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Review Article

CT angiography and magnetic resonance angiography findings after surgical and interventional radiology treatment of peripheral arterial obstructive disease Michele Anzidei MD, PhDa, Pierleone Lucatelli MD, EBIRa,*, Alessandro Napoli MD, PhDa, Sjoerd Jens MDb, Luca Saba MD, PhDc, Gaia Cartocci MDa, Pietro Sedati MDd, Alessandro d’Adamo MDa,e, Carlo Catalano MDa a

Vascular and Interventional Radiology Unit, Department of Radiological Oncological and Anatomo-pathological Sciences, “Sapienza” University of Rome, Viale Regina Elena 324, Rome 00161, Italy b Department of Radiology, Academic Medical Center, Amsterdam, The Netherlands c Department of Radiology, Azienda Ospedaliero Universitaria di CagliaridPolo Monserrato, Cagliari, Italy d Department of Radiology, Universita` Campus Bio-Medico di Roma, Rome, Italy e Dipartimento di Chirurgia Generale “P.Stefanini”, divisione di chirurgia vascolare d’urgenza. “Sapienza” universita` di Roma, Rome, Italy

article info

abstract

Article history:

In the last years, technical innovations in the field of CT angiography (CTA) and magnetic

Received 27 May 2014

resonance angiography (MRA) have allowed accurate and highly detailed evaluation of

Received in revised form

peripheral vascular pathologies. This has dramatically changed the diagnostic approach in

10 October 2014

treatment planning of peripheral arterial obstructive disease and also enabling early

Accepted 7 January 2015

identification of treatment failure or treatment-related complications after surgical or

Available online 14 January 2015

endovascular procedures. Although Doppler Ultrasound is the first-line imaging modality during follow-up after treatment, its role is currently diminishing in importance mostly

Keywords:

because of the proliferation of high-end CT and MR scanners capable of fast, reproducible,

Peripheral arterial obstructive

and highly reliable vascular imaging. The aim of this study is to review the various surgical

disease (PAOD)

and endovascular procedures for peripheral arterial obstructive disease and to provide CTA

CT angiography

and MRA samples of common and uncommon complications related to treatment.

MR angiography

ª 2015 Society of Cardiovascular Computed Tomography. All rights reserved.

Endovascular complications

Conflict of interest: The authors declare that they have no conflicts of interest. Authors had full control of all the data and information presented in this manuscript. * Corresponding author. E-mail address: [email protected] (P. Lucatelli). 1934-5925/$ e see front matter ª 2015 Society of Cardiovascular Computed Tomography. All rights reserved. http://dx.doi.org/10.1016/j.jcct.2015.01.007

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Fig. 1 e CT angiogram of a 79-year-old male patient previously treated with aortobifemoral bypass due to bilateral obstruction of the common and external iliac arteries (TASC D). Three weeks after treatment, right inguinal swelling occurred. Frontal volume rendering image (A) demonstrates bilateral small pseudoaneurysms at the femoral anastomotic sites (arrowheads). The soft-tissue visualization setting applied to the same image (B) shows a round mass at the right inguinal wall (asterisk). Hypodense perivascular collection (asterisk) is confirmed on both transversal Multi Planar Reconstruction (MPR) (C) and curved planar reformation (CPR) (D) images. The findings indicate a subacute seroma. Treatment is not required because of the absence of compression on the vascular structures.

1.

Introduction

In the last years, technical innovations in the field of CT angiography (CTA) and magnetic resonance angiography (MRA) have allowed accurate and highly detailed evaluation of peripheral vascular pathologies.1,2 This has dramatically changed the diagnostic approach in treatment planning of peripheral arterial obstructive disease (PAOD) and also enabled early identification of treatment failure or treatmentrelated complications after surgical or endovascular procedures. Radiologists should be familiar with the various types of treatment for PAOD, as prescribed by the TransAtlantic Inter-Society Consensus (TASC) II classification,3 as well as the related complications. Doppler ultrasonography (DUS) represents the first-line imaging technique for both diagnosis of PAOD and followup of most surgical or endovascular treatments. Although DUS is fast, relatively inexpensive, and widely accessible; it has limitations that are well known, including operator or scanner dependence and reduced field of view over long

vascular segments. Other major criticisms of DUS arise in particular anatomic regions, as in example the aortoiliac district (lack of visibility due to bowel interposition, high body mass index) or the lower limb district (reduced diagnostic accuracy in heavily calcified vessels, as commonly encountered in PAOD). Moreover, life-threatening complications that require a prompt treatment, such as bleeding, acute ischemia, distal embolization, or femoral pseudoaneurysm with retroperitoneal spread, could be misinterpreted or underestimated by DUS necessitating a second-line imaging. The role of DUS in patients’ follow-up after treatment, as well as in the initial diagnosis of vascular pathologies, is currently diminishing in importance, mostly because of the progressive diffusion of high-end CT and MR scanners capable of fast, reproducible, and highly reliable vascular imaging. The aim of this article is to review the various surgical and endovascular procedures for PAOD and to provide CTA and MRA samples of common and uncommon complications related to treatment.

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Fig. 2 e CT angiogram (CTA) and magnetic resonance angiogram (MRA) of a 62-year-old male diabetic and smoker previously treated with a surgical repair of an abdominal aortic aneurysm (aortobi-iliac graft), complaining of right leg claudication 2 years after treatment. Frontal volume-rendering image from pretreatment CTA demonstrates short obstruction (TASC C) of the right superficial femoral artery (A, dashed line). The treatment of choice was surgical recanalization with a crossover femorofemoral bypass graft. Two weeks after treatment, the patient reported recurrence of the symptoms and buttock claudication. The frontal maximum intensity projection (MIP) reconstruction of the posttreatment MRA (B) demonstrates patency of the graft (arrowheads) but shows retrograde obstruction of the right common and external iliac axis (dashed line) and distal obstruction of the popliteal artery (dashed line) and tibioperoneal trunk, with run-off circulation sustained by collateral vessels. The patient was subsequently treated with femorodistal bypass.

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Fig. 3 e CT angiogram of a 65-year-old male diabetic patient with obstruction of the left common and external iliac axis (TASC D) surgically treated with crossover femorofemoral bypass. Symptoms were left inguinal pain, swelling, and fever 20 days after treatment. Volume-rendering reconstruction (A) demonstrates patency of the Dacron bypass graft and the anastomotic sites (arrows). MPR transversal sections reconstructed along the bypass axis (B, C, D) demonstrate a fluid collection around the left femoral anastomosis (arrowheads) as well as some small air bubbles in the subcutaneous soft tissue (asterisks). The findings indicate localized graft infection, subsequently treated with aggressive antibiotic therapy.

2.

Imaging protocol

In our institution, all CTA examinations are performed on a 64- or a 128-slice multidetector CT scanner (Siemens Sensation 64 and Siemens Definition, respectively [Siemens Healthcare, Erlangen, Germany]) with the following scan protocol: section thickness of 0.6 mm, reconstruction interval of 0.5 mm, voxel size of 0.6  0.6  0.6 mm3, 100 kV, reference mAs for modulated tube current of 200, table feed of 40 mm/s. Patients are placed supine, feet first on the scanner table, legs slightly rotated internally. High injection flows of at least 4 mL/s and a contrast media concentration of 400 mgI/mL (Iomeron 400, Bracco S.p.A., Milan, Italy) are used to achieve high and homogeneous arterial opacification. Bolus tracking is performed in the lumen of the proximal abdominal aorta, or thoracic aorta in patients with axillofemoral bypass, to synchronize contrast administration and scan start (attenuation threshold of D200 HU). It should be considered that PAOD may alter arterial flow velocity, mostly below the knee, resulting in poor opacification of calf and foot vessels. In these cases, it can be useful to perform an additional “rescue scan” of the calf if needed, starting immediately in caudocranial direction after the end of the first acquisition. All MRA examinations are performed on a 1.5 T MR scanner (Siemens Avanto; Siemens Healthcare) with a gradient strength of 45 mT/m and maximum slew rate of 200 T/m/s,

equipped with a dedicated 32-channel peripheral phasedarray coil. Patients are imaged in the supine position using a monophasic protocol for contrast agent administration. Mask and postcontrast acquisitions of the aortoiliac, femoral, and calf regions are performed in the coronal plane using a 3dimensional gradient-echo sequence with centric k-space sampling (time of repertition (TR), 3.5 ms; time of echo (TE), 1.2 ms; flip angle (FA), 30 ; time of acquisition (TA), 14 or 24 s; slice thickness, 1/1.5 mm; matrix, 384  384 in the aortoiliac region, 448  448 in the femoropopliteal region, and 512  512 in the calf region; integral parallel acquisition technique (IPAT), 2). The synchronization between contrast injection (15 mL of gadobenate dimeglumine Gd-BOPTA, Bracco Spa, Milan, Italy, at a rate of 2 mL/s with 15 mL of saline flush) and start of the contrast-enhanced acquisition is obtained using a MR fluoroscopy bolus-tracking sequence at the level of the abdominal aorta. A modified high-resolution, 3-dimensional, spoiled gradient echo sequences (GRE) sequence can be optionally acquired in the anatomic region of interest on the coronal plane with centric k-space sampling (TR, 7.5 ms; TE, 2.3 ms; FA, 20 ; TA, 90 s; slice thickness, 0.7 mm; matrix, 512  512; IPAT, 2).

2.1.

Surgical procedures in the aortoiliac region

Surgery is the first choice of treatment of patients with Fontaine stage IIb, III, or IV with TASC II C or D lesions.3 Surgical

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Fig. 4 e CT angiogram of a 77-year-old male diabetic patient with obstruction of the left superficial femoral artery extended to the popliteal artery (TASC D), which was treated surgically with autologous femorodistal bypass. Twelve days after treatment, complaints of left leg pain, swelling, and fever occurred. Volume-rendering reconstruction (A) demonstrates patency of the venous graft (arrows). CPR (B) and MPR transversal images perpendicular to the bypass axis (C, D) demonstrate a fluid collection around the graft (arrowheads) with wall enhancement, as well as some small air bubbles in the swelled subcutaneous soft tissue. The findings indicate widespread graft infection, subsequently treated with graft explantation.

procedures for PAOD of the aortoiliac region include endarterectomy or aortofemoral or extra-anatomic bypass. Endarterectomy consists of dissection of the arterial wall and removal of the atherosclerotic plaque; at present, it has been replaced by alternative surgical techniques for most applications, and its only residual indication is represented by localized aortoiliac occlusive disease. The main advantage of endarterectomy is the absence of exogenous prosthetic graft that significantly reduces the risk of infection.4 Iliac endarterectomy is contraindicated in case of coexistent aneurysms or extension of atherosclerotic lesions below the iliac bifurcation. Aortofemoral bypass is the standard surgical procedure for treatment of aortoiliac atherosclerotic lesions and can be extended to exclude bilateral stenosis or obstructions (aortobifemoral bypass). During this procedure, a synthetic graft in polyester (Dacron) or polytetrafluoroethylene (PTFE) is connected from the aorta to common femoral or superficial femoral arteries. Dacron has better handling characteristics but needs preclotting and is prone to caliber dilatation in the

long term (10%e20%). On the other hand, the main advantage of PTFE is represented by its impermeability that avoids the need for preclotting. The proximal anastomosis may be either end to end, which is preferred in complete iliac or aortic obstruction, or end to side, thereby preventing devascularization of the pelvic region. Distal anastomosis is usually performed on the common femoral artery (CFA). Contraindications of aortofemoral bypass procedures are high surgical risk, aortoduodenal fistula, and prior extensive abdominal surgery. The patency rate at 5 and 10 years ranges between 85% and 90% and 70% and 75%.5 Extra-anatomic bypass procedures are performed on alternative, nonanatomic pathways and include axillofemoral and femorofemoral grafts. In the axillofemoral bypass, the subclavian artery provides the inflow to an extracavitary graft anastomosed to the ipsilateral CFA. This procedure can be performed under local anesthesia, being suitable in high-risk patients, including subjects with previous extensive abdominal surgery, infected aortic grafts, aortoduodenal fistula, or

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Fig. 5 e CT angiogram of a 59-year-old female diabetic patient previously treated with a right femoropopliteal bypass due to long obstruction of the superficial femoral artery (TASC C). Leg pain and inconclusive Doppler ultrasonography examination 7 months after treatment resulted into the performance of a CTA. Frontal volume-rendering image (A) demonstrates a polytetrafluoroethylene graft with corrugated appearance. CPR reconstruction (B) shows hypodense material in the bypass lumen (arrowhead ) near the proximal anastomosis, indicating bypass stenosis due to progressive atherosclerotic disease. The finding is confirmed at digital subtraction angiography (DSA) (C), which demonstrates severe stenosis of the graft lumen (arrowhead ) before angioplasty. chronic infrarenal aortic occlusion. Patency rates are 86%, 72%, 63% at 1, 3, and 5 years, respectively.6 The femorofemoral bypass (or crossover bypass) connects the 2 CFAs with a PTFE graft passing through a suprapubic subcutaneous tunnel. Its main indications are represented by unilateral occlusion of the common or external iliac artery and extension of an axillofemoral bypass (axillobifemoral bypass). The 5-year patency rate ranges from 40% to 80%.7

2.2. Surgical procedures in the femoropopliteal and below-the-knee regions The surgical strategy for femoropopliteal revascularizations depends on the distribution of the lesions, on the nature and the extent of previous surgical or endovascular procedures, and on the availability and location of autogenous veins for graft harvesting. Surgical procedures include profundoplasty or infrainguinal arterial bypass (IGAB). Profundoplasty is mainly carried out after an endarterectomy of the superficial femoral artery (SFA), performing an arteriotomy of the profunda femoris artery (PFA) closed using a vein or graft patch, thus resulting in an increased arterial caliber. The main indications of this procedure are represented by stenosis of the PFA with coexistent obstruction of the SFA in patients candidate to aortobifemoral bypass and/or occluded SFA with >50% stenosis of the PFA. IGAB is performed with the deployment of an autologous or synthetic bypass over an occluded arterial segment of the

lower limb (TASC II C or D lesions). The ideal bypass should be as short as possible and anastomosed to a disease-free distal arterial segment. According to the location of the anastomoses, IGAB can be classified as femoropopliteal bypass (above or below knee), femorocrural bypass (landing on a crural vessel, the anterior tibial, posterior tibial or fibular artery), poplitealdistal or popliteal-crural bypass. Distal bypasses are performed only when a femoropopliteal bypass is not possible. IGAB classification can also be based on the type of material and technique used. Autogenous venous bypasses are usually performed with the greater saphenous vein.8,9 When the greater saphenous vein is not available, the lesser saphenous vein, arm veins, or a spliced venous conduit can be used. Prosthetic bypasses include PTFE and polyester grafts.10,11 Regarding femoropopliteal and distal bypasses, the most important factors predicting short- and long-term patency are the state of the run-off and the completeness of the plantar arch. To improve the patency of prosthetic bypass in case of impaired run-off, an arteriovenous fistula can be created distally to the caudal anastomosis to improve the outflow and decrease the distal vascular resistance. In comparison with autogenous venous bypasses, synthetic grafts are less compliant, with higher rate of intimal hyperplasia and acceleration of distal atherosclerosis, higher frequency of thrombosis, infections, and anastomotic aneurysms. Moreover, failure of prosthetic grafts often leads to distal embolization, whereas failure of venous bypasses merely returns patients to presurgical condition. In composite graft bypasses,

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Fig. 6 e CT angiogram of a 68-year-old male diabetic patient with bilateral obstruction of the superficial femoral artery (TASC C) surgically treated with femoropopliteal bypass graft complaining of worsening intermittent claudication 4 months after treatment. Panoramic volume-rendering view (A) shows bilateral obstruction of the bypass. Anterior (A, B) and posterior (C) volume-rendering views of the proximal and distal anastomotic sites (arrowheads) clearly demonstrate bypass obstruction along the whole femoral region. The polytetrafluoroethylene graft has a typical corrugated surface because of the multiple overlapping rings that constitute the prosthetic wall, whereas the Dacron bypass shows a smoother surface. Hypertrophic collateral vessels maintain perfusion of both popliteal arteries. Conservative treatment was performed because of progressive atherosclerosis.

the proximal segment is made of polyester or PTFE, whereas the distal segment uses the available portions of autogenous veins. These complex vascular reconstructions are usually performed in patients with critical limb ischemia (CLI) for limb salvage purposes and are not indicated for palliation of intermittent claudication.

2.3.

Complications related to surgery

Surgery-related complications are caused by the procedure itself or by the progression of the underlying atherosclerotic disease and can be differentiated between early and late complications. Early complications include hematoma, seroma, lymphocele, postoperative hemorrhage, acute graft occlusion, and graft infection.

Hematoma, seroma, and lymphocele are common minor complications and can be treated in a conservative manner or with a percutaneous approach. Their appearance is that of well-capsulated fluid collections on both CTA (Fig. 1) and MRA images, with variable densities or signal intensities depending on the presence of thrombi, blood, or clots. Postoperative hemorrhage is often related to suture line breakage or poorly ligated arterial or venous branches and may be a life-threatening complication needing immediate surgical treatment in case of acute anemia. High-flow hemorrhages are usually easily identified as contrast agent extravasations on both CTA and MRA, whereas low-flow bleeding is often indirectly visualized as late enhancement of the perivascular hematoma in venous phase scans. Acute graft occlusion is less common and requires immediate treatment to prevent limb ischemia. This complication can occur within the first month after surgery and is often due

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Fig. 7 e Magnetic resonance angiogram of a 73-year-old female diabetic patient with bilateral obstruction of the superficial femoral artery (TASC C) and surgical revascularization of the left side with Dacron femoropopliteal bypass. Symptoms of recurrent left side claudication 2 months after treatment occurred. Panoramic MIP image (A) shows bilateral obstruction of the femoral vessels and failed opacification of the bypass. MPR reconstruction of equilibrium phase acquisition in the sagittal (B) and axial (C) planes clearly demonstrate thrombosis of the bypass lumen (arrowheads), allowing evaluation of the graft surface (asterisk) similar to CT angiogram. No treatment could be performed. to technical errors such as a venous injury, anastomotic stenosis, valvulotome injury, intimal flaps, small-caliber vein and kinks, or poor flow in the run-off vessel.12 Predicting

factors for bypass failure are distal graft end-diastolic velocity below 5 cm/s on Doppler ultrasonography, CLI, renal failure, diabetes, advanced age, ischemic heart disease, a

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Fig. 8 e CT angiogram of an 82-year-old male atherosclerotic patient with Leriche syndrome (TASC D) surgically treated with Dacron axillobifemoral bypass, complaining of bilateral intermittent claudication and right leg pain 12 months after treatment. Panoramic frontal volume-rendering reconstruction (A) demonstrates patency of the graft (arrowhead ). Close-up volume-rendering image on the femoral region (B) shows obstruction of the right superficial femoral artery due to progressive atherosclerosis as well as moderate kinking of the femorofemoral branch of the bypass near the left femoral anastomosis. The patient was treated with right femoral angioplasty and stenting.

postprocedural ankle or brachial index below 0,5, postoperative transcutaneous oximetry (PtcO2) of less than 35 mm Hg, and postoperative smoking.13,14 On both CTA and MRA, bypass obstruction is easily diagnosed when failed opacification occurs (Fig. 2). Graft infection is a potentially life-threatening complication and a risk factor for both bleeding and aortoenteric fistula. CTA and MRA can be helpful in confirming the diagnosis of graft infection, showing fluid collections at the anastomotic sites or along the graft body, with surrounding gas bubbles and soft-tissue swelling. Limited graft infections can be managed with antibiotic treatment (Fig. 3), whereas surgical revision is reserved to more severe cases (Fig. 4). Late complications include graft stenosis or occlusion due to recurrent obliterative disease or external compression, pseudoaneurysms, and aortoenteric fistulas. Graft stenosis or occlusion secondary to recurrent obliterative disease is commonly caused by progression of the underlying atherosclerotic disease and by intimal hyperplasia. Surgical revision is required in cases of anastomotic stenosis, whereas endovascular treatment with thrombolysis is sufficient in cases of midgraft stenosis. The appearance of graft stenosis on both CTA and MRA is similar

to that of a native vessel stenosis, with hypodense or hypointense material in the graft lumen causing focal caliber reduction (Fig. 5); chronic obstruction, similarly to acute obstruction, appears as complete absence of graft opacification (Figs. 6, 7). Thrombosis or stenosis of an extra-anatomic bypass can be caused by external compression, kinking, or progression of distal and proximal disease. Close monitoring of the bypass may rapidly identify graft failure, enabling preventive treatment (percutaneous angioplasty, placement of a patch or graft extension). CTA and MRA can be helpful in determining the site of compression, kinking (Fig. 8), or restenosis. Pseudoaneurysms and subsequent anastomotic dehiscence are mainly caused by excessive tension of the graft, kinking, or infection. On both CTA and MRA, pseudoaneurysms are usually identified as focal outpouching of the vessel walls in the proximity of an anastomotic site. The size of pseudoaneurysms is variable, ranging from few millimeters (Fig. 9) to several centimeters (Fig. 10), with larger ones often showing partial thrombosis of the lumen. Aortoenteric fistulas are life-threatening complications that need emergent surgical management. Even if diagnosed

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Fig. 9 e CT angiogram (CTA) of a 60-year-old female previously treated with an angioplasty of the left popliteal artery undergoing routine post-treatment CTA evaluation 6 months after treatment. Right oblique volume-rendering image shows (A) focal dilatation of the wall of the left common femoral artery at the DSA puncture site (arrowhead ). The small pseudoaneurysm is confirmed on the CPR reconstruction (B, arrowhead ) with automated lumen measurements both at the pseudoaneurysm level (C) and below (D). In this case, the patient was scheduled for short-term follow-up rather than for treatment because of the small size of the pseudoaneurysm.

and treated early, the outcome of operative treatment has a high morbidity and mortality rate (Fig. 11).

3. Endovascular procedures in the aortoiliac region Endovascular techniques play a fundamental role in the treatment of aortoiliac PAOD in patients with TASC II A or B

lesions owing to the high rate of technical success and the high patency rate in the long term. The 2 cornerstone techniques of endovascular treatment are percutaneous transluminal angioplasty (PTA) and stenting. PTA, performed either with an endoluminal or a subintimal approach, is usually adopted as a first-line treatment, with early clinical success rates that exceeds 90% in iliac artery stenoses and 5-year patency rates ranging between 54% and 92%.15

Fig. 10 e CT angiogram (CTA) of a 65-year-old male with dyslipidemia previously treated with an aortobi-iliac bypass graft due to bilateral acute iliac obstruction (TASC D). Routine post-treatment CTA evaluation 6 months after treatment was performed. Frontal volume-rendering image (A) shows an abnormal outpouching of the vessel wall close to the right iliac anastomosis (arrowhead ). The same finding is clearly demonstrated by the transversal MPR (B), reconstructed perpendicularly to the bypass axis, showing the focal interruption of the intimal profile (asterisk). The pseudoaneurysmal sac is partially thrombosed. Because of the critical location and the large size of the pseudoaneurysm, the patient was immediately scheduled for endovascular treatment.

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Fig. 11 e CT angiogram (CTA) of a 62-year-old female previously treated with an aortobi-iliac bypass graft due to bilateral acute iliac obstruction (TASC D) and right ureteral stenting due to stenosis caused by chronic graft infection presenting with hypovolemic shock after massive hematemesis. Precontrast CT images (A) demonstrate the bypass graft (arrowhead ) and hyperdense blood clots into the stomach and duodenum (asterisk). CTA images acquired during the arterial phase (B) show extremely delayed blood flow with failed opacification of the bypass graft (arrowhead ) as well as the right ureteral stent (asterisk). Additional images acquired in the venous phase, 60 seconds after contrast agent injection (C), demonstrate active extravasation of contrast agent from the graft wall into the duodenal lumen (arrowhead ), as well as bilateral striated nephrogram (asterisk), due to shock hypoperfusion.

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86% at 1 year, 42% and 60% at 3 years, and 41% and 58% at 5 years,18,19 with reduced risk of late restenosis using drugeluted angioplasty.20,21 Disadvantages of PTA include a low success rate in case of highly calcified plaques, due to the low radial force of the angioplasty, and the risk of flow-limiting dissection requiring endovascular repair. Stenting of the femoropopliteal region should be adopted in all cases in which PTA fails or cannot be performed, including treatment of heavily calcified lesions and flowlimiting dissection during PTA. The patency rate is strongly influenced by the stent material, ranging from 50% at 1 year for cobalt-based alloy stents22 to 66% to 87% at 4 years for nitinol stents,23,24 and 94% and 68% at 6 and 12 months, respectively, for drug-eluted stents and covered stent graft.25e27 The main disadvantages of stenting are represented by the costs and by the potential technical obstacles to further treatment in the same arterial segment (including distal bypass or subintimal recanalization). For both PTA and stenting, preprocedural occlusion, stenosis length, and compromised postprocedural infrapopliteal run-off vessel influence early restenosis or reocclusion.28,29 Finally, several studies reported initial clinical results of endoluminal plaque debulking techniques such as directional, laser, or mechanical thrombectomy.30e32 The main advantage of debulking techniques is represented by the possibility to treat arterial segments usually not suitable for stenting (common femoral artery, popliteal artery, and crural arteries). The reported primary and secondary patency rate at 18 months for all lesions is 52.7% and 75.0%, respectively.33 However, these techniques have not yet been implemented in daily clinical practice because of their high costs and the consistent risks of complications, including arterial wall laceration, periprocedural bleeding, arteriovenous fistula, and distal embolization.

5. Complications related to endovascular procedures Stenting of the iliac arteries is indicated when PTA fails or is inadequate because of elastic recoil of the arterial walls or if a flow-limiting dissection occurs resulting in significant residual stenosis (>30% stenosis on angiography and/or a residual peak-to-peak systolic pressure gradient of >5 mm Hg). Iliac artery stenting is a robust tool, with good short- and longterm patency rates, in managing aortoiliac PAOD.16,17 Both PTA and stenting can be performed via a retrograde ipsilateral common femoral artery puncture or via a retrograde contralateral common femoral artery puncture.

4. Endovascular procedures in the femoropopliteal and below-the-knee regions Endovascular tools to treat distal PAOD include PTA, stenting, and endovascular arterectomy. PTA, either endoluminal or subintimal, was the first tool developed for the treatment of PAOD. Its main advantages are represented by the low costs, by its repeatability, and by the possibility to perform distal bypass on the native vessel if the procedure fails. The primary patency rates of femoropopliteal PTA range between 47% and

As previously stated, endovascular procedures lead to excellent long-term outcome in the aortoiliac and femoropopliteal segments. Hence, the more frequent and clinically relevant complications are directly related to the procedure itself rather than to disease recurrence in the treated segment. Complications can be classified as early or late. Early complications include puncture-site hemorrhage and distal embolization. Puncture-site hemorrhage can be differentiated into groin, retroperitoneal, or intraperitoneal hemorrhage. Groin hematoma is caused by bleeding of the access site and resolves spontaneously in most patients. Retroperitoneal or intraperitoneal hemorrhage could be caused by an erroneous percutaneous access above the inguinal ligament or by a direct injury of the iliac axis. Erroneous percutaneous access can be minimized with ultrasound-guided femoral puncture. When bleeding is noticed during the procedure, balloon occlusion should be performed immediately and the placement of a covered stent should be considered; surgery is reserved to the cases in which in-procedure treatment fails. On the other hand, when bleeding is suspected after the procedure, the bleeding site must be

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Fig. 12 e CT angiogram (CTA) of a 75-year-old atherosclerotic female patient previously treated with endovascular repair of the abdominal aortic aneurysm who recently underwent percutaneous angioplasty due to left external iliac stenosis. The patient was referred for emergency CTA 5 hours after the procedure because of acute left inguinal pain, tachycardia, and hypotension. Frontal MIP image (A) shows massive extravasation of contrast agent in the pelvic region (arrow). MPR transversal sections show a large left retroperitoneal hematoma (B, asterisk) and active bleeding near the puncture site at the left common femoral artery (C, arrowhead ) due to wall laceration. The patient soon died due to massive hemorrhage before emergency stenting could be performed.

Fig. 13 e CT angiogram (CTA) of a 63-year-old atherosclerotic and obese male with a short subobstruction of the left common and external iliac axis (TASC B). He was treated with angioplasty and implantation of a self-expandable iliac stent. Right foot pain and finger ischemia occurred 24 hours after treatment. Frontal volume-rendering reconstruction demonstrates the stenosis site (A, dashed line) and the stent positioning (C, arrow). Volume-rendering close-ups on the right foot before (B) and after treatment (D) demonstrate disappearance of the dorsalis pedis artery (arrowhead ) due to plaque embolization during the endovascular procedure. The finding is confirmed by DSA (E, arrowhead ) obtained before emergency fibrinolysis.

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Fig. 14 e Magnetic resonance angiogram of a 67-year-old female with atherosclerosis and diabetes treated with stenting of the right external iliac artery due to severe stenosis (TASC B). Routine post-treatment MRA evaluation was performed 6 months after treatment; in this case, CT angiography was avoided because of a previous allergic reaction to iodinated contrast agents. Frontal MIP image (A) demonstrates partial loss of signal at the stent site due to magnetic susceptibility artifacts (arrow). Arterial flow in the right external iliac artery and right common femoral artery below the stent is preserved and can be considered as an indirect sign of stent patency. Equilibrium phase imaging (B, C), because of different acquisition parameters and heavier T2* signal dependence, shows complete loss of signal into the stent lumen (asterisk), simulating obstruction. No treatment was required.

Fig. 15 e CT angiogram of a 54-year-old male dyslipidemic patient previously treated with angioplasty and multiple stent implantation due to severe multifocal stenosis of the left superficial femoral artery (TASC B). He presented with recurrent claudication 6 months after treatment. CPR image (A) demonstrates several focal and hypodense thickenings of the inner surface of the stent complex, with severe stenosis at the proximal end of the stent (arrowhead ). The finding is confirmed at DSA (B), clearly showing proximal stent stenosis, before angioplasty. Transversal MPR images with sharp filters reconstructed perpendicularly to the stent axis confirm lumen stenosis, allowing optimal evaluation of the stent surface with automated lumen surface assessment, both at the stenosis site and below (C, D). Virtual angioscopic views (E, F) provide visualization of the intimal hyperplasia (asterisk) at the stenosis site.

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Fig. 16 e CT angiogram of a 62-year-old male diabetic patient with severe stenosis of the left superficial femoral artery (TASC B) treated with an endovascular approach. The procedure was complicated by stent obstruction and subsequently resolved with a femorodistal venous bypass. Panoramic frontal volume-rendering image (A) demonstrates the bypass course. Posterior volume-rendering view (B) demonstrates absence of vessel opacification (arrowhead ) between the distal end of the stent and the proximal popliteal artery, consistent with stent obstruction. Opacification of the distal and infraarticular segments of the popliteal artery is present, likely allowed by retrograde flow from the patent bypass. Saphenectomy clips are also demonstrated (asterisk). MPR transverse image (C) shows both the patent bypass and obstructed stent.

identified at imaging to plan appropriate treatment. In postinterventional hemorrhage, either CTA or MRA may demonstrate both the hematoma and the bleeding site (Fig. 12). It must be considered that smaller contrast agent extravasations may be visible only with venous or late phase acquisitions. Distal embolization can occur both during iliac PTA and stenting procedures. Although in some cases distal embolization may be asymptomatic, acute ischemia may occur, thus requiring thrombolysis or thrombectomy. CTA and MRA can be helpful in identifying distal embolization when a pretreatment examination is available for comparison (Fig. 13). Absence of previously normal distal arterial branches of the calf and foot at short-term follow-up is usually a confirmatory sign for clinically suspected distal embolization. A higher rate of distal embolization is associated with in-stent restenosis and chronic total occlusions in TASC II C and D lesions as compared with TASC A and B lesions.34 Late complications include pseudoaneurysms and stent occlusion or restenosis due to recurrent obliterative disease.

Treatment of pseudoaneurysms depends on their size. At first, manual compression should be attempted. In case the pseudoaneurysm is larger than 2 cm, percutaneous thrombin injection under ultrasound guidance or surgical revision should be considered. The CTA and MRA findings are similar to those of postsurgical pseudoaneurysms. Stent occlusion or restenosis can occur because of the progression of the underlying atherosclerotic disease proximal or distal to the stent and/or because of intimal hyperplasia. Reocclusion or restenosis has a wide spectrum of clinical manifestations ranging from mild claudication to CLI. Treatment can be proximal or distal angioplasty, recanalization, thrombolysis, or surgical bypass in selected cases.35 Because many stents produce susceptibility artifacts at MRA owing to their metallic composition (Fig. 14), CTA represents the modality of choice to evaluate these patients. For the same reason, CTA data sets should be preferably reconstructed with sharp filters to reduce blooming artifacts from stent walls, allowing better differentiation between the various degrees of

Table 1 e Summary of different surgical and endovascular treatment of both aortoiliac and femoropopliteal districts. Complications

MRA

Treatment

Additional information

Hypodense capsulated fluid collection (Fig. 1)

Fluid signal

Expectatively or percutaneous drainage

Postoperative hemorrhage

High flow: extravasation of contrast agent Low flow: late enhancement of perivascular hematoma

High flow: extravasation of contrast agent Low flow: late enhancement of perivascular hematoma

Immediate surgery, consider embolization Expectative if clinical signs are mild

Acute graft occlusion

Failed enhancement of arterial segment (Fig. 2A) Localized fluid collection with gas bubbles and soft-tissue swelling near the graft (Fig. 3) Localized fluid collection with gas bubbles and soft-tissue swelling near the graft (Fig. 4)

Failed enhancement of arterial segment (Fig. 2B) Localized fluid collection with gas bubbles and soft-tissue swelling near the graft Localized fluid collection with gas bubbles and soft-tissue swelling near the graft

Revascularization (surgical or endovascular) or/and thrombolysis Antibiotic treatment

Surgical graft explantation and revision of bypass to extraanatomical bypass

Risk factor for bleeding and aortoenteric fistula

Hypodense graft lumen (Fig. 5) causing focal caliber reduction or total absence (Fig. 6) of graft opacification

Hypointense graft lumen causing focal caliber reduction or total absence (Fig. 7) of graft opacification

Secondary to recurrent obliterative disease

Hypodense graft lumen causing focal caliber reduction or total absence (Fig. 8) of graft opacification Focal outpouching of the vessel walls near anastomotic site (Figs. 9, 10) Adhesion of bowel loop to treated vessel, associated to clinical evident bleeding

Hypointense graft lumen causing focal caliber reduction or total absence of graft opacification

- Stenosis of anastomosis: surgical revision - Stenosis or occlusion of midgraft region: endovascular thrombolysis PTA (percutaneous angioplasty), placement of patch or graft extension

Focal outpouching of the vessel walls near anastomotic site

2-cm Surgical revision

- Caused by extensive tension of the graft, kinking or infection

Adhesion of bowel loop to treated vessel, associated to clinical evident bleeding

- Emergent surgical treatment

- High morbidity and mortality rate

Graft infection: limited infection Graft infection: extensive infection Late Graft stenosis or occlusion

Thrombosis or stenosis of extra-anatomic bypass

Pseudoaneurysm

Aortoenteric fistula

Thrombus, blood, or clots in the collection may have variable densities and signal intensities - Life-threatening complication - If hemorrhage is suspected a venous phase acquisition should be made - Often related to suture line breakage Immediate treatment required to prevent limb ischemia Risk factor for bleeding and aortoenteric fistula

Caused by external compression, kinking or progression of distal or proximal disease

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Complications related to surgery Early Hematoma, seroma, or lymphocele

CTA

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- CTA is preferred because of the susceptibility artifacts in MRA - Reconstruct CTA with sharp filters to reduce blooming artifacts

Increased risk of bleeding

Stent occlusion or restenosis

Small hyperdense stent lumen (Fig. 14) or total absence of lumen opacification (Fig. 15)

Non-diagnostic because of susceptibility artifacts (Fig. 13)

- 2 cm or manual compression fails: percutaneous thrombin injection or surgical revision Proximal or distal PTA, stent placement, recanalization, thrombolysis or surgical bypass Focal outpouching of the arterial wall

Comparison of CTA or MRA with the previous acquisition(s)

Can also occur retroperitoneal or intraperitoneal

Expectative hemorrhage during procedure: consider stent placement if suitable according anatomy or surgical revision Thrombolysis or thrombectomy High flow: extravasation of contrast agent Low flow: late enhancement of perivascular hematoma Absence of arterial enhancement

Complications related to endovascular therapy Early Puncture-site hemorrhage High flow: extravasation of contrast agent (Fig. 11) Low flow: late enhancement of perivascular hematoma Distal embolization Absence of arterial enhancement (Fig. 12) Late Pseudoaneurysm Focal outpouching of the arterial wall

Table 1 e (continued )

Complications

CTA

MRA

Treatment

Additional information

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stenosis (Fig. 15) and obstruction (Fig. 16). Table 1 summarizes all type of different procedures and relatives complications.

6. Advantages and disadvantages of CTA and MRA The advantages and disadvantages of each imaging modality may be related either to factors intrinsic to the technique itself or to the clinical scenario. For what regards the first point, CTA can be considered particularly advantageous because of its wider clinical diffusion and its reduced costs (when comparing top-end CT and MR scanners), as well as for its faster and more simple acquisition modality. Apart from obvious considerations on the use of ionizing radiations that may encourage the use of MRA over CTA in younger patients or in subjects undergoing repeated examinations in short time intervals, it must be also considered that the use of iodinated contrast agents necessary for CTA is more commonly related to adverse events as compared with gadolinium-based contrast agents used in MRA36,37; similarly, cases of contrastinduced nephropathies related to iodinated contrast media exceed those of nephrogenic systemic sclerosis reported for gadolinium-based agents.38,39 For what regards the choice of the more appropriate technique basing on the clinical scenario, CTA allows faster image acquisition and is more easily accessible to life support and resuscitation units, making it the primary imaging option in emergency cases, such as critical limb ischemia or when an aortoenteric fistula or an active bleeding is suspected; CTA should be also preferred in the evaluation of stents because the accuracy of MRA is often impaired by susceptibility artifacts that may cause overestimation of stent restenosis, even if dedicated MR sequences have been developed to allow more accurate evaluation of stent lumen.40 On the other hand, MRA is capable of dynamic fluoroscopic-like acquisitions that may be extremely useful to differentiate between retrograde and anterograde flow in severely stenosed bypass grafts; similarly, difference in flow speed between the lower limbs is often a cause of suboptimal image quality in monophasic peripheral CTA acquisition in patients with severe obstructive disease, making dynamic MRA a more flexible option in this clinical setting.41

7.

Conclusion

Both CTA and MRA are valuable imaging tools to identify different types of complications related to endovascular and surgical procedures performed for PAOD. Knowledge of the various materials used for both endovascular and surgical interventions and of the signs of common and uncommon complications is essential for radiologists reporting on postprocedural CTA and MRA.

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