Metameric spinal AVM: Long-term symptomatic relief achieved by embolization of the extradural component

Abstract

Background

Metameric spinal cord arteriovenous malformations (AVMs) are rare lesions characterized by an intradural and extradural component. They are difficult to treat surgically by the endovascular route. We report a case in which symptomatic relief was achieved by embolization of the extradural component only.

Case presentation

A 35-year-old woman presented with acute worsening of back pain, weakness in the left leg and urinary retention. Spinal angiography showed a metameric spinal cord AVM with partial common venous drainage of the extradural and intradural components.

Conclusions

Targeted embolization of the extradural component led to dramatic improvement of the patient’s symptoms, probably by achieving venous decongestion. She remains neurologically stable at two years’ follow-up.

Introduction

Spinal cord arteriovenous malformation (SCAVM) is a rare vascular disorder that can lead to recurrent hemorrhage and neurological deficits.¹ Spinal arteriovenous metameric syndrome (SAMS) is an extradural–intradural subtype of SCAVM with two or more vascular malformations involving the spinal cord, bone, soft tissue, muscle or skin derived from the same metameric spinal artery.^2–4 We present a case of a 35-year-old woman who was diagnosed with a SCAVM and vertebral body arteriovenous malformation (AVM) with shared common venous drainage. The patient presented with pain and progressive neurologic deficit. Targeted treatment of the vertebral body AVM led to improvement of her symptoms.

Case report

History and examination

A 35-year-old woman presented with acute worsening of chronic back pain, weakness in the left leg and urinary retention. Her back pain had been present during the last four years and had led to opiate and intravenous (IV) drug use. On examination, there was weakness of left hip flexion and knee extension (grade 2–3/5), impairment of pain and temperature in the left anterior thigh and an absent left patellar tendon reflex. The clinical findings were localized to the left L3 and L4 nerve root distribution. Her urinary retention may have been secondary to spinal cord involvement at the level of the conus, or from inability to void while supine; her pain limited the use of a commode. Electrophysiological studies were noncontributory because of poor voluntary activation secondary to pain.

Imaging

A spine magnetic resonance imaging (MRI) demonstrated abnormal enlargement and a hyperintense T2 signal of the lower spinal cord and conus, extending up to the T10 level. There were dilated intra- and perimedullary vessels. There was no evidence of abnormal enhancement, mass lesion or hemorrhage. In addition, there was abnormal heterogeneous signal and flow voids within the L3 vertebral body (Figure 1).

Figure 1.

(a) Sagittal and (b) axial T2-weighted images of the lumbar spinal cord at presentation.

A spinal catheter angiogram (Figure 2) was performed and confirmed the presence of a complex AVM. There was a spinal cord component (Figure 2(a), (b), red arrow) supplied by the anterior spinal artery (ASA) (Figure 2(a), blue arrow), which arose from the left T12 intercostal artery (Figure 2(a), yellow arrow) and the posterior spinal artery (PSA) (Figure 2(c), purple arrow) from the left L1 lumbar artery (Figure 2(c), dark blue arrow). An AVM component was also identified within the L3 vertebral body on lateral and anteroposterior projections (Figure 2(f), blue dashed arrow) and was supplied by somatic branches of bilateral L3 segmental arteries with multiple prenidal aneurysms (Figure 2(f), yellow dashed arrow). The SCAVM drained inferiorly via two radicular veins (Figure 2(a), (b), (d), (e), green arrows) joining the epidural plexus at the L3 and L4 levels (Figure 2(e), (f), black dashed arrow). The L3 vertebral body AVM drained through epidural and perivertebral veins also at the L3 level (Figure 2(e), (f), black dashed arrow). Angiographic findings are summarized in Figure 3.

Figure 2.

Preembolization diagnostic spinal angiography.

Figure 3.

Drawing of the metameric arteriovenous malformation vascularization. The drawing shows two nidi (pink): one involving the spinal cord at the T12 level and one in the L3 vertebral body. The spinal cord nidus is fed by the anterior spinal artery, a branch of the left T12 radiculomedullary artery (red) and by a posterior spinal artery, a branch of the left L1 radiculomedullary artery (green). The L3 vertebral body nidus is fed by both L3 segmental arteries (red). Venous drainage of the spinal cord arteriovenous malformation is accomplished by two radicular veins (blue) that join the epidural venous plexus at the level of L3 and L4 (blue). The same epidural and perivertebral venous network is shared by the L3 vertebral body AVM.

Interventional procedure and postoperative course

Surgical or endovascular treatment of the SCAVM was considered high risk because of the intramedullary location and the dual ASA and PSA supply. In spite of the extensive spinal cord edema seen on MRI, the patient’s excruciating asymmetrical pain and objective neurological examination were localized to the left L3 and L4 nerve roots. The venous drainage from the L3 vertebral body AVM was thought to represent significant contribution and competition to the venous outflow of the SCAVM resulting in venous congestion, spinal cord edema and L3–L4 nerve root compression. Therefore, the decision was made to treat the L3 vertebral body AVM, which appeared less risky. Reducing the draining flow at L3 level would decrease competition and improve flow of the SCAVM draining veins, potentially resulting in secondary conus decongestion.

The patient underwent successful targeted endovascular arterial embolization of the bilateral L3 radicular arteries with Onyx-18 (eV3-Covedien, Irvine, CA, USA) as an initial treatment (Figure 4(a), black dashed arrow).

Figure 4.

(a) Embolization result and (b) sagittal T2-weighted image of the lumbar spinal cord at follow-up.

After the procedure, the patient had dramatic improvement of her back and leg pain and was voiding spontaneously. At six months’ follow-up, the patient’s pain was minimal; she was walking independently and had normal bladder and rectal sphincter control. The patient regained normal left leg motor strength and deep tendon reflexes. Her left anterior thigh sensory deficit persisted. The patient eliminated use of opiates and IV drugs. Her clinical condition remains unchanged at two years’ follow-up.

MRI and digital subtraction angiography follow-up imaging demonstrated significant regression of the spinal cord edema (Figure 4(b)) with resolution of shunting within the L3 vertebral body and partial regression of intramedullary flow voids.

Discussion

The definition of SAMS stems from the index case of Cobb syndrome described by Cobb⁵ in 1915. It is a congenital abnormality involving a cutaneous nevus and spinal AVM confined to the same metamere. In the developing embryo following segmentation, each somite, or metamere, further differentiates. Genetic mutation in the neural crest before migration and differentiation can result in multiple malformations in one or more tissues of the same metameric segment.⁴ SAMS classically involves multiple lesions derived from the same metameric spinal artery, but can span several metameres.^2–4,6,7 In our case, there were two discrete AVMs supplied by multiple segmental arteries from T12 to L3. This may represent a more extensive insult across multiple metameric territories resulting in dual expression of a single process. Alternatively, this phenotype may represent multiple AVMs sharing common venous drainage through normal anastomotic channels.

As SAMS is a relatively rare disorder, there is no clear consensus in the literature on the best management. Treatment options include surgical resection, endovascular embolization, a combined approach, or conservative management.^8,9 The goal of endovascular treatment is usually not cure, but symptom improvement or stabilization of a progressive disease with poor long-term functional prognosis.³ Niimi et al. reported a retrospective review of 28 SAMS.³ The most common presenting symptom was intradural hemorrhage, occurring in 18 of 28 patients; seven presented with nonhemorrhagic neurologic deficits and three presented with radicular pain without neurologic deficit. Twenty-six patients underwent endovascular embolization of the spinal SCAVM or related spinal cord aneurysms and six patients underwent embolization of extradural lesions. Twenty-three patients had clinical follow-up: Nine improved, seven were unchanged, and seven deteriorated.

This case is unique because embolization of the L3 vertebral body AVM was sufficient to decrease the venous congestion. This resulted in long-term symptom relief and resolution of the conus medullaris edema on MRI.

Conclusion

We describe a case of a complex metameric SCAVM presenting with debilitating symptoms. When the extradural component shares a common venous drainage with the intradural component, targeted embolization of the extradural component may be a safe and effective treatment for the relief of symptoms related to venous congestion.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.