A Rare Hepatic Arterial Variation Established in Preoperative MDCT Angiography

The standart surgical procedure for the tumors of pancreatic head, the bile duct close to this area, and duodenum is Whipple operation (pancreaticoduodenectomy). In this operation pancreatic head, entire duodenum, gallbladder, associated bile ducts and part of the stomach are removed. This procedure is exeedingly complex and so it is required to be experienced. A variation in the course of hepatic artery both increases the duration of the procedure and the risk of injury to the hepatic artery which can result in hemorrhage, ischemia and anastomotic leak [1,2]. In the anatomical observations made with large series of cases [3-5] various types of hepatic arterial variations were noted in 21-45% of cases. For this reason, in terms of the surgical success it is very important to establish variations before the operation. We present a case that have one of the rarest hepatic arterial variation in which CHA is directly originated from SMA, established by preoperative MDCT.


Introduction
The standart surgical procedure for the tumors of pancreatic head, the bile duct close to this area, and duodenum is Whipple operation (pancreaticoduodenectomy). In this operation pancreatic head, entire duodenum, gallbladder, associated bile ducts and part of the stomach are removed. This procedure is exeedingly complex and so it is required to be experienced. A variation in the course of hepatic artery both increases the duration of the procedure and the risk of injury to the hepatic artery which can result in hemorrhage, ischemia and anastomotic leak [1,2]. In the anatomical observations made with large series of cases [3][4][5] various types of hepatic arterial variations were noted in 21-45% of cases. For this reason, in terms of the surgical success it is very important to establish variations before the operation. We present a case that have one of the rarest hepatic arterial variation in which CHA is directly originated from SMA, established by preoperative MDCT.

Case
A 56 year old man presented to our hospital with epigastric pain and jaundice. He was evaluated and a tumor was established at uncinnate process of the pancreatic head by abdominal CT imaging. Therefore, he was scheduled for Whipple operation. After that, for staging and to assess the relation of the mass with vascular structures 3 phase MDCT Angiography was performed. 64 channel MDCT (Philips Brilliance 64) with 1 mm section thickness and 0.5 mm reconstruction interval was used and 120kVp and 300 mA were chosen. Non-ionic contrast agent (omnipaque 350mg/50ml, GE Healthcare Canada) was infused at 5ml/min and the region was imaged at arterial, portal and venous phases by using bolus tracking method. By reconstruction sagittal and coronal images were obtained from axial images. 3 dimensional images were made with MPR, MIP and VR methods. It was seen that celiac trunk was giving LGA and SA but not the CHA which was originating directly from SMA ( Figure 1). Its course then was superior to the head of the pancreas ( Figure 2). With the help of our radiology department intraoperative localization of CHA was made successfully. As a result with the knowledge of this variant anatomy assessed in MDCT Angiography our patient had a safe operation.

Discussion
In the classic anatomy, the common hepatic artery (CHA) originates from celiac trunk with left gastric artery and splenic artery. CHA then gives rise to gastro duodenal artery, proper hepatic artery which divides into right and left hepatic arteries. In order to describe the variations the terms accessory and replaced are used. Both of these terms can be referred as aberrant. Accessory vessel is one that supplies a part of the viscera in addition to its normal vascular supply but a replaced vessel originates from an atypical location and provides entire blood supply to this part of the viscera [6]. Existence of an aberrant hepatic arterial anatomy makes more difficult the procedure and increases the risk of complications [7]. Therefore, preoperative awareness of hepatic arterial variations is important for effective surgical and radiologic procedures and helps to avoid iatrogenic complications. DSA is the gold standart imaging modality for vascular structures but its invasive nature limits its use. With the use of MDCT Angiography vascular structures can be scanned in just one breath hold without any artifacts. Axial and three dimentional images give detailed information regarding vasculature.
In 1960s with a study on 200 cadavers Michels et al. made the first description including 10 types of variations classifying accessory and replaced hepatic arterial systems separately [3]. After that, in 1994 this classification was simplified to 6 types by Hiatt et al. after their study on 1000 donors liver for orthotopic liver transplantation [4]. The differentiation between accessory and replaced hepatic arterial system was not made in this revised form of the classification. In our case CHA originated directly from SMA (hepatomesenteric trunk), while LGA and SA are originating from celiac trunk. This variation is classified as type 9 in Michell classification with the frequency of 2.5% and type 5 in Hiatt classification with the frequency of 1.5%. Rammohan et al. [7] searched hepatic arterial anomalies in 225 patients who experienced pancreaticoduodenectomy while Perwaiz et al. [8,9] searched that in 200 patients and they saw only one case in each search that CHA was   originating directly from SMA. In these studies the frequency of the variation was reported as 2.3% and 0.5%. In the study made by Song et al. eliac trunk and hepatic artery variations were searched in 5002 patients and in 132 patients (2.64%) hepatomesenterik trunk and gastrosplenik trunk were established together. In this study also the course of CHA were classified according to pancreas (supra-trans and infra), portal vein (preportal-retroportal) and superior mesenteric vein (preSMV-postSMV)) [8]. In our case, the course of CHA was suprapancreatic and retro portal. When we look at the variations of hepatic artery as a whole we see that hepatomesenteric trunk variations are one of the rarest one [3,4,7,9,10]. In addition, not recognizing this variation during the operation can result in the ligation of CHA and necrosis of the liver [11].
In conclusion, MDCT is a non-invasive and quick imaging modality that makes 3 dimensional evaluation possible in the preoperative establishment of vascular anomalies. Before complex operations