CASE ILLUSTRATION
A 71-year-old female with a history of cholangiocarcinoma, previously treated with surgery and undergoing chemotherapy, presented with headache and neck pain. A brain magnetic resonance imaging (MRI), conducted to rule out metastasis, revealed an extradural tumor at the right C1–2 level. A cervical spine MRI with gadolinium contrast confirmed a 1.7-cm homogeneously enhancing extradural mass originating from the C2 root, slightly compressing the spinal cord without significant intradural involvement (Figure 1).
The right vertebral artery (VA) was observed arching over the VA groove of the C1 posterior arch, just above the tumor’s superior border. Although the tumor was small and symptoms were mild, surgical resection was indicated to rule out metastasis after the completion of chemotherapy. Based on these findings, a unilateral biportal endoscopic (UBE) approach was planned for tumor removal. Since preoperative MRI clearly delineated both the course and dominance of the VA, additional angiography or computed tomography (CT) angiography was not required.
BASIC SURGICAL CONCEPTS AND NUANCES
The surgical principles were mostly identical to those of conventional microscopic Schwannoma resection. After exposure of the tumor, epineurial and perineurial incisions were made over the enlarged C2 nerve root, then the encapsulated tumor in the perineurial space was exposed. Subperineurial dissection was performed circumferentially, allowing meticulous separation of the tumor from normal nerve fascicles and adjacent structures. For venous bleeding during subperineurial dissection, Cottonoid, Surgicel, and thrombin-soaked Gelfoam were used to achieve hemostasis. When the tumor was large, internal debulking was alternated with dissection to prevent blind maneuvers and avoid forced extraction before complete mobilization [1].
C1–2 extradural schwannomas typically originate from Schwann cells of the single nerve fascicle in the subperineurial layer near the C2 ganglion, extending medially and laterally. Even when the medial growth extends into the intradural space, the arachnoid membrane functions as an anatomical barrier protecting the spinal cord [2]. Since the tumor originates from the extradural space, a small to moderate intradural component can be removed by gentle pull-out from the extradural side. Kim et al. [3] demonstrated that unless the intradural portion is significant (cutoff value 14.86 mm), the tumor can be completely removed through the C1–2 interlaminar window without laminectomy or additional dural incision.
After complete dissection, the tumor was removed en bloc. Once the intradural portion was extracted, a pouch-like arachnoid membrane became visible through the expanded dural sleeve defect, revealing the spinal cord beyond. This “dural hole” represented a tumor-stretched dural sleeve rather than a surgical tear [4]. This finding confirmed that there was no residual intradural tumor component. If any residual tumor is suspected at this stage, intraoperative ultrasonography can be utilized to confirm intradural clearance [5]. The defect was closed with 5-0 nylon sutures. The C2 nerve root was preserved, and uninvolved fascicles were carefully spared [1].
SURGICAL TECHNIQUES BY UBE APPROACH
To adapt these microsurgical principles to an endoscopic setting, specific portal placement and safe docking strategies were developed. Two small skin incisions (<1 cm each) were made approximately 3 cm apart and 3 cm lateral to the midline. Docking was performed on the C2 lateral mass under fluoroscopic guidance to prevent VA injury (Figures 2, 3).
Epineurial and perineurial incisions were made using a hook-type radiofrequency (RF) wand, exposing the encapsulated tumor (Figure 4A). We performed an intraoperative frozen biopsy, which confirmed the neurogenic origin of the lesion, consistent with a Schwannoma. Circumferential dissection and hemostasis were simultaneously performed along the subperineurial plane with RF wands of various angles (mainly 90° and 45°) in low-energy mode. Continuous saline irrigation at approximately 30 mmHg provided hydrostatic tamponade, and together with the low-energy RF wand, effectively controlled venous oozing. The RF wand also enabled precise coagulation of small arterial feeders, maintaining a clear endoscopic field without the need for compressive hemostatic materials.
Because most feeding arteries arise from the medial or ventral aspect of the tumor, dissection was performed from lateral to medial, with gentle medial retraction and stepwise RF coagulation before detachment. When feeders were located close to the VA, the active surface of the RF wand was never directed ventrally, thereby preventing thermal spread.
After complete circumferential dissection and separation, the tumor was removed en bloc through the subperineurial plane (Figure 5). During this process, the small intradural component was naturally removed together through the expanded dural sleeve, as it was continuous with the extradural portion. The dural sleeve defect with a pouch-like arachnoid membrane, and the visible spinal cord beyond it, confirmed that no residual intradural tumor component remained (Figure 4B). In the UBE setting, the dural sleeve defect was sealed with TachoSil instead of direct suturing.
The C2 nerve root was preserved, with only the involved fascicular portion resected. The entire procedure was performed without laminectomy, preserving the posterior elements. No cerebrospinal fluid leakage or new neurological deficit occurred (Figure 6). The patient was discharged on postoperative day 2 with marked improvement in neck discomfort.
DISCUSSION
The present case demonstrates that the UBE approach can reproduce the same surgical principles and outcomes as conventional microscopic tumor resection at the C1–2 level. Because the fundamental microsurgical strategy remains unchanged, the surgical results are expected to be noninferior to those of the open approach, confirming its technical feasibility. Furthermore, UBE surgery offers additional advantages—it is minimally invasive, provides excellent visualization, and allows efficient control of epidural venous bleeding through continuous saline irrigation.
The most critical issue during the UBE procedure is the prevention of VA injury. Thorough preoperative evaluation of VA anatomy—including its dominance, course, and any anomalous loop—and, when necessary, angiography or CT angiography, are strongly recommended. Unlike the open microscopic approach, the endoscopic technique requires an initial docking step. Safe docking on the C2 lateral mass under fluoroscopic guidance minimizes the risk of injury to the VA, occipital artery, or even the spinal cord. During subperineurial dissection, particular caution is required near the ventral epidural space, where the VA courses closely; the active surface of the RF wand should never face ventrally to avoid thermal injury.
In tumors with a large intradural component, such as a dumbbell-shaped tumor, this method may have a risk of intradural residual tumor. Additional dural incision may be required to achieve complete removal in such cases. Since a small ultrasound probe compatible with the UBE procedure is not yet commercially available, intraoperative ultrasonography could not be utilized in this setting. The future development of miniaturized endoscopic ultrasound devices may significantly enhance intraoperative assessment and help ensure complete tumor removal.
CONCLUSION
This is the first case report of an extradural tumor at the C1–2 level successfully removed using the UBE technique. This case demonstrates that the UBE approach can safely replicate the core microsurgical principles of conventional open surgery while maintaining minimal invasiveness. We outline key principles for a successful and safe resection, including optimal portal placement, prevention of VA injury, and effective bleeding control. These findings support the potential of UBE as a feasible and safe alternative for selected high-cervical extradural tumors.
WRITTEN TRANSCRIPT
00:07 Patient Information
A 71-year-old woman with prior cholangiocarcinoma on chemotherapy presented with headache and neck pain. Screening brain MRI for metastasis showed an extradural lesion at right C1–2 level. Contrast-enhanced cervical MRI confirmed a 17-mm homogeneously enhancing extradural mass arising from the C2 root, causing mild cord compression with no significant intradural component. The right VA coursed along the C1 posterior arch groove just superior to the lesion. We planned UBE resection after completion of chemotherapy.
00:56 Portal Planning and Incision
This is how we make portal incisions and achieve successful docking. Two incisions, 3 centimeters apart, were made lateral to the midline. Docking was performed at the C2 level under fluoroscopic guidance. Because of the thin C1 posterior arch and the risk of VA injury, the C2 lateral mass and lamina were chosen as optimal docking points. After successful docking, we could further explore the tumor and the C1 posterior arch under endoscopic visualization. Here is the final appearance after docking. We use the scope retractor to enhance surgical maneuverability, and the working sheath to provide better water outflow during the operation.
01:46 Docking
After the endoscope was introduced to the docking point, the C2 lateral mass, lamina, and C1–C2 interlaminar space were exposed. The scope retractor was then moved cranially to palpate the C1 posterior arch, confirmed with the C-arm. During the entire procedure, we avoided advancing further cranially to prevent injury to the VA.
02:10 Tumor Exposure and Epineurial Incision
After exposure of the tumor, a hook-type RF wand was used to make an incision on the epineurial and perineurial layers, creating the subperineurial plane where the encapsulated Schwannoma was located. At this stage, normal nerve fascicles could be observed, and these should be preserved as much as possible. Feeding arteries must be carefully coagulated, because massive bleeding from a feeder can turn the endoscopic view into a red screen in the water-filled environment.
02:45 Subperineurial Tumor Dissection and Tumor Removal
Various types of RF wands can be used for subperineurial circumferential tumor dissection and bleeding control. We mainly used the 90° and 45° RF wands. Using pituitary forceps, the tumor was pulled, and RF dissection with bleeding control was then performed. In many cases, when the tumor was grasped with pituitary forceps, it broke apart, which facilitated internal tumor debulking and made further dissection easier. After repeated tumor dissection and internal debulking, the remaining mass could be removed in an en bloc fashion.
03:28 Bleeding Control
After the tumor had been removed, the feeders, mainly arising from the base and medial aspect, were coagulated using the RF wand. When using the RF wand at the base of the perineurium, care must be taken not to injure the VA. Bleeding control was completed with thrombin-soaked Gelfoam powder.
03:54 Final View
The final view showed that the tumor had been completely removed. The spinal cord was visible beyond the dural sleeve, confirming that there was no residual tumor in the intradural space. The dural defect was sealed with TachoSil to prevent postoperative cerebrospinal fluid leakage.
04:23 Operation Summary
By a minimally invasive endoscopic approach using 2 small incisions, the extradural Schwannoma at the C1–2 level was successfully removed. The operation time was 55 minutes, and the patient experienced only minimal surgical site pain, without any postoperative neurological deficits or complications.
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