Residency · Residency · General Surgery
Hepatic Anatomy and Liver Resection Principles
Overview
Safe hepatic resection requires detailed knowledge of Couinaud segmental anatomy, vascular inflow and outflow, and principles of parenchymal transection. Preoperative assessment of future liver remnant volume and strategies to augment it (portal vein embolization, ALPPS) are essential to prevent post-hepatectomy liver failure. Liver resection has become the standard of care for many primary and metastatic liver tumors, with perioperative mortality below 5% in experienced centers.
Couinaud Segmental Anatomy
Hepatic Veins (Outflow)
The three hepatic veins define the sectors of the liver. The right hepatic vein divides the right lobe into anterior and posterior sectors. The middle hepatic vein divides the liver into right and left lobes along the principal plane (Cantlie line). The left hepatic vein divides the left lobe into medial and lateral sectors. All three veins drain into the inferior vena cava.
Portal Pedicles (Inflow)
Each segment receives an independent portal pedicle consisting of a portal vein branch, hepatic artery branch, and bile duct. The right portal pedicle divides into anterior (segments V and VIII) and posterior (segments VI and VII) sectoral branches. The left portal pedicle runs along the umbilical fissure and branches to segments II, III, and IV.
The Eight Segments
Segment I (the caudate lobe) is unique in that it receives portal inflow from both the right and left pedicles and drains directly into the IVC via short hepatic veins, independent of the three major hepatic veins. The left lateral sector comprises segments II (superior) and III (inferior). The left medial sector is segment IV (with IVa superior and IVb inferior). The right anterior sector includes segments V (inferior) and VIII (superior). The right posterior sector consists of segments VI (inferior) and VII (superior).
Surface Landmarks
The Cantlie line, running from the gallbladder fossa to the IVC, divides the right and left lobes along the plane of the middle hepatic vein. The falciform ligament separates the left lateral sector (segments II and III) from the left medial sector (segment IV). The umbilical fissure contains the obliterated umbilical vein (ligamentum teres) and serves as a landmark for the left portal pedicle. The gallbladder fossa marks the right boundary of segment IV.
Hepatic Arterial Anatomy and Variants
Standard arterial anatomy (present in 55 to 65% of patients) consists of the common hepatic artery arising from the celiac trunk, giving rise to the right and left hepatic arteries. A replaced right hepatic artery from the SMA is found in 15 to 20% of patients and courses behind the portal vein through the portocaval space. A replaced left hepatic artery from the left gastric artery occurs in 10 to 15% and runs in the gastrohepatic ligament. Accessory arteries provide supplementary blood supply alongside the normal artery. Identification of these variants is critical before any hepatic or gastric surgery.
Preoperative Assessment
Liver Function Assessment
Several tools assess hepatic functional reserve. The Child-Pugh score (based on albumin, bilirubin, INR, ascites, and encephalopathy) classifies patients into A, B, or C categories, with Class C being a contraindication to major resection. The MELD score (based on bilirubin, INR, and creatinine) identifies increased risk when above 10. ICG clearance (indocyanine green retention at 15 minutes) of less than 10% indicates safe major resection and is widely used in Asia. Liver stiffness measured by FibroScan or elastography assesses the degree of fibrosis or cirrhosis.
Volumetric Assessment
CT volumetry calculates the future liver remnant (FLR) as a percentage of total liver volume. Minimum FLR requirements are 20% of total liver volume for normal liver, 30% for chemotherapy-treated liver, and 40% for cirrhotic liver. Insufficient FLR is the primary contraindication to major hepatectomy.
Strategies to Augment FLR
Portal vein embolization (PVE) involves embolizing the portal vein branch supplying the liver segment to be resected, inducing hypertrophy of the FLR over 4 to 6 weeks (typically a 30 to 40% volume increase). It is performed percutaneously by interventional radiology and is the standard approach before major right hepatectomy when the FLR is borderline.
ALPPS (Associating Liver Partition and Portal Vein Ligation for Staged Hepatectomy) is a two-stage procedure. Stage 1 involves in situ liver partition (splitting parenchyma along the Cantlie line) with portal vein ligation of the affected side. Stage 2 is a completion hepatectomy after 1 to 2 weeks of rapid hypertrophy, achieving 60 to 80% volume increase in 9 to 14 days. ALPPS is controversial due to higher morbidity and mortality (12 to 15% in early series) compared to conventional approaches and is appropriate for patients who fail PVE or when rapid hypertrophy is needed.
Hepatic vein embolization (liver venous deprivation) combines PVE with hepatic vein embolization and is an emerging technique that may induce faster hypertrophy than PVE alone with less morbidity than ALPPS.
Nomenclature of Hepatic Resections
Anatomic Resections
| Resection | Segments Removed | Notes |
|---|---|---|
| Right hepatectomy | V, VI, VII, VIII | Right of Cantlie line |
| Left hepatectomy | II, III, IV | Left of Cantlie line |
| Extended right (right trisectionectomy) | IV, V, VI, VII, VIII (± I) | Includes segment IV |
| Extended left (left trisectionectomy) | II, III, IV, V, VIII (± I) | Includes right anterior sector |
| Left lateral sectionectomy | II, III | Most common "minor" resection |
| Right posterior sectionectomy | VI, VII | Posterior sector only |
Anatomic resections follow segmental or sectoral boundaries. A right hepatectomy removes segments V through VIII (right of the Cantlie line). A left hepatectomy removes segments II through IV. An extended right hepatectomy (right trisectionectomy) includes segments IV through VIII, with or without segment I. An extended left hepatectomy (left trisectionectomy) includes segments II through V and VIII, with or without segment I. A left lateral sectionectomy (segments II and III) is the most common "minor" liver resection. A right posterior sectionectomy removes segments VI and VII. Single segments or two contiguous segments can also be resected as segmentectomy or bisegmentectomy.
Non-Anatomic Resection
Wedge resection or limited parenchymal resection follows the tumor margin rather than segmental boundaries and is appropriate for peripheral lesions where an adequate margin can be achieved.
Principles of Hepatic Resection
Inflow Control (Pringle Maneuver)
The Pringle maneuver involves compression of the hepatoduodenal ligament (portal triad) with a vascular clamp, occluding portal vein and hepatic artery inflow to reduce bleeding during parenchymal transection. Intermittent clamping (15 minutes on, 5 minutes off) is better tolerated than continuous clamping. Normal liver tolerates up to 60 to 90 minutes of warm ischemia, while cirrhotic liver tolerates less.
Parenchymal Transection Techniques
Several techniques exist for dividing liver parenchyma. The CUSA (Cavitron Ultrasonic Surgical Aspirator) uses ultrasonic fragmentation to break apart hepatocytes while preserving bile ducts and vessels for individual ligation and is the most widely used device. The harmonic scalpel and LigaSure provide energy-based sealing of small vessels. Staplers are used for major vascular pedicles and hepatic veins. The clamp-crush technique is the oldest method, using a Kelly clamp to crush parenchyma and isolate vessels and ducts. Water-jet dissection uses a high-pressure water stream. No single technique has been proven superior to the others.
Vascular Control and Outflow
Hepatic veins are short and drain directly into the IVC, making injury a risk for air embolism and hemorrhage. The anterior approach performs parenchymal transection before liver mobilization, avoiding tumor manipulation and venous injury during mobilization of large right-lobe tumors. Total vascular exclusion (Pringle maneuver combined with IVC clamping above and below the hepatic veins) is reserved for tumors involving the hepatic veins or IVC but is poorly tolerated hemodynamically. Selective hepatic vein control through extrahepatic or intrahepatic stapling of the relevant hepatic vein is often preferred.
Margin Assessment
For colorectal metastases, a 1 cm margin has been historically recommended, but margins greater than 1 mm (R0) are now considered adequate, as width of the negative margin does not affect survival as long as R0 is achieved. For HCC, anatomic resection (resecting the entire portal territory) is preferred over non-anatomic resection for better oncologic outcomes. For intrahepatic cholangiocarcinoma, a wide negative margin (greater than 1 cm when possible) is recommended.
Postoperative Considerations
Post-Hepatectomy Liver Failure
Post-hepatectomy liver failure (PHLF) is the most feared complication, with mortality of 50 to 80% in severe cases. It is defined by the 50-50 criteria: a prothrombin time greater than 50% of normal (INR above 1.7) and bilirubin above 50 micromol/L (2.9 mg/dL) on postoperative day 5. Prevention relies on adequate FLR assessment, PVE when needed, and avoiding excessive resection in cirrhotic patients.
Bile Leak
Bile leak occurs in 3 to 10% of cases and is managed with percutaneous drainage of biloma and ERCP with sphincterotomy and stent placement to reduce biliary pressure. Re-operation is rarely needed.
Hemorrhage
Intraoperative bleeding is minimized by maintaining low central venous pressure (CVP below 5 mmHg) during transection. Postoperative hemorrhage may require angioembolization or re-exploration.
<image>Detailed illustration of Couinaud segmental anatomy of the liver showing all eight segments labeled (I through VIII) from both anterior and posterior views. Include the three hepatic veins defining the sectors, the portal vein bifurcation into right and left branches with further segmental divisions, and surface landmarks (Cantlie line, falciform ligament, gallbladder fossa, umbilical fissure). Use color coding to differentiate the right anterior sector (V, VIII), right posterior sector (VI, VII), left medial sector (IV), left lateral sector (II, III), and caudate lobe (I).</image>
<image>Surgical illustration showing the Pringle maneuver technique: placement of a vascular clamp on the hepatoduodenal ligament to occlude the portal vein and hepatic artery. Include anatomical labels of the portal triad structures (portal vein, hepatic artery, common bile duct) and the surrounding anatomy. Show the liver with ischemic demarcation along the planned transection line after inflow occlusion.</image>
<image>Diagram comparing portal vein embolization (PVE) and ALPPS approaches for future liver remnant augmentation. For PVE: show the embolized right portal vein branch with resultant left lobe hypertrophy over 4-6 weeks. For ALPPS: show Stage 1 with in-situ liver partition plus portal vein ligation, then Stage 2 completion hepatectomy after 1-2 weeks of rapid hypertrophy. Include expected volume increase percentages and timeline for each approach.</image>
Clinical Pearls
The caudate lobe (segment I) is unique in that it receives portal inflow from both right and left pedicles and drains directly into the IVC via short hepatic veins, independent of the three major hepatic veins. A replaced right hepatic artery from the SMA, present in 15 to 20% of patients, courses behind the portal vein through the portocaval space and must be identified and preserved during pancreaticoduodenectomy and hepatic surgery. Low central venous pressure (CVP below 5 mmHg) during parenchymal transection significantly reduces blood loss. The Pringle maneuver (portal triad clamping) does not control hepatic vein back-bleeding, so major hemorrhage during transection may originate from the hepatic veins. Minimum future liver remnant requirements are 20% for normal liver, 30% after chemotherapy, and 40% for cirrhotic liver. The 50-50 criteria on postoperative day 5 (PT above 50% of normal plus bilirubin above 50 micromol/L) reliably predict post-hepatectomy liver failure and mortality. For colorectal liver metastases, R0 resection with margins greater than 1 mm is the oncologic goal -- a 1 cm margin is ideal but not mandatory. ALPPS achieves rapid FLR hypertrophy but carries higher morbidity than PVE and should be reserved for patients who fail PVE or need urgent resection.
References
- Couinaud C. Le foie: Etudes anatomiques et chirurgicales. Masson. 1957.
- Strasberg SM. Nomenclature of hepatic anatomy and resections: a review of the Brisbane 2000 system. J Hepatobiliary Pancreat Surg. 2005;12(5):351-355.
- Schnitzbauer AA, Lang SA, Goessmann H, et al. Right portal vein ligation combined with in situ splitting induces rapid left lateral liver lobe hypertrophy enabling 2-staged extended right hepatic resection in small-for-size settings (ALPPS). Ann Surg. 2012;255(3):405-414.
- Clavien PA, Petrowsky H, DeOliveira ML, Graf R. Strategies for safer liver surgery and partial liver transplantation. N Engl J Med. 2007;356(15):1545-1559.
