Posterior Techniques for Thoracic Disc Disorders

21 Posterior Techniques for Thoracic Disc Disorders

Raj Murali

Goals of Surgical Treatment

The goals of the transpedicular microsurgical approach are to remove a soft or a hard herniated thoracic disc and decompress the spinal cord and/or the nerve root.

Diagnosis

About 35 % of patients present with complaints of a radiating pain along the chest wall in the distribution of an intercostal nerve. In acute thoracic disc herniations, spinal pain may be experienced at the appropriate level. Central and paramedian disc herniations cause spinal cord compression. This may present as different types of myelopathy. Spastic paraparesis or Brown-Séquard syndrome may occur. Chronic thoracic disc herniations may not cause any pain at all and may occur only with neurologic deficits. The best diagnostic tests to confirm the diagnosis are magnetic resonance imaging (MRI) and computed axial tomography (CAT) scan. Sagittal views of an MRI scan can serve as a screening test for viewing the entire thoracic spine and correctly localize the site of a herniated disc. Select axial views are then obtained at the suspected site. An MRI scan is also very useful in giving information regarding spinal cord compromise, such as edema, displacement, myelomalacia, and syrinx formation. The scan is usually done with and without contrast and with all the usual sequences.

High-resolution computed tomography (CT) scans are also recommended once the site of thoracic disc herniation has been revealed by the MRI scan. CT scan will reveal information, such as calcification in the herniated disc and the relationship of the disc herniation to bony anatomic structures, such as the pedicle, which has important surgical implications (Figs. 21–1 and 21–2).

Axial images of CT and MRI scans are carefully reviewed to assess the mediolateral extent of disc herniation. Large calcific and centrally situated herniations are best managed by anterior transthoracic approaches. Paramedian and lateral herniations can be managed by the posterolateral transpedicular approach. Occasionally, in difficult cases, CT myelogram is also of value.

Indications for Surgery

1. Neurologic deficits, such as paraparesis.

2. Pain, especially radiating radicular pain.

3. Small herniated discs seen on a routine MRI scan of the thoracic spine do not require surgery.

4. Severe neurologic deficits seen in the presence of a small thoracic disc herniation need a full neurologic workup to exclude entities such as multiple sclerosis, motor neuron disease, and spinal cord arteriovenous malformation.

Contraindications

A large centrally located calcified disc with significant spinal cord compression and serious neurologic deficits, such as paraparesis (Fig. 21–3).

Advantages

1. The transpedicular approach is a direct x-ray-controlled approach, which can be performed by most spinal surgeons.

2. Does not require a thoracotomy or the need for a thoracic surgeon.

3. No spine stabilization is required.

Disadvantages

1. The angle of approach is such that this procedure is unsuitable for large centrally located and especially calcified herniated discs.

2. Some modifications of the transpedicular approach are required, especially in obese patients, to improve visualization. This usually involves adding a costotransversectomy to improve visualization.

3. Intraoperative radiographs or fluoroscopy is necessary for correct localization of level and appropriate pedicle.

Procedure

Preoperative Preparation

1. Corticosteroids are given, especially for patients presenting with myelopathy. Dexamethasone, 10 mg, is used. Solumedrol protocol, such as in spinal cord injury, is used in patients with severe myelopathy. This usually consists of administering methylprednisolone 2.5 g intravenously as a bolus before the commencement of the procedure followed by an infusion of methylprednisolone 10 g over a period of 23 hours given through an infusion pump.

2. Prophylactic antibiotics are used.

3. Somatosensory evoked potential monitoring is utilized and baseline parameters are established at the commencement of the case.

4. The patient is positioned prone on a laminectomy frame. Endotracheal anesthesia is used. The x-ray machine or C-arm fluoroscope is positioned and adjusted to clearly view the affected vertebral level in the anteroposterior view. One should make sure that the metal bars from the table or laminectomy frame does not obscure viewing the desired area. The pedicle below the affected disc should be visualized. Skin is then marked to make a 10-cm incision centered at the affected disc.

5. The paraspinous muscles on the side of herniation are mobilized with cautery. Complete muscle relaxation is provided by the anesthesiologist. The paraspinous muscles are dissected as far laterally as possible to expose the facet joints and the transverse processes. The paraspinous muscles are then retracted by a self-retaining retractor.