Technical Note: Intraoperative Injection of Indigo Carmine for Differentiating Neural Tissue During Unilateral Biportal Endoscopic Surgery
Article information
Abstract
Unilateral biportal endoscopy offers substantial advantages in spinal surgery but continues to carry a risk of neural injury due to the difficulty of distinguishing neural structures from surrounding tissues. This video article demonstrates the intraoperative use of indigo carmine to mitigate this risk. Indigo carmine selectively stains fibrous tissue and disc material while sparing nerve roots, owing to its impermeability to intact cellular membranes. This property enhances visual differentiation and promotes surgical safety. We present 2 cases involving 64-year-old female patients who underwent discectomy for ruptured L5–S1 discs. In both cases, intraoperative injection of indigo carmine into the working field or disc space effectively delineated neural elements from adhesive tissues and disc material. Postoperative imaging confirmed successful decompression. Indigo carmine represents a useful, surgeon-friendly, cost-effective, and time-efficient adjunct that improves visualization and helps prevent iatrogenic neural injury. Its use is particularly recommended for revision surgery, complex degenerative conditions, and for endoscopic spine surgeons in training.
WRITTEN TRANSCRIPT
0:04 Introduction
Endoscopic spinal surgery, including unilateral biportal endoscopy, has emerged as a pivotal technique among spinal surgeons [1,2]. This approach offers notable advantages, including muscle preservation, minimized tissue trauma, and effective treatment of spinal pathologies, primarily through enhanced surgical visualization and improved instrument manipulation. [3,4]. Nonetheless, a critical challenge persists: the risk of neural injury. This risk is largely attributable to the inherent difficulty in precisely differentiating neural structures from surrounding adhesive tissues during the procedure [5]. Consequently, a substantial literature has endeavored to address this technical challenge.
0:43 Indigo Carmine
Utilized in various medical procedures, 5,5′-indigodisulfonic acid sodium salt, typically known as indigo carmine, facilitates the selective staining of fibrous tissue and disc material, while preserving nerve roots. This selectivity is due to its characteristic impermeability into intact cellular membranes [6,7], which allows for clear visual differentiation of target tissues while safeguarding nerve roots. The efficacy of indigo carmine has gained its prominence in full endoscopic procedures and recently has further underscored its significance in improving surgical safety and efficacy in unilateral biportal endoscopy as well. This video article is a technical note with 2 cases on intraoperative injection of indigo carmine for preventing neural injury during unilateral biportal endoscopic surgery.
1:33 Case Presentation
A 64-year-old female patient presented with left ankle plantarflexion grade 1 motor weakness. The patient had a history of previous discectomy operation at left L5–S1 level.
1:44 Preoperative MRI
The preoperative MRI showed re-ruptured disc at left L5–S1 level.
1:50 Intraoperative Footage
The patient underwent left uniportal endoscopic discectomy at L5–S1 level.
1:54 Docking and Hemilaminectomy
After docking at L5 spinolaminar junction, careful hemilaminectomy was carried out.
2:00 Identifying Ligamneum Flavum
Lateral margin of remnant ligamentum flavum is identified.
2:04 Injection of Indigo Carmine
Ten milliliters of indigo carmine is injected and the endoscopic saline irrigation is clamped for ten seconds to provide time for staining. After staining, adhesive tissue and surface of dura can be distinguished by color under endoscopy. Repeated injection of indigo carmine can be performed when needed.
2:58 Discectomy
After careful dissection, ruptured disc particle is removed.
3:03 Postoperative MRI
The postoperative MRI shows removal of ruptured disc and decompressed root at the operated level.
3:09 Case Presentation
Next case is a 64-year-old female patient with right ankle dorsiflexion grade 1 motor weakness.
3:15 Preoperative MRI
The preoperative MRI showed ruptured disc at L5–S1 level compressing right L5 and S1 nerve roots.
3:23 Intraoperative Footage
The patient underwent right uniportal endoscopic discectomy at L5–S1 level.
3:42 Exposure of Right S1 Nerve Root
After hemilaminectomy of right L5 lamina, ligamentum flavum is identified and removed to expose right S1 nerve root.
3:50 Discectomy
A ruptured disc particle was removed from axillary area of right S1 nerve root.
3:58 Injection of Indigo Carmine
After exposing L5–S1 intervertebral disc, indigo carmine is injected into the disc space through ruptured annulus.
4:14 Decompression of L5 Nerve Root
The superior articular process is partially resected for right L5 nerve root decompression. After dissection around the nerve root, disc stained in indigo carmine is vividly visualized under endoscopic view.
4:47 Discussion
As demonstrated through 2 cases, indigo carmine can be injected into the disc space or onto the working field of endoscopy to help surgeons to distinguish between neural tissues and surrounding fibrotic tissues or disc particles. This can aid to prevent iatrogenic neural damage during tissue manipulation. On the other hand, hypersensitivity to indigo carmine has been reported [8,9] and its safety in intraoperative injection needs to be evaluated in larger population. Furthermore, the risk associated with injection procedures primarily stems from the potential for iatrogenic injury induced by the sharp tip of the needle. However, injection of indigo carmine utilizes a blunt-tipped needle, given that its intended purpose does not involve tissue penetration.
5:15 Conclusion
In conclusion, indigo carmine is a useful modality to prevent iatrogenic neural injury by providing enhanced visualization of different anatomic components. Its use is also surgeon-friendly, cost-effective, and time-efficient. Therefore, the intraoperative injection of indigo carmine is recommended for revision operations, cases involving severe degenerative changes, or for beginning endoscopic spinal surgeons.
Notes
Conflicts of interest
Il Choi, the corresponding author of this article, is an editorial member of J Minim Invasive Spine Surg Tech.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Informed Consent
No informed consent was obtained since the visual data including video and image contents used in this article are anonymized and retrospectively collected.