Biportal Endoscopic Foramen Magnum Decompression in an Arnold-Chiari Malformation: A Technical Note With a Case Report

Chan Yang Noh; Il Choi; Junsoo Jang

doi:10.21182/jmisst.2025.02621

Abstract

Chiari malformation, when accompanied by progressive neurological symptoms or syringomyelia, often necessitates surgical decompression. Although endoscopic spinal surgery continues to advance, its application in foramen magnum decompression remains limited. This video article demonstrates the biportal endoscopic foramen magnum decompression technique for Chiari type I malformation. We present the case of a 19-year-old female patient with progressive headache, motor weakness, and radiological evidence of 7-mm tonsillar descent with C2–7 syringomyelia. She successfully underwent biportal endoscopic foramen magnum decompression with C1 laminectomy. The procedure employed a triportal approach with safe docking on the C2 spinous process, allowing a minimally invasive C1 laminectomy and foramen magnum decompression extended to the suboccipital area. Postoperatively, computed tomography confirmed adequate decompression, and magnetic resonance imaging revealed expansion of the posterior fossa with resolution of tonsillar herniation. The patient experienced no complications or symptom recurrence at the 3-month follow-up. Despite a minor intraoperative–postoperative measurement discrepancy, which highlights the anatomical considerations required to achieve sufficient decompression, this video supports the feasibility of biportal endoscopic surgery. This approach may provide comparable clinical outcomes to conventional open surgery while offering minimally invasive advantages, though long-term follow-up remains essential.

Key Words: Arnold Chiari malformation, Foramen magnum, Laminectomy, Minimally invasive surgery

WRITTEN TRANSCRIPT

0:02 Introduction: Arnold-Chiari Malformation

Chiari malformation is a type of deformity of posterior cranial fossa and hindbrain characterized by abnormalities ranging from cerebellar tonsillar herniation through the foramen magnum to the absence of the cerebellum. Symptoms may include, but not limited to muscle weakness, neurogenic dysphagia, and apnea [1]. When accompanied with deteriorating symptoms or syringomyelia, this condition sometimes needs surgical decompression of posterior cranial fossa along with posterior laminectomy of atlas [2].

0:34 Introduction: Endoscopic Spine Surgery

As techniques of endoscopic spine surgery evolve, its efficacy in various spinal diseases is under debate [3,4]. There have been a few studies reporting endoscope-assisted foramen magnum decompression [5]. This video article aims to shed light on approach and procedural steps of biportal endoscopic foramen magnum decompression in Arnold-Chiari Malformation.

0:55 Case Presentation

A 19-year-old female patient presented with progressive headache and repeated intermittent motor weakness of extremities since adolescence.

1:02 Preoperative Imaging

The preoperative computed tomography (CT) showed assimilation of C1 posterior arch. The preoperative magnetic resonance imaging (MRI) showed 5.5 mm of cerebellar tonsillar descent through the foramen magnum with a syrinx in spinal cord at C2 and C5 through C7 level. No Atlantoaxial instability was observed on plain radiograph.

1:23 Intraoperative Footage

Diagnosed with Chiari type 1 malformation with syrinx, the patient underwent biportal endoscopic foramen magnum decompression with C1 laminectomy.

1:33 Skin Incision and Docking Point

As shown in the figure, 2 transverse skin incisions are made at C1 and C2 level. These 2 ports highlighted in green are used for C1 laminectomy. Through port 1 and 2, the initial docking point was spinous process of C2. Then C1 lamina was confirmed under intraoperative C-arm guidance.

1:58 Laminectomy of C1 Posterior Arch

The assimilation of C1 posterior arch detected in the preoperative CT was located and recognized as an anatomical landmark. A high-speed drill with diamond burr was used to perform decompressive laminectomy of C1.

2:50 Pulsation of Dura

After sufficient decompression of C1 lamina, mild pulsation of dura was observed.

3:06 The Triport Approach

Next, another skin incision, depicted as port number 3 in the figure, was made to be used as a working port. Using port number 1 and 3, highlighted in purple in the figure, foramen magnum decompression was performed.

3:20 Foramen Magnum Decompression

The foramen magnum was identified and further soft tissue dissection of targeted area was performed. Foramen magnum decompression was performed using high-speed drill and Kerrison punch.

4:20 A Measuring Technique

Decompression was extended to suboccipital area. To ensure sufficient decompression of the foramen magnum, a 2-cm-long silastic drain catheter was used as a measuring tool.

5:02 The Postoperative Imaging

The immediate postoperative CT scan shows post-laminectomy state of C1 posterior arch and 2 cm by 1.7-cm-sized craniotomy including foramen magnum. The immediate postoperative MRI shows expanded posterior cranial fossa and relieved cerebellar tonsillar herniation. No evidence of immediate regression in syrinx was observed.

5:28 Prognosis

The patient was discharged to home after 7 postoperative days. On 12 postoperative days after stitch-off, clinical photo shows no wound-related complications. No symptomatic recurrence was observed until the latest follow-up which was 3 months postoperatively.

5:46 Discussion

From a technical point of view, docking at C2 spinous process may help surgeons to navigate based on midline while also providing safe docking point preventing iatrogenic injury. Furthermore, triport approach with one communal port for endoscope is the key technique enabling surgeons to perform C1 laminectomy along with decompression of the foramen magnum while maintaining minimally invasive characteristic.

It is noteworthy that preoperatively targeted size of decompression of the foramen magnum was 2 cm by 2 cm and intraoperative measurement fulfilled the dimension. Nevertheless, postoperative CT scan revealed 1.7-cm-sized craniotomy. This discrepancy may originate from the fact that the surface of foramen magnum is curved while radiographic measurement is linear. Nevertheless, insufficient decompression of the foramen magnum can lead to inadequate expansion of the posterior cranial fossa, potentially causing recurrent clinical symptoms and delayed regression of syringomyelia. Therefore, surgeons must account for the margin of measurement error when performing endoscopic foramen magnum decompression. Consequently, the patient in this case report will undergo close long-term follow-up.

In some cases of Chiari malformation, dural management including expansile duroplasty and manipulation of arachnoid membrane is necessary. While expansile duroplasty and arachnoid membrane manipulation typically present technical challenges or limitations in endoscopic approaches, advancements in endoscopic spine surgery techniques and instrumentation are progressively mitigating these constraints [6,7].

Furthermore, bleeding is one of the major obstacles to overcome in endoscopic spine surgery. In endoscopic foramen magnum decompression, subtle venous bleeding after occipital decompression was automatically controlled by the pressure of saline irrigation system. In case of heavier bleeding from emissary veins, temporary manipulation of irrigation pressure and wax-based hemostatic agents can be employed to mechanically block the bleeding. As for more severe bleeding from occipital sinus, oxidized cellulose and thrombin coated collagen material can be employed in combination for hemostatic effect. Despite various hemostatic tools and materials there is always potential for conversion to conventional open surgery, and this should be well-informed in written consent prior to endoscopic surgery.

6:35 Conclusion

This video article suggests the viability of biportal endoscopic surgery in foramen magnum decompression and C1 laminectomy. Though requiring more follow-up data for efficacy, this technique could yield clinical outcomes similar to conventional open foramen magnum decompression, while providing the benefits of a minimally invasive approach. Lastly, due to its limitations, careful selection of patients and strict indication are necessary.