Diagnostic Angiography of Specific Vascular Territories

Introduction

The purpose of this article is to provide a concise review of fundamentals of angiography of major noncoronary arterial circulation. To put this in perspective, it is important to remind ourselves that angiography of an arterial tree is only warranted when the clinical presentation and noninvasive imaging have predicted a high likelihood of the presence of a flow-limiting lesion and the invasive study is used as a means of planning the treatment. Other indications for angiography include vasculitis and aneurysms. However, in a proper patient setting, when there are inconsistencies among various noninvasive modalities, angiography can be justified as the gold standard to determine lesion severity.

Contrast Agents

Contrast agents can be divided into 3 categories: iodinated contrast agents, gadolinium chelates, and carbon dioxide (CO2).

There are two major classes of tri-iodinated contrast agents: ionic and nonionic. Adverse reactions to iodinated contrast agents are unfortunately common, but the majority are minor. Most of the minor complications are linked to the osmolality of the contrast agent, so that the overall incidence is lower with nonionic contrast agents. The two major adverse reactions to iodinated contrast agents are anaphylaxis and renal failure. True anaphylaxis is distinguished from a vasovagal response by tachycardia and respiratory distress. The incidence of life-threatening anaphylaxis due to iodinated contrast is approximately 1 per 40,000 to 170,000, with mild reactions such as urticaria and nasal stiffness occurring more commonly (especially with ionic contrast).

Renal failure following administration of iodinated contrast agents is a clinical entity as part of a broad spectrum of clinical presentation of contrast-induced nephropathy (CIN), which is defined as rise of serum creatine by 0.5mg/dl or 25% following the invasive procedure. The rise usually starts within 24–36 hours following exposure to contras, peaking at 72–96 hours. Patients are usually oliguric, but may become anuric. Management is usually expectant, as the creatinine should return to baseline in 7–14 days. However, in patients with severe preexisting renal insufficiency and diabetes, the risk of permanent dialysis may be as high as 15%, despite the use of low-osmolar contrast agents, hydration (with normal saline), or use of acetylcysteine (600–1200 mg every 12 hours before and after the procedure). Iodinated contrast is administered during the angiographic procedures by a hand or power injection. A typical strategy is to use mechanical injection for aortography and hand injection for selection angiography. In either case, the contrast can be diluted with saline in a 50/50 ratio.

Alternative contrast agents. The low but real incidence of adverse reactions to iodinated contrast agents has led to the use of alternative contrast agents in selected circumstances, particularly in patients with past histories of the true anaphylactic reactions to iodinated contrast, or unstable renal function. Two alternative contrast agents have been described for patients who cannot tolerate iodinated contrast agents: carbon dioxide (CO2) gas and gadolinium chelates.

Carbon dioxide gas. Experience is most extensive with CO2, which functions as a negative contrast agent. The gas briefly displaces the blood volume in the lumen of the vessel, resulting in decreased attenuation of the X-ray beam. The digital subtraction technique is therefore essential for diagnostic imaging. The buoyant nature of CO2 results in preferential filling of anterior structures. The CO2 gas is highly soluble, excreted from the lungs. CO2 can be used for abdominal aortography, selective visceral injections, and lower-extremity runoffs. Mechanical injectors for CO2 are not available in the United States. Therefore, all injections must be performed by hand.

CO2 is contraindicated for angiography of the thoracic aorta, cerebral arteries, or upper-extremity arteries due to potential neurological complications.

Gadolinium chelates. Gadolinium chelates were developed as contrast agents for magnetic resonance imaging (MRI). The safety profile of these contrast agents is superior to that of iodinated contrast, and there appears to be lower nephrotoxicity. Digital subtraction angiography is necessary, as the low gadolinium concentration in the available formulations results in relatively weak opacification of deep arteries. The main limitations of this agent are the expense, the small total volume that can be used, and the relatively low radiopacity. Gadodiamide-based arteriography has been used during renal artery interventions in patients with baseline renal insufficiency. This technique may enhance the renal-protective effect of renal artery stenting in this high-risk population with renal artery stenosis.¹ However, recent evidence points to the association between exposure to gadolinium-containing contrast agents during MRI studies and incidence of nephrogenic fibrosing dermopathy (NFD) in patients with advanced renal disease.²

Imaging

There are two basic modes of recording angiographic images, Cineradiography and digital subtraction angio- graphy (DSA). Cineangiography simply takes multiple X-ray pictures of the contrast-filled vessel, as well as the surrounding tissue. For static vascular structures that are surrounded by radiodense structures, the frame per second (fps) needs to be adjusted, and the usual 15–30 fps used for coronary intervention, is not appropriate. The advantage of cineangiography is lower amounts of radiation and the ability to track the entire vessel. For imaging certain vascular beds, such as the aortic arch and lower extremity, the image intensifier must be large enough to accommodate the area of interest.

For DSA, the initial images obtained when stepping on the X-ray pedal are used to generate the baseline image from which all radio-opaque structures are subtracted. Subsequent images obtained following contrast injection will be the subtracted images and will, therefore, demonstrate only the contrast-filled vascular structures. The DSA imaging modality requires that the patient not move during image acquisition. In vascular territories where the vessels may move during respiration or swallowing (e.g., carotid, vertebral), the patients must also suspend these activities during the image acquisition. A limitation of this technique is that it does not allow panning of the field of view. In comparing the two imaging modalities, it is important to consider that in general DSA mode requires more radiation per frame, but it may lead to lower total body radiation because it requires a lower number of frames.

Carotid and Vertebral Arteries

Anatomic considerations. The right common carotid artery (CCA) in most cases arises from the bifurcation of the innominate artery.³ It may rarely arise as a separate branch off the aortic arch, or in conjunction with the left CCA (i.e., common carotid trunk). In contrast, the origin of the left CCA is variable. In approximately 75% of cases, it arises as the second great vessel off the aortic arch, in a plane posterior to the innominate artery. In remaining cases, the left CCA either shares its origin off the aortic arch with the innominate artery (10–15%), or it may arise from the innominate artery (i.e., Bovine origin, 10%).

At the level of the upper border of the thyroid cartilage, each CCA bifurcates into an external and internal branch. During diagnostic angiography, the angle of mandible serves as a useful landmark for the carotid bifurcation, although significant variation in the level of carotid bifurcation is common. The external carotid artery (ECA) is easily recognized, owing to its numerous branches to the face, scalp, and thyroid. A basic understanding of the anatomy of the ECA is important because this vessel and its branches are often wired during carotid intervention. Anterior branches arise in the following order: the superior thyroid, lingual, and facial. The occipital branch arises posteriorly at the level of facial artery. The ECA terminates by giving off the internal maxillary branch that is directed anteriorly, and the superficial temporal branch that runs along the path of ECA toward the temporal-scalp region.

In its proximal portion, the internal carotid artery (ICA) lies posterior and medial to the ECA. These relationships may be appreciated in the lateral projections. By convention, the ICA is divided into four sections:

1. The pre-petrous or cervical segment. This defines the segment of vessel between the CCA bifurcation and the petrous bone, and contains no arterial branches. Most carotid intervention involves treatment of atherosclerosis of the ostium and proximal portion of this segment of ICA. 2. The petrous portion. This refers to the L-shaped section of vessel (i.e., angled 90?) that courses through the petrous bone. 3. The cavernous portion. This courses through the cavernous sinus. 4. The supraclinoid segment. This gives off the important ophthalmic, posterior communicating, and anterior choroidal branches, and terminates in the middle and anterior cerebral arteries. The ophthalmic artery supplies the ipsilateral retina and optic nerve and is an important route for collateral flow between the ECA and ICA via the supraorbital branch, in addition to the maxillary branches and other branches of the facial artery. Likewise, the posterior communicating branch links the ICA with the posterior cerebral artery, establishing an important collateral flow between the anterior and posterior cerebral circulation.

Angiography

Catheter angiography of the extra cranial carotid and vertebral arteries should begin with a flush aortic injection through a 5 Fr pigtail catheter positioned so that the side holes are in the transverse portion of the aortic arch and the end of the catheter proximal to the take-off the innominate artery in the ascending aorta above the aortic valve. Next, DSA is performed with a 9-inch or large image intensifier at 4 fps in a 30–60 degrees LAO (left anterior oblique projection). This obliquity (usually 45 degrees) opens up the arch to show the origins of the innominate, left common carotid, and left subclavian vessels. The injection rate, using a power injection, is from 20–30cc per second for 2 or 3 seconds. If there is a question about the right common carotid or subclavian artery origin, a second injection in the right anterior oblique (RAO) projection should be obtained. Lower rates of contrast injections (15–20 cc over 1–2 sec) may be used in children and young adults.

Next, selective common carotid angiography is performed. For right common carotid artery (RCCA), the innominate artery is first selectively engaged with a 5 Fr diagnostic catheter [catheter shape should be based on aortic arch type and angle of vessel take off (JB1), Judkins right (JR4), Headhunter (HA-1), or Bernstein catheter for simple arches and Vitek or Simmons catheter for complex arches. An angiographic “road map” of the innominate artery in the RAO caudal projection can be helpful to open the bifurcation and facilitate access to the RCCA. A hydrophilic wire (0.035-inch angle glide wire) is then advanced into the RCCA and the diagnostic catheter is advanced over the wire. For selective left common carotid artery (LCCA) angiography, similar principles of diagnostic catheter choices apply. Once optimal position of the catheter is achieved in RCCA or LCCA, cine angiography or DSA of the common carotid, internal and external carotids in the oblique and lateral views are obtained using hand injections of 7–9cc contrast. It is important to visualize the intracranial distributions of the cerebral arteries, including the Circle of Willis, in both the AP and lateral views. This is done to evaluate for additional atherosclerotic disease (carotid siphon 2nd most common site), evaluate collateral flow, and obtain baseline imaging for comparisons. It can also be used to screen for other pathologies such as: aneurysms, arteriovenous malformations (AVMs), and space-occupying mass. The angiography is done in DSA mode at 3–6 fps with contrast injection at 3–4cc/sec for a total of 6–8cc.

Two criteria are used to quantify carotid stenosis: the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria and the European Carotid Surgery Trialists’ Collaborative group (ECST). According to NASCET criteria, the normal reference internal carotid diameter is the maximum diameter of the ICA distal to the lesion. While according to the ECST criteria, the estimated position of the external wall of the carotid sinus determines the normal reference diameter. Thus, overestimating the lesion stenosis. The NASCET criteria have less variability and more widely used than the ECST criteria.

The Artery of Adamkiewicz

Although a detailed description of the spinal cord arterial supply is beyond the scope of this review, knowledge of the anatomy of the artery of Adamkiewicz is critical for physicians involved in surgical or endovascular treatment of thoracoabdominal aneurysms. Patients who undergo graft replacement of thoracoabdominal aortic aneurysms are at risk for ischemic spinal cord injury, and paraplegia occurs in 5–10% of cases.4 This complication is caused by occlusion of the artery of Adamkiewicz.⁵ The artery of Adamkiewicz is the great anterior radiculomedullary artery that forms the anterior spinal artery in the thoracolumbar region. This artery often originates from the left posterior intercostal artery at the level of T9-T12, but it may also originate from higher levels and on the right side. Although this artery has been originally characterized by selective angiography, currently MRA and CTA are safer methods of identifying this artery.

Abdominal Aorta and Iliac Arteries Anatomy. The abdominal aorta begins at the level of the diaphragmatic crura and terminates in a bifurcation into the common iliac arteries. This bifurcation is usually in the region of the L4–L5 disk interspace. The aorta is constant in location and presence, although there is extensive variability of the anatomy of the branch vessels. The average diameter of the abdominal aorta is 1.5–2.0 cm at the diaphragm and 1.5 cm below the renal arteries. The anterior branches of the abdominal aorta are the celiac, superior mesenteric (SMA), gonadal, phrenic, and inferior mesenteric arteries (IMA). The lateral branches are the renal and middle adrenal arteries. The posterior branches are the lumbar arteries (one pair for each lumbar vertebral) and the middle sacral artery (arising at the aortic bifurcation).

The anatomy of the testicular and ovarian arteries is similar in the abdomen, but divergent in the pelvis. In 70% of individuals, the gonadal arteries arise from the anterior surface of the abdominal aorta just below the renal arteries. The most common variant location for gonadal artery origins is the renal arteries (20%), followed by the adrenal, lumbar, or even iliac arteries. The gonadal arteries pass to the pelvis along the anterior surface of the psoas muscles, adjacent to the gonadal veins and ureters, and anterior to the iliac vessels. In the pelvis, the testicular arteries have a lateral course, entering the spermatic cord to continue into the scrotum. These arteries are the sole blood supply to the testes. The ovarian arteries have a more medial path, through the suspensory ligament of the ovary. The ovarian arteries provide branches to the ovary and fallopian tubes. The artery then continues medially to the uterus, where it anastamoses with the uterine artery in the broad ligament.

The lumbar arteries are paired vessels that arise from the posterior wall of the abdominal aorta at the levels of the lumbar vertebrae. The origin of the paired lumbar arteries may be separate, or conjoint. These vessels anastamose with the intercostal and other chest wall arteries superiorly, the epigastric arteries anteriorly, and the internal iliac arteries inferiorly. These anastamoses can form the basis of collateral supply to the lower extremities in cases of distal aortic occlusive disease. The lumbar arteries provide the primary blood supply to the anterior and posterior musculature of the vertebral column. They also provide some flow to the musculature of the abdominal wall. This is of importance whenever embolization of lumbar artery for a nonneurologic indication is contemplated. In a small percentage of patients, the lower anterior spinal artery (artery of Adamkiewicz) will arise from the L1 or L2 lumbar artery.

The median sacral artery arises from the posterior wall of the aorta just proximal to the aortic bifurcation or as a common trunk with the L5 lumbar arteries. Occasionally, the median sacral artery will arise from a common iliac artery. This artery maintains a midline course in the pelvis, providing branches to the sacrum and coccyx. The median sacral artery is distinguished angiographically from the superior hemorrhoidal branch of the IMA by its posterior location and lack of terminal bifurcation.

The aorta bifurcates at the level of L4-L5 interspace into the right and left common iliac arteries. Angiography. Conventional angiography of the abdominal aorta is usually performed with a 5- or 6-Fr pigtail or other flush catheters. The tip of the catheter is positioned at or just above the origin of the celiac artery (usually T12-L1 interspace). If the renal artery origins are obscured, repositioning the catheter at the level of renal arteries and filming with a 10–15 degree left anterior oblique angulation will display the vessels. In patients with contraindications to iodinated contrast, CO2 or gadolinium can be used, although CO2 can be trapped in the aneurysm sacs. When evaluating a patient with an AAA prior to endograft, a graduated measuring catheter should be used and the distance from the renal arteries to the internal iliac arteries should be included in the field of view.

Flush pelvic angiography can be performed with the same catheter positioned 2–3 cm proximal to the aortic bifurcation to ensure that all of the side holes are in the aorta. The area included in the field of view should extend from the distal aorta to just below the common femoral artery bifurcation. Oblique views are crucial owing to the natural tortuosity of the pelvic arteries and to visualize the internal iliac artery origins. The posterior oblique projection usually displays the origin of internal iliac artery.

Renal artery angiography anatomy. The bilateral renal arteries arise from the lateral aspect of the descending aorta at the level of 1st and 2nd lumbar vertebrate, just inferior to the anterior origin of the superior mesenteric artery (SMA). The origin of the right renal artery is often slightly higher than that of the left renal artery. The right renal artery orifice is located on the anterolateral wall of the aorta, frequently quite close to the SMA. The right renal artery courses posterior to the inferior vena cava, the right renal vein and the retroperitonium. The left renal artery originates in a more lateral location, and courses through the retroperitonium posterior to the left renal vein. The renal artery is usually 4–6 cm in length and 5–6 mm in diameter. Each renal artery gives rise to a small proximal branch to the adrenal gland and the renal capsule. In the region of renal pelvis, the artery bifurcates into anterior and posterior divisions. The anterior division supplies the upper and lower poles and the anterior portion of the mid kidney. The posterior division supplies primarily the posterior renal parenchyma, with supplemental supply to the upper and lower poles. The divisional arteries divide into segmental arteries (apical, upper, middle, lower, and posterior) which quickly give rise to the interlobar arteries. At the corticomedullary junction the interlobar arteries divide into the arcuate arteries. The terminal branches of the renal artery are the interlobular arteries which ultimately supply the glomeruli.

There are several variations in renal artery anatomy that warrant discussion. The most common variant is the presence of an accessory renal artery. This is generally a smaller caliber renal artery that typically arises inferior to the main renal artery. If the accessory renal artery is of similar caliber to the main renal artery, thus supplying a large portion of the renal blood supply, revascularization of the stenosed accessory renal arteries can be justified. A second anatomic variant is early subdivision of the main renal artery into segmental branches just beyond its origin.

Angiography. Conventional angiographic evaluation of the renal arteries begins with an aortogram at the level of L1-L2, such that the sideholes of the catheter are at the level of renal arteries.6 Placement of the catheter at too high a level will fill the superior mesenteric artery which may obscure the ostium of the right renal artery. Perform cineangiography at 12.5–15 frames/sec in the Anterior-posterior (AP) or 5 degree LAO projection. The injection rate, using power injector, should be 15–20 cc per second for 2–3 seconds.

Selective renal angiography from the femoral approach can be performed with 5-Fr JR4, an IMA catheter, or a cobra-shaped catheter. Occasionally, a “shepherd’s crook”, such as an Omni SOS catheter may be used in inferiorly-oriented renal artery take off. In performing selective angiography, one must be cautious of the fact that the right renal artery can arise in a very anterior position, so that a steep left anterior oblique, or even a lateral view, may be necessary to visualize this renal artery ostium. It is preferable to use DSA for selective imaging of the renal arteries to better delineate the renal parenchyma.

A brachial approach may be required to select a renal artery owing to steep angle of origin, severe infrarenal aortic tortuosity, or aortoiliac occlusion. In these cases, selective angiography of renal arteries is accomplished using a multipurpose catheter.

Lower-extremity angiography anatomy. The blood supply to the lower extremities can be divided into runoff vessels (major conduits to the distal extremity) and muscular branches that supply the musculoskeletal structures.^7,8 In most instances, the status of the runoff vessels is the primary clinical concern. However, in the presence of occlusion of the runoff vessels, the muscular branches become the principal source of collateral blood supply. The common femoral artery (CFA) is the continuation of the external iliac artery. This vessel is usually 6–9 mm in diameter and 5–7 cm in length, with frequent and variable small, unnamed muscular branches. The CFA extends from the inguinal ligament to the origins of the superficial femoral (SFA) and profunda femoris (PFA) arteries just distal to the inferior margin of the femoral head. Occasionally, the artery will bifurcate while it is still anterior to the femoral head (high bifurcation). The CFA is contained within the femoral sheath, a continuation of the abdominal fascia. The sheath is funnel-shaped, with a broad base opening towards the abdomen. In addition to the artery, the sheath contains the femoral vein (medial to the artery) and the femoral canal (the most medial structure). The femoral nerve lies lateral to the femoral sheath, within the femoral triangle formed by the sartorious muscle laterally, the adductor longus muscle medially, the inguinal ligament superiorly, and the iliacus, psoas major, pectineus, and adductor longus muscles posteriorly.

The origin of PFA has a lateral and posterior orientation relative to the SFA. The PFA provides proximal branches to the hip, the lateral and medical femoral circumflex arteries, before descending deep in the thigh adjacent to the medial edge of the femur. There are multiple branches from the PFA to the muscles of the thigh before it terminates above the adductor canal. These muscular branches anastomose with muscular branches of the SFA and popliteal arteries.

The SFA is remarkable for the almost complete lack of variability in this vessel. The origin of the SFA from the CFA is anterior and medial to the PFA. The SFA runs beneath the Sartorius muscle in the thigh, anterior to the femoral vein. The artery passes through the adductor canal in the distal thigh, where it becomes the popliteal artery. The SFA is usually 6–7mm in diameter.

The popliteal artery is the continuation of the SFA from the adductor canal to the origins of the tibial vessels below the knee. In clinical practice, the joint line of the knee divides the artery into above-knee and below-knee segments. Although these are not official anatomic terms, the popliteal artery should always be described in this manner as the type of intervention, and subsequent outcomes are influenced by the level of disease. The average diameter of the popliteal artery is 4–5 mm. Usually the popliteal artery bifurcates into the anterior tibial artery and tibioperoneal trunk at the distal edge of the popliteus muscle. The runoff vessels in the calf consist of the anterior tibial, posterior tibial, and peroneal arteries.

Angiography. Although angiography of the abdominal and iliac arteries can be accomplished using pigtail catheters with either Acist contrast delivery or use of a power injector, determining the anatomy of lower-extremity arteries, requires selective angiography of the each SFA. This is accomplished using either contralateral retrograde access or ipsilateral antegrade sheath insertion. In the latter case, aortic bifurcation is crossed either with JR4, IMA, or Omni Flush (SOS) catheter using 0.35" angled glidewire. In either case, we recommend using manifold with Isosmolar (Visipaque) contrast mixed half and half with normal saline. Positioning the legs is an important consideration during runoff angiograms. The legs should be held as close together and as stationary as possible, without tight straps or tape that could compress and create artifactual occlusions. The latter is most likely to occur at the ankles and feet.

The angiography can either be done as a run off or DSA using sequential overlapping levels as it progresses down the extremity. In case of DSA, for external iliac and proximal portion of SFA, we recommend using 4 fps setup. For mid-SFA to popliteal artery, we recommend 2 fps and for infrapopliteal 1.5 fps setup. The frame rate for below-the-knee imaging depends of the presence and severity of occlusive disease. An appropriate time delay should be considered.

In order to examine the bifurcation of the CFA, ipsilateral oblique angles (for example, for RCFA use of RAO) are very useful. In particular, in cases were the target is a totally occluded SFA at its ostium, ipsilateral oblique allows examining the presence or absence of stump.

Conclusion

Over the last two decades arterial revascularization has been slowly but steadily moving from open surgical to endovascular procedures. Detailed knowledge of the arterial vascular anatomy is a crucial element to enable safe and successful vascular catheterization for the purpose of diagnosis and treatment. However, knowledge of vascular anatomy alone is not sufficient. Physicians performing endovascular interventions should develop practical expertise in imaging equipment, contrast agents, diagnostic and interventional catheters, techniques for obtaining optimal angiographic images of the various vascular territories, as well familiarity in avoiding and treating complications that may ensue in the process.