Keywords spinal dural arteriovenous fistula - embolization - retrocorporeal artery
Introduction
Endovascular treatment has emerged as the primary treatment option for the management
of spinal dural arteriovenous fistula (SDAVF). The goal of endovascular embolization
is to achieve embolic penetration into the nidus and proximal segment of the draining
vein. Though less invasive, the successful obliteration of fistula is achieved in
70 to 90% of the patients and recurrence of fistula is observed in as high as 15 to
30% of the patients.[1 ]
[2 ] Among the several factors that decide the outcome of endovascular treatment, difficult
navigation and inability to place microcatheter close to the fistula remain important
concerns that predict successful percolation of embolic agent into the venous side
of the fistula. Recently, endovascular approach to fistula through retrocorporeal
artery has been described as an alternative route to achieving successful embolization.[3 ] We describe two cases of SDAVF that were completely obliterated through retrocorporeal
route after an unsuccessful standard endovascular approach. The relevant anatomy of
retrocorporeal artery and the technical nuances are discussed herein.
Case Description
Case 1
A 56-year-old woman presented with slowly progressive weakness of the right lower
limb in association with burning paresthesias of the right leg and urinary urgency.
Clinical examination revealed bilateral asymmetric paraparesis (right > left). Magnetic
resonance imaging (MRI) showed long-segment intramedullary hyperintensity involving
the lower dorsal cord and the conus with presence of flow voids along the dorsal surface
of the cord. The patient underwent spinal angiography, which showed SDAVF with arterial
feeder from radicular branch of the right D11 intercostal artery. Under general anesthesia,
a 7F renal guide catheter (RGC, Medtronics) was placed in the aorta and the right
D11 intercostal artery was selectively catheterized using a 4F Judkins left coronary
catheter (Cordis, Warren, New Jersey, United States). The radicular artery was cannulated
using a Marathon microcatheter and Mirage microguidwire (Covidien/Medtronics, Irvine,
California, United States). The fistula embolization was performed with 17% n-butyl
cyanoacrylate (n-BCA) without satisfactory antegrade percolation. Subsequent angiogram
of left D11 intercostal artery showed the fistula opacification from the left D11
artery via the retrocorporeal artery. The retrocorporeal artery was then cannulated
and the microcatheter was advanced into the proximal aspect of the artery. The fistula
was completely embolized with 17% n-BCA ([Fig. 1 ]). Clinical follow-up at 1 year showed significant improvement in neurologic status
and magnetic resonance evaluation revealed no recurrence of fistula.
Fig. 1 Patient 1: Right D11 intercostal angiogram (A ) shows spinal dural fistula. The microcatheter is placed proximally due to tortuosity
(arrow in B ) and selective angiogram reveals fistula as well as significant proximal reflux (C ). Check angiogram shows occlusion of fistula (D ); however, a contralateral intercostal angiogram reconstitutes occluded intercostal
artery through retrocorporeal artery (E and arrow in F ). Selective angiogram confirms this observation (G ), which is occluded by n-BCA. Note glue cast in the nidus and draining vein (H ).
Case 2
A 65-year-old man presented with paresthesias of both lower limbs along with progressive
paraparesis, which acutely worsened to complete paraplegia with loss of all sensations
below the level of D8. MRI showed presence of flow voids suggesting the possibility
of spinal dural fistula. Spinal angiography revealed SDAVF with arterial feeder from
radicular branch of left D12 intercostal artery and he was subsequently planned for
endovascular treatment. The left D12 intercostal artery was catheterized using a 4F
vertebral glide (Terumo, Shizuoka, Japan) diagnostic catheter and the radicular feeder
was cannulated using a Marathon/Mirage (Covidien/Medtronics) microcatheter and microguidewire
combination. The fistula was subsequently embolized using 15% NBCA. Significant reflux
of embolic material was noted with minimal antegrade percolation. The right D12 intercostal
artery angiogram showed the fistulous network opacified through the retrocorporeal
branch and hence this artery was cannulated and the microcatheter was navigated into
its proximal segment. The fistula was embolized using NBCA, achieving complete angiographic
fistula obliteration ([Fig. 2 ]). Mild clinical improvement was noted at 6 months; however, no further imaging studies
were obtained as patient declined further follow-up.
Fig. 2 Patient 2: Intercostal angiogram (A ) and selective microcatheter angiogram (B ) show spinal dural fistula that was embolized with n-BCA with poor nidal percolation
(arrow in C ). Intercostal angiogram shows fistula opacification (D ) that is clearly demonstrated after microcatheter injection from retrocorporeal artery
(interrupted arrows in E ). Unsubtracted frame (F ) shows glue cast in the proximal vein (arrow).
Discussion
The successful embolization of SDAVF is determined by the continuous penetration of
embolic agent into the nidus and the proximal segment of the draining vein. Among
several factors, favorable microcatheter angiographic patterns and concentration of
NBCA were identified as significant factors that predict endovascular obliteration
of SDAVF.[2 ] The appropriate placement of microcatheter close to the fistula is often hindered
by small and tortuous feeding arteries. In such instances, the interventionist hopes
to achieve adequate venous penetration by varying the concentration of glue or by
altering the NBCA[4 ] injection technique. Inadequate percolation and proximal occlusion of the feeder
precludes further endovascular approaches and necessitates surgical disconnection
of the fistula to achieve complete cure. Recently, selective catheterization of retrocorporeal
artery and successful embolization have been described as an alternative route in
failed conventional endovascular techniques.[3 ]
The retrocorporeal artery arises from the dorsal spinal branch of the intercostal
or lumbar artery and forms a rhomboid-shaped epidural arterial anastomotic network
with adjacent and contralateral segmental arteries.[5 ] Proximal occlusion of the segmental arteries opens up several anastomotic communications
and reforms the artery distal to occlusion. Because these anastomoses are preformed,
immediate reconstitution of the occluded artery can be expected, and if present, it
may serve as alternative conduits to access the fistula. The artery is often small,
fixed in the epidural space, and has a relatively straight course. Hence, the microguidewire
can be advanced sufficiently into the artery to allow it to track along without prolapse
into the parent artery. Because of small size of the artery, the microcatheter creates
a wedge flow situation and ensures antegrade percolation of embolic agent into the
fistula and proximal vein, even if the catheter tip is not close to the site of the
fistula. In both the cases demonstrated, embolization was performed through the retrocorporeal
artery after initial unsuccessful attempt at embolization through the primary feeding
radicular artery. The cannulation of the artery was relatively easy and microcatheter
could be placed in proximal segment of the retrocorporeal artery. Complete angiographic
embolization of fistula was achieved without significant proximal reflux.
Our report therefore suggests that the retrocorporeal artery is a safe and effective
route to tackle fistula that persists following embolization via standard endovascular
approach. Careful analysis of adjacent segmental artery angiograms should be performed
and presence of this artery must be carefully searched for, so that embolization can
be attempted through this route, before considering surgery as the sole treatment
option.
