Panduranga Seetahal-Maraj1, Dylan Thomas1
1 Department of Neurosurgery, San Fernando General Hospital, Trinidad & Tobago
Department of Neurosurgery,
San Fernando General Hospital,
Trinidad & Tobago.
Copyright: This is an open-access article under the terms of the Creative Commons Attribution License which permits use, distribution, and reproduction in any medium, provided the original work is properly cited.
©2022 The Authors. Caribbean Medical Journal published by Trinidad & Tobago Medical Association.
Symptomatic thoracic disc herniation is a rare pathology, with a quoted incidence of one in one million persons. We present a case of a middle-aged male with bilateral neuropathic pain in both lower limbs, associated with myelopathy. His MRI revealed a midline disc herniation at T10-11, with myelomalacia of the thoracic cord.
Surgical decompression and fusion were performed, utilising a costotransversectomy to enable a safe lateral approach to the midline disc. The ultrasonic bone cutter aided in performance of this procedure, and we report on our experience with this instrument. The patient had resolution of his radiculopathy and weakness postoperatively.
A 51-year-old male presented to the spinal clinic with a four-month history of bilateral lower limb pain and progressively worsening lower limb weakness and stiffness. The pain was described as burning in nature, 6/10 severity, and originated in the groin, with radiation down both anterior and posterior aspects of the lower limbs. There was no history of trauma or heavy lifting.
The patient reported needing to use a walking stick when ambulating for longer than a minute, due to worsening weakness. No urinary retention or incontinence was noted. The remainder of the history was significant for poorly controlled hypertension.
Clinical examination revealed a spastic gait, with increased tone in the lower limbs only. Power was noted to be 4/5 at the iliopsoas and quadriceps bilaterally, and 5/5 in the ankle dorsiflexors, extensor hallucis longus and plantar flexors. He was hyper-reflexic (3+) with upgoing plantar reflexes. No clonus was present.
A sensory level to fine touch and vibration sense was noted at L1. Rectal examination was normal, and neurologic examination of the upper limbs was unremarkable. His modified Japanese Orthopedic Association (mJOA) score was 7/11. A suspected diagnosis of thoracic cord compression with myelopathy was made, and this was thought to be responsible for his neuropathic-type pain.
Standing X-rays of the whole spine to assess global sagittal balance was done, and CT and MRI of the whole spine requested. There was no deformity noted in the sagittal or coronal planes. MRI findings were of a partially calcified, midline herniated thoracic disc, at T10-11, with significant flaval ligament hypertrophy and facet joint arthrosis.
The spinal cord was compressed at T10-11 (3.3 mm AP diameter, normal 6.5 ±2 mm) and the central canal stenosed. On T2 weighted sequences, a hyperintense signal was noted on the medulla relative to the surrounding structures. This was consistent with myelomalacia of the thoracic spinal cord and explained the patient’s myelopathic findings.
The patient was counselled on the findings and advised that urgent surgical decompression and fusion was required to prevent worsening of myelopathy and potential bowel/bladder dysfunction. The surgical plan included a posterolateral approach to the T10-11 disc-space, via a right costotransversectomy, with pedicle screw and rod fusion of T10-12.
The patient was positioned prone after general anaesthesia induction, with the eyes protected and all bony prominences padded. X-ray localisation of T10-11 was performed and followed by a standard midline approach to the spine. Subperiosteal dissection of paraspinal musculature was taken laterally to expose the right T11 rib head for 3 cm, and the pleura was protected.
Pedicle screws were placed at T10-12 on the left, and T10 and 12 on the right. The ultrasonic bone cutter was then used to perform a T10 laminectomy. Right inferior T10 and superior T11 facetectomy followed this, and after careful dissection of the soft tissues a right T11 costotransversectomy was completed. Adequate exposure was achieved, to facilitate entry into the disc space without undue traction on the neural elements. This was done with minimal blood loss, and no dural injury. The thoracic segmental vessels were isolated and protected.
A rod was placed in the left T10-12 pedicle screws, and distraction applied to open the T10-11 disc-space. Entry into the disc space was then performed with a 15 blade, and disc material removed with a combination of disc forceps, saline irrigation and curettes. At no time was there traction on the thecal sac, due to the lateral exposure and working corridor gained by a costotransversectomy.
Confirmation of crossing the midline with the discectomy was done using X-rays, ensuring adequate discectomy. This was followed by final rod placement and securing of the construct with end caps. Standard layered closure of muscle, fascia and skin was performed.
Postoperatively, the patient noted immediate cessation of all lower limb neuropathic pain, and improved power in the hips and quadriceps. He was ambulant on postoperative day 1, and urinary catheter removed within 24 hours. He was discharged on day 2, with 5/5 power in the lower limbs, and pain-free. His mJOA score was 9/11 at this time, and at 6-month follow-up, his mJOA score was 10/11. There was no recurrence of his pain, and the patient had a satisfactory neurological recovery.
Thoracic disc herniation causing clinically significant spinal cord compression was first reported in 1838 by Key, and remains a rarely encountered entity.1 The quoted incidence of a symptomatic disc is one in one million persons, with estimates of 0.1-3% of all disc herniations. Analysis of surgical procedures for a disc herniation reveals that 0.5% are for thoracic discs. 1,2
The typical patient is between 30-50 years of age, with no gender predilection. An association has been noted with Scheuermann’s kyphosis. 3,4 The majority are located below T7-8, with T11-12 being most common due to posterior longitudinal ligament weakness in this region, along with increased mobility when approaching the thoracolumbar junction. Greater flexion/extension and sagittal shear stress at the thoracolumbar junction are thought to be increase the risk for disc herniation. These discs can be either soft or calcified, and central or lateral. These characteristics determine the choice of surgical approach. 3,4
The thoracic spinal cord has a large antero-posterior diameter (normal 6.5 x 8 mm) when compared to that of the thoracic spinal canal (normal 16.8 x 17.2 mm) (3). Limited space is available around the thoracic cord, particularly when combined with flaval ligament hypertrophy.
The thoracic kyphosis also flattens the dura against the posterior disc elements. Finally, it is reliant on watershed perfusion to the medulla in certain regions. These factors create a low tolerance to disc herniations/intracanal pathology and make it vulnerable to the development of myelopathy and myelomalacia. 3
This is determined by the degree of thoracic cord compression. The most common symptom is non-specific back pain. Radicular pain and hypoesthesia in the involved intercostal dermatome can also be elicited. Compression of the conus medullaris can create neuropathic-type pain, as evidenced in our patient.
In the clinical setting, patients usually are first seen when myelopathy is present. Weakness that worsens with activity or even paraparesis/paraplegia may be present. Urinary sphincter dysfunction is rare but has been reported. 4,5
Spinal cord syndromes, including anterior cord syndrome if the anterior spinal artery is compromised, may also be evident. Examination may reveal a spastic/scissoring gait, and a sensory level at the dermatomal correspondence to the disc herniation. Power may be reduced, and hyperreflexia with upgoing plantar reflexes can also be found.
The investigation of choice is MRI of the thoracic spine, which can highlight disc herniations that efface the CSF signal and compress the cord. The position of the disc influences the surgical approach used. T2-weighted sequences can also reveal hyperintensities on the medulla of the spinal cord, which implies myelomalacia of the affected segment.
CT scan aids in determining if the disc is calcified, and allows for bony measurements to be made prior to fusion. 2,3,5
Laminectomy alone was abandoned in the 1960s, due to worse outcomes with this procedure. 3,4 It requires manipulation on the thecal sac and cord to remove the herniated disc, which is anterior to the cord. This is not well-tolerated, particularly in myelopathic patients, and up to 30% of patients did worse or were paraplegic after laminectomy.(6)
Approaches are now broadly classified as anterior (thoracotomy, mini-thoracotomy, thoracoscopy) or posterolateral (trans-pedicular, trans-facet, costotransversectomy, extracavitary). 3,4,7-11 There is no single best approach, and the procedure used is dictated by patient factors, disc location, surgeon experience and familiarity/comfort with the technique. The ultimate aim is safe surgery with no/minimal patient morbidity.
In the current patient, a costotransversectomy was utilised to approach the midline disc from posterolaterally, and this technique will be discussed. The anatomy encountered in this approach is familiar to most spinal surgeons. The patient is positioned prone and a midline incision utilized, which spans 2-3 segments above and below the target level. This allows a more lateral working corridor when compared to a transpedicular approach, and therefore greater access to the anteriorly placed disc. The caveat to this is an extensive paraspinal muscular and bony dissection, which can lead to greater postoperative discomfort when compared to other approaches. The rib that articulates with the lower vertebral body (T11 for a T10-11 disc) is identified and stripped laterally for 2-3cm. The rib head is then disarticulated, and laminectomy and facetectomy performed to complete the exposure. The ipsilateral pedicle is drilled until the disc space is exposed, whereby it can be sharply entered, and discectomy undertaken. Retropleural exposure can be done safely, with placement of a chest tube only necessary if the pleura is breached.
Figure 1: MRI showing disc herniation and surgical fixation
Top row – Sagittal (left) and axial (right) T2W MRI revealing T10-11 central disc herniation. There is significant cord compression and myelomalacia.
Bottom row – exposure with pedicle screw placement and laminectomy of T11 (left), intraoperative check confirming crossing of midline with disc forceps (middle), final instrumentation (right).
Figure 2: Intraoperative findings and postoperative imaging
Top row – use of ultrasonic bone cutter to perform facetectomy.
Bottom row – AP and lateral check x-rays postop, showing good position of implants, and the degree of right T11 costotransversectomy performed.
Experience with the ultrasonic bone cutter
The ultrasonic bone cutter has been utilized in the performance of spinal surgery, as a means to reduce the risk of neural injury and blood loss, with studies showing a comparable safety profile to the high-speed drill.12-14 In our setting, it is not always readily available. However, we had the opportunity to utilize this device during our case. The laminectomy, facetectomy and rib head removal were all accomplished with this instrument, with no attributable blood loss and no dural tears. In our setting, where blood and blood products are not always in ready supply, this reduction in blood loss during bony work may be an advantage when compared to the conventional drill.
Regarding use of the bone cutter, it is important to have adequate irrigation/cooling, to prevent thermal injury to the neural elements. Withdrawing the cutter frequently, to allow for dissipation of heat is recommended. The tip should not be left in one position for a prolonged period of time, to avoid thermal injury. Insulation of metal objects in the field, including suction tips, should be done to prevent heat conduction and indirect neural injury.
This is dependent on the size of the disc and duration of myelopathic symptoms, with early diagnosis and treatment affording better outcomes.1,3 In one study, 77% of small-medium and 53% of giant thoracic disc herniations improved neurologically after surgery.15 Our patient had a four-month history of symptoms, and > 50% canal stenosis, however he made an impressive neurologic recovery.
These are dependent on approach, and anterior approaches are found to have an increased risk of pulmonary-related complications (atelectasis, pleural effusion, pneumothorax). Neurological deterioration including paraplegia and worsening of myelopathy is known to occur and may be directly related to traction on the thecal sac or vascular insufficiency. CSF leaks are more common with giant calcified discs, and require repair intraoperatively.3
Thoracic disc herniations are uncommonly encountered and can pose a significant diagnostic challenge. Due to the unforgiving anatomy of the thoracic spinal cord, neurologic decline can be rapid. MRI is the gold standard investigation, and it aids in determining the surgical approach. Both anterior and posterior approaches can be used, and disc location as well as surgeon familiarity are key factors in making this choice. The ultrasonic bone cutter has been shown to be of benefit in the performance of spinal surgery, especially in reduction of blood loss. Good patient outcomes can be achieved even with myelopathic signs, when early decompression is done.
Informed consent was obtained from the patient, for use of all pictures and reporting. No identifying features are displayed.
Acknowledgements – None
Competing interests – None
Ethics approval – Not applicable
Funding – None
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