13 Paracentral Disc Herniations of the Thoracic Spine Abstract Paracentral disc herniations of the thoracic spine are uncommon pathological entities. Patients have diverse clinical presentations and require surgical therapy to treat motor deficits or intractable sensory disturbances caused by the condition. Although anterior surgical approaches are frequently employed for both central and paracentral thoracic disc herniations, posterior approaches are a common viable option for the latter. Multiple approach options exist, and careful selection of the appropriate treatment strategy must take into account the anatomy of the disc herniation, patient habitus, and surgeon comfort. Keywords: back pain, discectomy, myelopathy, radiculopathy, thoracic disc herniation Clinical Pearls • Thoracic disc herniations are uncommon and patients can present with expected symptoms, such as radicular pain and myelopathy, as well as atypical symptoms, such as dysesthetic chest and abdominal pain. • Preoperative workup should include magnetic resonance imaging and computed tomography to identify the degree of disc calcification. • Adequate preoperative imaging to determine landmarks for identification of correct spinal levels is critical, and surgeons should consider placement of an intraosseous fiducial. • Aside from anterior approaches, multiple posterior approaches can be used for discectomy, and approach selection should focus on how oblique a trajectory is needed to access the disc space and the herniated disc fragment. • A transdural approach can be used successfully to reduce the obliquity of the surgical trajectory needed for discectomy. • Pedicle screw instrumentation should be used in most cases to allow early postoperative mobility and facilitate greater intraoperative removal of bony elements. Thoracic disc herniations are uncommon, comprising less than 1% of all symptomatic disc herniations with an incidence of approximately 1 in 1 million persons.1,2 On the basis of the limited evidence in the medical literature, the natural history of thoracic disc herniations is unclear. Approximately 75% of patients with small disc herniations or asymptomatic individuals with an incidental diagnosis can remain clinically stable on follow-up and may not require further treatment.3,4 Those who become symptomatic or who have radiographic evidence of spinal cord compression require surgical intervention. This chapter focuses on surgical strategies for paracentral thoracic disc herniations, with a focus on posterior approaches. Anterior approaches, either through an open transthoracic approach or with a thorascope port access technique, are suitable for paracentral discs, but are used more frequently to treat midline or giant disc herniations; these approaches are discussed elsewhere in this book. Symptoms of thoracic disc herniation are varied and include multiple sensory and motor manifestations that depend on the anatomical configuration of the disc herniation.2 Paracentral disc herniations may impinge on exiting or passing thoracic nerve roots, causing radicular or dysesthetic pain along the back, chest wall, abdomen, or viscera.5,6 Larger disc herniations that cause mass effect on the thecal sac can result in motor deficits and myelopathy. Patients with suspected thoracic disc disease initially should undergo magnetic resonance imaging (MRI) ( Additional preoperative imaging should also be pursued to aid intraoperative verification of the correct surgical level. Misidentification of the surgical level is a devastating complication in thoracic disc surgery, and it is a common cause of patients requiring reoperation.8 Full visualization of landmark anatomy, such as rib heads, must be obtained preoperatively. For obese patients or those with variant anatomy, intraoperative fluoroscopic image quality is likely to be poor, so a preoperative intraosseous CT-guided radiographic fiducial can be placed in the pedicle or transverse process adjacent to the disc herniation. The fiducial allows easy confirmation of the appropriate level during surgery ( The earliest surgical experience with resection of herniated thoracic discs relied on laminectomy alone and resulted in major morbidity rates ranging from 18 to 75%.1,9 Several explanations may account for these poor results, but the most widely accepted is that a laminectomy by itself does not provide enough lateral exposure of the underlying disc space, necessitating manipulation of the thecal sac, which may cause mechanical injury. Consequently, a myriad of alternative surgical approaches with progressive degrees of removal of bony elements has been developed and described to facilitate safe discectomy. Commonly referenced approaches include transfacet pedicle-sparing,10 transpedicular,11 costotransversectomy,12 lateral extracavitary,13 and, more recently, transdural approaches.14,15 Fig. 13.1 (a) Sagittal T2-weighted magnetic resonance image (MRI) shows a large disc herniation at the T6-7 interspace with cranial migration behind the T6 vertebral body. (b) Axial and (c) sagittal thoracic computed tomography (CT) images show mixed calcification within the herniated disc with a right paracentral location. (d) Sagittal CT shows an intraosseous fiducial (arrow) that was placed within the left T6 transverse process at the level of the pedicle. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.) Choosing an appropriate approach can initially be daunting because of the number of options, their technical nuances, and the comfort level of the surgeon. To simplify the decision-making process, we recommend a cognitive framework centered on how much bone must be removed to adequately access and visualize the disc herniation. Considerable discussion exists on whether instrumented fusion should be performed with thoracic discectomy.16 In general, aside from situations in which only limited unilateral facet removal is performed in a healthy patient without abnormal curvature or preoperative back pain, we recommend concurrent placement of pedicle screw instrumentation and arthrodesis during discectomy for several reasons. The first is that pedicle screw placement allows for more aggressive removal of bony elements without concern for causing spinal instability, and it removes the psychological barrier, especially for less experienced surgeons, to achieving greater exposure when it is needed intraoperatively. Second, pedicle screws allow safe intervertebral distraction, facilitating dissection and mobilization of the herniated disc. Lastly, segmental arthrodesis secures physiological thoracic alignment, and in theory facilitates postoperative mobilization by reducing increased motion across the operative segment. After the appropriate approach is selected, surgery proceeds in the following stepwise fashion at our institution. Patients are positioned prone on a Jackson table (Mizuho OSI, Union City, CA), and the incision is planned using anteroposterior and lateral fluoroscopy. A midline incision and dissection are adequate for the majority of patients, but a paramedian incision 2 cm off midline, ipsilateral to the side of disc herniation, may be used if an extremely oblique surgical trajectory is planned. The exposure of bony elements encompasses the medial facet border on the contralateral side to the ipsilateral transverse process or farther along the rib head.
13.1 Introduction
13.2 Preoperative Considerations
13.2.1 Clinical Presentation
13.2.2 Preoperative Workup
Fig. 13.1a) followed by computed tomography (CT) if a herniated disc is confirmed and the patient is deemed to require surgical intervention. The addition of CT-based imaging allows the extent of disc calcification to be visualized, which can guide selection of the surgical approach (
Fig. 13.1b, c). Disc calcification is common and was found in 65% of cases (53 of 82 discs) in a large clinical series.7 Extensive, densely calcified discs are more difficult to mobilize intraoperatively or may be fused to the dura and thus require a larger exposure and potentially an anterior approach to resect and repair the thecal sac.
Fig. 13.1d). Unfortunately, this tool is frequently underutilized.
13.3 Surgical Technique
13.3.1 Selection of Approach
Fig. 13.2a shows an axial view of the bony elements that must be removed to visualize the thecal sac and underlying disc herniation, as well as the corresponding trajectories that can be used after removal. As seen in 
Fig. 13.2b, proceeding from midline to lateral requires the incremental removal of the bony elements (i.e., lamina, facet, pedicle, transverse process, and rib heads) that must be removed to allow increasingly more oblique access to the disc space. Factors that favor limiting the removal of bony elements to only the lamina and facet include disc herniations located more laterally, limited disc calcifications, and thin patients, as these factors allow a shorter working distance and consequently require a less oblique approach to visualize the disc space. More extensive removal of bony elements that encompasses the pedicle, transverse process, rib head, and varying degrees of the rib body is needed to visualize medially located discs, to access the disc in obese patients with a longer working distance, and to remove heavily calcified discs.
13.3.2 Instrumentation
13.3.3 Extradural Discectomy
Thoracic Key
Fastest Thoracic Insight Engine
