History

A 3-year-old neutered male Labrador Retriever was evaluated at the emergency service for rapid onset of hind limb paralysis. The referring veterinarian had treated the dog for 2 previous episodes of hind limb dysfunction; the first episode occurred 2 months ago and resolved completely with the administration of carprofen. The second episode did not respond to the administration of NSAIDs, diazepam, or doxycycline; the dog was then treated with prednisone, and the paresis resolved. The dog had no history of travel or tick exposure.

Two days before evaluation at the emergency service, paresis reoccurred and became progressively worse, leading to paralysis. Physical examination revealed mild pyrexia (39.3°C [102.7°F]), increased patellar reflexes, bilateral conscious proprioceptive deficits of the hind limb, and minimal motor activity; neurologic deficits were localized to the T3-L3 region. A CBC revealed leukocytosis with a left shift; results of serum biochemical analysis and urinalysis were within reference ranges. Survey radiography of the thoracolumbar portion of the vertebral column was performed; the lateral radiographic view revealed loss of detail in the retroperitoneal space suggestive of a mass. Findings on abdominal ultrasonography were consistent with a mass lesion in the central retroperitoneal area. Computed tomography of the thoracolumbar portion of the vertebral column was performed (Figure 1).

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Transverse computed tomographic image (A; slice thickness, 5 mm) of the vertebral column at the level of L3 in a 3-year-old neutered male Labrador Retriever with a history of rapid onset of hind limb paralysis. Insert (B) is a magnified image of L3.

Citation: Journal of the American Veterinary Medical Association 236, 1; 10.2460/javma.236.1.33

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Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

Computed tomography revealed a large (approx 16-cm-long) hypoattenuating multilobulated mass within the epaxial and hypaxial muscles with extension through a neural foramen and into the spinal canal of T3 through L3, resulting in spinal cord compression (Figure 2). Differential diagnoses for the mass included neoplasia, granuloma, and abscess. Given the clinical signs and signalment, the 2 most likely diagnoses were granuloma and abscess.

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Same computed tomographic image as in Figure 1. Notice the hypoattenuating multilobulated mass in the epaxial and hypaxial muscles that is outlined (white arrows). Extension of the mass through the neural foramen resulted in spinal cord compression.

Citation: Journal of the American Veterinary Medical Association 236, 1; 10.2460/javma.236.1.33

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Comments

The owners elected to have the dog euthanatized. Necropsy revealed a large firm mass in the retroperitoneal area that extended into the spinal canal. The mass was removed and identified on gross examination as an abscess. The mass was regionally extensive; histologic examination of the mass revealed chronic active myositis with mild degeneration, necrosis, fibrosis, and dissecting fibroplasia of the subjacent epimysium and perimysium of the epaxial muscles. Cytologic findings were consistent with a chronic-active inflammatory process. The underlying cause of the inflammation was unclear, and there was no foreign material or evidence of neoplasia. Bacterial culture results for the purulent exudate were positive for Escherichia coli.

Computed tomography, as well as magnetic resonance imaging, has emerged as a frontline diagnostic tool for identification of abscesses within the epidural space of the vertebral column, whereas, historically, myelography had been used. The advantage of computed tomography over myelography is that it allows differentiation of epidural abscesses from other epidural lesions. It also has the ability to detect bony changes earlier than survey radiography, and the cross-sectional anatomy is useful for surgical planning. Computed tomographic findings for epidural abscesses have been described as having a loss of the low attenuating epidural fat, poorly defined hypoattenuating lesions in the paraspinal region, ring enhancement following IV administration of contrast medium, and gas in the soft tissues.¹ Computed tomographic images of the dog of this report revealed a multilobulated hypoattenuating lesion both ventral and dorsal to the vertebral column that extended through the neural foramen causing compression of the spinal cord, resulting in the hind limb paralysis. No known cause was determined, but hypotheses include an undetected bite wound or a previous injection.

The most frequently reported clinical signs of dogs with epidural abscesses are fever, spinal nerve hyperesthesia, and spinal cord dysfunction, which often rapidly progresses to para- or tetraparesis.² Two of the 3 most common clinical signs were observed in the dog of this report (ie, fever and hind limb paresis). Epidural abscess is a rare condition in people, and therefore, diagnosis and initiation of treatment is usually delayed, resulting in a poor prognosis for regaining neurologic function.^1–3 There has been only 1 report³ of an affected dog that survived, and that dog did not have substantially improved neurologic function at time of hospital discharge. In the dog of this report, clinical signs progressed slowly until the sudden onset of paralysis. By the time the diagnosis was made, the size of the mass and invasion into the spinal canal offered a poor prognosis for successful treatment and return of neurologic function.