INTRODUCTION
Thoracic disc herniation is a rare spinal pathology, with an estimated incidence of approximately 1 per million individuals [1]. Among these, lesions occurring at the midthoracic level (T4–9) are even more uncommon and often present with vague or nonspecific symptoms, making early diagnosis challenging. Anatomical constraints at these levels also make surgical access difficult.
Unlike lumbar or cervical disc herniations, thoracic lesions frequently lack distinctive radicular pain, leading to delays in diagnosis and frequent misinterpretation as postherpetic neuralgia or rib fractures. Traditionally, open thoracic discectomy has been the standard surgical treatment. However, such procedures are associated with significant morbidities and prolonged recovery times [2,3]. In recent years, minimally invasive approaches using uniportal endoscopic techniques have been introduced and reported for thoracic spine pathologies [4]. However, based on the available literature, a biportal endoscopic transforaminal approach for herniated discs at the midthoracic level has not been previously reported.
This technical note describes a biportal endoscopic transforaminal approach for the treatment of a calcified herniated disc at the midthoracic level, with a focus on key procedural techniques and considerations.
TECHNICAL NOTE
1. Anatomical Consideration
Unlike the cervical and lumbar regions, the thoracic spine articulates with the ribs through costal facets, creating unique anatomical constraints that significantly limit surgical access. When approaching from the midline, extensive dissection of paraspinal tissue is often required, and in many cases, costotransversectomy is necessary to obtain sufficient visualization of the surgical field. Although the rib can initially act as an obstructing structure, once its relationship to the disc level is clearly identified, it becomes a highly reliable anatomical landmark that assists in determining both the surgical corridor and the precise location of the pathology.
In the midthoracic region, the rib and corresponding disc level nearly coincide because of the demi-facet configuration, which serves as a useful reference point for determining the surgical trajectory (Figure 1).
At the midthoracic level, the thoracic nerve roots course cranially, which necessitates careful consideration to prevent injury to the exiting root during surgery. This anatomical configuration, however, allows for a relatively safe surgical approach to the disc level (Figure 2).
2. Case Presentation
An 84-year-old female patient presented with a 1-year history of persistent left flank pain. She had previously undergone acupuncture treatment at a traditional Korean medicine clinic and was treated with medication for presumed postherpetic neuralgia at a dermatology clinic, but her symptoms remained unresolved. Thoracic spine magnetic resonance imaging (MRI) revealed a left paracentral and left foraminal herniated intervertebral disc at the T6–7 level (Figure 3). The patient subsequently underwent disc removal using a biportal endoscopic transforaminal approach under spinal anesthesia with intravenous sedation. Immediate postoperative pain relief was noted, and she was discharged without complications on postoperative day 2. Postoperative MRI confirmed complete removal of both the foraminal and central disc herniations at the T6–7 level that had been visualized preoperatively (Figure 4) (Supplementary Video Clip 1).
3. Surgical Procedure
1) Patient positioning and operative setup
For thoracic procedures, spinal anesthesia, epidural anesthesia, or general anesthesia can all be utilized. In this case, the procedure was performed under spinal anesthesia combined with intravenous analgesics. The patient was positioned prone on a Wilson frame. Irrigation was achieved by gravity using a saline bag positioned 40 cm above the surgical field, providing a natural flow and maintaining a pressure of approximately 20–30 mmHg, instead of using a pump system. A 0° endoscope was primarily employed, although the use of a 30° endoscope may allow for improved visualization in certain situations.
2) Skin incision and portal creation
The location of portal is generally created approximately 2.5 cm lateral to the pedicle margin. However, the exact incision site should be tailored to the individual patient. Preoperative computed tomography and MRI are used to design the optimal trajectory from the skin to the target lesion, and the incision is planned accordingly (Figure 5).
3) Soft-tissue management
At the midthoracic level, the rib lies at the same level as the intervertebral disc. Under fluoroscopic guidance using a C-arm image intensifier, the position of the blunt dissector is confirmed, and the paraspinal muscle is detached from the rib and facet to create an operative corridor. The remaining muscle fibers are then cleared with the aid of an endoscope, using a shaver or radiofrequency electrocautery, to expose and identify the facet (Figure 6A).
4) Facet resection and disectomy
After clearing the soft tissue, the facet joint is identified. Using a 3-mm-diameter burr, the facet is carefully drilled while confirming the joint margin under endoscopic visualization (Figure 6B). The dissection is then advanced medially along the rib toward the disc space, where the herniated disc is identified and removed (Figure 6C).
At the thoracic level, the spinal cord is particularly vulnerable during manipulation, requiring meticulous caution. However, the transforaminal approach allows access to even midline herniated discs without the need for cord retraction, enabling safe decompression up to the central portion. If the working angle is insufficient, partial drilling of the rib can be performed to widen the operative corridor and improve visualization.
4. Ethical Approval
This study was exempt from institutional review board approval because it is a single case report involving no more than 3 patients and does not contain any identifiable personal information. Informed consent was waived because this study is a retrospective case report and does not contain any images or information that could identify the patient.
DISCUSSION
Thoracic disc herniation is a very rare condition, and surgical experience with this pathology is limited due to its anatomical constraints [5]. Traditionally, open thoracotomy and costotransversectomy have been the main surgical approaches. However, these techniques are associated with extensive soft-tissue disruption, significant blood loss, and a high risk of pulmonary complications [6,7]. Although removal of calcified thoracic disc herniations using a microscope has been reported, limited visualization and restricted instrument maneuverability often make it difficult to achieve adequate decompression, particularly in cases where paracentral and foraminal lesions coexist or when the disc material is calcified [8].
Calcification is a hallmark of symptomatic thoracic disc herniation, reported in up to 70% of cases, which is significantly higher than in the lumbar or cervical spine [7]. Unlike soft herniations, calcified 'hard' discs rarely undergo spontaneous regression and often present with chronic, refractory symptoms such as the flank pain observed in our patient. Furthermore, the inelastic nature of calcified material poses a substantial surgical risk, as any minor displacement during removal can lead to irreversible spinal cord injury. The biportal endoscopic approach addressed these challenges by providing a magnified, clear view to safely fragment the calcified lesion without cord retraction.
Uniportal endoscopy also has inherent limitations in securing a sufficient endoscopic view and manipulating instruments, which may restrict its usefulness in such complex cases. In contrast, biportal endoscopic spine surgery (BESS) allows for a wider endoscopic field and more flexible instrument manipulation through 2 independent portals, facilitating meticulous decompression and effective removal of the lesion. In particular, the transforaminal approach provides access to a broad range of pathology extending from the midline to the foramen, making it advantageous in cases of combined paracentral and foraminal herniations or when the disc material is calcified. Although Kim et al. [9] reported the surgical treatment of thoracic degenerative diseases using biportal endoscopy, their cases were limited to the lower thoracic levels. The indication for a transforaminal approach includes thoracic disc herniations compressing the spinal cord or the exiting nerve root from the midline to the lateral zone, and it is particularly effective for ventrolateral or foraminal lesions. However, in cases involving hard, centrally located calcified discs or compression caused by posterior elements, this technique may be difficult to apply, and posterior decompression is often required. Therefore, preoperative imaging must be carefully evaluated to precisely identify the location and characteristics of the lesion, and the anatomical relationship between the rib and vertebral body should be considered when planning the surgical trajectory.
The anatomical proximity of the pleural cavity is a primary concern during midthoracic endoscopic procedures. In the midthoracic region, the rib head served not only as a surgical landmark but also as a protective anatomical barrier. By docking the endoscopic instruments strictly on the dorsal surface of the rib and the transverse process, we established a safe surgical corridor. Since the rib is situated superficial to the pleura (Figure 7), maintaining the surgical plane along the bony boundary of the rib effectively prevents unintended deep penetration into the thoracic cavity. This 'rib-based' approach significantly minimizes the risk of pleural injury or pneumothorax, providing a more secure environment for decompression compared to approaches that lack such clear posterior bony landmarks.
Performing endoscopic surgery in the thoracic spine requires extreme caution, as the surgical site corresponds to the spinal cord level, making it highly vulnerable to mechanical trauma and increased pressure. In general, during endoscopic procedures at the spinal cord level, the irrigation pressure should be maintained below 30 mmHg to prevent cord compression and ischemia [10]. Furthermore, since a blockage in the water outflow can lead to a rapid and dangerous increase in pressure, meticulous monitoring of the outflow patency is essential. For this reason, it is recommended to utilize gravity-based irrigation rather than a mechanical saline pump to ensure a more consistent and safer pressure environment [11].
BESS is increasingly being adopted as a versatile surgical option for a wide range of spinal pathologies. Kim et al. [9] have reported on the treatment of various adult lesions in the thoracic spine using the BESS technique. Furthermore, they have demonstrated its efficacy in performing thoracic interbody fusion and managing severely deformed cases [12,13]. In the context of revision surgery, Ko et al. [14] and Kim et al. [15] have described the clinical utility of BESS for decompression and transforaminal interbody fusion. Beyond degenerative conditions, the indications for BESS continue to expand into areas such as spinal infections and tumors, reflecting its broad clinical applicability across diverse fields [16,17].
This condition is extremely rare and the number of eligible patients is limited. Therefore, large-scale case-control studies evaluating clinical outcomes are challenging and further research is needed. Another limitation is that the outcomes are highly influenced by the surgeon’s experience and proficiency. As this is a water-based procedure, a precise understanding of thoracic anatomy is essential. If the technique is performed incorrectly, irrigation fluid may enter the pleura or lung, leading to serious pulmonary complications. In lumbar endoscopic surgery, intraperitoneal fluid collection and abdominal distension caused by extravasation of irrigation fluid have been reported [18]. Considering the thoracic proximity to the pleural cavity, such complications may be even more critical in thoracic procedures, requiring meticulous caution.
This technique offers the advantages of reducing soft-tissue damage and shortening postoperative recovery by utilizing a minimally invasive approach. Although BESS has been mainly applied to lumbar and cervical spine surgeries, the present case demonstrates an expansion of its indications to the midthoracic region, highlighting the clinical significance of this approach.
CONCLUSION
Midthoracic disc herniation is a challenging condition to access and remove using traditional surgical methods. However, with a precise understanding of the relevant anatomy and proper preoperative planning, safe and effective decompression can be achieved using a biportal endoscopic transforaminal approach, as demonstrated in this case. This technique overcomes many of the limitations of conventional approaches and may serve as a promising minimally invasive treatment option for thoracic spine pathology. Further accumulation of cases and long-term follow-up studies are required to validate its efficacy and safety.
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