renal arteriovenous malformations ( avms ) are rare anomalous arterial and venous connections commonly presenting with spontaneous hematuria and recurrent flank pain .
a liquid embolizer composed of ethylene - vinyl alcohol ( evoh ) dissolved in dimethyl sulfoxide ( dmso ) , mixing with tantalum powder for radio - opacity , is emerging as a new treatment modality for visceral avms due to its inherent benefit of obtaining good nidal penetration and ease of embolizer control .
we present a case of renal avm after onyx embolization , which is the first reported case of hyperdense striations along the renal medulla , secondary to tantalum powder on computed tomography ( ct ) .
( chang gung memorial hospital ) and waived the need for the patient 's inform consent . a 65-year - old woman , without a significant history , presented to our institution with intermittent gross hematuria and left flank pain for 10 days .
physical examination , noncontrast ct , cystourethroscopy , and laboratory examinations were all unremarkable , except for hematuria ( color of urine : red and red blood cell count > 500  /l ) and blood clot in the left renal pelvis .
blood test showed no obvious anemia ( red blood cell count 4.43  million/l and hemoglobin level 13.6  g / dl ) .
subsequent renal artery ct angiography demonstrated a tangled cluster of vessels in the left peripelvic region with arterial feeders and early draining vein , consistent with a cirsoid - type renal avm ( figure 1a , ct image ) and confirmed by conventional transcatheter angiography ( figure 1a , angiography image ) .
two arterial feeders arising from posterior segmental artery of the left kidney supply the renal avm .
one is originated from the proximal portion of the posterior segmental artery , and the other one is from the distal portion ( figure 1a , ct image ) .
( a ) pretreatment image ( ct image ) ct angiography ( cta ) with volume - rendering reformatted image of the left kidney ( a ) demonstrated a cirsoid - type renal arteriovenous malformation ( avm ) at the upper pole of the left kidney with arterial feeder ( bold arrow ) and draining vein ( triangular arrowhead ) .
oblique coronal image with maximal - intensity projection showed two arterial feeders ( thin arrows , proximal and distal ) arising from posterior segmental artery of the left kidney supply the renal avm ( angiography image ) .
transcatheter angiography of the left kidney confirms the cta findings of renal avm ( bold arrow ) .
( b ) post - treatment image ( left ) noncontrast - enhanced ct performed on the 5th postembolization day shows fine linear hyperdense striations in the left renal parenchyma ( bold arrow ) .
note the confinement of the hyperdense striations within the renal contour ( red triangular arrowhead ) and also the height difference between the peripelvic embolizer ( small arrowhead ) and the striations ( bold arrow ) exclude beam - hardening artifact .
( right ) control angiography after the embolization showed complete obliteration of the renal avm with resultant infarction at the lateral aspect of the mid portion of the kidney ( bold arrows ) .
ct , computed tomography . as an effort to achieve a satisfactory distal penetration of the nidus , we used onyx instead of coil and n - butyl cyanoacrylate ( nbca ) . to ensure adequate mixing and homogenous radiopacity of the onyx mixture , the vials were kept on a shaker ( vortex - genie ; scientific industries , inc .
onyx 34 ( 8% evoh and 92% dmso , onyx 34 ; micro therapeutics , inc . ,
irvine , ca , usa ) is chosen for the embolization of distal feeder to achieve higher occlusion speed .
the microcatheter was preflushed with dmso , and onyx 34 was injected slowly under fluoroscopic control until occlusion of the distal feeder .
the total amount of injected onyx 34 was 0.8 ml . angiography after embolization of the distal feeder showed occlusion of distal feeder and lateral portion of the nidus , but the avm was still supplied by the proximal feeder .
therefore , we cannulated the proximal feeder using a marathon flow - directed microcatheter coaxially through a 6 fr .
since the angiography of the proximal feeder showed a relative slow - flow vascular malformation , embolization was performed with onyx 18 ( 6% evoh and 94% dmso , onyx 18 ; micro therapeutics , inc . , irvine , ca , usa ) to obtain a better penetration into the nidus .
the total amount of injected onyx 18 was 0.6 ml . no obvious visible overflow of onyx was seen during the embolization procedure , but subtle overflow of onyx can not be completely excluded under angiography .
control angiography after embolization of both feeders demonstrated complete obliteration of the renal avm , with a resultant infarction at the lateral aspect of the middle left kidney ( figure 1b , right image ) .
nonenhanced abdominal ct was performed on the 5th postembolization day to follow up the extent of injected onyx .
onyx was localized within the expected region of the avm . however , diffuse fine hyperdense linear striations were incidentally found along the course of the left upper renal medulla , which favored the presence of tantalum powder rather than intravascular migration of embolizer ( figures 1b , left image ) .
the patient was discharged uneventfully , and follow - up ct 3 months later confirmed the disappearance of the tantalum powder from the renal medulla and the resolution of the renal striation sign ( figure 2 ) .
both blood test ( red blood cell count 4.50  million/l and hemoglobin level 13.4  g / dl ) and urinary analysis ( color of urine : yellow and red blood cell count 1  /l ) were normal during postembolization follow - up .
multipanel imaging with comparison of the initial postembolization ct at 5 days after embolization and the subsequent ct at 3 months follow - up revealed the resolution of the striated tantalum powder .
( a ) post - treatment follow - up ( 5 days ) : axial ct scan at the level of onyx embolizer ( left ) and at a level below the onyx embolization ( right ) revealed presence of hyperdense renal striation sign(arrows ) .
( b ) post - treatment follow - up ( 3 months ) : axial ct scans at the same levels confirmed disappearance of the tantalum powder .
treatment of renal avm is often necessary when complications such as heart failure , uncontrolled hypertension , hemorrhage , or recurrent flank pain occur , as the case of our patient .
the optimal treatment of renal avm should include complete eradication for the vascular lesion while preserving the maximal - functioning renal parenchyma . in this study ,
transarterial embolization became the treatment of choice because the peripelvic location of the nidus posed a high risk of renal parenchymal injury , if surgery was performed .
even though several embolic materials are available , the lava - like flow pattern and long solidification time of onyx allow better nidal penetration and more controllable embolization procedure , which is particularly beneficial in treating visceral avm .
in addition , onyx injection can be interrupted and continued again until the desired result is achieved . even if the catheter was entrapped by onyx , catheter removal
onyx 18 has a lower evoh concentration , resulting in slower occlusion speed and allows better nidal penetration distally , whereas onyx 34 has a higher concentration of evoh and allows a higher occlusion speed , but less nidal penetration ability .
the two mixtures can be selected according to the need of embolization speed and distal nidal penetration . as previously mentioned , we employed onyx 34 for the distal feeder to achieve higher occlusion speed and onyx 18 for the proximal one for better nidal penetration .
as for the other embolizers , metallic coils are not suitable embolic agents because the delivery catheters can not superselectively enter the nidus for the placement of the coils .
the proximal coil embolization may result in development of collateral branches that are difficult to treat .
nbca , which is a tissue - adhesive liquid embolic material , has the ability to penetrate and occlude at the level of the nidus of the avm .
however , there is a risk that the catheter tip may adhere to the vessel wall .
the catheter should be retrieved before nbca polymerizes , which requires great experience and skill .
in addition , due to the low viscosity , the embolic material may be washed away before it polymerizes .
although beam - hardening artifact can be an image mimicker of the renal hyperdense striation sign , the confinement of the hyperdense striations within the kidney contour , along with the height difference between the peripelvic embolizer and the striations , can allow differentiation of these two entities .
this finding is further confirmed by follow - up ct with disappearance of the hyperdense striation sign .
we believe the renal hyperdense striation sign is secondary to the presence of tantalum powder in the renal medulla . in one animal experimental study of transarterial embolization of the kidney , with nbca mixed with tantalum powder , and reported by gnther et al , particles of tantalum powder ( average particle size of 75  m )
were found to deposit in the arteries and in the glomeruli of kidneys on histologic specimens after the embolization , and tantalum particles smaller than 7  m were found in the pulmonary vascular system .
the particle size of onyx tantalum powder ranged from 0.7  m to 22  m , and it is reasonable to suspect that the diffuse linear hyperdensities in the renal parenchyma might be related to the deposition of the tantalum powder .
congenital renal avms had tortuous varicous vessels , which are found immediately beneath the urothelium , which is the cause of the hematuria .
bypassing of the filtration barrier with subtle overflow may explain for the presence of tantalum powder in the renal medulla .
follow - up ct image reveals resolution of the striated tantalum powder , and the renal function remains normal , which probably implied that the phenomenon would not be problematic in patients with normal renal function .
however , we do not know if the phenomenon affects the renal function in patients with renal insufficiency .
further studies in patients with renal function impairment may be helpful , and the recognition of the renal hyperdense striation sign is important to avoid confusion with embolizer migration and understand its influence on renal function .
despite its frequent usage in neural intervention , the application of onyx in avm of visceral organs is gradually graining interest , especially in cases in which delicate nidal penetration of the avm is desired .
renal hyperdense striation sign should be recognized to avoid confusion with embolizer migration , and further studies in the effect of tantalum powder in patients with renal function impairment may be helpful to understand its influence of renal function .
 abstractonyx is an emerging treatment modality for visceral vascular malformations , especially in cases in which delicate nidal penetration of the arteriovenous malformation ( avm ) is desired . 
 a computed tomography ( ct ) image presentation of hyperdense striations along the renal medulla secondary to the tantalum powder has not been previously reported.a 65-year - old woman presented to our institution with intermittent gross hematuria and left flank pain for 10 days . 
 both ct and conventional angiographies confirmed cirsoid - type renal avm , which was successfully treated with onyx . 
 follow - up ct after treatment revealed presence of hyperdense striations along the renal medulla , which resolved during later image follow-up.despite its frequent usage in neural intervention , the application of onyx in visceral avm is gradually gaining interest , especially in cases in which delicate nidal penetration of the avm is desired . 
 renal hyperdense striation sign should be recognized to avoid confusion with embolizer migration , and further studies in patients with renal function impairment may be helpful in understanding its influence of renal function . 
INTRODUCTION
CASE PRESENTATION
DISCUSSION
CONCLUSION