Imaging Overview

The role of catheter angiography has changed substantially with the development of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI). These developments have allowed computed tomographic angiography (CTA) and magnetic resonance angiography (MRA) to demonstrate the visceral arterial and venous structures with clarity in many patients. Although catheter angiography remains a critical test in highly selected patients with hepatobiliary and pancreatic disease, the indications for this procedure are quite different than a decade ago.

In the 1980s and 1990s, selective angiography was commonly used as a diagnostic and staging technique. Indications would include ascertaining the organ of origin of an abdominal mass, assessing for vascular invasion by pancreatic or cholangiocarcinoma, and preoperative planning prior to hepatic resection. CT (see Chapter 16) and MRI (see Chapter 17) have completely replaced catheter angiography for these indications. In a prior edition of this book published in 2000, it was suggested that catheter angiography was a dying specialty and that angiographers should accept their fate with grace. However, a new age has dawned, and the volume of selective visceral angiography has increased considerably. The majority of these arteriograms are performed for the purpose of a diagnostic assessment prior to performing catheter-based interventions including radioembolizations (see Chapter 84A), chemoembolizations (see Chapter 83), chemoperfusions (see Chapters 86 and 89), and embolizations of bleeding arteries (see Chapter 25). In addition, endovascular therapies have replaced open surgical arterial interventions in patients with primary vascular pathology using angioplasties, stents, and the placement of stent grafts.

Another technologic advance that involves catheter angiography is the development of hybrid imaging. Hybrid imaging couples two imaging modalities to create unique images that can provide information that would not be available with either technique alone. Catheter angiography can be coupled with a cross-sectional imaging modality, usually MDCT but occasionally MRI. The images can be postprocessed and rendered in a three-dimensional format to provide an anatomic depiction that would not be available by either technique alone. This hybrid imaging is particularly useful in delineating complex splanchnic venous anatomy in patients with portal vein occlusive disease being evaluated for potential portal systemic shunting procedures.

This chapter will be divided into two sections: one will cover arteries, the other will discuss veins. Regarding arteriography relevant to hepatobiliary and pancreatic surgery, we will discuss arteriographic anatomy and technique, arteriography prior to arterial interventions and surgery, localization of occult neuroendocrine tumors of the pancreas, arterial diseases, and hemorrhage. Our discussion on splanchnic veins will include venographic anatomy, venous sampling, techniques of catheter-based venous imaging, and venous imaging prior to surgical or percutaneous venous interventions.

Arteries

Arteriographic Technique

Over the past two decades, technologic advances have improved the safety and efficiency of catheter angiography. The historical technique of cut-film angiography is no longer available and has been replaced by highly sensitive flat-panel digital detectors. These detectors are capable of generating a volumetric data set that allows an image to be displayed in multiple formats. Rotational angiography with three-dimensional postprocessing and C-arm computed tomography (CCT) using the angiographic imaging unit are replacing digital subtraction image-intensified designs.

Unless serious comorbidities are present, catheter angiography is routinely performed as an outpatient procedure. The purpose of the examination should be evaluated by the angiographer to confirm that the examination is indicated and can be conducted with a high level of safety. The patient should be interviewed, and consent should be obtained prior to the procedure. A limited physical examination should be completed that includes a detailed pulse examination and assessment of the airway, heart, and lungs to ensure the safety of conscious sedation.

The relevant laboratory parameters include serum creatinine or estimated glomerular filtration rate, hematocrit level, platelet count, and international normalized ratio (INR), and these should be reviewed. The necessity of obtaining laboratory values in otherwise healthy patients without a clinical risk of renal impairment or abnormal bleeding is controversial.

If the patient has impairment of renal function, a number of prophylactic measures have been recommended to diminish the risk of contrast-induced renal failure. These measures include intravenous hydration with a sodium bicarbonate solution as well as the administration of N-acetyl cysteine. The effectiveness of these prophylactic measures is controversial; however, they carry a minimal risk to the patient and have been adopted by the majority of practitioners.

The risk of bleeding from the puncture site is low, and hematomas complicate 1% of femoral punctures and 3% of upper extremity punctures. An abnormal bleeding profile related to thrombocytopenia or prolongation of the INR increases the risk of hemorrhage. The necessity to correct an underlying coagulopathy is dependent upon the specific procedure to be performed and the preference of the angiographer. Most centers desire a platelet count in excess of 50,000 × 10⁶ per liter and an INR of 1.5 or less. For 6 hours prior to the examination, the patient should be given nothing by mouth, as mild to moderate conscious sedation improves the patient’s experience, although the procedure itself is not painful and can be performed solely with local anesthetic agent. Intravenous hydration is recommended before, during, and after the arteriogram to diminish adverse effects of contrast media on renal function. The patient should also be encouraged to drink plenty of fluids following the procedure.

The favored puncture site is the right common femoral artery, although the left common femoral artery, axillary artery, brachial artery, or radial artery may be used as alternatives when clinically appropriate. The desired puncture area is cleansed and the patient is draped in sterile fashion. In most centers, arterial entry is performed under real-time ultrasound guidance using a 21-gauge micropuncture set. The use of ultrasonography allows assessment of the quality of the common femoral artery, depicts the position of the profunda femoris, and detects the presence of aberrant veins extending ventral to the puncture site. Following entry into the vessel, the appropriate catheter is inserted for catheterization of the desired vessel. After diagnostically adequate images are obtained, the catheter is removed, and one of a variety of closure devices is deployed to seal the arteriotomy. Patients are observed in a postprocedural area until they have recovered from sedation, and most can be discharged home 2 to 4 hours later.

Arteriographic Anatomy

Arterial anatomy has been discussed elsewhere (see Chapter 1A, Chapter 1B ) and will only be briefly reviewed here. The most frequently encountered anatomy (Fig. 19.1) is the left gastric artery, splenic artery (SA), and common hepatic artery (HA) taking origin from the celiac axis. The common HA divides into the gastroduodenal artery (GDA) and proper HA, with the latter dividing into the right and left hepatic arteries. The right gastric artery most often originates from the base of the left HA, and the cystic artery most often originates from the right HA, but considerable variations in the origins of these arteries exist. Moreover, accessory duodenal arteries, either representing a supraduodenal or a retroduodenal artery, are frequently encountered; this is critical to recognize when planning chemoembolization and radioembolization.

FIGURE 19.1 Conventional celiac artery anatomy. CA, celiac axis; LGA, left gastric artery; SA, splenic artery; CHA, common hepatic artery; GDA, gastroduodenal artery; RGA, right gastric artery; RHA, right hepatic artery; LHA, left hepatic artery; CyA, cystic artery; RGEA, right gastroepiploic artery.

The normal arterial supply to the liver is shown in Figure 19.2 (see the Extrahepatic Vasculature section in Chapter 1B), which shows the commonly recognized variations of the left hepatice artery (LHA), taking origin from the left gastric artery, and the right hepatic artery (RHA), taking origin from the superior mesenteric artery (SMA). It is important to recognize that either a part or the entirety of the right and left hepatic arteries may have these variant origins. When the entire vessel has a variant origin, it is termed replaced. If the entire trunk does not take a variant origin, the vessel is termed accessory. For example, if the right lobe is supplied by a right HA originating from the common HA, as well as a right HA taking origin from the SMA, the latter would be termed an accessory right HA. If the entire right lobe was supplied by an artery taking origin from the SMA, it would be called a replaced right HA.

FIGURE 19.2 Arterial anatomy of the liver. PHA, proper hepatic artery; RHA, right hepatic artery; LHA, left hepatic artery. Additional vessels are labeled in accordance to the Couinaud segment they supply.

In most patients, the arteries to Couinaud segments I, II, III, and IV are branches of the left HA, and arteries to segments V, VI, VII, and VIII are branches of the right HA. The most variable segmental branch is to segment IV. Although most frequently the artery to segment IV takes origin from the LHA, it may also take origin from the RHA, assuming the misnomer of a “middle hepatic” artery in older works. Separate origins of segment IVa, usually from the LHA, and segment IVb from the RHA are frequently identified. Also, a branch from the segment IV artery is often seen extending outside of the liver, supplying the falciform ligament. Recognition of this vessel is important when conducting chemoembolization or radioembolization to avoid nontarget embolization.

The RHA conventionally divides into an anterior (ventral) and posterior (dorsal) branch. The anterior branch usually is more vertically oriented and supplies segments V and VIII. The posterior branch is usually more horizontally oriented and supplies segments VI and VII. More than one projection is usually required to ascertain with certainty which is the anterior branch and which is the posterior branch. In the right anterior oblique projection, the anterior branch moves medially and the posterior branch moves laterally when compared with the posteroanterior (PA) projection. The entire segmental arterial supply to the liver should be accounted for prior to hepatic arterial therapy, major hepatic resection, partial hepatectomy, or living-donor liver transplantation (LDLT, see Chapter 98B).

The arterial supply to the pancreas is somewhat variable. The most consistent supply is to the pancreatic head, afforded by an arcade formed by the inferior pancreaticoduodenal (IPD) branch of the SMA to the anterior superior and posterior superior pancreaticoduodenal branches of the GDA (Fig. 19.3). The transverse pancreatic artery runs along the middle portion of the long axis of the pancreas and may take origin from the arterial arcade in the head of the pancreas, directly from the GDA, or as a branch of the dorsal pancreatic artery, which variably originates from the common HA or SA (Fig. 19.4). A number of small branches from the SA supply the pancreatic body and tail, but the number and location of these arteries vary and must be identified in each individual patient when clinically relevant.

FIGURE 19.3 Arterial anatomy of the pancreas. GDA, gastroduodenal artery; PSPD, posterior-superior pancreaticoduodenal artery; ASPD, anterior-superior pancreaticoduodenal artery; RGA, right gastric artery.

FIGURE 19.4 Arterial anatomy of the pancreas. DP, dorsal pancreatic artery; TP, transverse pancreatic artery.

Preoperative Angiography: Historical Perspective

Prior to the advent of multidetector computed tomography angiography (MDCTA), visceral angiography was performed to assess the resectability of pancreatic and biliary tract tumors by demonstrating the presence or absence of vascular invasion. The sensitivity of catheter angiography for this purpose was low, and MDCTA has replaced catheter angiography for this indication. Using angiography for diagnosis of a hepatic mass, such as differentiating a cavernous hemangioma from a hepatocellular carcinoma, is no longer performed, as no improvement in diagnostic accuracy can be achieved over conventional cross-sectional imaging techniques (see Chapters 16 and 17).

Preoperative arterial mapping of the arterial anatomy of the liver also was routinely performed in some centers prior to major hepatic resections. This procedure has also been replaced by MDCTA and is no longer performed routinely. On rare occasion, there is a specific piece of critical anatomic information that cannot be ascertained with certainty by MDCTA, such as the origin and course of the artery to segment IV prior to a living-donor partial hepatectomy. In this circumstance, catheter angiography can be useful to answer the question.

On extremely rare occasions, large tumors are identified on cross-sectional imaging, but the organ of origin cannot be determined. The majority of these are large sarcomas of the retroperitoneum, but excluding a pancreatic source may be difficult. A similar situation can occur with large right adrenal or renal tumors blending with the hepatic parenchyma. In these highly selected cases, catheter angiography can be useful in delineating the organ of origin by demonstrating the primary arterial supply.

Arteriography in Conjunction with Arterial Interventions

By far the most common use of arteriography is planning an arterial-based intervention such as chemoembolization, radioembolization, or chemoperfusion to treat a primary or metastatic hepatic malignancy. These specific interventions will be discussed elsewhere in this book, and a detailed description will not be repeated here. However, some points deserve emphasis.

Accurate delineation of arterial anatomy has increased in importance remarkably as radioembolization (see Chapter 84A) and chemoembolization (see Chapter 83) have gained widespread application. The inadvertent administration of radiation or chemotherapeutic agents into arteries supplying the stomach or duodenum can lead to significant adverse outcomes. When performing procedures designed to necrose tumor, it is imperative that normal structures be spared. To accomplish this, variant anatomy must be recognized. The importance of accessory branches to the duodenum, including the supraduodenal and retroduodenal arteries, is now well known. Communications from intrahepatic branches to the lower esophagus, stomach, and diaphragm are of equal importance (Miyayama et al, 2009; Liu et al, 2005).

With current angiographic technology, it is possible to obtain a volumetric digital image during the arterial injection of contrast media and to display the images in a computerized tomographic format (i.e., C-arm CT) (Wallace et al, 2008). Using this technique it is possible to identify extrahepatic perfusion from aberrant hepatic arterial branches that may be unrecognized on the basis of the angiogram alone (Fig. 19.5).

FIGURE 19.5 Extrahepatic perfusion detected with C-arm computed tomography (CCT). A, Selective cystic arteriogram shows the gallbladder and several branches extending medially (arrow). B, CCT performed during contrast injection of the cystic artery confirms aberrant perfusion of the duodenum (arrowheads).

(Courtesy Daniel Sze, Stanford University.)

Hemorrhage

Bleeding from the liver, pancreas, or spleen is most often secondary to iatrogenic or noniatrogenic trauma, but it may occur spontaneously in patients with mycotic aneurysms or pancreatitis. Angiography is usually not used to ascertain whether arterial hemorrhage is present but rather to precisely localize and treat the offending vessel. Embolization of arterial bleeding will be discussed elsewhere in this book, but salient features will be reviewed in this chapter.

Splenic Bleeding

The most common cause of bleeding from the spleen is blunt trauma, and nonoperative management is currently the standard of practice. SA embolization has been established as a method to increase the success rate of nonoperative management of traumatic splenic injuries (Dent et al, 2004). A comparative study between two cohorts consisting of 625 patients over a 15-year period revealed an improved success rate of nonoperative management from 77% to 96% with the advent of splenic embolization (Rajani et al, 2006). The indications for splenic arteriography and splenic arterial embolization are based upon CT findings and include active contrast extravasation, splenic vascular injuries, and significant hemoperitoneum. Moreover, the American Association for the Surgery of Trauma recommends angiography for grade III, IV, and V splenic injuries (Raikhlin et al, 2008).

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