Replaced Right Hepatic Artery from SMA: Anatomical Definition and Clinical Significance
What This Means
A replaced right hepatic artery (RRHA) emanating from the superior mesenteric artery (SMA) is an anatomical variant where the right hepatic artery originates from the SMA instead of its normal origin from the proper hepatic artery, and this variant completely replaces the normal arterial supply to the right liver lobe. 1
Anatomical Context
Normal vs. Replaced Anatomy
Normal anatomy: The right hepatic artery typically originates from the proper hepatic artery in approximately 86.6% of cases 1
Replaced anatomy: When the right hepatic artery arises from the SMA (occurring in approximately 8.3% of cases), it is termed "replaced" because it substitutes for the normal arterial pathway entirely 1
Key distinction: A "replaced" artery is different from an "accessory" artery—the replaced vessel is the sole arterial supply to the right liver, whereas an accessory artery would exist alongside a normal right hepatic artery 1, 2
Typical Course
The RRHA arising from SMA characteristically courses dorsal (posterior) to the bile duct system to reach Calot's triangle and enter the right liver lobe 1
This posterior course places it at risk during hepatobiliary surgical procedures, particularly cholecystectomy and pancreaticoduodenectomy 1, 3
Critical Clinical Implications
Surgical Planning
The presence of a RRHA from SMA fundamentally alters surgical approach and resectability assessment, particularly in pancreatic head tumors. 4
Pancreatic surgery: According to NCCN guidelines, solid tumor contact with variant arterial anatomy (including replaced right hepatic artery) affects borderline resectability classification, and the presence and degree of tumor contact must be documented as it directly impacts surgical planning 4
Preservation requirements: During pancreaticoduodenectomy for pancreatic head masses, the RRHA must be preserved to prevent right hepatic lobe infarction, which may require leaving a portion of the gastroduodenal artery within the pancreatic parenchyma 3
Resection implications: Inadvertent injury or ligation of a RRHA during surgery can result in massive hemorrhage or hepatic infarction of the right liver lobe 2
Preoperative Detection
Preoperative identification through CT angiography or MR angiography is mandatory before any hepatobiliary or pancreatic surgery. 2, 3
Cross-sectional imaging with arterial phase contrast enhancement reliably identifies this variant preoperatively 2, 3
Failure to identify this variant preoperatively represents a critical error that can lead to unintentional vascular injury 2
Multidisciplinary team discussion including radiologists, surgeons, and oncologists is essential when this variant is present in the setting of pancreatic or hepatic malignancy 3
Interventional Radiology
For transcatheter arterial chemoembolization (TACE) or other hepatic interventions, the RRHA from SMA must be selectively catheterized to adequately treat right-sided liver lesions 2
Hepatocellular carcinomas in the right liver may be primarily supplied by the RRHA when this variant is present 2
Common Clinical Pitfalls
The most dangerous error is failing to recognize this variant before hepatobiliary surgery, leading to inadvertent vessel injury. 2, 3
During cholecystectomy: The RRHA may be mistaken for the cystic artery in Calot's triangle due to its posterior course 1
During pancreatic resection: Standard pancreaticoduodenectomy technique may inadvertently sacrifice the RRHA if not identified preoperatively, causing right hepatic lobe necrosis 3
In liver transplantation: Split liver procedures and living donor hepatectomy require precise identification of this variant to ensure adequate arterial inflow 5