Unilateral biportal endoscopic surgery for intradural lumbar disc herniation: illustrative case

Abstract

BACKGROUND

The authors successfully removed a type B intradural lumbar disc herniation (IDH) using unilateral biportal endoscopic (UBE) technology, without CSF leakage, even though the nerve root sheath was not sutured. This emphasizes the diagnostic and therapeutic role of UBE technology in managing type B IDH.

OBSERVATIONS

An 82-year-old male patient with multilevel lumbar disc herniation underwent endoscopic discectomy and lumbar laminoplasty at the symptomatic level using UBE technology. During surgery, under endoscopic visualization, a white, mass-like protrusion was observed on the surface of the responsible nerve root, consistent with type B IDH. The nerve root sheath was incised, and the herniated nucleus pulposus was successfully removed without CSF leakage. The nerve root sheath was left open without repair.

LESSONS

Using UBE technology to treat lumbar disc herniation, if an abnormal bulge or white, mass-like protrusion is observed on the nerve root under endoscopic visualization, clinicians should highly suspect the presence of type B IDH. In such cases, the nerve root sheath can be incised along the direction of the nerve root to safely remove the herniated disc material. Notably, repair of the nerve root sheath is not required, and no CSF leakage occurred in this case.

https://thejns.org/doi/10.3171/CASE25795

Intradural lumbar disc herniation (IDH) is a rare type of disc herniation in which the nucleus pulposus protrudes into the dural sac, accounting for approximately 0.26%–0.30% of all lumbar disc herniations, with around 92% of cases occurring in the lumbar spine.¹ Mut et al. classified IDH based on cadaveric dissection into two types: type A, in which the nucleus pulposus protrudes into the dural sac; and type B, in which the nucleus pulposus penetrates into the nerve root sheath.² We report a case of type B IDH involving the L4 nerve root, successfully managed with unilateral biportal endoscopic (UBE) surgery. A detailed, step-by-step description of the endoscopic technique is provided, and the clinical outcome was excellent.

Illustrative Case

An 82-year-old male presented with a 2-month history of recurrent pain and numbness in the left lower limb, exacerbated by walking. He also reported intermittent claudication, requiring rest after walking approximately 20 m, and a 2-year history of chronic low back pain. MRI revealed subcutaneous soft tissue swelling in the lumbar region; multisegmental disc herniations at L2–3, L3–4, L4–5, and L5–S1; and lumbar spinal stenosis (Fig. 1). On physical examination, there was tenderness on percussion and palpation over the lower lumbar region. The straight leg raise test on the left lower limb was negative. Muscle strength in the left lower limb was graded 4, the left Achilles reflex was present, and no pathological reflexes were observed. All other limbs were normal. The preoperative lower limb visual analog scale (VAS) score was 5, and the lumbar Japanese Orthopaedic Association score was 15. Postoperatively, the lower limb VAS score improved to 2, with no surgical complications reported.

FIG. 1.

Preoperative sagittal T1-weighted (A), sagittal T2-weighted (B), and sagittal (C) and axial (D) STIR MR images and CT 3D sagittal reconstruction (E) at the L3–4 level. The orange arrow indicates spinal cord compression. The green arrow denotes the annular high-signal intensity of the protruding intervertebral disc on the sagittal view. The blue arrow indicates that a portion of the herniated disc lies beneath the L4 traversing nerve root and is displaced dorsally and laterally relative to the nerve root. The red circle indicates the beak sign on the preoperative T2-weighted MR image.

Surgical Technique

The patient underwent UBE discectomy and laminoplasty at the L3–4 and L4–5 levels. The surgical procedure for the L3–4 level is described below, with endoscopic visualization shown in Fig. 2. The L4–5 level was managed with a routine procedure and is not described further.

FIG. 2.

Endoscopic intraoperative sequence from removal of the herniated disc at the L3–4 level through dissection of type B IDH. The star marks the whitish nodular protrusion on the surface of the L4 nerve root. The pentagon indicates a defect in the ventral nerve root sheath, identified by probing with a micro nerve dissector. The inverted triangle highlights the ventral defect of the nerve root sheath, now fully exposed after complete removal of the nucleus pulposus that had migrated into the sheath; this defect is continuous with the disc space.

After induction of anesthesia, the patient was placed prone. Under G-arm guidance, the left L3–4 interlaminar space was localized and marked. The surgical field was disinfected with iodophor and draped in sterile fashion. Two incisions, measuring 0.5 cm and 1 cm, were made cranially and caudally along the left L3–4 interspace. A needle was inserted to confirm the left L3–4 interlaminar space, followed by sequential dilation and insertion of the endoscopic system. A portion of the left lamina and ligamentum flavum was resected to perform laminoplasty and gain access to the spinal canal. On exploration, the dural sac appeared distended. Using a dural dissector and micro nerve dissector to gently separate the left dura and nerve root, intracanal adhesions were identified. Further dissection and exploration revealed compression of the left L4 nerve root and the dural sac. A free-floating disc fragment was observed posterior to the L3–4 intervertebral space and was completely removed. After excision of the herniated nucleus pulposus and loose disc material from the disc space, reexploration of the L4 nerve root revealed localized high tension, firm consistency, and a whitish nodular protrusion beneath the nerve root sheath. A scalpel was used to carefully incise the L4 nerve root sheath longitudinally along the nerve’s axis, followed by subsheath dissection. A soft tissue mass measuring approximately 10 × 5 mm was isolated and excised and then sent for postoperative histopathological examination (Fig. 3). The decompression was then extended along the epineurium to ensure adequate neural mobilization. Hemostasis was achieved with a radiofrequency probe, and radiofrequency annuloplasty was performed. At the conclusion of the procedure, the dural sac was observed to be relaxed, and the L4 nerve root demonstrated excellent mobility and freedom of compression.

FIG. 3.

A: Intraoperative view of the material excised from within the nerve root sheath, suspected to be herniated disc tissue. B: Postoperative histopathological examination (H&E, original magnification ×100) confirmed the presence of fibrous tissue and nucleus pulposus cells.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Although preoperative imaging studies may reveal certain abnormalities suggestive of IDH, the definitive diagnosis is typically established intraoperatively.³ The diagnosis in this case was confirmed intraoperatively following the identification of an abnormal mass, with subsequent correlation of intraoperative findings and retrospective review of preoperative imaging, and final validation by postoperative histopathological analysis. Because of the low incidence of IDH, most reported cases have been published as individual case reports. Historically, open surgical approaches have been the primary treatment modality for IDH.

The surgical technique used by Ducati et al. is as follows.⁴ Through an open approach, hemilaminectomy was performed followed by dural incision. Under microscopic visualization, disc fragments were meticulously dissected and removed. The ventral dural defect was occluded with hemostatic material packing, while the dorsal dural incision was closed with continuous sutures. Kasliwal and Shimer treated a type B IDH patient under open-field visualization.⁵ Under open visualization, the type B IDH was successfully removed. Intraoperatively, no CSF leakage was observed, and the dural defect at the nerve root sleeve was left unrepaired. Kim et al. used spinal endoscopic techniques in the treatment of a patient with type A IDH.⁶ With advancements in spinal endoscopic techniques, uniportal endoscopic surgery was utilized for type A IDH. Under endoscopic visualization, a dorsal durotomy was performed through the single portal. The dural defect was reconstructed using a dural patch combined with Gelfoam packing without primary suture repair or surgical drain placement. Postoperatively, no CSF leakage was observed.

In this case, we provide the first detailed endoscopic description of the intraoperative visualization of and surgical technique for the treatment of type B IDH using UBE surgery (Fig. 2). Initially, the plan was for the patient to undergo conventional lumbar discectomy and laminoplasty. After complete removal of the herniated nucleus pulposus and decompression of the lumbar spinal canal, we performed a thorough intraoperative exploration of the dural sac. We observed marked swelling of the L4 nerve root and, notably, a whitish nodular protrusion on its surface—a finding previously unreported in the literature. To confirm the nature of this lesion, we made a longitudinal incision in the nerve root sheath using a micro knife, extended the defect along the longitudinal axis, and carefully excised the nodular mass along with a portion of the adjacent sheath. The excised tissue was sent for histopathological examination, which confirmed the presence of fibrous tissue and viable nucleus pulposus cells, consistent with intrasheath disc herniation.

Postoperatively, we reviewed the patient’s medical history, preoperative imaging findings, and surgical video. This case involved an elderly male with IDH at the L3–4 level—a demographic and spinal level consistent with the second most commonly affected segment in the literature.^7,8 Additionally, the patient had a 2-year history of chronic low back pain, and preoperative imaging revealed multilevel lumbar spinal stenosis. Intraoperatively, under endoscopic visualization, we observed severe scar adhesions within the spinal canal—a finding consistent with observations reported by several authors.^9,10 In this case, only the two symptomatic levels were addressed during surgery.

MRI is the gold standard for the preoperative diagnosis of IDH.¹¹ Characteristic imaging features include 1) iso- to hypointense signal intensity on both T1- and T2-weighted sequences; and 2) peripheral ring-like enhancement on postcontrast T1-weighted images, resulting from granulation tissue proliferation and neovascularization surrounding the herniated disc material, while the central nucleus pulposus remains nonenhancing.

Patients with IDH may exhibit characteristic MRI signs (Fig. 4) such as the “beak sign” (a beak-like protrusion penetrating the spinal dura mater and protruding into the intradural space) and the “Y-sign” (the intradural disc herniation, which had entered the intradural space, separated the spinal dura mater from the arachnoid mater, creating two limbs of a Y-shaped configuration; these limbs converged distally to form the stem of the Y). However, in this case, only the beak sign—corresponding to the tapering, pointed appearance of the herniated disc fragment compressing the dural sac—was clearly visible (Fig. 2b). The Y-sign was atypical or absent. Additionally, the presence of intraspinal gas on CT 3D reconstruction has been reported as a supportive imaging finding in the diagnosis of IDH, thought to result from the passage of air through a dural or nerve root defect during disc rupture.¹² However, in this case, no intraspinal air was detected on postoperative CT 3D imaging—a finding consistent with the variable and often transient nature of this sign. Following removal of the extruded nucleus pulposus, we meticulously explored the L4 nerve root and identified a defect on its ventral surface that communicated directly with the L3–4 intervertebral disc space. This anatomical finding strongly suggests that the herniated disc material had penetrated intradurally through a tear in the L4 nerve root, rather than via a nerve root sheath defect alone, indicating a nerve root–mediated pathway of IDH.

FIG. 4.

A: The red circle marks the disc herniation exhibiting a beak-like morphology as it enters the spinal canal. B: The faint red area demonstrates the Y-sign, characterized by its Y-shaped configuration.

In type A IDH, primary dural closure following nucleus pulposus removal is traditionally recommended to prevent postoperative CSF leakage. However, endoscopic suturing of the nerve root sheath—the true site of breach in many IDH cases—remains technically demanding due to limited visualization, narrow working space, and the fragility of neural tissues. Notably, multiple recent studies have demonstrated that, in the absence of intraoperative CSF leakage, dural repair can be safely omitted without increasing the risk of postoperative pseudomeningocele or meningitis.^6,13 In this case, meticulous intraoperative inspection revealed no active CSF egress from the nerve root sheath defect, despite its communication with the L3–4 disc space. Given the technical challenges of endoscopic microsuturing in this anatomical location and the accumulating evidence supporting nonrepair strategies, we chose to leave the sheath unsutured. At the end of the surgery, we placed a No. 12 negative-pressure drainage set into the responsible interspace. After confirming complete airtight closure by suturing, no fluid resembling CSF was observed to drain. Postoperatively, the patient remained free of CSF-related complications. The volume and color of drainage recorded on the nursing chart can reflect this point, supporting the feasibility of a conservative, nonrepair approach in selected type B IDH cases. Throughout the hospitalization period, the patient reported no symptoms of dizziness. At the last follow-up after discharge, the patient’s preoperative symptoms had resolved completely, and the patient reported no discomfort. These findings confirmed that no delayed postoperative CSF leakage occurred.

Lessons

UBE technology enables the detection and minimally invasive treatment of patients with type B IDH. Intraoperatively, when abnormal bulging of the nerve root is observed along with a white, nodular protrusion visible under endoscopic visualization, IDH should be suspected, and the preoperative MR images should be re-reviewed to confirm the diagnosis. After dissecting the nerve root sheath along its longitudinal axis and removing the herniated disc material, closure of the sheath is not mandatory.

Acknowledgments

Funding is acknowledged from Northern Jiangsu People’s Hospital (FCJS202523 to Z.Z.) and Jiangsu Provincial Commission of Health and Family Planning (Jiangsu Provincial Health and Family Planning Commission) (MS2021079 to Z.Z.).

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Zhang, Xu. Acquisition of data: Xu, Wang, Chen, Chang. Analysis and interpretation of data: Xu, Wang, Chen, Chang. Drafting the article: Zhang, Xu, Jamal, Wang. Critically revising the article: Xu, Jamal. Reviewed submitted version of manuscript: Xu, Yang. Approved the final version of the manuscript on behalf of all authors: Zhang.

Correspondence

Zhiqiang Zhang: Northern Jiangsu People’s Hospital Affiliated to Yangzhou University, Yangzhou City, Jiangsu Province, China. 18051060808@163.com.