MRCS PART A · APPLIED BASIC SCIENCES
Hepatobiliary landmarks & anatomical variants
Define the landmark, trace the connection, then test what a variant changes. Two selected anatomy objectives and four original SBAs. No dissection, clipping, repair or treatment instructions; a schematic relationship is not procedural clearance.
2 topics · 4 original SBAs
1 · Boundaries are not contents
Your task: State the modern hepatocystic boundaries and distinguish a usual arterial origin from an invariant rule.
What bounds the modern hepatocystic triangle?
Cystic duct, common hepatic duct and inferior liver surface. These define the region; a structure inside it is not automatically one of its boundaries.
Why can two descriptions of Calot's triangle disagree?
The original definition used the cystic artery as the superior boundary. The modern hepatocystic definition uses the liver surface. Specify the definition rather than treating the names as perfectly interchangeable.
Is the cystic artery always a single right-hepatic branch within the triangle?
That is the usual pattern, not an absolute. Its origin, number and course vary; more than one artery or a course outside the region can occur.
Does finding one vessel exclude a second?
No. A documented anatomical pattern may include separate supplying arteries. Recognising one structure does not prove the rest of a patient's map.
Does the label 'inside the triangle' identify an artery's destination?
No. A vessel's origin and course towards its supplied tissue matter. Right hepatic arterial variation can bring a hepatic vessel close to the gallbladder.
What must this lesson not be used for?
It cannot establish that any visible structure is safe to divide. It teaches named relationships, not operative identification or a bailout strategy.
2 · Trace drainage and supply before naming the variant
Your task: Recognise sectoral biliary drainage and distinguish replaced from accessory arterial supply.
Must every right posterior sectoral duct first join the right anterior duct?
No. Cholangiographic studies show alternative drainage, including into the left hepatic, common hepatic or cystic duct. The conventional right-duct confluence is not universal.
Does a duct near the gallbladder necessarily drain only the gallbladder?
No. Its upstream territory may be liver. Location alone cannot distinguish a cystic duct from a sectoral hepatic drainage route.
If it is the sole outlet for a sector, is it redundant?
No. In that specified model, obstructing it impedes drainage from the sector. An alternative outlet must be demonstrated, not assumed from the word 'variant'.
What separates a replaced hepatic artery from an accessory one?
A replaced artery supplies a territory whose usual artery is absent. An accessory artery coexists with the usual arterial supply. An unusual origin alone does not distinguish them.
If a right hepatic artery arises from SMA, which fact is still needed?
Whether the usual right hepatic branch is present. SMA origin is compatible with either replaced or accessory supply.
Does a second route mean its contribution is dispensable?
No. 'Accessory' describes coexistence, not a guarantee of negligible supplied territory or adequate alternative flow.
Does this give a rule for vessel sacrifice or duct repair?
No. Individual territory, functional reserve and operative assessment remain outside this anatomy exercise.