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Anatomical Variations in the Branching Pattern of Hepatic Segmental Arteries-A Cadaveric Study |
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Snigdha Das, Ashwini C Appaji 1. Assistant Professor, Department of Anatomy, Tripura Medical College and Dr BRAM Hospital, Mathikere, Tripura, India. 2. Associate Professor, Department of Anatomy, M S Ramaiah Medical College, Agartala, Bengaluru, Karnataka, India. |
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Correspondence Address : Dr. Ashwini C Appaji, Department of Anatomy, M S Ramaiah Medical College, MSRIT Post, Mathikere, Bengaluru, Karnataka, India. E-mail: ashwinishivaprasad@gmail.com |
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| ABSTRACT |  | |||||||||||||||||||||||||||||||||||||||||||||||||||||
: Introduction: The hepatic arterial anatomy is variable. Preoperative evaluation of intra-hepatic arterial pattern is relevant for the surgeons during hepatic surgery as well as for the radiologists while doing endovascular interventions like transarterial chemo-embolization, arterial angiogram etc. Aim: To identify the variable branching pattern of hepatic segmental arteries. Materials and Methods: Thirty one formalin embalmed adult livers (both male and female) were dissected and cleaned to observe the branches of hepatic artery to the segments in terms of their point of origin. The branching patterns were photographed. Results: The most common variant arteries were found to be the segment I and IV arteries in terms of their point of origin (71% and 61.3% livers respectively). The origin of other segmental arteries (II, III, V, VI, VII and VIII) were more or less constant. It was also found that segmental arteries can be single or multiple {dual branches were seen for segment I (40%), III (3.2%), IV(19.4%0, VII (3.2%), VIII (12.9%)}. Conclusion: The variant arterial branching patterns are of great importance in the field of hepatic surgery especially during split and living donor liver transplantations including segmental resection. It will help to reduce the postoperative complications such as hepatic necrosis. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Keywords : Hepatic segments, Liver transplantation, Segmental arteries of liver | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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DOI and Others :
DOI: 10.7860/IJARS/2019/41683:2500
Date of Submission: Apr 02, 2019 Date of Peer Review: Apr 24, 2019 Date of Acceptance: Jun 12, 2019 Date of Publishing: Jul 01, 2019 FINANCIAL OR OTHER COMPETING INTERESTS: None. |
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| INTRODUCTION |
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Hepatic arterial anatomy is more complex and variable. On the basis of intrahepatic branching patterns of blood supply and biliary drainage, liver creates 8 segmentations (segment I to VIII) (Table/Fig 1). Usually, proper hepatic artery before entering into liver parenchyma divides into right and left hepatic arteries. The right hepatic artery divides into an anterior (supplying liver segments 5 and 8) and a posterior segments (supplying liver segments 6 and 7). The anterior segment often gives a branch to segment 1 (caudate lobe) and to the gallbladder. The left hepatic artery branches into medial segmental artery supplying segment 4 and lateral segmental artery supplying segment 2 and 3 (1). During 4th week of development, the liver arises from larger cranial part of hepatic diverticulum which develops from the foregut. Liver receives oxygenated blood from umbilical vein during embryogenesis. The amount of oxygenated blood received by the liver through umbilical vein determines the functional hepatic segmentation (2). Among all the hepatic segments, the segment IV always has been the area of interest in description of segmental anatomy of liver because of a different pattern of blood supply to this segment. The artery to segment IV has been called by many names such as middle hepatic artery, medial segmental artery, artery to quadrate lobe, left medial artery and segment IV artery (3). Now-a-days the split liver transplantation is an established procedure where there will be splitting of a single donor liver into right (segment V to VIII) and left lobes (segment II and III) (1). Thereby, two recipients will be benefitted by one single liver. While doing the above mentioned procedure, the surgeons should be aware of the blood supply to segment I and IV because these segments are the intermediate hepatic segments. Vascular hepatic segmentations are important during segmental resections, partial hepatectomy and liver transplantation procedures. The knowledge of hepatic segmental arterial variation is important for the hepato-biliary surgeons and radiologists to deal with interventional procedures like chemoembolization (4). Hence, this present study attempts to observe variable branching patterns of segmental arteries to hepatic segments. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Material and Methods |
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A cadaveric study was done from February, 2013 to February, 2014 in the Department of Anatomy of MS Ramaiah Medical College, BR Ambedkar Medical College, Bangalore Medical College, Sapthagiri Institute of Medical Science, Kempegowda Institute of Medical Science, Bangalore, Karnataka, India. After taking Institutional Ethical Committee clearance, thirty one formalin embalmed livers without any gross abnormality were dissected to observe the intrahepatic segmental arterial pattern. Standard median vertical incision (extending from xiphi sternum to upper border of pubic symphysis) was given in the anterior abdominal wall. Superficial fascia, muscles and peritoneum were removed to expose the abdominal organs. Abdominal aorta and its branches were cleaned. Further dissection was done to expose the liver. Common hepatic artery was identified. Following this, the liver specimen was removed from the abdominal cavity along with hepatic artery and further cleaned. The soft tissue at the porta-hepatis was dissected to expose the branches of hepatic artery. Finally the segmental branches of hepatic artery were identified and traced individually to observe the point of origin (5),(6),(7). The main trunk and the segmental arteries were clearly dissected painted by using red Asian paint. The branching pattern of the right and left hepatic artery was traced and accordingly the segmental arteries of liver were identified and looked for presence or absence, number of branches and their point of origin. The findings were recorded and photographed using HD Digital Sony camera (16 megapixel). The variant branching patterns of segmental arteries were documented. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Results |
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Each segmental artery was traced first to see whether it is present or absent. Then number of branches for each segment and their point of origins were noticed. The findings are mentioned below in forms of tables. (Table/Fig 2) showing absence or presence of segmental arteries, Segment I artery was absent in 6 specimens segment V artery was absent in 4 specimens and Segment VI artery was missing in 1 specimen (Table/Fig 3). Multiple branches were observed in segment I, III, IV, VII and VIII. So segmental branches of liver are not always single, there can be multiple branches feeding a single segment (Table/Fig 4). The variant origins were noticed in all the segmental branches arteries except the origin of Segment VI artery. The Segment I and Segment IV artery were found to be more varied in origin among all other arteries in 72% livers and 61.3% livers respectively. The most common varied artery is Segment I artery according to its presence or absence, number of branches and point of origin (Table/Fig 5),(Table/Fig 6),(Table/Fig 7),(Table/Fig 8),(Table/Fig 9) (Table/Fig 10) shows that the arteries to segment I and IV showed more variations in origin than normal established pattern. The origin of segment I and IV arteries could be either from RHA or LHA or both RHA and LHA in almost equal proportions. The origins of other segmental arteries are more or less constant. Segment II and III arteries were found to take origin from LHA or branches of LHA and segment V, VI, VII and VIII arteries from RHA or branches of RHA. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Discussion |
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The knowledge of the anatomy of segmental branches of hepatic artery will help in segmental resection of liver. Now-a-days, trans-arterial chemoembolization is the treatment of choice for hepato-cellular carcinoma. For this purpose, micro catheter can be positioned even in segmental branches of hepatic arteries depending on the location and distribution of the lesion (6). The arterial supply to hepatic segment I and segment IV was found to be more variable. It may be because of their intermediate position in between right and left section of liver. Segment I Artery Segment I refers to the caudate lobe of the liver. Normally, Segment I is supplied by a branch arising from RHA (segment I artery). It can also be supplied by multiple small branches arising from the LHA and RHA (8). Michel NA showed the normal origin of segment I artery from RHA in 35% livers, whereas the most common variant origin was found to be arising from both RHA and LHA (8). In the present study, the most common variant origin of segment I artery was found to be arising from LHA (32% livers) and from both RHA and LHA (32% livers). It was also arising from PHA in 7% livers which have not been mentioned in the literature (Table/Fig 11). Gupta CD et.al., divided the caudate lobe (segment I) into caudate lobe proper and caudate process. Caudate process was found to be supplied by RHA in 94.12% livers. The caudate lobe proper was again subdivided into right and left portions. The right portion was supplied by RHA in 60% livers and LHA in 40% livers and the left portion by LHA in 91.77% livers (9). Kune GA and Segall HN also mentioned the presence of multiple small branches originating from both right and left hepatic arteries supplying caudate lobe (10),(11). The specimens which did not show their regular segment I arteries could be supplied by small branches given off by the adjacent segmental. Moreover, the caudate lobe is located behind all other segments, so it could get blood supply from adjacent segmental arteries. These could be the reason of absent segment I artery. Segment IV Artery Normally the segment IV artery is a branch of LHA. It can also be named as artery to quadrate lobe, medial segmental artery or middle hepatic artery (3). (Table/Fig 12) (3),(9),(12),(14),(14) shows that the most common origin of segmental artery IV to be from either LHA or RHA. HA origin of Segment IV artery was less significant in other studies. The present study showed a similar pattern but the percentage is well distributed among all the four points of origin. These variations are important during split and living donor liver transplantation. During hemi-hepatectomy, the incision is made across the cantlie’s line which is the line connecting the gall bladder and inferior vena cava. So the Segment IV artery arising from right hepatic artery is important in donors as the incision along the cantlie’s line can cut the artery. Pre-operative evaluation of artery to segment IV is important to retain hepatic function and avoid ischaemic complication. During right hepatectomy, in patients with RHA type and HA type of origin of segment IV artery, the RHA or HA should be cut distal to the origin of segment IV artery, otherwise it can compromise the blood supply to left lobe of liver (15). Alghamdi T et al., divided the arterial supply of segment IV in 79.3% liver by a line drawn from left side of inferior vena cava at the top of and lateral to falciform ligament to medial point of gallbladder fossa (16). Lateral to the above mentioned line, the part of segment IV was supplied by the branches from RHA and the area medial to it by branches of LHA. The middle hepatic artery (artery to segment IV) was originating from RHA (31%), from LHA (31%), from PHA (3.4%) and from both RHA and LHA (3.4%) liver. It was found to be absent in rest 31% livers. These type of variations are important to know for split-liver resection and ALPPS (associating liver partition and portal vein ligation for staged hepatectomy) procedures. If liver parenchyma is divided with the knowledge of arterial supply of segment IV, then ischaemia, necrosis to segment IV can be prevented (16). Abdulrasool H et al., also observed the artery to segment IV arise from PHA and RHA (17). Other Segmental Arteries Segment II and III Arteries: Presence or absence: The segment II and III arteries were present in all the specimen (Table/Fig 1). Multiple segmental branches to Segment II were noticed in one liver specimen. Point of Origin: The segment II and III arteries take origin from lateral segmental branch of LHA. The segment II and III arteries are also called as lateral superior area artery and lateral inferior area artery respectively (9). From (Table/Fig 13) it was noticed that the point of origin for both segmental branches (II and III) was from LHA or branches of LHA. Segment V and VIII Arteries: Presence or absence: In the present study, the segment V artery was found to be absent in 12.9% (4/31) livers and the segment VIII artery was present in all the specimen (31) (Table/Fig 2). Multiple segmental branches to Segment VIII were noticed in 4 specimens (12.9%). The branch to segment V was consistently single. Point of Origin: The segment V and VIII arteries take origin from anterior segmental branch of RHA. The segment V and VIII arteries are also called as anterior inferior area artery and anterior superior area artery respectively (9). Segment VI and VII Arteries: Presence or Absence: In the present study, the segment VI artery was found to be absent in 3.2% (1/31) livers and the segment VII artery was present in all the specimen (100%) (Table/Fig 2). Multiple segmental branches to Segment VII were noticed in 1 specimens (3.2%). The branch to segment VI was consistently single. Point of Origin: The segment VI and VII arteries take origin from posterior segmental branch of RHA. The segment VI and VII arteries are also called as anterior inferior area artery and anterior superior area artery respectively (9). From the above (Table/Fig 14), it was observed that arteries to segment V, VI, VII & VIII were originating either from RHA or AS/PS branches of RHA. So it was observed from the present study that most variated arteries are segment I and IV arteries in terms of their point of origin as compared to other segmental arteries because of their intermediate position. Embryology Multiple ventral segmental arteries arise from both primitive dorsal aortae at fourth week of development. Most of these ventral segmental arteries disappear. Tenth ventral segmental artery give rise to coeliac trunk. Developmentally, 3 hepatic arteries will be there to supply 3 sectors of liver: 1) left hepatic artery arising from left gastric artery (supplying left sector); 2) middle hepatic artery from coeliac trunk (supplying para-median sector); and 3) right hepatic artery from superior mesenteric artery (supplying right sector). Among these 3 hepatic arteries, only middle hepatic artery persists and ultimately forms proper hepatic artery (18). In adult, the embryonic para-median sector becomes caudate and quadrate lobes. The embryonic middle hepatic artery supplying the para-median sector give rise to arteries to the caudate and quadrate lobes (segment I and IV). In adult, the proper hepatic artery (embryonic middle hepatic artery) divides into right and left hepatic artery (3). Hence, the variant origin of arteries to segment I and IV can be described embryologically. So artery to segment I and IV can take origin either from RHA or LHA or PHA. Being in the intermediate position, the origin of segment I and IV arteries show more variations. The arterial patterns are not constant as they are formed from diffuse vascular network during the development of cardiovascular system. This could be the reason of variant origins of segmental arteries (9). Each hepatic segment is independent functionally and in terms of blood supply. But inter-arterial anastomosis can be observed occasionally (1). Presence of this intra-hepatic anastomotic pattern could be the reason of multiple branches to one hepatic segment. So the surgeons should be aware of multiple branches to hepatic segments. Clinical Importance The knowledge of hepatic segmental arteries is of immense importance for the exact identification of each hepatic segment. With this knowledge, radiologists can confirm the location of segmental artery on conventional angiogram or any lesion of segments at CT scan. Liver cancer is very common worldwide. The treatment of choice for hepatocellular carcinoma is trans-arterial chemoembolization (6). Selective intra-arterial radiation therapy is also done to treat non-resectable hepatic tumours. Selective catheterization is possible with the proper knowledge of hepatic segmental arteries. If trans-arterial chemoembolization is done for a wrong branch without the knowledge of anatomy of hepatic vasculature and its variations, then it can lead to disposition of chemotherapeutic agents in inappropriate hepatic segments (6). Now-a-days, Living Donor Liver Transplantation (LDLT) is the choice of treatment for end-stage liver disease. If there is injury to hepatic arteries during LDLT, it can lead to hepatic artery thrombosis followed by impairment of adequate blood supply to the retained liver lobe of the donor or graft loss in recipient. Hepatic artery thrombosis commonly involves segment IV artery or middle hepatic artery or artery to quadrate lobe (7). Functionally quadrate lobe is included to the left lobe of liver (19). So, there are two important aspects to keep in mind during right lobe LDLT and left lobe LDLT: 1) Preservation of LHA and MHA (artery to quadrate lobe) in the donor to supply the remaining left lobe; and 2) Reconstruction of LHA and MHA to maintain the viability of graft containing left lobe in recipient respectively. It is seen that when LHA gives MHA, then modification of surgery is not needed for the preservation of MHA in right lobe LDLT and for reconstruction of MHA in the graft of recipient in left lobe LDLT. Hence, chances of injury to MHA as well as postoperative hepatic artery thrombosis will be less. But when MHA comes from RHA, then during right lobe LDLT, as right lobe graft includes RHA, so preservation of MHA in donor will be difficult which might reduce the survival rate of left lobe of liver in donor and during left lobe LDLT, the viability of left lobe graft will be poor as RHA (from which MHA was arising) is preserved in donor with right lobe. So when MHA arises from RHA, the chances of MHA injury are high. Therefore liver with presence of accessory hepatic artery would be better for LDLT (7). LIMITATION The sample size was small and samples were cadaveric specimens. Identification of sub-segmental branches was beyond the scope of study as the procedure was piece meal dissection. Getting specimen also was difficult for piece meal dissection as the used liver specimen cannot be reused for academic purpose. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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