Yael Merbl and Annie Vivian Chen‐Allen Washington State University, Pullman, WA, USA Cranial thoracic compressive spinal lesions are less frequently encountered in veterinary medicine compared to the thoracolumbar spine [1]. This difference partially arises from the cranial thoracic spine being more stable than the thoracolumbar spine. Additionally, traumatic injuries of the spine at this region are less common; however, this region of the spine is being approached more frequently in the last decades for diseases such as caudal cervical spondylo‐myelopathy and cranial thoracic disk protrusions as well as resection of tumors (Figure 9.1). The surgical approach to the cranial thoracic (T1–T9) spine is also less commonly reported in veterinary medicine and is described mainly in case reports and small case series [2–6]. Several reports describe the surgical approach to the caudal cervical and cranial thoracic region through a lateral incision [7–9]. Another report recently described a dorsolateral hemilaminectomy approach for treatment of neoplastic [1] and intervertebral disk disease [1, 10], and other disease processes causing spinal cord compression. Lastly, a case report described a ventral approach to stabilize T2–T3 luxation via sternotomy [11]. The appropriate/chosen approach depends on the disease process, goals of surgery, as well as the surgeon’s level of comfort for that procedure. A dorsolateral hemilaminectomy is at the focus of this chapter as it is the most common procedure at this region. Figure 9.1 Magnetic resonance imaging. (a) Sagittal T2 weighted image depicting the intradural extramedullary oval shaped, well defined, space occupying mass, at the level of T3. (b) Sagittal T1 weighted image post gadolinium showing moderate homogenous contrast enhancement. (c) Transverse T1 weighted image post gadolinium showing the lesion occupying at least 80% of the spinal canal. The articular processes of all the cranial thoracic spine (up to the tenth thoracic vertebra) are in a nearly dorsal plane so that the cranial articular process is dorsal (Figure 9.2a) and the caudal articular process is ventral [12]. The plane differentiation is very different from the thoracolumbar spine making the articulation less recognizable at the cranial thoracic region compared to the thoracolumbar region (Figure 9.2b). Close attention should also be paid to the regional arterial blood supply. The course of the arteries located in this region have been previously described [12]. The arteries the surgeon should be familiar with are the dorsal scapular artery (Figure 9.3, white arrowhead) that arises from the cranial surface of the costo‐cervical trunk, approximately the middle of the medial surface of the first rib. Then, this artery continues dorsally and leaves the thoracic cavity cranial to the first rib. The dorsal scapular artery at the proximal end of the first rib inclines dorso‐caudally, crosses the lateral surface of the first costotransverse joint, and branches in the dorsal part of the thoracic portion of the serratus ventralis muscle. The second artery is the thoracic vertebral artery (Figure 9.3, black asterisk). This artery continues medially to the first rib and passes through the costotransverse foramen dorsal to the neck of the rib. Caudal to the second and third ribs that it crosses, the thoracic vertebral artery sends a small intercostal artery ventrally, which anastomoses with the intercostal branches (Figure 9.3, black arrows). Lastly, when performing the facetectomy of the thoracic vertebra, the inter‐arcuate branches of the internal vertebral venous plexus can be found within the inter‐arcuate ligament. It may be necessary to cauterize or ligate prior to transecting these branches [13]. While retracting the muscles to expose the vertebras at this level, special consideration should be given to the anatomy and blunt dissection and retraction should be conducted with care. If an artery is accidentally injured, bipolar cautery can be used to achieve hemostasis for the smaller vasculatures. If bleeding continues, digital pressure utilizing gauze and gel foam can be used as well. Sometimes it will not be possible to locate the bleeding site as the ruptured artery will retract into the deeper muscle layers. Attempts should be made to find the retracted artery if bleeding is significant. If the artery is accidentally torn and larger in size, hemostats can be used to achieve hemostasis and ligation with sutures or hemoclips may be needed.
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The Cranial Thoracic Spine: Approach via Dorsolateral Hemilaminectomy
Indications
Surgical Anatomy
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