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51
Orthopaedic Knowledge Update 7
Koval, KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL. American Academy of Orthopaedic Surgeons. 2002 Ch. 51, pp. 621-626.
Kirkham B. Wood, MD, Amir Mehbod, MD
Chapter 51: Thoracic Disk Herniation
Introduction
Thoracic disk herniations are relatively rare compared with those of the cervical or lumbar spine. An incidence of 1 in 10,000 to 1 in one million has been estimated, which represents 0.25% to 0.75% of all symptomatic spinal disk herniations. More than 75% occur below the level of T8 and most commonly occur during the third, fourth, and fifth decades of life. Multiple herniations have been reported as comprising 5% to 15% of most series of symptomatic individuals.
The prevalence and natural history of asymptomatic thoracic disk herniations has been well documented. In an MRI study of asymptomatic individuals, 73% had positive degenerative findings at one or more levels, which included 37% with disk herniations (50% multiple) and 40% with annular tears, Scheuermann's changes, or deformity of the spinal cord. In a follow-up study more than 26 months later, none of these individuals became symptomatic.
Classification
Thoracic disk herniations are classified according to spinal level and position. They are most often mediolateral, (70% to 94% in most series) (Fig. 1), and rarely, intradural (5% to 12%) (Fig. 2). There is no strong association between the position, level, composition, or size of a thoracic disk herniation and the symptoms it may produce. For instance, a central herniation may typically cause myelopathy but can produce radicular pain, referred discomfort, or no symptoms at all. Lateral disk herniations are more likely to produce an ipsilateral radiculopathy, but a traction phenomenon can lead to radicular symptoms on the contralateral side.
Etiology
The mechanical etiologies for thoracic disk herniations are diverse and have included torsion, repetitive twisting, athletic activity, sneezing, and coughing. Thirty-three percent to 50% of patients with symptomatic thoracic disk herniations will report a history of trauma, but the actual role trauma plays in the production of these herniations is controversial and poorly defined.
Biomechanical tests have shown the most common mechanism for thoracic disk herniations to be a combination of torsion and bending load, whether flexion, extension, or lateral. The unique anatomy of the thoracic spine decreases the risk of intervertebral disk injury by the splinting effect of the thoracic rib cage and the resistance of the thoracic facets to flexion loads. The decreased height of the thoracic disk compared with that of the lumbar spine may also contribute to the low incidence of disk protrusions.
Other conditions that may be associated with a thoracic disk herniation include ossification of the posterior longitudinal ligament or the ligamentum flavum, and thoracic spinal stenosis. When present, such conditions can increase the symptomatology in even minor disk protrusions. Degeneration of the involved disks is commonly associated with thoracic disk herniations, especially in the older population, which tends to have calcification of the disks. Calcification can increase adhesions between the disk protrusion and the adjacent dura. The natural kyphosis of the thoracic spine places the spinal cord next to the posterior longitudinal ligament and disk and even a small disk herniation may then compress the cord and cause symptoms. Lumbar and cervical disk herniations have less calcification in comparison.
Clinical Presentation
The diagnosis of thoracic disk herniations can be difficult because of the relative paucity of classic findings. Because of the extreme variations in presentation, diagnosis is often delayed. Symptoms can be vague and often mimic other pathologic conditions including not only lumbar disk disease and neurogenic claudication, but also cardiac, abdominal (gallbladder), and intrathoracic maladies, and even multiple sclerosis. Pain is the principal initial symptom and can be localized or circumferential, often aggravated by coughing, sneezing, and Valsalva-like maneuvers. Numbness in a dermatomal pattern is also common. Progressive levels of neurologic embarrassment can eventually lead to motor weakness, bladder dysfunction, and rarely, paralysis.
The clinical presentation of symptomatic thoracic disk herniations can be divided into three categories: mechanical, radicular, and myelopathic. Mechanical axial back pain can occur secondary to the derangement of the intervertebral disk itself, typically resulting in localized pain into the mid or lower thoracic region. Mechanical features include improvement of symptoms with rest and exacerbation by activity or prolonged sitting.
Radicular pain can arise as a result of impingement of disk material on or traction of exiting nerve roots. The nerve corresponding to the more caudal vertebral body is the root typically involved; for example, an anterolateral T8-9 disk herniation will produce a T9 radiculopathy. Patients may complain of pain in the anterior chest wall in a band-like dermatomal distribution. A differential diagnosis is the pain from herpes zoster (shingles). Axial pain also can be a component of the complaint. Radicular pain is more common with herniations of the upper thoracic spine, especially lateral protrusions, wherein they may cause symptoms similar to a cervical disk herniation such as upper arm pain, radiculopathy, and paresthesias.
Myelopathic symptoms can occur when the disk material impinges significantly on the spinal cord. Symptomatology can range from subtle pain and sensory changes to motor disturbances or frank paraparesis. Bowel and bladder changes can be seen in 10% to 20% of symptomatic thoracic disk herniations.
During the physical examination the patient's posture is noted in both sagittal and coronal planes. Gait disturbances such as a wide base ataxic gait or foot drop should be noted. The Romberg sign is a useful tool for detecting changes in proprioception. A careful sensory examination may reveal a clear level of demarcation corresponding to the level of impingement. Upper motor neuron signs, such as hyperreflexia, clonus, and Babinski, may be present.
The differential diagnosis is expansive given the wide range of symptoms. Spinal and nonspinal pathology should be considered. Spine-related diagnoses include degenerative spondylosis, spinal and spinal cord tumors, multiple sclerosis, and transverse myelitis. Nonspinal pain origins include pancreatitis, aneurysms, and retroperitoneal neoplasms.
Diagnostic Imaging
Upright AP and lateral radiographs of the thoracic spine should be obtained first to rule out obvious fractures and/or tumors. The degree of kyphosis, osteophytes, and vertebral wedging can be noted. Thirty percent to 70% of symptomatic thoracic disk herniations have calcified disk material, as opposed to less than 10% without herniation. MRI is the neuroradiographic study of choice (Fig. 2) and should be interpreted with a heightened awareness because of the high prevalence of asymptomatic herniations. In patients for whom MRI is not an option, myelography with CT can evaluate for spinal cord encroachment on axial views with sagittal reconstructions. The procedure is invasive, but its sensitivity and specificity are comparable to that of MRI. A CT scan is also excellent for identifying disk calcifications.
A common error in the surgical treatment of thoracic disk herniation is misidentifying the level of injury. The thoracic anatomy can be more variable than in the lumbar or cervical spine, with a different number of vertebrae and ribs. A chest radiograph is important in the preoperative work-up to count the number of ribs to verify the proper level. A myelogram can also be helpful in describing the protrusion and allowing accurate identification of the pathologic level.
In instances of unclear presentation, thoracic diskography can be performed safely by experienced and skilled physicians as a provocative diagnostic test to determine the presence and location of axial thoracic pain. The procedure can be very useful in situations of multiple levels of thoracic pathology with varying grades of herniation. A large herniation with spinal cord deformation is a strict contraindication to diskography because the installation of the saline contrast runs a risk of further cord compression.
Nonsurgical Treatment
Most patients with thoracic disk herniations do not need surgical intervention, especially in the absence of neurologic findings. Only 0.2% to 2.0% of thoracic disk herniations are treated surgically each year. Symptoms will usually resolve as the natural history dictates. In a review of 55 patients with 72 symptomatic disk herniations, 73% did not require surgery and were able to return to work and vigorous sports activities.
Nonsurgical treatment consists of activity modification, low-impact aerobic exercises, and bracing. Anti-inflammatory medications and the judicious use of mild narcotics can help provide symptomatic relief. In addition, patients with radicular symptoms can be treated with a course of oral steroids or corticosteroid injections of the intercostal nerves.
Surgical Treatment
Indications for surgical intervention include myelopathy, progressive neurologic deficit, or pain at an unacceptable level in those in whom a minimum of 6 months of adequate nonsurgical treatment has failed. Multiple surgical approaches have been described for thoracic diskectomy, depending on the level of involvement, relationship to the spinal cord, and consistency of the disk herniation.
The strict posterior approach via laminectomy can alleviate compressive forces from the ligamentum flavum and lamina, but does not specifically address the anterior compression. The potential for trauma to the spinal cord during this mobilization for exposure of the disk makes this approach unattractive and therefore it should be avoided.
The transpedicular approach is another posterior approach in which exposure is provided by limited excision of the posterior lamina, facet joints, and the pedicle caudal to the disk (Fig. 3, A), allowing for excision of lateral and paramedian disk material. Advantages include less dissection and less cord retraction; however, visualization can be somewhat limited. Excessive bone removal may also destabilize the spine.
A lateral extracavitary exposure is performed via an extrapleural resection of the medial portion of the rib costotransverse joint, facet, and pedicle in the superior aspect of the vertebral body inferior to the disk herniation (Fig. 3, B). This approach provides good exposure for central-lateral and lateral disk herniations at any level; however, disruption of the paraspinal muscles and the degree of bone resection are points of concern.
A costotransversectomy is a posterolateral extrapleural approach first used in the early 20th century for the treatment of tuberculosis. Exposure is provided by resection of medial ribs costotransverse joint, facet, and pedicle (Fig. 3, C). The posterior medial portion of the rib and its articulation with the transverse process and the superior aspect of the vertebral body inferior to the disk herniation is resected. This approach provides exposure of multiple levels, including the uppermost thoracic disks, and is especially useful for lateral herniations. Similar to the lateral extracavitary approach, it has the disadvantage of disrupting the paraspinal muscles in addition to large amounts of bone resection. Costotransversectomy should not be used for large central calcified herniations when large osteophytes are present, where an anterior approach is safer.
An anterior transthoracic approach allows excellent anterior exposure of T5-12 for most lateral and anterior disk herniations. The use of strut grafts or anterior instrumentation is facilitated by this direct approach. The base of the rib articulating with the vertebral body just caudal to the disk herniation is typically removed. The inferior pedicle is partially or completely removed. A partial diskectomy is performed, using a burr, and a trough can be created in the posterior vertebral body and the remaining disk material brought through (Fig. 3, D). The disadvantages of this approach include the need for a thoracotomy and the possibility of pneumothorax, pulmonary contusion, pneumonia, effusion, and atelectasis all adding to the potential morbidity of the operation.
Thoracoscopy is an emerging technology that allows thoracic diskectomy, fusion with bone graft, and possible instrumentation over a wide range of the anterior thoracic spine. Thoracoscopy is probably best suited for noncalcified herniations. Calcified protrusions are likely to have dural adherence and should be treated with an anterolateral approach.
Fusion and instrumentation are controversial topics. Although some surgeons perform fusions after diskectomy, others routinely do not. In general, fusion is an accepted part of treatment in cases that involve multiple levels of diskectomy, Scheuermann's disease, or excessive resection of bone leading to potential instability. For diskectomies over a few levels (less than three) cancellous autograft can be harvested from adjacent ribs near the costovertebral junction, an especially attractive option in thoracoscopy. Small fibular allograft rings can be packed with local autograft and provide increased structural stability. For longer fusions, especially those with instrumentation, standard bone grafting harvesting techniques (for example, iliac crest) are recommended. Because of the inherent stability of the thoracic spine, however, instrumentation is not routinely used for fusions, except in cases of multilevel diskectomy at the thoracolumbar junction.
Annotated Bibliography
Fessler RG, Sturgill M: Review: Complications of surgery for thoracic disc disease. Surg Neurol 1998;49:609-618.
A good review of peer-reviewed publications reporting clinical data relating to thoracic diskectomy and the potential complications associated with various surgical approaches.
Regan JJ, Ben-Yishay A, Mack MJ: Video-assisted thoracoscopic excision of herniated thoracic disc: Description of technique and preliminary experience in the first 29 cases. J Spinal Disord 1998;11:183-191.
An excellent review of the techniques of and avoidance of pitfalls with the thoracoscopic treatment of disk herniations.
Wood KB, Schellhas KP, Garvey TA, Aeppli D: Thoracic discography in healthy individuals: A controlled prospective study of magnetic resonance imaging and discography in asymptomatic and symptomatic individuals. Spine 1999;24:1548-1555.
Thoracic diskography was performed in 10 healthy individuals without thoracic pain. Findings showed that prominent Schmorl's nodes may be intensely painful even in life-long asymptomatic individuals. Thoracic diskography also was found to demonstrate disk pathology not readily apparent on MRI.
Classic Bibliography
Arce CA, Dohrmann GJ: Herniated thoracic disks. Neurol Clin 1985;3:383-392.
Awwad EE, Martin DS, Smith KR Jr, Baker BK: Asymptomatic versus symptomatic herniated thoracic discs: Their frequency and characteristics as detected by computed tomography after myelography. Neurosurgery 1991;28:180-186.
Brown CW, Deffer PA Jr, Akmakjian J, Donaldson DH, Brugman JL: The natural history of thoracic disc herniation. Spine 1992;17(suppl 6):S97-S102.
Schellhas KP, Pollei SR, Dorwart RH: Thoracic diskography: A safe and reliable technique. Spine 1994;19:2103-2109.
Wood KB, Blair JM, Aepple DM, et al: The natural history of asymptomatic thoracic disc herniations. Spine 1997;22:525-530.
Wood KB, Garvey TA, Gundry C, Heithoff KB: Magnetic resonance imaging of the thoracic spine: Evaluation of asymptomatic individuals. J Bone Joint Surg Am 1995;77:1631-1638.
