endovascular aortic aneurysm repair ( evar ) has developed into a feasible and successful alternative to open surgery for the treatment of abdominal aortic aneurysms . evar can be offered to many patients with a suitable anatomy of the aorta and iliac arteries , regardless of comorbid conditions [ 13 ] . despite the known excellent early results of evar in terms of the reduction in perioperative mortality , rate of complications and length of hospitalization , many patients require re - intervention during the middle and long - term follow - up because of procedure - related complications . for this reason , surveillance of these patients is crucial to determine the long - term performance of these devices [ 4 , 5 ] . because of the rapid diffusion of evar and the increased number of patients who undergo multidetector ct ( mdct ) follow - up , the radiologist should be familiar with the full spectrum of possible procedure - related complications in order to allow their early diagnosis and treatment . the purpose of this article is to present a spectrum of post - evar complications as seen with mdct . regardless of the scanner available ( 4 , 16 or 64 row ) , a thick - slice unenhanced acquisition can be performed to visualize the position of the stent - graft to reveal calcifications and to plan the following contrast - enhanced examination by selecting the acquisition volume and placing a region of interest in the aorta at the level of the celiac trunk ( if bolus - tracking software is used ) . contrast - enhanced images in the arterial phase are obtained during bolus intravenous injection of 90130  ml of iodinated high - concentration non - ionic contrast medium , administrated with an automated injector at a flow rate of 34  ml / s through an antecubital vein . ct acquisition protocol parameters and scanning coverage ranges are illustrated table  1 and fig .  1 . scanning should start when the examined structures have reached an ideal level of opacification ; therefore , the scan delay must be individualized to the patient by using bolus - tracking software to capture 100 hu on the abdominal aorta . at the end of the arterial acquisition , delayed images focused on the graft must be acquired , performed at least 60  s and up to 120  s after contrast material injection . the cta examination can be complemented by postprocessing reconstructions , including maximum- intensity projection ( mip ) , curvilinear reformation ( cvr ) and volume rendering ( vr ) .table 1ct acquisition protocol parametersscannerrotation time ( s)collimationtable feed ( mm / s)slice thickness ( mm)slice interval ( mm)duration ( s)4 slice0.54    1  mm251.25125 - 3016 slice0.516    0.625  mm27.50.6250.62525 - 3064 slice0.564  0.625 mm800.6250.625<15fig .  1scanning coverage of unenhanced and enhanced ct - acquisition ct acquisition protocol parameters scanning coverage of unenhanced and enhanced ct - acquisition an aortic stent - graft is a device composed of a metallic portion ( nitinol , elgiloy , and stainless steel ) and graft material ( polyester , ptfe ) . on ct images only the metallic portion is visualized . on the basis of the general morphology , there are three types of stent - grafts available for treating abdominal aortic aneurysms : straight , aorto - uni - iliac grafts and bifurcated . straight aortic tube grafts have the proximal and distal attachment sites in the aorta , above the aortic bifurcation ( aorto - aortic ) . the aorto - uni - iliac device is a stent - graft that is deployed from the supra - aneurysmal aorta to one iliac artery only ; the opposite iliac artery is then occluded with an endovascular occlusion device in order to prevent retrograde blood flow into the aneurysm sac , and a femoro - femoral crossover graft maintains blood flow into the opposite limb ( fig .  2 ) . bifurcated stent - grafts are extended to the iliac arteries . on the basis of proximal fixation , the suprarenal fixation device has an uncovered metallic portion placed above the ostia of the renal arteries and a covered portion placed below the renal arteries : the radiological markers placed between the uncovered and covered portion are represented by two metallic points located on the stent - graft metallic structure at the opposite position [ fig . the fenestrated device has a covered metallic portion of the graft that incorporates any visceral vessels such as the renal arteries , superior mesenteric artery or celiac trunk ; the patency of the incorporated vessels is maintained by the associated placement of covered stents ( fig . 2vrt ( a ) and mip ( b ) images : aorto - uni - iliac device associated with a surgical femoro - femoral cross - over graft . 3scout view and axial images showing the two metallic radiological markers placed in the opposite site between the uncovered and covered portion in a suprarenal fixation devicefig . 4mip ( a ) and vrt ( b ) images show a fenestrated stent - graft with a covered metallic portion that incorporates the renal arteries , which are made patent by the associated placement of covered stents ( c ) vrt ( a ) and mip ( b ) images : aorto - uni - iliac device associated with a surgical femoro - femoral cross - over graft . the left iliac limb is occluded by an  occluder  ( arrows ) scout view and axial images showing the two metallic radiological markers placed in the opposite site between the uncovered and covered portion in a suprarenal fixation device mip ( a ) and vrt ( b ) images show a fenestrated stent - graft with a covered metallic portion that incorporates the renal arteries , which are made patent by the associated placement of covered stents ( c ) stent - graft and distal branches are considered patent if a uniform and homogeneous contrast enhancement is detected within them . on the other hand , graft thrombosis is recognized as an intraluminal , concentric or eccentric hypodense area within the stent - graft on ct images obtained after contrast - media injection . angulation of the prosthesis could lead to a stenosis or thrombosis with consequent reduction of either the inflow or outflow , with increased possibility of in - stent thrombosis and stenosis , which can be manifest in about 319  % of cases [ 8 , 9 ] . graft occlusion appears as a complete non - enhancing intraluminal area within the stent - graft . graft limb occlusion may be directly due to compression of the limb in the proximal neck or in a narrow distal aneurysm neck , or to kinking or compression of the limb in a narrow or tortuous iliac artery . in case of iliac limb thrombosis , a femoro - femoral cross - over graft can be made , whereas a main body occlusion needs a complete surgical conversion . 5axial ( a ) and cpr ( b  c ) images show a stent graft thrombosis causing significant intraluminal stenosis axial ( a ) and cpr ( b  c ) images show a stent graft thrombosis causing significant intraluminal stenosis fractures or distortions of the metallic stent - graft structure are rare but important complications : these complications are better visualized on 3d rather than axial images ( fig . another complication that must be promptly recognized is stent - graft migration that occurs because of poor attachment of the stent to the aortic wall , which can cause sac reperfusion and subsequent aneurysm rupture.fig . 6mpr ( a ) and mip ( b ) images show a distortion of the metallic stent - graft structure . the integrity of the graft material as demonstrated by the linear and defined margin of the contrast - medium inside the stent - graft needs to be observed ( arrows ) . a type - ii endoleak is also detected ( * in b ) mpr ( a ) and mip ( b ) images show a distortion of the metallic stent - graft structure . the integrity of the graft material as demonstrated by the linear and defined margin of the contrast - medium inside the stent - graft needs to be observed ( arrows ) . unless the graft can be extended proximally , treatment is usually carried out by conversion to open repair . only migration of more than 4  mm this is related to a number of factors , including inadequate proximal fixation ( incorrect sizing , conical - shaped neck , short neck and angulation of the neck ) , progressive dilatation of the proximal neck and aneurysm size , as well as iliacal fixation [ 1012 ] . mdct angiography clearly detects minimal stent - graft migration : the diagnosis is based on the comparison of 1-month follow - up ct images evaluating the relationship between the proximal end of the stent - graft and lumbar vertebral body or renal artery origin on 3d and axial images , respectively ( fig . 7).fig .  7one  month ( a ) and 1  year ( b ) post - evar follow - up sagittal mip images . at 1  year follow - up the stent graft appeared to have migrated distally with a significant angulation of the main body one  month ( a ) and 1  year ( b ) post - evar follow - up sagittal mip images . at 1  year follow - up the stent graft appeared to have migrated distally with a significant angulation of the main body since aneurysm exclusion is expected to be correlated with shrinkage , surveillance of aneurysm dimensions is mandatory for asserting the adequacy of aneurysm exclusion from the blood flow and for guiding the need for reintervention in selected cases . the aneurysm volume may increase slightly immediately after evar ( 34  mm ) , given the additional volume and the external force exerted by the stent - graft or , alternatively , the swelling of the aneurysm sac induced by perigraft thrombosis . on the other hand , the volume tends to increase if sac perfusion is present or decreases during the follow - up in the absence of endoleaks . diameter measurements are most accurate if performed on axial images perpendicular to the aortic long axis , but volume assessment has been proven to be more accurate than diameter in the early detection of aneurysm growth ; however , volume assessment is time - consuming and requires advanced processing , dedicated equipment and skilled operators . endoleak is defined as a persistent blood flow within the sac excluded from the stent - graft , and it occurs in 2.445.5  % of patients after evar . on cta images , the endoleak appears as a high attenuation area outside the graft but within the aneurysm sac , detected on arterial and/or delayed phase images , but generally absent on unenhanced images . unenhanced images can be helpful to avoid false - positive diagnoses , allowing the differentiation of calcifications in the aneurysm sac from an endoleak ( fig . because endoleaks have variable flow rates , they can be detected at variable times after contrast material injection . for this reason , a delayed phase has been recommended : in detail , this phase could detect endoleaks not visualized during the arterial phase , the so - called low - flow endoleaks . early endoleaks occur in the first 30  days following evar , while endoleaks that fail to seal within 30  days are called persistent endoleaks . proper classification of an endoleak is important for its subsequent management [ 16 , 17].type i is caused by separation of the device from the arterial wall , resulting in leaks originating at the proximal and/or distal attachment sites of the graft because of a technical ( e.g. , suboptimal stent - graft diameter ) or anatomical ( e.g. , a short , irregular , ulcerated or angulated landing zone without an optimal conformation of the stent - graft to the curved aortic contour ) problems , or to its caudal migration . on cta images , it often appears as a huge and circumferential leak , adjacent to the proximal or distal end of the prosthesis ( figs .  9 and 10).type ii endoleaks are caused by back - filling of the aneurysm sac via branch vessels , such as the lumbar arteries and inferior mesenteric artery excluded by the stent - graft . on cta images , the type ii endoleak is most pronounced at the periphery of the aneurysmal sac , with little or no contact with the prosthesis , is commonly located in a posterior or lateral position , and is associated with opacification of the lumbar arteries . if an endoleak is located in the anterior position , a retrograde flow into the sac by the inferior mesenteric artery must be suspected ( fig . 11).type iii endoleaks arise from a fabric tear , modular or graft disconnection , and are more likely when multiple prostheses with short overlapping areas are used . on cta images , the leak is strictly adjacent to the prosthesis , with little or no contact with margins of the aneurysmal sac , without opacification of the lumbar arteries or inferior mesenteric artery ( fig . 12).type iv involves vascular flow caused by the high porosity of the graft , most likely created by the numerous suture holes holding the graft material to the stent . they are usually only detected on conventional angiograms performed at the end of the procedure.type v or endotension refers to a growth of the aneurysm sac but without demonstrable reperfusion defects ( fig . the combined analysis of unenhanced ( a ) , arterial ( b ) and late - phase enhanced images ( c ) allows the correct characterization of the thin hyperdensity within the sac ( arrows ) as a linear calcificationfig . 9axial ( a ) and mip- ( b ) images show the stent - graft caudal migration with subsequent proximal type - i leak ( * ) fig . 10axial ( a ) and cpr ( b ) images show an incomplete distal attachment of the right iliac limb causing a type i leak , as confirmed by dsa ( c)fig . axial ( a ) and thin mip ( b , c ) images show back - filling of the aneurysm sac through the inferior mesenteric arteryfig . 12vrt ( a , b ) , mip ( c ) and cpr ( d ) images show a type iii endoleak due to a right iliac limb disconnection and distal migrationfig . follow - up mdct examinations performed at 6  months ( a ) and 12  months ( b ) show an increase in sac diameter without evidence of endoleaks type i is caused by separation of the device from the arterial wall , resulting in leaks originating at the proximal and/or distal attachment sites of the graft because of a technical ( e.g. , suboptimal stent - graft diameter ) or anatomical ( e.g. , a short , irregular , ulcerated or angulated landing zone without an optimal conformation of the stent - graft to the curved aortic contour ) problems , or to its caudal migration . on cta images , it often appears as a huge and circumferential leak , adjacent to the proximal or distal end of the prosthesis ( figs .  9 and 10 ) . type ii endoleaks are caused by back - filling of the aneurysm sac via branch vessels , such as the lumbar arteries and inferior mesenteric artery excluded by the stent - graft . on cta images , the type ii endoleak is most pronounced at the periphery of the aneurysmal sac , with little or no contact with the prosthesis , is commonly located in a posterior or lateral position , and is associated with opacification of the lumbar arteries . if an endoleak is located in the anterior position , a retrograde flow into the sac by the inferior mesenteric artery must be suspected ( fig . type iii endoleaks arise from a fabric tear , modular or graft disconnection , and are more likely when multiple prostheses with short overlapping areas are used . on cta images , the leak is strictly adjacent to the prosthesis , with little or no contact with margins of the aneurysmal sac , without opacification of the lumbar arteries or inferior mesenteric artery ( fig . type iv involves vascular flow caused by the high porosity of the graft , most likely created by the numerous suture holes holding the graft material to the stent . they are usually only detected on conventional angiograms performed at the end of the procedure . type v or endotension refers to a growth of the aneurysm sac but without demonstrable reperfusion defects ( fig . the combined analysis of unenhanced ( a ) , arterial ( b ) and late - phase enhanced images ( c ) allows the correct characterization of the thin hyperdensity within the sac ( arrows ) as a linear calcification axial ( a ) and mip- ( b ) images show the stent - graft caudal migration with subsequent proximal type - i leak ( * ) axial ( a ) and cpr ( b ) images show an incomplete distal attachment of the right iliac limb causing a type i leak , as confirmed by dsa ( c ) type ii endoleak . axial ( a ) and thin mip ( b , c ) images show back - filling of the aneurysm sac through the inferior mesenteric artery vrt ( a , b ) , mip ( c ) and cpr ( d ) images show a type iii endoleak due to a right iliac limb disconnection and distal migration type v endoleak ; axial images . follow - up mdct examinations performed at 6  months ( a ) and 12  months ( b ) show an increase in sac diameter without evidence of endoleaks type i and type iii endoleaks require prompt treatment as they are associated with a high risk of sac rupture . however , the most common endoleak found in endovascular stent - grafting is the type ii endoleak . renal artery stenosis , occlusion and dysfunction represent the main concern with evar , especially in patients with inadequate anatomy of the proximal aneurysm neck , pre - existing renal disease or in whom suprarenal fixation was used . axial ct images are commonly used to monitor the patency of these arteries following stent - graft placement and to detect renal infarction following suprarenal stent grafting . however , both mip and cpr are useful and complementary to axial images for the detection of stenosis and occlusions because of the tortuous course of the renal arteries . the additional views provided by ct angiography allow displaying the renal arteries in multiple planes and projections , which is often necessary for depiction of stenosis . in renal infarction , contrast - enhanced ct scans demonstrate a sharply demarcated , wedge - shaped area of decreased attenuation in the kidney   ( fig . however , to date no significant correlation has been found between evar and renal impairment [ 1920].fig . the right kidney appeared decreased in size and showed an area of parenchymal hypoperfusion due to infarction mip images obtained before ( a ) and after ( b ) evar . the right kidney appeared decreased in size and showed an area of parenchymal hypoperfusion due to infarction usually a transfemoral approach is used to perform evar , exposing the femoral artery by a vertical groin incision . the large - caliber delivery sheaths used for evar , up to 26 fr , increase the morbidity rate compared to the usual catheter size used for routine diagnostic angiography . the minimum vessel diameter required to allow passage of the evar device is 78  mm . access site complications include dissection , demonstrated by a linear endoluminal hypodense area ( intimal flap ) ( fig . 15a  b ) or arterial rupture , with contrast material extravasation outside the artery . other complications are pseudoaneurysms , especially close to the entrance site , hematomas near the femoral incision , demonstrated by a high - attenuating area ( fig . 15c ) , infections and lymphoceles .fig .  15axial ( a ) and mip ( b ) images show an endoluminal hypodense line within the right external iliac artery representing a dissection ; c axial image shows bilateral small hematomas at the femoral incision site axial ( a ) and mip ( b ) images show an endoluminal hypodense line within the right external iliac artery representing a dissection ; c axial image shows bilateral small hematomas at the femoral incision site mdct is the method of choice both in the pre- and postoperative setting of evar procedures . a better understanding of the procedure followed , the devices used , the normal postoperative imaging features and the possible procedure - related complications ensures an optimal planning and follow - up of patients who undergo an evar procedure . finally , in order to better determine the long - term performance of these devices , strict surveillance of all patients is mandatory this article is distributed under the terms of the creative commons attribution license which permits any use , distribution , and reproduction in any medium , provided the original author(s ) and the source are credited .