CASE REPORT
This is an educational case of a giant calcified thoracic disc herniation, addressed by a transforaminal endoscopic procedure. The patient was a 73-year-old female with a body mass index of 35 kg/m2, who was suffering from atraumatic gluteal and leg pain, with a weakness in the legs and progressive gait disturbance. She was using a walker to assist with ambulation. No reported bladder or bowel dysfunction. A detailed neurological examination was performed demonstrating a spastic paraparesis sub T10, American Spinal Injury Association Impairment Scale D. The imaging included a magnetic resonance imaging (MRI) of the thoracic and lumbar spine, demonstrating a giant thoracic disc herniation at the level T11–12 and computer tomography (CT) indicating calcification of the herniation.
Different surgical treatment options were considered, including standard open approaches such as anterior approaches with hemicorpectomy or a posterior costovertebrectomy. Such approaches usually have significant surgical morbidities, and stabilization is often required additionally. Further, endoscopic approaches were evaluated as alternatives. Transforaminal thoracic endoscopic discectomy (TETD) was identified as the most suitable option to reduce surgical collateral damages in an America Society of Anesthesiologists physical status classification grade III-Patient.
Surgery was performed in a standard prone position under general anesthesia with fluoroscopic guidance. Intraoperative neuromonitoring was not used in this case, as no advantages or consequences were expected for decompression of already existing central neurological symptoms [1]. Performing surgery under local anesthesia would have been a valuable alternative but is not yet widely accepted in our patient population. When working in the thoracic spine, identification of the targeted level is a unique challenge [2]. We used intraoperative C-Arm and counted the levels from the sacrum up to T11–12. Furthermore, the correct level was confirmed by identifying the last rib at T12.
The trajectory was determined by combination of an anteroposterior and lateral fluoroscopic view of the targeted intervertebral disc space, based on calculation on the preoperative axial MRI; before surgery, the skin entry point was determined on MRI by drawing a line from the posterior disc space at the medial pedicular line, under the lateral margin of facet joint, and onto the skin [3].
A needle was percutaneously advanced under fluoroscopic guidance to reach the desired intervertebral disc transforaminally. A skin-incision was made around the needle. A guidewire was placed into the needle and sequential dilators were advanced over the guidewire. The working channel was advanced over the final dilator, and the endoscope was introduced. In this case, a 10.5-mm endoscope with a working channel of 5.6 mm with a 20° angled lens was used.
The exiting nerve root (T11) was visualized. The nerve root was sacrificed to achieve a safer approach to the herniated disc. We consider this to be a valuable option, but only for thoracic nerves without motoric function, and only if the gain in approach is significant and needed.
The nerve root is mobilized from the surrounding soft tissues and adhesions using a blunt dissector. With bipolar electrocautery the nerve root is coagulated and then with an endoscopic scissor transected.
The inferior apical aspect of the superior articular process was reduced using an endoscopic burr. If needed (not performed here), the superior part of the lower pedicel and/or the inferior part of the upper pedicle can be reduced (less then 25%) for better access, depending on size and location of the herniation. After sufficient access to the spinal canal, the calcified disc herniation was resected piece by piece. In the presented case the herniation was not fully calcified. The procedure would have been even more challenging in the case of a fully calcified herniation. Considering expected adhesions to the dura, the last layer of the disc herniation was not resected (“eggshell-technique”) to avoid a dural lesion. Headache, seizures, vision impairment, fluctuations in blood pressure have been identified as potential complications linked to irrigation during endoscopic procedures following an incidental durotomy. In cases with dural lesions irrigation fluid might access the intradural space, leading to a direct pressure increase [4]. Further investigations in a cadaver model to assist endoscopic spine surgeon in educated decision making concerning pump pressure settings are currently performed at our institution. Consequently, if an incidental durotomy occurs, measures should be taken to prevent related complications. These include reduction of the pump pressure below 40 mmHg, avoiding to “look into the dural lesion” to minimize direct jet stream, application of a fibrin-sealed collagen sponge (TachoSil, Corza Medical, Westwood, MA, USA) and fibrin glue or sealant. To avoid instrument-induced medullary compression, the insertion of instruments should be incrementally and always under direct visualization.
Full decompression and visualization of the liberated anterior aspect of the pulsating dura was achieved.
The postoperative MRI confirmed sufficient decompression of the spinal cord. Postoperative CT verified the enlarged foramen T11–12 without bony destabilization of the segment.
The patient was discharged into rehabilitation after the surgery. She reported a significant pain relieve with no need for pain killers after the surgery and the neurological function improved by spinal cord independence measurement from 68 to 87 points [5].
Informed consent from the patient to use the presented radiological and intraoperative video material was obtained.
DISCUSSION
Thoracic disc affects 11%–14% of the population [6,7]. The lower thoracic levels are more commonly affected. Most cases are asymptomatic. Symptomatic cases contribute to only 0.15% to 4% of all discectomies of the spine [8-10]. Since the majority of thoracic disc herniations are calcified, a CT scan is recommended to confirm the amount of suspected calcified disc herniation, as this would have a consequence for the technique of resection. The definition of a giant thoracic disc herniation is when more than 40% of the canal diameter is occupied [11]. Surgery for thoracic disc herniations are rare and can be challenging. The main goal is to achieve sufficient decompression without manipulation of the spinal cord. Traditional approaches include anterior hemicorpectomies and fusion or posterior costovertebrectomies and fusion with associated surgical morbidities. The transforaminal approach (TETD) using an endoscope seems to be the least invasive approach and a valuable option in skilled and trained hands. The combination of an angled field of view and freedom of movement of the endoscope results in adequate working area access. This technique preserves postoperative spinal stability and can significantly reduce postoperative pain [3]. The limitation of this surgical technique is the steep learning curve, not only due to the confined transforaminal access, but also because due to the relative rarity of patients with symptomatic thoracic disc herniations who require surgery. Therefore, we have presented a step-by-step guide for the TETD procedure.
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