Posterior Paramedian Endoscopic Thoracic Discectomy

29 Posterior Paramedian Endoscopic Thoracic Discectomy

Raj Nangunoori, Diana H. Jho, David H. Jho, and Hae-Dong Jho

Summary

In this chapter, the reader will find a thorough guide on the background, rationale, surgical technique, postoperative care, and tricks on how to perform thoracic discectomies via an endoscopic transthoracic technique. The surgical treatment of thoracic disc herniations is challenging. The authors not only achieve a good description of the procedure but also walk the reader step-by-step on how to perform this technique safely.

Keywords: thoracic disc herniation thoracic endoscopic discectomy thoracic disc endoscopic surgery thoracoscopic surgery

29.1 Introduction

Posterior paramedian endoscopic discectomy is a minimally invasive surgical technique for thoracic disc herniation. Surgical treatment for thoracic disc herniation has been considered more technically challenging with potentially higher risks than cervical or lumbar disc herniation, in part due to decreased buffer space for the neural elements and increased sensitivity with more tenuous vascular supply of the spinal cord in this region. The senior author’s (H.-D. Jho) experience with posterior paramedian approach to thoracic disc herniation has evolved from a modified transpedicular approach to the current posterior paramedian approach in his practice over time. The posterior paramedian endoscopic approach is probably most analogous to the surgical approach for lumbar disc herniation, but there are some key technical differences that are critical for procedural safety. A paramount consideration is that the disc herniation is often ventral to the spinal cord in a relatively narrow spinal canal, and the disc may be associated with osteophytes and calcifications, reducing the capacity or safety of thecal retraction. The use of an endoscope with fixed pneumatic holder can provide a direct ventral view of the anterior aspect of the dura. The details of the surgical technique are described.

29.2 Evolution of the Paramedian Approach

Surgical treatments for symptomatic thoracic disc herniations have historically been complicated by anatomic and physiologic factors of the thoracic spine region, which include potentially tenuous and anatomically variable vascular supply, anatomic challenges in safely accessing the ventral aspect of the spinal canal while limiting morbidity and without compromising biomechanical stability, and the limited capacity and tolerance of the thoracic spinal cord to retraction, which may additionally be worsened by the presence of significant disc calcifications or osteophytes. The earliest clinical description of thoracic disc herniation was in 1938 by Key, although the first attempt at surgical decompression was not until 1922.1^,² Early thoracic disc surgery was performed with basic midline laminectomy techniques. Spinal cord damage occurred with high frequency in midline laminectomy techniques, which emphasized the need to develop different approaches to treat thoracic disc herniations.³^,⁴ To avoid iatrogenic injury to the spinal cord, various approaches were developed with the common goal of treating the compressive component of disc herniation, with minimal manipulation of the spinal cord. These surgical approaches included: (1) Posterior approaches such as transpedicular or transfacet techniques, (2) posterolateral approaches such as costotransversectomy or lateral rachotomy or lateral extracavitary approach, (3) lateral transthoracic approaches such as transpleural or extrapleural techniques, and (4) anterior approaches such as transsternal or thoracoscopic techniques.⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰ Most of the posterolateral, lateral transthoracic, and anterior approaches typically involve more invasiveness and increased tissue dissection compared to posterior approaches or thoracoscopic techniques, such that some surgeons further developed thoracoscopic techniques to potentially reduce morbidities and to reduce postoperative healing periods.¹¹ However, the steep learning curve and specialized equipment, including the differences in surgical instruments for thoracoscopic surgery versus conventional spine surgery, can make the incorporation of thoracoscopic approaches into routine practice challenging.

In regards to posterior approaches, Patterson and Arbit first described the transpedicular approach in a series of three patients in 1978.¹² Stillerman et al introduced a transfacet pedicle-sparing approach in 1995, in which the medial portion of the facet complex was removed for exposure.¹³ However, since the dura covering the thoracic spinal cord abuts the pedicle of the vertebral body just below the target level disc herniation, the surgical exposure may be inadequate without removal of the superior-medial portion of the pedicle despite a partial facetectomy. In order to acknowledge and honor the original report of the transpedicular approach, we had initially published our technique as a variant of the transpedicular approach, as a hybrid technique with partial drilling of the pedicle and medial facets for exposure. Medial facetectomy combined with drilling of the superior-medial portion of the lower pedicle provides surgical access of approximately 3 to 5 mm lateral to the spinal cord. Once the drilling is complete, the exposed lateral dura corresponds to the subarachnoid space of approximately 2 to 3 mm width lateral to the spinal cord, allowing for some potential gentle retraction of the dura medially, which can provide more working space. The bony exposure combined with the lateral subarachnoid space provides a total working window width of 5 to 8 mm lateral to the spinal cord, and this posterior paramedian endoscopic thoracic discectomy was developed by the senior author (H.-D. Jho) as a minimally invasive alternative using endoscopy to mitigate the risks of spinal cord manipulation.¹⁴ The term “paramedian approach” is used to describe this approach, which utilizes natural anatomic corridors while minimizing risk for iatrogenic instability.

The main advantage of this approach is that it utilizes normal tissue planes and minimizes the risk of causing instability. The use of an endoscope can provide a direct ventral view of the anterior aspect of the dura. However, these advantages come at a significant cost, as this is a technically very demanding approach that requires adequate training. Calcified and midline thoracic discs would not be good targets.

29.3 Patient Selection

Symptomatic thoracic disc herniations are relatively rare compared to cervical and lumbar disc herniations, with incidence rates in the literature widely ranging from 0.1 to 0.0001%.13^,¹⁵ Clinical presentation for thoracic disc herniation may be variable, and up to 37% of patients with radiographic evidence of a disc herniation may be incidental and clinically asymptomatic.¹⁶^,¹⁷^,¹⁸^,¹⁹ Surgical indications for thoracic disc herniations can include myelopathy, radiculopathy, and focal paraspinal back pain, depending on the overall clinical scenario. Patients with myelopathy may classically present with sensory disturbances (e.g., hypesthesia, paresthesia, dysesthesia), motor disturbances such as progressive paraparesis or paraplegia, spastic gait disturbances, rarely Brown-Séquard syndrome, and/or bowel and bladder dysfunction.²⁰^,²¹^,²²^,²³ The goal of surgery for myelopathy is decreasing or preventing further progression of spinal cord dysfunction, although some neurologic improvement may be seen on a variable spectrum. The patients should be counseled in advance that the symptoms of myelopathy may not improve completely. Another surgical indication may be thoracic radiculopathy, which may manifest as a radicular band of pain, intercostal neuralgia, or point tenderness. Thoracic disc herniation symptoms may occasionally overlap with referred pain from cardiac, intra-abdominal, or even pelvic pathologies.²⁴^,²⁵^,²⁶^,²⁷ Thoracic disc disease may very rarely mimic neurogenic claudication, which is much more typical in the context of lumbar spinal stenosis.²⁸ It is especially important in unusual cases to use a thorough history and physical examination to correlate radiographic findings with clinical symptoms. When diagnostic measures are sufficiently exhausted and thoracic disc herniation is the only significant pathology seen on imaging, surgical intervention might be carefully considered in those cases. When midline thoracic back pain is the only symptom, surgery can be performed only if the location of pain matches with the level of pathology, and pain is truly intractable. But these patients should know that axial thoracic back pain might not be completely resolved despite successful surgical decompression at the region of the herniated disc.

The endoscopic technique described is designed to be versatile and has been utilized by the senior author (H.-D. Jho) with customized adjustments made to the degree of ventral bone drilling depending on the medial to lateral location of the disc and calcified versus soft disc material. In general, a soft disc or lateral location of the disc makes thoracic disc surgery more favorable, similar to other approaches for thoracic disc herniations. If the general principles described are utilized, this approach may be used regardless of the location or degree of calcification due to the versatility of the approach and direct visualization provided by the endoscope.

29.4 Preoperative Planning and Patient Positioning

One of the problems that may be encountered preoperatively is the lack of sagittal scout imaging views that include the entire spine. Sometimes the level of disc herniation is variably counted from the top down or from the sacrum up on radiology reports or labeling or levels. Sometimes there may be anatomic variations such as 4 or 6 lumbar vertebrae, transitional lumbosacral vertebra, 11 or 13 thoracic vertebrae with associated ribs, Klippel-Feil deformity or other segmentation variations in the spine, and other anatomic anomalies that could potentially complicate the accurate localization of levels. These variations highlight the necessity for at least a complete sagittal scout image to accurately localize the level of pathology.

Surgical instruments for performing this procedure include: an endoscope tower which contains a monitor, light source, and video recording system, motorized lens cleansing device, 4-mm rod-lens endoscopes (0-, 30-, and 70-degree lenses), a gas-powered endoscope holder, and a slender high-speed drill (Fig. 29.1a, b). For surgery, the patient is initially placed in lateral position with the pathology side facing up while under general endotracheal anesthesia, with initial lateral positioning for localization before turning the patient and/or rotating the table ventrally approximately 30 degrees for the operative position, such that the coronal plane of the patient forms a 60-degree angle with the horizontal plane (which will be termed the “60-degree position”). The 60-degree position is most similar to but not as much ventrally rotated as the three-quarter prone or park bench position. An axillary roll is placed under the dependent side, and the patient is padded and gently secured to the table with tape. Two or three 18-gauge spinal needles are placed in serial fashion (counting upwards from the sacrum) against the laminar bone at the spinolaminar junction just lateral to midline, and the surgical level is confirmed using fluoroscopy or alternatively overlapping X-rays. Usually the first needle is placed at the upper lumbar region, and a second needle is placed rostral to the first needle in the thoracic spine and adjusted to the target site. For upper thoracic levels, a third needle may be required. Once the correct level of surgery is localized with the spinal needles, the target site needle is used for injection of 0.5 mL of methylene blue into the soft tissue at the target level. Another 18-gauge spinal needle is inserted 5 cm lateral to the midline on the target side and the tip is placed at the laminar bone at the spinolaminar junction. The midline needles are removed, but the single laterally inserted needle is kept and draped into the field. The laterally inserted needle and methylene blue serve as landmarks to confirm the surgical level intraoperatively (Fig. 29.2a, b).