Minimally Invasive Approaches to Thoracic Disk Herniations

Thoracic disk herniations are uncommon surgical lesions that exist along a continuum of surgical complexity from the relatively straightforward to the extremely challenging depending on their anatomic relationship to the spinal cord and their intrinsic tissue characteristics. Several different approaches are available to spine surgeons, some of which are not incorporated into common clinical practice. Historically, poor results following laminectomy, particularly with central, calcified herniations, led to the use of posterolateral and transthoracic approaches that allow more direct access to the herniation but are associated with significant approach-related morbidity. Minimally invasive techniques offer the advantages of these approaches while mitigating the exposure-related morbidity.

Case Presentation

A 63-year-old woman came for treatment after experiencing several months of leg weakness, gait instability, pain, and paresthesias in her anterolateral right thigh, and urinary urgency with intermittent incontinence. Her symptoms progressed over several months despite physical therapy.

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PMH: Unremarkable
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PSH: Unremarkable
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Exam: Neurologic examination revealed mild bilateral leg weakness to confrontation, disproportionately increased reflexes in the legs, and a mildly spastic gait. On her initial office visit/neurologic examination, the patient had noticeable progression of leg extensor weakness, had a progressive foot drop, and had developed a sensory deficit at the midthoracic level.
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Imaging: magnetic resonance imaging (MRI) and computed tomography (CT) imaging showed a ventral T7-8 thoracic disk herniation with partial calcification and cord compression ( Figure 4-1 , A and B ).

FIGURE 4-1

A, Preoperative magnetic resonance imaging scan demonstrating a T7-8 left paracentral disk herniation. B, Computed tomography scan of the area showing partial calcification. C, Exposure afforded through the minimally invasive retropleural approach.

Tips from the Masters 4-1

Thoracic disk herniations are heterogeneous with respect to internal consistency and relationship to the thecal sac and spinal cord. Before any particular approach is elected, careful assessment of these characteristics with MRI and CT is required.

Given the patient’s pathologic features and neurologic progression, she was offered surgical decompression.

Minimally Invasive Surgical Options

Transfacet Approach

Several variations of the transfacet approach to a thoracic disk herniation have been described. These vary in terms of muscle dissection, retractor type (self-retaining or tubular), method of operative visualization (microscope vs. endoscope), and extent of facet resection (lateral, partial, or “window”). This approach is similar to the more familiar approach for resection of a lumbar disk herniation. The advantages of this approach are a direct exposure over the lateral disk that affords a small incision and minimal muscle disruption, complete or relative sparing of the pedicle of the inferior vertebral segment, and disk removal without risk of entering the thoracic cavity.

The main disadvantage of this approach is its dorsal angle of attack, which can be problematic with central and/or calcified disks. Soft lateral, contiguous disk herniations that extend beyond the edge of the thecal sac are the ideal indication for this approach. Such fragments can be delivered into the foramen with minimal retraction on the thecal sac. For the patient described in the Case Presentation, the calcified nature and the central location of the disk herniation were felt to be contraindications to this approach.

Tips from the Masters 4-2

Transfacet approaches are most suitable for lateral and preferably soft disk herniations that can be removed with minimal manipulation of the thecal sac.

Thoracoscopic Approach

The thoracoscopic approach takes advantage of a more anterior approach that provides an advantageous angle of attack for midline lesions. The evolution of specialized instrumentation developed for thoracic surgery has mitigated the morbidity of an open thoracotomy. The placement of three working ports through several small incisions between the intercostal muscles provides access into the thoracic cavity after the ipsilateral lung has been deflated. A camera is placed through one port, while instruments for the resection of the disk are inserted through the remaining two ports. The approach is then similar to that with an open thoracotomy, with dissection of the parietal pleura and removal of the rib head overlying the disk space. The superior edge of the inferior pedicle may be drilled away for orientation and improved exposure.

The major advantages of this approach are the direct line of sight and angle of resection that allow for the safe resection of a calcified midline disk, particularly when the spinal cord is draped over the disk. The disadvantages include the potential approach-related pulmonary complications, two-dimensional viewing screen, possible surgeon inexperience with thoracoscopic instruments, and the requirement for an approach surgeon.

Minimally Invasive Retropleural Approach

Because of the ventral position of the disk herniation and its partial calcification in the patient described in the Case Presentation, an approach that offered a lateral angle of attack was felt to be more suitable. The retropleural approach described by Otani and colleagues and McCormick and colleagues affords a lateral approach without pleural violation or the need for single lung ventilation, but still requires a relatively large exposure with extensive soft tissue manipulation. Utilizing the benefits of minimally invasive tubular retractor systems, a modification is presented that minimizes the morbidity of the traditional retropleural approach.

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