INTRODUCTION
Thoracic disc herniation (TDH) is a challenging clinical condition, that requires timely diagnosis and appropriate surgical management. TDH is rare and accounts for only 0.15 to 4% of all surgically treated disc herniations, with a frequency of 1 per 1,000,000 people. It is more common in adults between 30 and 50 years old. It mainly occurs between T8 and L1 and most frequently causes myelopathy at the T10–11 and T12–L1 levels [1,2].
TDH remains asymptomatic for some time before diagnosis [2]. The clinical symptoms most frequently associated with TDH are intercostal neuralgia and back pain, present in approximately 92% of cases [1]. Neurological deficits occur in about 60% of cases. Sensory disorders include paresthesia and hypoesthesia in the affected dermatomes [1]. TDH may present with lower limb weakness and gait disturbances, progressing in severe cases to spastic paraparesis and paraplegia, associated with bladder and sphincter dysfunction [1].
The thoracic spinal cord is more vulnerable to compression because of its anatomical features. Thoracic kyphosis may promote compression of the dural sac against the posterior part of the intervertebral disc. The denticulate ligaments limit movement of the spinal cord within the dural sheath, making it much more sensitive to compression. The thoracic spinal cord is considered a “watershed zone” due to the lower number of segmental arteries supplying it. The artery of Adamkiewicz provides the major blood supply to the anterior thoracolumbar spinal cord [3]. It often arises from the left side between the T9 and L1 vertebrae, and TDHs are mainly located in this region [1].
Surgery for TDHs is very complex because of the particular anatomical location, and the technical issues related to several surgical approaches reported to date. Surgery aims to prevent spinal cord compression and symptoms worsening. Due to the vascular features of the thoracic spinal cord, complete functional recovery after surgery is often unattainable in those patients with severe myelopathy at the time of surgery [4].
The posterior transdural approach (PTA) is indicated for symptomatic, soft, centrally located TDHs, as reported before [4-7]. However, calcified TDH represent a contraindication for the PTA, because of the issues related to the removal of this particular type of disc herniations [4-6].
TDH may be calcified in approximately 40% of cases and is defined as ‘giant’ when it occupies more than 40% of the spinal canal diameter [1]. Calcified disc fragments via the intradural route may cause accidental mechanical damage to the spinal cord, increasing the morbidity associated with the approach [4-6]. Medial and calcified TDHs can be approached via a transthoracic or extracavitary route; however, intraoperative and postoperative complications are significantly higher than PTA [1,2,6].
In this technical note, we present in a step-by-step manner a modified PTA, which can also be used for the removal of calcified TDHs, minimizing intraoperative complications, particularly those related to spinal cord exposure during the transdural approach.
The modified PTA differs conceptually from the standard PTA. After laminectomy and omolateral pedicle resection, the modified approach involves a small posterior dural opening, allowing controlled CSF release while preserving the anterior dura. The spinal cord remains protected by the dural sheath, and direct manipulation is minimized. On the other hand, the standard transdural approach requires a larger dural opening, including the anterior dura, which increases the risk of direct spinal cord mobilization and CSF fistula associated with anterior dural opening.
TECHNICAL NOTE
1. Case Presentation
We present the case of a 74-year-old patient with progressive hyposthenia and bilateral lower limb deficit. Preoperative magnetic resonance imaging revealed a median-paramedian bilateral TDH at the D10–11 level, partially calcified, and associated with anterior and posterior osteophytes causing spinal canal stenosis (Figure 1). The disc herniation caused spinal cord compression, resulting in myelopathy and severe spastic paraparesis of the lower limbs. Autonomous ambulation was not possible, and the patient was able to maintain the standing position for a few seconds. Electromyography and neurophysiological evoked potentials showed signs of bilateral pyramidal tract involvement in the thoracolumbar region. Based on the clinical and imaging findings, surgery was planned.
2. Technique Description
Under general anesthesia, the patient was positioned in the prone position. Intraoperative neurophysiological monitoring (IONM) was conducted, with constant neurologists monitoring in the operating room. A radiological landmark was placed on the spinous process of D11, and a centered midline skin incision was performed. The spinous processes and laminae of D10 and D11 were exposed. The operating microscope was positioned.
Laminectomy of D10 and D11 was performed using a high-speed microdrill, followed by removal of the right D11 pedicle and the medial half of the ipsilateral transverse process. This step represents our modification of the conventional transdural approach for central TDH and allows for a wider surgical corridor [4] (Figure 2).
A superior small midline dural opening was then performed, with cerebrospinal fluid (CSF) releasing (Figures 2 and 3A). CSF drainage improves spinal cord microcirculation and facilitates tension relief and mobilization of the dural sac. In this way, the spinal cord remains protected by the dural sheath, while avoiding the closed CSF column that can cause circulatory alterations due to surgical sac traction, as observed in extradural approaches.
Following CSF release, the dural sac collapsed and was progressively dissected away from the disc until the dorsal herniation was identified. Spinal cord traction in the lateromedial direction was almost absent, and the only maneuver required was the careful handling of the dural sheath, which behaved like a ‘deflated balloon’.
After exposing the lateral part of the right paramedian dorsal disc herniation (Figure 3B), the disc was then incised with a microblade and the herniated fragments were mobilized without applying any traction to the dural sac, which was relaxed and easily manageable during the whole procedure (Figure 4). This aspect allows mobilization of the dural sac and bilateral management of the dorsal disc herniation, even calcified (Figure 5A).
Complete decompression of the spinal cord was achieved. The dura was closed with a 7-0 microsuture in a watertight fashion (Figure 5B) and sealed with fibrin glue. Thereafter, TachoSil (Corza Medical, Austria) was applied to secure the microsuture. Careful hemostasis of the peridural plexuses was achieved.
At the end of surgery, IONM showed improved potentials compared to baseline. During the postoperative period, the patient regained partial motor function in the left lower limb, with improved flexion while in bed. Three months after surgery, and after a period of intensive physiotherapy, the patient showed progressive improvement in lower limb movements.
3. Ethics Statement
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.
DISCUSSION
The reported modification of the previously published PTA allows the removal of both soft and calcified TDHs, thereby overcoming the limitations of the standard approaches [4-6]. Resection of the ipsilateral caudal pedicle and transverse process allows for a wider surgical corridor. The subsequent dural opening with CSF drainage enable the removal of the herniated fragment without applying tension to the spinal cord [4] (Figures 2 and 6).
The CSF drainage before disc removal through a small midline dural opening, is related to a protective effect on the spinal cord by lowering the pressure within the intradural compartment, thereby promoting microcirculation and spinal cord preservation [4,8].
The dural opening is performed safely after laminectomy and pedicle resection, which ensures optimal visualization even in cases of severe stenosis. The procedure is carried out under high-magnification microscopy and continuous IONM to minimize the risk of neural injury.
CSF drainage should be controlled and gradual to minimize the risks of intraoperative hypotension and over-drainage. Only a small volume of CSF is released, sufficient to allow the dural sac to collapse gently like a “deflated balloon” while maintaining hemodynamic stability. Close monitoring of the patient’s blood pressure, together with continuous IONM, is therefore essential to safely apply this technique.
CSF drainage allows also for the release of dural sac tension and its optimal management avoiding direct traction on the spinal cord [4,8] (Figures 2, 3, 6). As known, traction on the spinal cord would occur with a closed dural sac, as in extradural lateral approaches, where traction on the cerebrospinal column could compromise spinal cord microcirculation [1,2,4].
In our case, no postoperative CSF leakage was observed. Meticulous microsurgical closure using 7-0 sutures, reinforced with fibrin glue and TachoSil, aims to achieve a watertight seal. According to the literature, small, well-closed posterior dural openings are associated with a relatively low complication rate. The reported incidence of posterior CSF leakage after standard transdural approaches is approximately 4%–8% [9]. The small size of the dural opening in the variant we propose further reduces the risk of CSF fistula compared with the standard transdural approach, in which the dural opening is larger.
Compared with the transdural approach, the main advantage of this variant is the reduced risk of CSF fistula on the anterior part of the dural sac [4]. Postoperative CSF fistula is mainly associated with anterior dural opening during herniated disc removal and subsequent anterior dissection of the dural sac. In this modified transdural approach, anterior dissection of the dura from the disc, performed with a relaxed dural sac, is usually easier, thereby reducing the risk of dural injury. Moreover, in cases with fusion between the calcified disc and the dura, anterior decompression is still possible by leaving a thin layer of disc material in place to prevent accidental dural opening.
In addition, the spinal cord remains protected by the dural sheaths, reducing the risk of intraoperative injury, especially during the removal of calcified disc parts. In this way direct manipulation of the spinal cord is minimized (Figure 2). During the procedure, IONM is mandatory, because even if the spinal cord is protected by the CSF release, potential spinal cord damage is still possible.
Compared to the standard transdural approaches, this variation allows for the removal of calcified herniations while keeping the spinal cord protected by the dural sheath and CSF drainage, thereby markedly reducing the risk of CSF fistula associated with anterior dural opening [4-6].
Compared with transthoracic approaches, often necessary for calcified TDH removal, this technique significantly minimizes pulmonary risks, such as pneumothorax, atelectasis, and pleural effusions, as well as the inherent challenges of transthoracic surgery, including the demanding surgical access through thoracotomy or thoracoscopy and the need to mobilize the lung and the pleura to reach the disc [1,2,6].
In this case, spinal stabilization was not required, as bone removal was limited to a 2-level laminectomy at D10–11 and unilateral resection of the D11 pedicle, with preservation of the contralateral pedicle and facet joints. Instrumented fusion should be considered in cases at risk of significant postoperative instability, such as those involving multilevel laminectomy, bilateral pedicle or facet joint resection, or preexisting spinal instability [10].
The modified PTA is therefore indicated for both soft and calcified TDHs that are centrally located. Adequate exposure is achieved through laminectomy and pedicle resection, followed by controlled CSF release, which creates sufficient operative space to allow the safe removal of even giant and migrated herniations. Among the limitations of this approach are cases with severe dura–disc adhesions, which restrict mobilization of the dural sheath and hinder optimal exposure of the herniated material.
CONCLUSION
This approach is indicated for the surgical management of both soft and calcified TDHs. Drilling of the ipsilateral caudal pedicle and transverse process allows for a wider surgical corridor. Subsequent CSF drainage facilitates tension release within the dural sac and improves spinal cord microcirculation. The spinal cord remains protected and can be gently mobilized to remove herniated fragments without excessive neural traction. Maintaining the anterior dura intact minimizes the risk of CSF fistula and complications related to anterior dissection. Compared with transthoracic approaches, this technique also reduces pulmonary and overall surgical risks.
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