Coeliac Trunk Variants
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Direct answer
Classic coeliac trunk anatomy — common hepatic, left gastric and splenic arteries arising from a single stem — is present in only about 55-75% of people (Michels' original autopsy work found about 55%, modern CT angiography up to about 75%). Michels' ten-type classification of hepatic arterial anatomy dominates the subject: a replaced or accessory left hepatic artery from the left gastric artery and a replaced right hepatic artery from the superior mesenteric artery each occur in roughly 10-11%. Beyond the hepatic branches, the coeliac and superior mesenteric systems may share a common hepatomesenteric trunk, or communicate through the arc of Buhler and the pancreaticoduodenal arcades, which become life-saving collaterals in coeliac stenosis.
What you must remember
- Michels type I is the textbook pattern, quoted at about 55% in Michels' autopsy series and up to about 75% in modern CT angiography — quoting the range earns credit.
- Type II (replaced or accessory left hepatic from the left gastric): roughly 10%; the artery runs in the gastrohepatic ligament and is divided at hazard during gastric and hiatus surgery.
- Type III (replaced right hepatic from the superior mesenteric): roughly 10-11%; it ascends behind the pancreas and portal vein to the porta hepatis and gives a palpable "hilar pulse" posteriorly.
- Types IV-VIII: accessory right hepatic from the superior mesenteric, accessory left from the left gastric, and their combinations — each rarer but conceptually the same lesson: know where the hepatic blood actually comes from.
- Type IX (hepatomesenteric trunk) and type X: hepatic artery arising wholly from the superior mesenteric or the left gastric — dangerous if the wrong vessel is clamped.
- Arc of Buhler: a persistent embryonic ventral anastomosis between the coeliac trunk and superior mesenteric artery, reported in 1-4% of people, which can maintain hepatic flow when the coeliac origin is stenosed.
- Collateral rule: pancreaticoduodenal arcades and the arc of Riolan connect the coeliac and mesenteric systems, which is why chronic coeliac compression may be nearly silent until it is not.
A pancreaticoduodenectomy planned around a variant
Picture a patient with a periampullary tumour booked for a Whipple procedure. The pre-operative CT angiogram reports a replaced right hepatic artery from the superior mesenteric artery. During the operation the surgeon must identify it posterior to the pancreatic head and portal vein before mobilising the duodenum, because this single vessel is the entire arterial supply of the right lobe; dividing it converts a curative resection into hepatic infarction. The artery is traced to its origin, protected throughout the retroperitoneal dissection, and the specimen is removed without touching it.
The same discipline applies to liver transplantation and to gastric surgery. A replaced left hepatic artery in the lesser omentum can be severed during lesser curve dissection or hiatal hernia repair, and a hepatomesenteric trunk changes the whole clamping strategy at the porta. Meanwhile, a different patient with coeliac stenosis from median arcuate ligament compression may have preserved liver perfusion purely because blood runs retrograde from the superior mesenteric artery through the pancreaticoduodenal arcades — the arc of Buhler, when present, enlarging to help. Recognising the variant on imaging, therefore, is not anatomy for its own sake; it decides which vessel is sacred in that particular body.
Where students slip
The classic slip is treating Michels' classification as a list to memorise rather than a question to answer: where does each lobe's artery originate? Examiners at Indian profs commonly ask for only two facts — the commonest variant (replaced or accessory left or right hepatic, depending on the series, each about 10%) and the most dangerous at laparotomy (replaced right hepatic from the superior mesenteric, because of its retroportal course). A second slip is confusing "replaced" with "accessory": replaced means the conventional vessel is absent and the variant is the sole supply, accessory means an extra vessel alongside a normal one — the distinction changes what ligation will do.
Frequently asked questions
What is Michels type I hepatic arterial anatomy?
The conventional pattern in which the common hepatic artery arises from the coeliac trunk and divides into proper hepatic and right and left hepatic branches, present in about 55-75% of people.
Which hepatic artery variant matters most in pancreatic surgery?
A replaced right hepatic artery from the superior mesenteric artery, because it courses behind the pancreatic head and portal vein and is the sole supply of the right lobe.
What is the arc of Buhler?
A persistent embryonic anastomosis between the coeliac trunk and the superior mesenteric artery, seen in roughly 1-4% of people, serving as a collateral channel in coeliac stenosis.
How do a replaced and an accessory hepatic artery differ?
A replaced artery substitutes for the normal vessel, whereas an accessory artery supplements it; ligation is catastrophic only when the vessel is the sole supply.
What is median arcuate ligament syndrome?
Compression of the coeliac trunk by the diaphragmatic crural ligament during expiration, causing postprandial epigastric pain with a bruit, often compensated by pancreaticoduodenal collaterals.