A 9-year-old 7.5-kg (16.5-lb) castrated male Dachshund was referred for emergency evaluation because of an acute onset of pelvic limb paraplegia of < 24 hours' duration. The owners reported that the dog had seemingly been in pain the previous day and had become unable to walk as the day progressed. On neurologic examination, the dog was nonambulatory with mild kyphosis and pelvic limb paraplegia, yet had superficial pain sensation and clinically normal spinal reflexes in both pelvic limbs. Muscle mass, motor function, proprioception, and spinal reflexes of the dog's thoracic limbs were clinically normal, and no response was elicited on cervical, thoracic, or lumbar paraspinal palpation. There were no perceivable deficits in the dog's cervical range of motion, the cutaneous trunci reflex was intact bilaterally, and function of the cranial nerves was appropriate on examination. Mild, symmetric epaxial muscle atrophy was evident; however, the remainder of the musculoskeletal examination revealed no clinically relevant abnormalities, and the dog had no prior reported medical problems. On the basis of the dog's history and physical examination findings, the presumptive diagnosis was IVDD with an acute lesion between T3 and L3.
The Dachshund was anesthetized for myelographic CT of the thoracolumbar portion of the vertebral column from the caudal aspect of T3 to S3. At the L2-3 IVD space, soft tissue material was present along the ventral aspect of the spinal canal, and the spinal cord was slightly compressed. The ventral aspect of the subarachnoid space was attenuated; however, thickness of the dorsal aspect at this location was clinically normal. At the L3-4 IVD space, a mineralized soft tissue structure attenuated the ventral and dorsal aspects of the subarachnoid space, and moderate spinal cord compression was present. A transitional vertebra was present at the thoracolumbar junction, and the first lumbar vertebral body had expanded transverse processes that were rib-like in appearance. It was concluded that there was an L3-4 IVD space extradural lesion causing moderate spinal cord compression, consistent with IVD extrusion (Figure 1). Chronic IVD extrusion at L2-3 resulting in subtle spinal cord compression was also suspected. On the basis of these results and in the light of the dog's rapidly progressing clinical signs, surgery was elected. Cefazolin (22 mg/kg [10 mg/lb], IV, once) was administered, and a left L3-L4 hemilaminectomy was performed. Chronic disk extrusion was observed; however, not all of the extruded disk material could be removed owing to the chronicity of the lesion and adherence of the disk material to the cord. The visible portion of the spinal cord was mildly to moderately deformed, but did not appear swollen or bruised.
Sagittal CT myelographic images (bone algorithm; 120 kV and 200 mA) of a 9-year-old 7.5-kg (16.5-lb) castrated male Dachshund with an acute onset of pelvic limb paraplegia of < 24 hours' duration. A—Mild spinal cord deformation is visible at the L2-3 IVD space. B—Disk extrusion and moderate spinal cord compression are visible at the L3-4 IVD space. R = Right aspect of the vertebrae. V = Ventral aspect of the vertebrae.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
Sagittal CT myelographic images (bone algorithm; 120 kV and 200 mA) of a 9-year-old 7.5-kg (16.5-lb) castrated male Dachshund with an acute onset of pelvic limb paraplegia of < 24 hours' duration. A—Mild spinal cord deformation is visible at the L2-3 IVD space. B—Disk extrusion and moderate spinal cord compression are visible at the L3-4 IVD space. R = Right aspect of the vertebrae. V = Ventral aspect of the vertebrae.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
Sagittal CT myelographic images (bone algorithm; 120 kV and 200 mA) of a 9-year-old 7.5-kg (16.5-lb) castrated male Dachshund with an acute onset of pelvic limb paraplegia of < 24 hours' duration. A—Mild spinal cord deformation is visible at the L2-3 IVD space. B—Disk extrusion and moderate spinal cord compression are visible at the L3-4 IVD space. R = Right aspect of the vertebrae. V = Ventral aspect of the vertebrae.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
Because of the absence of acutely extruded disk material at the L3-4 IVD space, cervicothoracic CT was performed on the dog prior to recovery from anesthesia. Imaging included the vertebral column from the caudal aspect of the skull to the cranial aspect of T8. At the T1-2 IVD space, a 26-mm-long, mineralized, soft tissue mass along the ventral aspect of the spinal canal severely compressed the spinal cord and displaced it dorsally and to the right. The spinal cord was severely flattened at this location, and spinal cord compression persisted to the caudal aspect of T2. Intervertebral disk degeneration was present at the site; however, there was no evidence of aggressive osseous lesions. The remainder of the thoracic and cervical portions of the vertebral column were unremarkable on CT images. On the basis of these findings, it was concluded that a ventral and left-lateralized extradural lesion at the T1-2 IVD space compatible with IVD extrusion was severely compressing the spinal cord (Figure 2). After the images were obtained, the dog was allowed to recover from anesthesia and was treated overnight with fluid therapy and pain medication.
Sagittal CT image of the T1-2 IVD space following preoperative myelography and L3-L4 hemilaminectomy of the same dog as in Figure 1. Severe disk extrusion and spinal cord compression are evident. See Figure 1 for key.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
Sagittal CT image of the T1-2 IVD space following preoperative myelography and L3-L4 hemilaminectomy of the same dog as in Figure 1. Severe disk extrusion and spinal cord compression are evident. See Figure 1 for key.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
Sagittal CT image of the T1-2 IVD space following preoperative myelography and L3-L4 hemilaminectomy of the same dog as in Figure 1. Severe disk extrusion and spinal cord compression are evident. See Figure 1 for key.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.215
The next morning, the Dachshund's neurologic status was unchanged, and surgery was performed to relieve the spinal cord compression at the T1-2 IVD space. A dorsal laminectomy was considered; however, the authors were concerned that the T1 and T2 spinous processes along with the proximity of the scapulae would diminish visualization of the spinal cord and restrict maneuvering of instruments. Additionally, there was concern about postoperative morbidity associated with the extensive soft tissue dissection needed with a dorsal approach. Therefore, a ventral slot decompression was elected.
The dog was anesthetized, and a ventral midline incision was made from the base of the larynx to the second sternebra. The sternocephalicus and sternohyoideus muscles were separated via blunt and sharp dissection, exposing the trachea and manubrium. Gelpi retractors were used to carefully retract the trachea, esophagus, and carotid sheath away from midline. A median sternotomy was made solely through the length of the manubrium with an oscillating saw. The pleural space was not entered, and negative intrathoracic pressure was maintained throughout the surgery. An Army-Navy retractor was used to carefully retract the sternum caudally without causing damage to the surrounding soft tissue structures. The transverse processes of C6 were identified and used as landmarks to locate the T1-2 IVD space. The longus colli muscles were bluntly dissected to expose the T1-2 anulus fibrosus. The ventral aspect of the anulus was fenestrated, and a straight pneumatic drill was used to create a ventral slot. A large amount of disk material was removed from the spinal canal with a nerve root retractor and suction. The spinal cord was visualized and appeared mildly bruised and swollen. After completion of the procedure, the segments of the manubrium were brought into apposition with circumferential ligatures of size-0 polydioxanone. The sternocephalicus and sternohyoideus muscles were apposed with a simple continuous pattern, and the remainder of the closure was routine. Complications encountered included mild hemorrhage from the ventral vertebral sinus that was controlled with application of suction and a sterile, compressed hemostatic sponge.a
Postoperative care was routine, with pain management (an NSAID, an opioid, and gabapentin), IV fluid therapy, and urinary bladder management. The Dachshund maintained good sensation in the pelvic limbs postoperatively and had no appreciable neurologic deficits in its thoracic limbs. The dog's pelvic limb motor function and ability to urinate were regained at days 2 and 3 after surgery, respectively.
Discussion
Intervertebral disk disease is a serious and common issue in dogs. Dachshunds are a chondrodystrophic breed and are at a greater risk of developing IVDD. The breed prevalence of IVDD is around 19%, but is higher in certain lineages.1–4 Intervertebral disk disease consists of degeneration of disk material that over time can result in protrusion of the anulus fibrosus or extrusion of disk material into the spinal canal, causing spinal cord compression and neurologic deficits, including paralysis. In Dachshunds, Hansen type I disk extrusion is more common. This occurs when the nucleus pulposus is extruded through the anulus fibrosus and into the spinal canal.2 The severity of spinal cord trauma is based on the velocity of extrusion, the ratio of the spinal cord and vertebral canal diameters, and the degree and duration of compression.5 Hansen type II IVDD is also common and is characterized by gradual anulus fibrosus protrusion into the spinal canal.6,7
Disk extrusion at T1-2 in dogs is rare, particularly in small breeds.8–9 To the authors' knowledge, IVDD at the T1-2 IVD space in Dachshunds has been previously reported10,11 only twice in the veterinary literature. The first report10 described a Dachshund with a chronic history of cervical pain that was evaluated for an acute onset of pelvic limb paresis without signs of cervical pain. A T1-2 IVD extrusion was diagnosed, and a dorsal decompressive laminectomy from T1 through T3 was performed. The dog regained voluntary motor function in the pelvic limbs, but died suddenly 2 weeks after surgery with no cause of death determined. The more recent report11 described a Dachshund with chronic neurologic deficits in the left thoracic limb and acute pelvic limb paresis. A T1-2 IVD lesion was diagnosed, and a modified dorsal decompressive laminectomy of T1-T2 was performed. Postoperatively, the dog of that report lacked deep pain sensation in its pelvic limbs, developed clinical signs consistent with ascending myelomalacia, and was euthanized.
The rarity of T1-2 IVD extrusion is most likely a result of the dorsal intercapital ligament, which attaches the paired ribs and travels dorsally over the IVD at this space.10 Furthermore, lateral extrusion is more common than dorsal extrusion, likely because of the increased strength and thickness of the dorsal longitudinal ligament in this region. With lateral IVD extrusion, nerve root compression can occur, resulting in ipsilateral thoracic limb pain and lameness.12
The lack of clinically detected thoracic limb abnormalities in the dog of the present report could have been attributed to the central nature of the cord compression. Additionally, the T1-T2 spinal cord segments partially innervate the radial, median, and ulnar nerves, with the T1 segment only supplying 29% of the radial nerve innervation and 2% of the median nerve innervation and the T2 segment only supplying 1% of radial nerve innervation and 17% of median nerve innervation. Thus, other spinal cord segments can compensate for loss of T1-T2 innervation and result in the absence of clinical lower motor neuron deficits in the thoracic limbs despite the presence of a T1-2 lesion.13,14
Because of the inability of neurologic examinations to consistently localize lesions between C6 and T2 in dogs and the lack of routine inclusion of the T1-2 IVD space on advanced imaging, the incidence of T1-2 IVD space lesions could be greater than reported. Therefore, the authors recommend inclusion of the T1-2 IVD space during CT or MRI of the vertebral column in chondrodystrophic dogs with signs suggestive of myelopathy from T3 through L3. A study15 from 2008 highlighted the inaccuracy of the withdrawal reflex to pinpoint a lesion between C6 and T2, and the authors recommended not limiting imaging on the basis of neurologic localization. This has also been suggested for large-breed dogs with myelopathy between T3 and L3, particularly in German Shepherd Dogs, which have been reported to make up 52.4% of large-breed dogs with T1-T9 IVDD.8,9
In humans, T1-2 IVD herniation has been rare16–19 and has generally manifested with clinical signs including neck pain, pain radiating into an upper arm, and hand weakness. Horner syndrome and axillary sensory loss have also been reported.17,18 Decompression of this site in humans has been achieved through anterior, posterior, and posterolateral approaches.16–19 The anterior approach, the preferred approach in human medicine at the time of the present report,18,19 may require a sternotomy as was the case with the Dachshund of the present report.
The ventral approach to the T1-2 IVD space, in the authors' opinion, was appropriate for removal of nucleus pulposus material and decompression of the spinal cord in the dog described in the present report. Compared with the previously published dorsal laminectomy for management of T1-2 IVD extrusion, the authors believed that the ventral slot approach allowed for substantially less cord manipulation, particularly for a disk extrusion that was both lateral and ventral. Additionally, a greater amount of soft tissue dissection would have been required for a dorsal approach, potentially resulting in greater morbidity during the postoperative period. Intraoperative risks of the ventral approach used included severe hemorrhage and loss of negative intrathoracic pressure, neither of which occurred and both of which were also possible complications of a dorsal laminectomy in this region. Hemorrhage from the vertebral sinuses and vasculature within the carotid sheath was possible, particularly if these structures were traumatized during retraction. The use of careful, controlled retraction was paramount in this procedure because of the presence of several vital structures in the thoracic inlet.
The use of an assistant to apply steady, caudal retraction on the thoracic inlet is recommended by the authors to enhance visibility of the T1-2 IVD space without causing trauma to the esophagus or carotid sheath as they enter the thoracic inlet. A sternotomy of the manubrium could most likely be necessary for improved visibility and manipulation of the surgical site. Controlled ventilation could also be required to allow for surgical drilling without interference by excessive motion of the thorax. Although a straight pneumatic drill was used in this case, an angulated pneumatic drill may be preferred for reaming because of the positioning of the site so caudally within the thoracic inlet. Additional postoperative concerns were analogous with those associated with the cervical ventral slot procedure, including pain, tracheitis, esophageal laceration, aspiration pneumonia, laryngeal paralysis resulting from damage to the recurrent laryngeal nerve, respiratory or cardiac depression resulting from iatrogenic injury to the vagosympathetic trunk or tectotegmental tracts of the spinal cord, and death.20
The dog of the present report was reexamined 3 weeks after surgery and was ambulatory, with paraparesis, and reportedly improving daily at home. The dog was reevaluated again 9 weeks after surgery and was ambulatory with mild proprioceptive deficits in the left pelvic limb. The owners also reported that the dog was comfortable and energetic at home. On the basis of the successful outcome, this technique could be considered in the future for dogs with T1-2 IVD lesions, particularly in small-breed dogs for which the proximity of their scapulae could make dorsal laminectomy difficult. Additionally, consideration should be given to broadening neuroanatomic localization on advanced imaging modalities to include the T1-2 IVD space in dogs with signs of a myelopathy between T3 and L3.
ABBREVIATIONS
| IVD | Intervertebral disk |
| IVDD | Intervertebral disk disease |
Footnotes
Gelfoam Sponge, Pfizer Inc, New York, NY.
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