described for a Labrador Retriever with signs of neck pain secondary to a wooden foreign body.2 Although speculative, it is possible that the lesion in the dog of the present report was the result of a penetrating foreign body, despite lack of identification of an external wound, tract, or foreign material at surgery.1 The signalment and clinical findings of the dog of the present report are also consistent with steroid-responsive meningitis arteritis syndrome.3 Steroid-responsive meningitis arteritis syndrome occurs in young dogs and is associated with fever, signs of neck pain, and neutrophilic pleocytosis in CSF.3 Several breeds are predisposed, including Boxers.4 The treatment for steroid-responsive meningitis arteritis consists of immunosuppressive corticosteroids.3 Immunosuppressive therapy, however, in the face of an infectious etiology may lead to high morbidity and mortality rates. Therefore, as for the dog of the present report, establishment of a definitive diagnosis (ie, infectious vs noninfectious etiology) and the use of advanced imaging such as MRI are of utmost importance before implementing treatment.
Magnevist, Berlex Imaging, Wayne, NJ.
1. Holloway A, Dennis R, McConnell F et al. Magnetic resonance imaging features of paraspinal infection in the dog and cat. Vet Radiol Ultrasound 2009; 50:285–291.
2. Young B, Klopp L, Albrecht M et al. Imaging diagnosis: magnetic resonance imaging of a cervical wooden foreign body in a dog. Vet Radiol Ultrasound 2004; 45:538–541.
3. Tipold A, Schatzberg SJ. An update on steroid responsive meningitis-arteritis. J Small Anim Pract 2010; 51:150–154.
4. Behr S, Cauzinille L. Aseptic suppurative meningitis in juvenile Boxer dogs: retrospective study of 12 cases. J Am Anim Hosp Assoc 2006; 42:277–282.