The close relationship of hepatic arterial branch­es to structures in the porta hepatis and their frequent anatomic variations, compounded with the presence of tumors that often exhibit a tro­pism toward vasculature, render branches of the hepatic artery particularly susceptible to injury during HPB surgery. Fortunately, much experi­ence has been gained to aid our understanding of the anatomic and clinical factors that predispose the liver and biliary tree to complications follow­ing ligation of hepatic arterial branches. A thor­ough understanding of these clinical principles, comprehensive knowledge of normal and variant anatomy, careful preoperative radiologic evalu­ation, and meticulous intraoperative technique will allow surgeons to safely navigate potentially fatal clinical scenarios and minimize complica­tions following complex hepatobiliary and pan­creatic resections.

transfusions; however, larger studies are required to confirm this assumption [20]. The correlation between blood loss and blood transfusion and postoperative infection has been demonstrated in multiple studies involving hepatic resections for colorectal metastases, hepatocellular carcinoma, and cholangiocarcinoma [3–6, 8, 11, 21]. Metic­ulous surgical technique and advances in hemo­static approaches for liver and pancreas resection have led to a significant decrease in perioperative blood loss and the need for blood transfusion in patients. Despite this, a number of factors con­tribute to poor postoperative outcomes following liver and pancreas surgery.

evaluate for any complications in the periopera­tive period as well as to assess the enhancement characteristics of postoperative fluid collections in order to improve detection of infected collec­tions rather than postoperative fluid. The use of intravenous contrast and multiphasic imaging also allows for the assessment of patency of the hepatic vasculature. However, iodinated contrast agents must be used cautiously or not at all in the setting of acute or chronic renal failure and in patients with an iodinated contrast allergy, unless they are appropriately pretreated. Oral contrast is not mandatory but if tolerated will likely be of benefit in aiding the detection of bowel pathology or to distinguish postoperative fluid collections from adjacent loops of bowel. On CT examina­tion, abscesses generally are hypoattenuating on both contrast-enhanced and noncontrast exami­nations with attenuation values between 0 and 45 Hounsfield units, and are most commonly di­rectly adjacent to the resection bed. Infected col­lections typically demonstrate a rim of contrast enhancement and will usually result in adjacent inflammatory changes in the peritoneal cavity or retroperitoneal fat. The presence of gas within a collection either as an air-fluid level or bubbles of gas can be a specific sign for postoperative in­fection, however is not commonly present. High­er attenuation collections in the postoperative bed may represent hematoma or the residual of hemostatic material used intraoperatively. Post­operative intrahepatic abscesses are also hypoat­tenuating and are generally well-defined masses, which may be unilocular with smooth margins or complex with internal septations and irregu­lar contours [27]. The presence of gas within a collection either as an air-fluid level or bubbles of gas can be a specific sign for postoperative infection, although it is not commonly present. Higher attenuation collections in the postopera­tive bed may represent hematoma or residual he­mostatic material used intraoperatively. The use of oxidized regenerated cellulose (Surgicel) can be identified in the surgical bed up to 1 month after placement. During placement, air likely gets trapped with blood within the interstices of the oxidized cellulose sponge and produces focal

the collection. Abscesses commonly demonstrate inhomogeneous areas of low T1 signal intensity with intermediate to high T2 signal intensity. After the administration of gadolinium contrast, an infected fluid collection will often display pe­ripheral rim enhancement. Intrahepatic abscesses may also demonstrate some mild perilesional edema, which manifests as intermediate to high signal intensity on T2-weighted images. Air within a collection will demonstrate a signal void on all acquired sequences and may be difficult to differentiate from calcifications; however, the shape and location of the signal void should allow the correct diagnosis. Diffusion-weighted imag­ing also has been shown to be helpful in distin­guishing infected fluid collections from cystic or necrotic tumors and noninfected fluid collections with abscesses typically showing restricted dif­fusion [31]. Also, in the postoperative setting, if there is concern for bile leak or bile duct injury, the use of hepatocyte-specific contrast agents can add functional information to that obtained using conventional T2-weighted imaging and may be particularly useful in identifying the site of a bile leak, or identifying an area of biliary stricture which may be contributing to the hepatic abscess [32]. Multiphasic MRI protocols also are ideally suited to evaluate the patency of the hepatic vas­culature, which may be a complicating factor in the development of abscess formation. Surgicel demonstrates marked low signal intensity on T2­weighted images and is easy to distinguish on MRI from a postoperative fluid collection [33].