Surgical resection of arteriovenous fistula at the cauda equina

Abstract

Introduction

Although spinal arteriovenous fistula (AVF) has been reported widely, AVF at the cauda equina is quite rare. We described a case of AVF at the cauda equina that was fed by the distal radicular artery (DRA).

Case presentation

A 50-year-old woman presented with sudden weakness of the lower extremities. Magnetic resonance imaging (MRI) revealed a lesion with a highly intense signal at the conus medullaris, which was surrounded by several low-intensity signals (flow voids). Digital subtraction angiography revealed AVF at the cauda equina and that it was fed by the DRA, which was directly fed by the L3 segmental artery. We performed surgical resection of the AVF while monitoring motor-evoked potentials. The patient’s postoperative course was uneventful, and her neurological symptoms gradually resolved. MRI 2 years after surgery showed the disappearance of both intramedullary edema and the flow voids.

Discussion

For the AVF, located at the cauda equina and fed by the DRA in this case, surgical resection or endovascular embolization could have been selected. We performed open surgery to achieve complete obliteration of the AVF, which led to postoperative functional recovery without any adverse events. However, only a limited number of AVFs at the level of the cauda equina have been reported, and treatment standards have not been established. Further studies of AVFs at the cauda equina are necessary to clarify the epidemiological characteristics and clinical outcomes with an appropriate sample size.

Introduction

Spinal arteriovenous fistula (AVF) is an abnormal shunt between arteries and veins of the spine without a capillary network. Myelopathy or radiculopathy can result from circulatory disturbance or hemorrhage caused by vascular congestion [1]. Although several spinal AVFs have been reported to date [1–3], cases that occurred at the level of the cauda equina have been reported infrequently [4–7]. The vascular anatomy around the cauda equina is not generally known, but two arteries can serve as feeders for the fistula at the cauda equina: the proximal radicular artery (PRA) and the distal radicular artery (DRA) [8, 9]. Because diagnostic and therapeutic processes are different for the PRA- and DRA-derived AVFs [4, 7], it is important to understand the vascular anatomy and circulatory dynamics of the cauda equina. To the best of our knowledge, only 11 cases of AVFs at the cauda equina have been reported, and of those 11 AVFs, seven were fed by the DRA [4–7]. We encountered a patient with AVF of the cauda equina that was fed by the DRA, and we present detailed clinical and intraoperative findings of this rare case.

Case presentation

A 50-year-old woman presented with sudden weakness of the lower extremities 1 year before she was referred to our hospital. She had no related medical history. Her symptoms worsened, urinary frequency increased, and her walking performance deteriorated. Although radiographs showed no structural anomaly, sagittal T2-weighted magnetic resonance imaging (MRI) revealed a lesion with high signal intensity at the conus medullaris and some low-intensity signals around it, which indicated chronic venous congestion and flow voids (Fig. 1). A diagnosis of spinal AVF was suspected based on the clinical symptoms and MRI findings.

Fig. 1. Preoperative magnetic resonance imaging.

T2-weighted magnetic resonance imaging revealed a high-intensity lesion around the conus medullaris and flow voids, all indicating spinal cord edema.

To clarify the location of the spinal AVF, digital subtraction angiography (DSA) was performed. In these findings, the AVF at L2 was fed by the radicular artery through the right L3 lumbar artery (Fig. 2). A continuously enlarged draining vein ran upward along the surface of the spinal cord. This vein was fed directly by the L3 segmental artery, which indicated that this lesion was an AVF at the cauda equina and was fed by the DRA (Fig. 2). Although endovascular obliteration for this AVF was a therapeutic option, we found it difficult to advance catheter to the shunt due to tortuosity of the feeder. Therefore, we selected direct surgery rather than endovascular treatment.

Fig. 2. Digital subtraction angiography.

Digital subtraction angiography revealed the arteriovenous fistula (black arrow) of the cauda equina at L2 and the enlarged draining vein (white arrowhead) by the right L3 lumbar artery (white arrow). The feeder was a distal radicular artery (black arrowhead).

To perform intraoperative angiography, the catheter was inserted into the right L3 lumber artery during the surgery. After total laminectomies at L1–L3, we opened the dura mater and identified the AVF, which consisted of a feeding artery and an enlarged draining vein (Fig. 3a). The AVF and vessels adhered to the cauda equina nerve roots, and we peeled off the fistula and feeders carefully while monitoring motor-evoked potentials. After the caudal and cranial vessels of the fistula were temporarily clipped, we confirmed that contrast medium did not reach the AVF, and motor-evoked potentials were not decreased 10 min later. Permanent clips were applied to the vessels as close as possible to the fistula (Figs. 3b, c), and then the fistula was removed (Fig. 3d).

Fig. 3. Intraoperative findings.

a The arteriovenous fistula (black arrow) and the cauda equina (black arrowhead) beneath the pia mater was exposed. b The caudal feeding vessel (white arrow) was cut, and permanent clips were applied. c In a similar way, the cranial feeding vessel (white arrowhead) was cut and clipped. d The fistula was removed.

The patient’s postoperative course was uneventful, and her neurological symptoms gradually resolved. MRI 2 years after surgery showed disappearance of both intramedullary edema and the flow voids (Fig. 4).

Fig. 4. Postoperative magnetic resonance imaging.

The high-intensity lesion and flow voids had disappeared by the time of follow-up T2-weighted magnetic resonance imaging 2 years after surgery.

Discussion

The present case had AVF at the cauda equina that was fed by the DRA. We demonstrated that direct resection resulted in functional improvement without perioperative complications or recurrence for at least 2 years after surgery. We had found only one report of AVF fed by the DRA, but that study comprehensively focused on the AVF below the conus medullaris [7]. We precisely reported intraoperative findings and the clinical course in our patient. We believe that this report helps inform the therapeutic indications of this extremely rare vascular anomaly.

AVFs below the conus medullaris account for 13.3% of all spinal AVFs, and they are divided into three types according to the location: dural AVF, AVF at the filum terminale, and AVF at the cauda equina [7]. However, the difference in vascular anatomy among the types is not generally known because of the rarity of such AVFs. Moreover, the angioarchitecture of arteries around the cauda equina is considered more complicated than the artery of the filum terminale, which originates mainly from the termination of the anterior spinal artery. The proximal third of the cauda equina is supplied from the PRA, which arises from the vasa corona, anterior spinal artery, or posterior spinal artery. In particular, it is considerably difficult to distinguish between the PRA and artery of the filum terminale on DSA because both arteries are supplied from the anterior spinal artery and run close to each other [4]. On the other hand, the distal two-thirds of the cauda equina is supplied by the DRA, which branches from the segmental artery [8]. In our case, the AVF at the cauda equina was fed by the DRA and could be detected easily on DSA because the right L3 lumbar artery was directly connected to the feeding artery. However, Hong et al. indicated that there might be some cases with AVF which was mainly fed by the DRA and simultaneously received PRA-derived feeder. The presumed pathology was that the feeder from PRA was masked during the DSA because its blood flow was suppressed by the main feeder from the DRA [7]. Although the fistula was not fed by PRA in our patient, we had to carefully assess the blood flow of both radicular arteries on DSA and even during surgery.

Either surgical resection or endovascular embolization or both are selected for treating AVF at the cauda equina [4–7]. Hong et al., in reporting cases of AVF below the level of conus medullaris, demonstrated that surgical resection resulted in complete vascular obliteration in 100% of cases, whereas embolization achieved obliteration at a rate of 56.0% [7]. Thus, we opted for open surgery rather than endovascular treatment to achieve complete obliteration, and postoperative functional recovery without any adverse events was achieved. Efficacy of surgical resection was also validated in other types of AVF or AVM [10, 11]. However, the number of reports about AVF at the level of the cauda equina is limited, and the treatment standards have not yet been established. Further studies of AVF at the cauda equina are necessary to clarify the epidemiological features and clinical outcomes with an appropriate sample size.

Compliance with ethical standards

Conflict of interest

The authors declare no competing interests.