- Department of Neurosurgery, Baylor College of Medicine, Houston, TX, USA
Edward A.M Duckworth
Department of Neurosurgery, Baylor College of Medicine, Houston, TX, USA
DOI:10.4103/2152-7806.81065Copyright: © 2011 Trinh VT. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Trinh VT, Duckworth EA. Surgical excision of filum terminale arteriovenous fistulae after lumbar fusion: Value of indocyanine green and theory on origins (a technical note and report of two cases). Surg Neurol Int 14-May-2011;2:63
How to cite this URL: Trinh VT, Duckworth EA. Surgical excision of filum terminale arteriovenous fistulae after lumbar fusion: Value of indocyanine green and theory on origins (a technical note and report of two cases). Surg Neurol Int 14-May-2011;2:63. Available from: http://sni.wpengine.com/surgicalint_articles/surgical-excision-of-filum-terminale-arteriovenous-fistulae-after-lumbar-fusion-value-of-indocyanine-green-and-theory-on-origins-a-technical-note-and-report-of-two-cases/
Background:Intradural filum terminale arteriovenous fistulas (AVFs) are uncommon. We report two cases of this rare entity in which we used indocyanine green (ICG) videoangiography to identify the fistulous connection of each lesion.
Case Description:Two male patients presented with unresolved lower extremity weakness and paresthesias following lumbar fusion surgery. In each case, angiography showed an AVF between the filum terminale artery (FTA), the distal segment of the anterior spinal artery (ASA), and an accompanying vein of the filum terminale. A magnetic resonance image (MRI) obtained before lumbar fusion was available in one of these cases and demonstrated evidence of the preexisting vascular malformation. Surgical obliteration of each fistulous connection was facilitated by the use of ICG videoangiography. This emerging technology was instrumental in pinpointing fistula anatomy and in choosing the exact segment of the filum for disconnection.
Conclusion:Our findings indicate that intradural filum terminale AVFs may have a congenital origin and that ICG is a useful tool in their successful surgical management. As these cases demonstrate, spine surgeons should remain vigilant in evaluating patients based on their clinical symptomatology, even in the presence of obvious lumbar pathology.
Keywords: Arteriovenous fistula, filum terminale, indocyanine green videoangiography, intradural, perimedullary
Intradural filum terminale arteriovenous fistulas (AVFs) are exceedingly rare. Only three reports have focused specifically on an AVF arising from the filum terminale artery (FTA).[
We present two cases of filum terminale AVF, which were treated surgically with the use of indocyanine green (ICG) videoangiography. Interestingly, both of our patients underwent lumbar fusion years prior, and reported progressive symptoms after their surgeries. Pre-lumbar fusion imaging in one of our patients (unavailable in the other) showed evidence of an unrecognized AVF, indicating that the lesion was present prior to lumbar surgery, and possibly congenital, rather than iatrogenic.
A 57-year-old, left-handed gentleman, with a history of back pain and leg weakness presented with complaints of bilateral lower extremity numbness and difficulty walking. He underwent an L4-S1 postero-lateral fusion 2 years prior, without getting any relief from the symptoms [
A neurological examination revealed bilateral proximal and distal lower extremity weakness, decreased lower extremity pinprick sensation and proprioception, decreased anal sphincter tone, and perineal hypoesthesia. Digital subtraction angiography demonstrated filling of the anterior spinal artery (ASA) extending past the conus and appearing to fistulize directly into a spinal vein in the region of the patient's previous surgery [
(a) Early phase spinal angiogram of the left T-10 intercostal artery injection, showing filling of the anterior spinal artery and the site of the filum terminale arteriovenous fistulas. (b) Later phase spinal angiogram showing initial fistulization. (c) Venous phase of spinal angiogram showing dilated and tortuous draining veins of the malformation
A 63-year-old, right-handed gentleman, with a history of chronic back pain presented to an outside facility in 2007 with numbness and weakness in his right foot. He underwent an L4-L5 interbody fusion and pedicle screw-rod fixation. Following surgery, his back pain improved, but he complained of slowly worsening numbness and weakness involving his lower extremities. He sustained multiple falls postoperatively, including a fall that resulted in fractures of his femur and wrist.
An electromyography (EMG) suggested bilateral chronic L4 to S3 radiculopathy. A magnetic resonance image (MRI) obtained from after his lumbar fusion demonstrated flow voids in the lumbar cistern and increased T2 signal in the thoracic cord and conus medullaris. A spinal angiogram showed an AVF located around L4–L5. However, the precise location of artery–vein transition was not apparent despite sophisticated neurovascular imaging [
Under general anesthesia, each patient's old incision was opened and dissection carried down to his respective spinal instrumentation.[
Artery and vein penetrating the thick, fibrous dura at the filum terminale with fibrofatty changes (bold arrow). Abrupt transition occurs between the feeding arterial vessel and venous vessel. Filum terminale vein at the center of the image is enlarged and filum terminale artery is distorted (black arrow)
Complications and postoperative course
Case 1 had two complications associated with his surgery. Intraoperatively, there was cauterization injury to his S3–S4 nerve roots due in part to obscured tissue planes from extensive epidural scarring. Impaired perineal sensation, rectal tone, and sphincter control improved during the course of admission and during his follow-up. He gained full control of his bowel and bladder within 90 days of his surgery. Scarring also made creating a hermetic seal of the thecal sac difficult, and a symptomatic pseudomeningocele formed and was repaired 1 month after his original surgery. Case 2 had no perioperative complications.
Both patients experienced dramatic improvement in lower extremity function immediately, which continued in the weeks and months following surgery. The patients reported increased and new sensations in the legs, and both were able to discard their walkers and ambulate independently.
Intradural ventral AVFs are characterized by a fistulous connection between the ASA and enlarged venous channels in the subarachnoid space.[
AVFs of the terminal filum are rare. A review of the literature yields only four reported cases of intradural terminal filum AVF fed by the artery of the filum terminale.[
Treatment modality: Surgical obliteration
For the treatment of each of these filum terminale AVF, we chose surgical disconnection rather than endovascular embolization to provide definitive treatment. Multiple studies have concluded that surgery has advantages over endovascular embolization in terms of cure rate and complication rates.[
In our cases, embolization was precluded given the anatomic relationship of the fistula to the ASA. Embolization of filum terminale AVF is complicated by the structural anatomy of the FTA; not only is the FTA serpiginous, risking penetration, but also its vascular integrity diminishes as it descends distally.[
Use of indocyanine green
Surgical management of filum terminale AVF requires accurate visualization of the vascular anatomy and precise localization of the fistula. Failure to identify the site of fistulization can result in occlusion of normal vessels, leading to spinal cord or nerve root infarction.[
ICG was first introduced for neurosurgical vascular application by Raabe et al.,[
As highlighted by our operative technique, ICG allows tracking of the sequential arterial, capillary, and venous angiographic changes in real time. Temporary occlusion of the vasculature allowed us to start, stop, and pause the progression of vessel filling. The videoangiogram delineated how the ASA split into two vessels and how a third branch (the FTA) descended to fistulize exactly where the filum met the tip of the apex of the thecal sac (case 1) or at the level of L5 (case 2). In both cases, the arterial phase demonstrated abnormal early filling of the fistula and the filum terminale veins. After surgical extirpation of the fistula, ICG videoangiography demonstrated physiologic filling of the filum terminale veins and preservation of normal vasculature.
Compared with the use of radiological contrast agents, intravenous ICG is not associated with risk from radiation exposure or renal failure.[
Theory on origins
Venous drainage of the filum has been at the center of previous theories on the origin of filum terminale AVFs. Tender et al.[
Rosenblum et al.[
Sagittal T2-weighted MRI of thoracolumbar spine revealing flow voids (arrow) in the low thoracic spinal levels, indicative of a spinal arteriovenous malformation. This MRI was obtained prior to lumbar fusion surgery and demonstrates evidence of arteriovenous fistulas in the presence of degenerating L4 disc
Vascular injury is a well-known complication following lumbar disc surgery.[
We report the use of ICG videoangiography in the surgical treatment of two rare cases of filum terminale AVF. ICG videoangiography allowed intraoperative localization of the fistulae sites and confirmation of their disconnection from the venous drainage system. The unique anatomy of the filum terminale presents navigational challenges for endovascular treatment, and microsurgery, especially with the aid of ICG, may be the treatment of choice for most of these lesions. Evidence of arteriovenous fistula on pre-lumbar disc surgery MRI in case 1 and resolution of myelopathy following surgical extirpation of both fistulas suggest that 1) the filum terminale arteriovenous fistulas were the original cause for symptoms and 2) intradural filum terminale AVF may be congenital in origin.
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