Use of an endoscope for spinal intradural pathology - Endo

The concept of direct visualization of the spinal cord via intradural endoscopy emerged in the 1930s but wasn't widespread until recent advancements made such procedures safer and more reliable. This article delves into the clinical applications of spinal intradural endoscopy, highlighting its benefits, safety, limitations, and its categorization in literature related to cystic and inflammatory diseases, tethered cord syndrome, intradural extramedullary tumors, spinal arteriovenous malformations (AVMs), and percutaneous cordotomy for intractable pain. View Details

In this review, we summarized recent clinical reports describing how spinal intradural endoscopy has provided direct and magnified visions inside the spinal canal from small and limited exposure. More importantly, to discuss its usefulness, safety, and limitations, we categorized available literature as follows: cystic and inflammatory diseases in the subarachnoid space, tethered cord syndrome, intradural extramedullary tumors, spinal arteriovenous malformations (AVM), and percutaneous cordotomy for intractable pain (Table 1).

Application of spinal endoscopy for intradural lesions

Cystic and Inflammatory Diseases in the Subarachnoid Space

A small, flexible fiberscope can be introduced into the intradural space with minimal incision. Anatomical studies show that the sizes of the ventral and dorsal subarachnoid space are 1-3 mm and 2-6 mm, respectively, allowing endoscopes with an external diameter of less than 2 mm to navigate safely along the spinal cord. Multiple authors have demonstrated the effectiveness of spinal endoscopy for spinal arachnoid cysts. In surgical practice, following several levels of hemilaminectomy, the endoscope is inserted into the cyst cavity through a bone window and dura. Surgeons can maneuver the endoscope to penetrate or remove the cyst wall, aided by intraoperative fluoroscopy to confirm its position relative to vertebral levels. This method helps establish communication between the cyst cavity and the subarachnoid space, thereby improving neurological symptoms (Figure 1). Long-term follow-up is essential for determining recurrence rates, but endoscopic treatment remains an important surgical option.

Figure 1 A case of spinal arachnoid cyst in a 3-year-old girl treated by a 2 mm flexible endoscope. (A) Preoperative T2-weighted MR image revealing an intradural arachnoid cyst extending from the C-7 to the L-3 vertebral level; (B) intraoperative pictures showing how we inserted an endoscope through a 2-levels hemilaminectomy; (C) an endoscopic view showing the caudal cyst wall (single asterisk) and the cauda equina (double asterisk). Figures were obtained and modified with permission (

A case of spinal arachnoid cyst in a 3-year-old girl treated by a 2 mm flexible endoscope. (A) Preoperative T2-weighted MR image revealing an intradural arachnoid cyst extending from the C-7 to the L-3 vertebral level; (B) intraoperative pictures showing how we inserted an endoscope through a 2-levels hemilaminectomy; (C) an endoscopic view showing the caudal cyst wall (single asterisk) and the cauda equina (double asterisk). Figures were obtained and modified with permission ( 9 ).

The same endoscopic approach can be used for subarachnoid inflammatory diseases where observation or biopsy is needed. Endoscopes provide extensive views along the spinal cord's dorsal and ventral surfaces. For example, a spinal endoscopic biopsy confirmed a diagnosis of neurosarcoidosis by evaluating a nodular lesion in the lumbar cord. One notable case involved endoscopic treatment of neurocysticercosis caused by the tapeworm Taenia solium. The extensive use of a flexible spinal endoscope facilitated the removal of parasites and cysticerci, clearing thickened arachnoid membranes and restoring cerebrospinal fluid (CSF) flow under direct endoscopic vision. Less invasive endoscopic spinal procedures have also successfully treated anteriorly located sacral meningocele and superficial siderosis.

These examples underscore the wide range of intraspinal subarachnoid conditions, including arachnoid cysts and arachnoiditis, that can be treated with spinal endoscopy. For extensive and multi-level subarachnoid pathologies, open surgery typically requires large incisions. A flexible endoscope, which can be advanced through a small opening, offers a less invasive alternative.

Tethered Cord Syndrome

Endoscopy has shown diagnostic and therapeutic potential for tethered cord syndrome. In the lower lumbar vertebrae, the endoscope can advance through the cauda equina to visualize the filum terminale, as the lumbar region has a relatively wider space compared to the thoracic or cervical regions. Yörükoglu and colleagues introduced a percutaneous fully endoscopic interlaminar approach to the filum terminale during cadaveric studies. Clinical applications confirmed the utility of endoscopic observation in visualizing the filum terminale in patients with tethered cord syndrome. A laminectomy and a 2-mm dural incision were sufficient for inserting the flexible endoscope, allowing surgeons to identify posterior displacement of the filum terminale, a diagnostic marker for tethered cord syndrome.

Endoscopic untethering techniques for tethered cord syndrome have been described by various authors. With the interlaminar approach and a 1-cm durotomy, a rigid endoscope can open the dura, coagulate and cut the filum terminale, and close the dura with continuous sutures. Despite the limited number of cases, percutaneous endoscopic interlaminar untethering could become a viable option soon.

Intradural Extramedullary Tumor

Barami et al. were among the first to use an endoscope in assisting the removal of ventrally located intradural extramedullary tumors. Spinal endoscopy offers clear views of the ventral spinal cord without the need for retraction, which is challenging with a microscope. Parihar and colleagues demonstrated that endoscopic surgery is feasible for spinal tumors at any vertebral level, successfully removing 18 tumors with specific sagittal and axial diameter limitations. Zhu et al. confirmed the feasibility of an interlaminar approach for endoscopic tumor removal, safely dissecting vital structures such as arteries and spinal nerve roots using a bipolar flexible radiofrequency probe. The interlaminar approach minimizes bone destruction, resulting in less postoperative pain, minimal blood loss, and a shorter recovery period for patients. Successful outcomes depend on individualized surgical planning and achieving satisfactory dural closure. Ensuring watertight CSF leak closure can expand the application of spinal endoscopy in similar surgeries.

Spinal AVM

Endo et al. presented cases where an angled endoscope was valuable for direct surgery on spinal AVMs. For example, perimedullary AV fistulas in the cervical region are often on the ventral spinal cord surface, making them difficult to see through a posterolateral approach. Using an endoscope combined with posterolateral exposure, sufficient views of the ventral spinal cord can be obtained without extensive rotation. Hemilaminectomy and a paramedian 2cm dural incision create enough space for inserting a rigid angled endoscope, offering comprehensive circumferential views of the spinal cord. When supplemented with indocyanine green (ICG) fluorescence endoscopy, the technique benefits from enhanced visual detail of vascular anatomy and blood flow, aiding the precise management of spinal cord vascular lesions (Figure 2).

Figure 2 A case of craniocervical junction epidural arteriovenous fistula with a ruptured anterior spinal artery aneurysm. The anterior spinal artery aneurysm was successfully clipped by posterior approach with assisted use of rigid angled indocyanine green endoscopy. (A) Anteroposterior view of the selective right vertebral artery angiogram showing a ruptured aneurysm of the ASA (arrow). (B) Endoscopic view. The aneurysm located next to the ASA was clipped using a Yaşargil titanium clip. (C) Endoscopic image from indocyanine green video-angiography demonstrating obliteration of the aneurysm and preservation of the ASA (arrows). (D) Three-dimensional reconstructed image from a rotational angiogram of the right vertebral artery, confirming complete obliteration of the aneurysm and preservation of the ASA. Figures were obtained and modified with permission (

A case of craniocervical junction epidural arteriovenous fistula with a ruptured anterior spinal artery aneurysm. The anterior spinal artery aneurysm was successfully clipped by posterior approach with assisted use of rigid angled indocyanine green endoscopy. (A) Anteroposterior view of the selective right vertebral artery angiogram showing a ruptured aneurysm of the ASA (arrow). (B) Endoscopic view. The aneurysm located next to the ASA was clipped using a Yaşargil titanium clip. (C) Endoscopic image from indocyanine green video-angiography demonstrating obliteration of the aneurysm and preservation of the ASA (arrows). (D) Three-dimensional reconstructed image from a rotational angiogram of the right vertebral artery, confirming complete obliteration of the aneurysm and preservation of the ASA. Figures were obtained and modified with permission ( 24 ).

Intractable Pains

Developments in technology have produced smaller-diameter spinal endoscopes, facilitating percutaneous endoscopic procedures. For example, Tanaka et al. employed a percutaneous endoscope to perforate a spinal arachnoid cyst and restore CSF flow. The tiny size of the endoscope, comparable to that of a needle, enables percutaneous puncture and offers magnified views of the spinal cord surface. Fonoff and colleagues advanced percutaneous endoscopic procedures for managing intractable pain. Utilizing dual percutaneous channels, the endoscope provides clear views of the spinal cord's pial surface and the tip of a radiofrequency cordotomy probe. Real-time visualization facilitates accurate electrode targeting, reducing the likelihood of injury to spinal cord vessels or nerve roots. Consequently, these procedures effectively control pain without causing CSF leaks. A recent review suggests that cordotomy could be an option for managing cancer pain, with endoscopic procedures likely to increase in response to the growing number of patients requiring minimal invasive treatments.

Limitations

This review underscores the significant benefits of intradural spinal endoscopy, emphasizing that both flexible and rigid-angled endoscopes offer unique views unattainable with microscopes. However, the limitations of endoscopic instruments, particularly regarding manipulation, still exist. Achievements in endoscopic procedures have mostly been confined to basic maneuvers, as highlighted in various studies. The potential for bleeding and the challenges in achieving hemostasis during endoscopic procedures are noteworthy. Surgeons should be prepared to transition to microsurgical techniques if needed, serving as a backup in spinal intradural endoscopic surgeries.

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Another important issue is how to avoid postoperative CSF leak. In endoscopic lumbar spinal surgery, the dural tear rate is reported to be as high as 8.6%. While there is no gold standard for managing dural tears or closures in endoscopic spine surgery, direct dural suturing techniques from endonasal surgery and minimally invasive spine surgery could prove beneficial. If surgeons become more adept at achieving watertight dural closures under endoscopy, it could significantly expand the application of endoscopic spine surgeries for both intradural and extradural pathologies.

Conclusions

The existing literature confirms the increased utilization of spinal endoscopy for various intradural pathologies. An endoscope can provide direct views of the spinal cord through small incisions. Maneuvering a fiberscope along the spinal cord allows the approach and surgical management of longitudinal lesions across multiple vertebral levels. Additionally, an endoscope provides magnified views from different angles compared to a microscope. Rigid angled endoscopes enable the management of ventral spinal cord tumors or vascular lesions using a posterolateral approach. Technical advancements have paved the way for percutaneous procedures in select clinical indications. With ongoing technical progress and accumulating experience, intradural endoscopy is poised for broader applications in treating spinal conditions.

Acknowledgments

The authors thank Enago (www.enago.jp) for the English language review.

Funding: None.

Provenance and Peer Review: This article was commissioned by the Guest Editors (Hisashi Koga and Alf Giese) for the series “Full-endoscopic Spine Surgery” published in Journal of Spine Surgery. The article was sent for external peer review organized by the Guest Editors and the editorial office.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/jss.2020.01.06). The series “Full-endoscopic Spine Surgery” was commissioned by the editorial office without funding or sponsorship. The authors declare no other conflicts of interest.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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