High-cervical Perimedullary Arteriovenous Fistula at C2: Staged Posterior Flow Control Followed by Transoral Direct Obliteration with Long-term Independence

Yuji UEDA; Katsumi HARADA; Naoko FUJIMURA; Yasuaki IMAJO; Manabu YAMAMOTO; Kunihiko HARADA

doi:10.2176/jns-nmc.2025-0406

Abstract

Perimedullary arteriovenous fistulas at the craniocervical junction are rare, frequently present with subarachnoid hemorrhage, and require accurate identification of the shunt point―particularly in lesions involving the anterior spinal artery―to achieve durable cure. A 64-year-old man presented with dense posterior fossa subarachnoid hemorrhage caused by a high-flow craniocervical junction arteriovenous shunt supplied predominantly by a markedly enlarged right C2 radiculomedullary artery. Selective catheterization was unsuccessful. On day 1, suboccipital craniectomy with C1 laminectomy enabled posterior flow control by clipping the dominant feeder; however, the ventral shunt point could not be safely visualized. Postoperative angiography demonstrated persistent shunting with prominent anterior spinal artery contribution. One month later, definitive transoral anterior obliteration was performed in a hybrid operating room. Intraoperative digital subtraction angiography and intra-arterial indocyanine green angiography demonstrated caudal-to-rostral flow reversal from the anterior spinal artery into the ascending anterior spinal vein at the shunt point, located within the anterior median fissure on the ventral pial surface. The shunt was directly obliterated by simultaneous clipping of the anterior spinal artery branch and draining vein, with additional coagulation of minor feeders. Halo immobilization followed by delayed posterior C1-2 fixation was performed. Final angiography and serial magnetic resonance angiography confirmed complete cure, and the patient returned to work 10 months postoperatively, maintaining functional independence for more than 5 years. This case illustrates that, in carefully selected anterior spinal artery-involved high-flow craniocervical junction perimedullary arteriovenous fistulas, a staged strategy combining posterior flow control and definitive anterior direct obliteration can provide a safe and durable solution.

Introduction

Perimedullary arteriovenous fistulas (pAVFs) at the craniocervical junction (CCJ) are rare but challenging lesions due to their pial location, high-flow hemodynamics, and frequent involvement of the anterior spinal artery (ASA). Endovascular cure is often limited by complex angioarchitecture and the risk of spinal cord ischemia, whereas microsurgery remains the most definitive strategy for ASA-involved lesions. Ventral approaches such as transoral or endoscopic odontoid routes can provide direct access to the anterior CCJ but require meticulous planning and stabilization strategies. We report a staged treatment strategy in which acute posterior flow control reduced rerupture risk and provided a reliable landmark for precise transoral direct obliteration in a hybrid operating room, resulting in long-term functional independence.

Case Description

A 64-year-old man developed a thunderclap headache after several days of prodromal pain and then became comatose with respiratory arrest during transport. Computed Tomography showed dense subarachnoid hemorrhage (SAH), predominantly in the posterior fossa (Figure 1a). Computed Tomography Angiography demonstrated a dilated vessel ascending from the ventral cervical cord (Figure 1b). Digital Subtraction Angiography (DSA) revealed a high-flow arteriovenous fistula supplied by a markedly developed right C2 radiculomedullary artery (RMA) with a ventral medullary varix; selective catheterization was unsuccessful (Figures 1c and 1d).

Figure 1

Preoperative imaging.

(a) Non-contrast CT showing dense subarachnoid hemorrhage predominantly in the posterior fossa.

(b) 3-dimensional CTA demonstrating a markedly enlarged right C2 RMA (small arrows) and an abnormally dilated anterior medullary vein (arrows) forming a ventral medullary varix (arrowhead).

(c) Right vertebral angiography demonstrates a markedly enlarged right C2 RMA (small arrows) and the ASA (black arrowheads) supplying a focal arteriovenous shunt point (star), with early venous drainage into an ascending perimedullary vein extending toward the posterior fossa (large arrows).

(d) An oblique view of the right vertebral angiography further confirms that the right C2 RMA (arrows) is the dominant arterial feeder to the shunt. Selective catheterization of the feeder was unsuccessful.

ASA: anterior spinal artery; CT: computed tomography; CTA: computed tomography angiography; RMA: radiculomedullary artery

First stage (posterior flow control). On day 1, suboccipital craniectomy and C1 laminectomy were performed (Figure 2a). After evacuating the subarachnoid clot and sectioning the dentate ligament to increase cord mobility, the ventral shunt point was not safely visible from the posterior. The dominant right C2 RMA was therefore clipped to achieve posterior flow control (Figure 2b-d). This maneuver was intentionally planned as temporary hemodynamic stabilization rather than definitive treatment. The patient recovered consciousness without rebleeding or delayed ischemia. Early postoperative angiography showed a persistent shunt with conspicuous ASA contribution (Figure 3a, b).

Figure 2

First operation (posterior approach).

(a) Intraoperative view after suboccipital craniectomy and C1 laminectomy.

(b, c) Intraoperative ICG video angiography demonstrating rapid arterialized flow through the dominant right C2 radiculomedullary artery (arrowhead).

(d) The dominant feeder was clipped to achieve posterior flow control; however, the ventral shunt point on the pial surface could not be safely visualized from the posterior approach.

ICG: indocyanine green

Figure 3

Second operation (transoral approach).

(a) Postoperative CTA obtained after the first-stage posterior surgery showing disappearance of the ventral medullary varix, despite persistence of the arteriovenous shunt.

(b) Follow-up digital subtraction angiography demonstrating residual arteriovenous shunting (circle) supplied by the ASA (arrowheads), with early venous drainage into an ascending perimedullary vein (arrows).

(c) Transoral exposure after placement of the Davis-Crowe retractor. The anterior arch of C1, the odontoid process, and the superior aspect of the C2 vertebral body were removed. The prior posterior clip (small arrow) served as a reliable anatomical landmark for orientation.

(d1-d3, e1-e3, f1-f2) Intraoperative DSA and intra-arterial indocyanine green angiography demonstrating caudal-to-rostral flow reversal from the ASA (arrowheads) into the ascending draining vein (arrows) at the shunt point (star), located at the anterior median fissure (black arrow). Because these images are presented in the surgical view with inversion, the caudal side is shown at the top and the cranial side at the bottom. A 3-mm Sugita AVM clip was applied to occlude both the ASA branch and the draining vein at the shunt point. Serial intraoperative DSA revealed residual shunting, prompting additional clip application, after which complete obliteration was confirmed by digital subtraction angiography and intra-arterial indocyanine green angiography.

(g) Dural closure using a polyglycolic acid sheet and fibrin glue. All images are presented in the surgical view, with the caudal side at the top and the cranial side at the bottom.

ASA: anterior spinal artery; CTA: computed tomography angiography; DSA: digital subtraction angiography

Second stage (transoral direct obliteration). At 1 month, a transoral C1 anterior arch resection and odontoidectomy were undertaken in a hybrid operating room. With intraoperative DSA, intra-arterial indocyanine green (IA-ICG) video angiography, and continuous motor evoked potentials (MEP) and somatosensory evoked potentials (SEP) monitoring, a minimal dural opening exposed the anterior median fissure. The prior posterior clip served as a reliable landmark (Figure 3c). The reversal point, where descending ASA flow converted to the ascending draining vein, was identified by DSA/IA-ICG (Figure 3d-f) and obliterated using Sugita AVM clips (aneurysm/AVM clip system; Mizuho Co., Ltd.); minor feeders were coagulated. On-table DSA and IA-ICG confirmed complete shunt elimination with stable neuromonitoring (Figure 3d-f). The dura was closed using a polyglycolic acid sheet and fibrin glue (Figure 3g).

Stabilization and outcome. A halo vest was applied postoperatively. Given limited C1 arch preservation and prior C1 laminectomy, delayed posterior C1-2 fixation (Magerl technique) was performed at 3 months (Figure 4a, b). Follow-up angiography and serial magnetic resonance angiography demonstrated complete cure (Figure 4c, d). The patient returned to work 10 months postoperatively and remains functionally independent more than 5 years after surgery (modified Rankin Scale score, 1).

Figure 4

Stabilization and follow-up.

(a, b) Postoperative radiographs showing bilateral C1-2 transarticular screw fixation.

(d) Follow-up MRA demonstrating no recurrence.

MRA: magnetic resonance angiography

Discussion

Craniocervical junction pAVFs are rare but often present with SAH, necessitating timely and definitive shunt obliteration to prevent rerupture and progressive myelopathy.¹^-³⁾ Because the shunt resides on the pial surface and frequently receives robust collateral supply, durable cure hinges on accurate shunt-point identification and pial-level disconnection rather than proximal occlusion alone.²^,⁴⁾

Lesion classification and shunt location

The present lesion's angioarchitecture warrants careful consideration. The dominant arterial supply arose from a markedly enlarged C2 RMA, with secondary contribution from the ASA―features that may overlap with radiculopial AVFs with perimedullary venous drainage.²^,⁴⁾ However, intraoperative findings and angiographic assessment demonstrated that the shunt point resided within the anterior median fissure on the ventral pial surface, directly connecting the ASA to the ascending anterior spinal vein without an intervening nidus. We therefore consider this lesion to lie within the spectrum of perimedullary AVFs with radicular contribution, acknowledging the anatomical and conceptual overlap between these entities; in this context, direct intraoperative confirmation of a pial shunt is the most reliable basis for classification.²^,⁴⁾

Rationale for staged management

Our strategy deliberately staged treatment. The first operation―posterior flow control by clipping the dominant C2 RMA―was intended for temporary hemodynamic stabilization, reducing immediate stress and rerupture risk, while creating a reliable landmark for the second-stage anterior approach. After inflammation subsided and the patient stabilized, the second operation directly targeted the shunt at the anterior median fissure. This sequence enabled safe identification of the reversal point where descending ASA flow converted to the ascending drainer and allowed precise clip application at the pial shunt point, which is particularly advantageous in high-flow ventral lesions not safely accessible from a posterior approach.²^,⁴⁾

Endovascular considerations

Endovascular treatment was considered but proved unsuitable in this case. Selective catheterization of the dominant feeder failed, and the close involvement of the ASA rendered embolization unsafe because of the risk of anterior spinal cord ischemia. In ASA-involved, high-flow lesions, endovascular cure can be unreliable, and microsurgery remains the most definitive option for durable disconnection at the shunt point.⁵^,⁶⁾

Role of the hybrid operating room and definition of ASA flow reversal

A hybrid operating room was central to procedural safety. Intraoperative DSA combined with IA-ICG angiography provided real-time visualization of arterial inflow and venous egress, permitted on-table confirmation of complete obliteration, and facilitated immediate correction when residual shunting was detected―all while continuous neuromonitoring verified functional integrity.⁷^,⁸⁾ ASA flow reversal was defined by caudal-to-rostral transit from the ASA into the ascending perimedullary vein at the shunt point on DSA/IA-ICG, with disappearance after clip application.

Approach selection

Approach selection was guided by precise anatomy. Alternative ventral routes, such as the high cervical lateral approach, may be considered for ventrolateral targets. In the present case, the shunt was located within the anterior median fissure without lateral offset, requiring a direct midline corridor for controlled pial-level clip placement. Therefore, the transoral approach provided the most direct access under angiographic guidance. The nasopalatine line can serve as a practical framework to determine the feasibility of endonasal versus transoral corridors depending on the rostral-caudal extent of the lesion.⁹^,¹⁰⁾

Stabilization strategy

Preservation of the C1 anterior arch is desirable to reduce postoperative instability.¹¹^-¹³⁾ In this case, adequate exposure required resection of the C1 arch, and prior C1 laminectomy had already disrupted ring continuity, increasing the risk of instability. Halo immobilization was selected as temporary stabilization during the interval between staged procedures. Definitive posterior C1-2 fixation was intentionally delayed until completion of transoral shunt obliteration to minimize infection risk associated with oral surgery and to allow reassessment of stability after definitive vascular cure. Delayed posterior fixation using the Magerl technique provided durable stabilization; alternative constructs (e.g., Goel-Harms) may be preferable depending on bone quality, extent of resection, and surgeon experience.¹⁴^,¹⁵⁾

Limitations and generalizability

This report describes a single case, and conclusions must be interpreted accordingly. Nonetheless, the >5-year recurrence-free course with on-table angiographic confirmation suggests that, in carefully selected patients with ASA-involved high-flow CCJ arteriovenous shunts, staged posterior flow control followed by image-guided anterior pial-level obliteration in a hybrid operating room may provide a safe and durable solution. Treatment should be individualized based on angioarchitecture, shunt location, and institutional expertise.¹^,²^,⁸^,¹⁶⁾

Conclusion

In ASA-involved, high-flow CCJ arteriovenous shunts, a staged strategy of posterior flow control followed by definitive transoral direct obliteration in a hybrid operating room can achieve a safe and durable cure. Accurate intraoperative identification of a pial shunt within the anterior median fissure is critical for successful treatment and appropriate lesion classification.

Conflict of Interest Disclosure

The authors declare no conflict of interest.

Ethics and Consent

Written informed consent was obtained from the patient for publication of this case report and images. This study adhered to the Declaration of Helsinki. According to Tokuyama Central Hospital policy, institutional review board approval was not required for a single-patient case report.

References

Corresponding author

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