Abstract
BACKGROUND
Compared to dural arteriovenous fistulas (AVFs), the pathogenesis of extradural AVFs is unclear. Furthermore, the outcomes of surgical and endovascular treatments are inferior to those of dural AVFs, and in some cases, there are reports of poor outcomes.
OBSERVATIONS
A 74-year-old male hemodialysis patient presented with gradually progressive gait disturbance. MRI showed high T2 signal intensity in the lower spinal cord, and angiography revealed a dural AVF. The patient was referred to the authors’ hospital. Multiple small arteries were found to have refluxing veins in the dura at T12–L1 on the right side, and a diagnosis of epidural AVF was made, leading to direct surgery. During exoscopic microsurgery, the venous pouch located on the lateral ventral side was exposed, and intradural and extradural hemodynamics were confirmed using indocyanine green (ICG) videoangiograhy, followed by complete coagulated occlusion. Postoperatively, the patient’s symptoms improved.
LESSONS
There have been few cases of epidural AVF treated with exoscopic ICG videoangiography for intradural and extradural observation and healing.
Keywords: spinal epidural arteriovenous fistula, venous congestive myelopathy, venous pouch, exoscopic microsurgery, indocyanine green videoangiography
Abbreviations: AV = arteriovenous, AVF = AV fistula, ICG = indocyanine green, IVF = intervertebral foramen, MIP = maximum intensity projection, RMA = radiculomedullary artery, RMV = radiculomedullary vein
Differential diagnosis between dural arteriovenous fistula (AVF) and epidural AVF presenting with congestive spinal cord disorders can be difficult.1,2 The former occurs most frequently in the thoracic spine, while the latter occurs most frequently at the lumbar spine and are commonly seen after surgery or trauma.2 The difference between the two is that epidural AVFs have extradural feeders and multiple intradural drainers, making endovascular treatment less effective.2 A multicenter study in Japan showed that direct surgery for epidural AVFs had better outcomes than endovascular treatment.3
We report a case of thoracolumbar epidural AVF and discuss its microvascular pathology based on preoperative angiography, intraoperative intradural and extradural indocyanine green (ICG) videoangiography, and a direct surgical approach, especially its differences from dural AVF.
Illustrative Case
A 74-year-old man undergoing hemodialysis was referred to our hospital because of gradually progressing gait disturbance. During treatment for a humerus fracture caused by a fall, spinal cord MRI revealed high signal intensity in the thoracic spinal cord (L1–T7 levels) and a low flow void due to the patient’s tendency to fall (Fig. 1A). Axial imaging of the T12–L1 plane revealed a T2 hypointense venous pouch area in the right ventrolateral epidural space (Fig. 1B). Selective spinal angiography was performed and revealed an arteriovenous (AV) shunt from the right T12–L1 lumbar artery (Fig. 1C). Slab maximum intensity projection (MIP) imaging revealed a retrograde radiculomedullary vein (RMV) ascending within the dura mater after forming a vascular network from the radiculomedullary artery (RMA) around the L1 nerve root (Fig. 1D). Axial MIP images showed a venous pouch in the right T12–L1 intervertebral foramen (IVF) (Fig. 1E), and coronal MIP images revealed a venous pouch in the right extradural space. Intradural reflux veins were also confirmed (Fig. 1F). Sagittal MIP images revealed many feeding arteries in the right IVF (Fig. 1G). In this case, we chose open surgery rather than endovascular surgery because there were multiple thin feeders in this patient and we needed to make a definitive diagnosis of whether the AVF was dural or epidural in nature.
FIG. 1.
A:Sagittal MR image showing intramedullary fractures and flow voids at the L1–T7 levels. B:Axial MR image (T12–L1) showing a T2 low signal area in the ventral epidural space on the right side (asterisk). C: Selective lumbar angiogram of the right T12–L1 revealing an AV shunt (asterisk). D: MIP image clearly showing an AV shunt, with multiple feeders (asterisk) and two drainers (double asterisks). E:Axial MIP image showing a venous pouch (asterisk) in the right T12–L1 IVF. F: Coronal MIP image showing a venous pouch (asterisk) in the right T12–L1 IVF and an RMV (double asterisks) flowing back from the dural sheath into the dura mater. Yellow arrows incidate a shunt point. G:Multiple feeding arteries were found in the right IVF (IV For). DS = dorsal somatic branch; PL = prelaminar artery.
Under general anesthesia, a right hemilaminectomy amd partial medial facetectomy were performed at the right T12–L1 with the patient in the prone position, followed by a medial partial facetectomy at T12–L1 using an exoscope (ORBEYE, Olympus). A venous pouch was observed around the right L1 nerve root (Fig. 2A), which was also confirmed by ICG videoangiography (Fig. 2B). When examining the dura, an arterialized RMV and its branches were confirmed (Fig. 2C), and reverse flow was also observed on ICG videoangiography (Fig. 2D). This draining vein was clipped (Fig. 2E), and after confirming that there was no change in electrophysiological monitoring, it was coagulated and severed (Fig. 2F). After suturing the dura mater, the venous pouch was thoroughly coagulated and occluded. There were no particular problems after the surgery, and the patient was discharged with improvement in symptoms. Postoperative 3D-CTA confirmed the disappearance of the AVF, and MRI confirmed the disappearance of spinal cord congestion and reduction of the T2 high signal area. Although the patient still had paraplegia, he was able to walk with a walker after rehabilitation. He is currently undergoing MRI follow-up.
FIG. 2.
A:A right T12–L1 hemilaminectomy was performed, and a venous pouch (asterisk) was found in the IVF. B:ICG angiogram revealing the venous pouch (asterisk). C: After incising the dura and unfolding it, we were able to confirm an RMV (arrow) that runs retrograde from the root sleeve into the dura, and two draining veins (arrowhead and double arrowheads) that ascend cranially within the dura. D: ICG angiogram confirming an RMV (arrow) running retrograde from the root sleeve into the dura mater, and two draining veins (arrowhead and double arrowheads) running retrograde into the dura mater toward the head. E:The penetration site in the dura was clipped under electrophysiological monitoring and coagulated and cut, and the disappearance of the draining vein was confirmed. F:A hemoclip was found in the dura mater, and epidural coagulation and burning of the venous pouch (double asterisks) were performed.
Informed Consent
The necessary informed consent was obtained in this study.
Discussion
Observations
Clinical and Imaging Findings of Spinal Dural and Epidural AVFs
Dural AVFs have the RMA as their feeder, and reflux into the dura is via a bridging vein. On the other hand, epidural AVFs have multiple feeders, such as the prelaminar artery and dorsal somatic branch, and sometimes feeders from the contralateral side are also seen.2 Furthermore, while dural AVFs are located within the dura mater itself, epidural AVFs are located outside the dural nerve sheath. The latter, also known as a venous pouch, is a characteristic finding.2 It is often difficult to differentiate between the two using selective spinal arteriography, and epidural AVFs are often diagnosed as dural AVFs preoperatively.2,3 Kiyosue et al. reported that the “horizontal T sign” present in the inner pedicle line is characteristic of dural AVFs and is extremely useful for diagnosis.2 In epidural AVFs, a venous pouch can be seen on the outside of the dura mater on T2-weighted or contrast-enhanced MRI, and a radicular vein ascending backward into the dura mater is a characteristic feature.4 The textbook by Thron et al. is easy to understand regarding the reflux pattern from the venous pouch of an epidural AVF to the RMV via the dural sheath into the dura.5 In epidural AVFs, it can be assumed that venous hypertension or occlusion occurs outside the venous pouch of the dural sheath.
Exoscopic Surgical Treatment of Spinal Epidural AVF
In recent years, remarkable advances in endovascular treatment have made it possible to treat epidural AVFs.6,7 In particular, when a shunt (venous pouch) is present in the ventral area, endovascular treatment is more likely to be effective than direct surgery.6 However, a multicenter study in Japan showed that surgical treatment was significantly more effective than endovascular treatment for initial treatment.3 It was reported that the independent risk factor for surgical treatment failure was the number of drainers, while for endovascular treatment failure it was the number of feeders.3 As a result, there are increasing reports of the effectiveness of direct surgery for epidural AVF.8,9 Laing et al. reported that in cases in which endovascular treatment of epidural AVF was unsuccessful, facetectomy could be performed to ensure reliable treatment of the venous pouch due to incomplete occlusion of the feeder.8 Furthermore, this case was the first to demonstrate that the use of ICG videoangiography allows for more reliable feeder placement. It also makes it easier to identify multiple intradural drainers. The hemodynamics from intraoperative findings in this case of epidural AVF are shown (Fig. 3).
FIG. 3.
Intraoperative findings in this case of epidural AVF. The asterisk indicates the AV shunt at the dural sleeve. DL = dorsal somatic branch.
Lessons
Preoperative diagnosis of dural and epidural AVF is very difficult. Even with recent advances in endovascular treatment, these conditions have a high risk of recurrence, so understanding the microanatomy and pathology is paramount. When performing direct surgery, it is important to perform exoscopic ICG videoangiography both intradurally and extradurally.
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: Uchikado, Ohkubo, Morioka. Acquisition of data: Uchikado, Ohkubo. Analysis and interpretation of data: Uchikado, Ohkubo, Morioka. Drafting the article: Uchikado, Takashima, Ohkubo, Morioka. Critically revising the article: Uchikado, Ohkubo, Morioka. Reviewed submitted version of manuscript: Uchikado, Ohkubo, Makizono. Approved the final version of the manuscript on behalf of all authors: Uchikado. Statistical analysis: Uchikado, Ohkubo. Administrative/technical/material support: Uchikado, Ohkubo. Study supervision: Uchikado, Ohkubo, Nakamura, Kawano, Morioka.
Correspondence
Hisaaki Uchikado: Uchikado NeuroSpine Clinic, Hakata, Fukuoka, Japan. uchikado@me.com.
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