Biportal endoscopic foramen magnum decompression and C1 posterior arch resection for Chiari malformation type I: Technical note

Abstract

Background:

Chiari malformation type I is commonly treated with posterior fossa decompression and C1 posterior arch resection to restore cerebrospinal fluid flow at the craniocervical junction. Although open microsurgical decompression remains the standard approach, minimally invasive techniques may reduce soft-tissue disruption and postoperative morbidity. Biportal endoscopy may provide adequate visualization and instrument maneuverability at the craniocervical junction.

Methods:

A 60-year-old female presented with a 2-year history of progressive Valsalva-induced occipital headache and bilateral upper-limb paresthesias. Magnetic resonance imaging demonstrated a 5.7 mm descent of the cerebellar tonsils without syringomyelia. The patient underwent biportal endoscopic suboccipital decompression and partial C1 posterior arch resection using a 30° endoscope, high-speed burrs, Kerrison rongeurs, radiofrequency, and continuous saline irrigation. No dural opening or duraplasty was performed.

Results:

The operative time was 135 min, with minimal blood loss and no intraoperative complications. Postoperative CT confirmed adequate osseous decompression, including a 21 × 22 mm suboccipital craniectomy and a 10 mm C1 posterior arch resection. Postoperatively, the patient improved clinically without complications and was discharged on postoperative day 2.

Conclusion:

Biportal endoscopic foramen magnum decompression with C1 posterior arch resection appears feasible in selected adult patients with Chiari malformation type I.

INTRODUCTION

Posterior fossa decompression with or without duraplasty remains the standard surgical treatment for selected symptomatic patients.[6,9,10] Biportal endoscopy provides adequate visualization and instrument maneuverability at the craniocervical junction.[3-5] Further minimally invasive, endoscopic approaches reduce soft-tissue disruption while facilitating adequate bony decompression.[1,7,8] In this technical note, a 60-year-old female successfully underwent a biportal endoscopic foramen magnum decompression with C1 posterior arch resection for a symptomatic Chiari malformation type I.

CLINICAL PRESENTATION

Two years before presentation, this now 60-year-old female developed progressive throbbing occipital headaches, characteristically exacerbated by Valsalva maneuvers, associated with bilateral upper-limb paresthesias. The craniocervical junction magnetic resonance imaging demonstrated a 5.7 mm descent of the cerebellar tonsils below the foramen magnum, without associated syringomyelia [Figure 1].

Figure 1:

Sagittal T2-weighted magnetic resonance image showing a 5.7 mm descent of the cerebellar tonsils below the foramen magnum, consistent with Chiari malformation type I.

Surgical technique

The patient underwent a minimally invasive biportal endoscopy with a 30° endoscope to perform a foramen magnum decompression and C1 posterior arch resection for a Type I Chiari malformation. Other instrumentation included 1–3 mm Kerrison rongeurs, bone curettes, 4 mm cutting and diamond burrs, and radiofrequency. Prone position with the head secured and the neck flexed approximately 20° [Figure 2], under fluoroscopic guidance, the midline was identified [Figure 3]. The bilateral portal sites were planned 2 cm inferior to the inion and 1 cm lateral to the midline [Figure 4]. The external occipital crest was used as the midline landmark for the suboccipital craniectomy [Figure 5]. The posterior tubercle of C1 was drilled using a 4 mm cutting/diamond burr and then resected with 1–3 mm Kerrison punches [Figure 6].

Figure 2:

Patient positioning in the prone position with the arms placed alongside the body, the face fully supported on the facial pad, and the neck flexed approximately 20° to facilitate posterior craniovertebral junction exposure.

Figure 3:

Intraoperative fluoroscopic image used to identify the craniovertebral midline before portal placement.

Figure 4:

Skin marking of the midline (red line), inion (blue triangle), and planned biportal entry sites (black lines), approximately 2 cm inferior to the inion and 1 cm lateral to the midline.

Figure 5:

Endoscopic identification of the external occipital crest, marked with a yellow star, used as a midline landmark to guide the suboccipital craniectomy and facilitate identification of the C1 posterior arch.

Figure 6:

Endoscopic identification of the C1 posterior tubercle, marked with a green star.

The inferior occipital edge at the foramen magnum was exposed, and bone removal was complete with a 4 mm diamond burr and 2 and 3 mm Kerrison rongeurs until the dura mater was adequately exposed [Figure 7]. An 8-Fr Nelaton catheter marked at 2.5 cm was used to confirm the decompression [Figure 8]. No dural opening or duraplasty was performed.

Figure 7:

Endoscopic view after suboccipital bone removal using an eggshell technique. The occipital dura is marked with a blue star, and the red lines outline the margins of the suboccipital craniectomy.

Figure 8:

Intraoperative measurement of the suboccipital craniectomy using an 8 Fr Nelaton catheter marked with silk at 2.5 cm, indicated by the pink star, to confirm the extent of bone decompression.

RESULTS

The operative time was 135 min. Estimated blood loss was minimal, and no intraoperative complications were observed. A postoperative computed tomography scan documented the adequate extent of bone resection/decompression (craniectomy 21 × 22 mm, and the C1 posterior arch resection measured 10 mm) [Figure 9]. Postoperatively, the occipital headache and bilateral upper-limb paresthesias improved. She exhibited no postoperative complications, and she was discharged on the 2^nd postoperative day [Figure 10].

Figure 9:

Postoperative computed tomography demonstrating the extent of osseous decompression. (A) Sagittal computed tomography (CT) image showing the craniocaudal dimension of the suboccipital craniectomy (22 mm). (B) Axial CT image showing the extent of C1 posterior arch resection (10 mm). (C) Axial CT image showing the transverse width of the suboccipital craniectomy (21 mm). (D) Three-dimensional posterior reconstruction confirming adequate suboccipital craniectomy and C1 posterior arch resection.

Figure 10:

Postoperative appearance of the two transverse skin incisions after foramen magnum decompression and C1 posterior arch resection.

DISCUSSION

Biportal endoscopic foramen magnum decompression with C1 posterior arch resection was successfully achieved in this patient with a Type I Chiari Malformation. Similar minimally invasive and endoscopic techniques for Chiari malformation have been previously described, with the advantages including reduced muscular dissection and postoperative morbidity.[1,4,5,7,8] Biportal endoscopy provides magnified visualization while allowing the use of standard instruments, including high-speed burrs and Kerrison rongeurs.[3-5] Fluoroscopy aids midline confirmation and portal planning.[2] Duraplasty may benefit selected patients but carries higher rates of cerebrospinal fluid-related complications [Table 1].[9,10]

Table 1:

Literature summary of endoscopic and minimally invasive posterior fossa decompression techniques for Chiari malformation type I.

CONCLUSION

Biportal endoscopic foramen magnum decompression with C1 posterior arch resection was feasible in this selected adult patient with Chiari malformation type I. Larger studies with longer follow-up are required to determine its safety, reproducibility, and clinical benefit. An added concern would be the learning curve involved in performing these procedures, as the potential for significant morbidity and mortality in inexperienced hands could be a significant deterrent to the promotion of this new biportal endoscopic technique.

Ethical approval:

Institutional Review Board approval is not required.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of Interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.