Overview
Definition:
Segmental hepatic resection refers to the surgical removal of one or more of the liver's anatomically defined segments based on the Couinaud classification system
This system divides the liver into eight functionally independent segments, each with its own vascular inflow and outflow, independent of adjacent segments
This precise anatomical understanding allows for more targeted and potentially less morbid resections compared to traditional lobectomies.
Epidemiology:
The application of Couinaud's segmental anatomy is crucial in managing various benign and malignant liver pathologies, including primary liver cancers (hepatocellular carcinoma, cholangiocarcinoma), liver metastases, and complex benign lesions
The incidence of liver resections varies globally but is increasing with advances in surgical techniques and perioperative management.
Clinical Significance:
Accurate identification and understanding of Couinaud's segments are paramount for successful liver surgery
It enables surgeons to preserve adequate functional liver parenchyma, minimize blood loss, reduce postoperative complications like liver failure, and achieve oncologic clearance in malignant cases
This precise approach is vital for improving patient outcomes and survival rates.
Couinaud Segmental Anatomy
Description:
Couinaud's system is based on vascular segmentation, with each segment receiving blood from an individual branch of the portal vein and hepatic artery, and draining into a specific branch of the hepatic vein
The liver is divided into a right lobe, left lobe, caudate lobe, and quadrate lobe, which are further subdivided into eight segments numbered I to VIII in a clockwise direction from the caudate lobe.
Segment I:
Caudate lobe
receives blood from branches of right and left portal veins
drains directly into IVC.
Segments Ii Iii:
Left lobe
segment II is superior-left lateral, segment III is inferior-left medial
receive branches from left portal vein and hepatic artery
drain into left hepatic vein.
Segment Iv:
Left lobe
medial segment
receives branches from left portal vein and hepatic artery
drains into left hepatic vein (subdivided into IVa and IVb).
Segments V Viii:
Right lobe
segment V is inferior-anterior, VI is inferior-posterior, VII is superior-posterior, VIII is superior-anterior
receive branches from right portal vein and hepatic artery
drain into right hepatic veins.
Indications For Segmental Resection
General Indications:
Resection of focal liver lesions including primary liver tumors (HCC, cholangiocarcinoma), colorectal metastases, neuroendocrine metastases, and selected benign tumors like adenomas or hemangiomas causing symptoms
Also indicated for some traumatic injuries and parasitic cysts.
Oncologic Indications:
Resection of malignant tumors where negative margins can be achieved with segmental removal
Crucial for early-stage HCC in suitable candidates and for isolated metastases amenable to complete excision.
Non Oncologic Indications:
Large symptomatic hemangiomas or adenomas, recurrent pyogenic cholangitis requiring removal of affected segments, hepatic trauma with localized bleeding or devascularization, and parasitic cysts causing complications.
Preoperative Assessment And Planning
Imaging Modalities:
Contrast-enhanced CT scan (arterial, portal venous, and delayed phases) is essential for precise lesion localization, vascular anatomy assessment, and to delineate segment boundaries
MRI with gadolinium offers superior soft tissue contrast and can be complementary
Doppler ultrasound can assess portal flow.
Functional Liver Assessment:
Assessment of liver function is critical to ensure adequate remnant liver volume and function
Tests include INR, albumin, bilirubin, platelet count, and increasingly, indocyanine green (ICG) retention test or advanced liver stiffness measurements (e.g., FibroScan) to estimate future liver remnant (FLR) function.
Surgical Planning:
Detailed preoperative planning involves identifying the exact location and size of the lesion, its relationship to major vascular structures (portal veins, hepatic veins, hepatic artery, IVC), and planning the safest plane of resection
Multidisciplinary tumor boards are vital for complex cases.
Surgical Technique And Principles
Approach:
Laparoscopic or robotic-assisted segmental resections are increasingly favored for their minimally invasive benefits
Open laparotomy remains essential for extensive or complex cases, or when laparoscopic expertise is limited
Preoperative planning dictates the choice of approach.
Division Of Vasculature:
The key to safe segmental resection lies in meticulous identification and division of the individual segmental portal venous and arterial inflow, and hepatic venous outflow
This is often done before parenchyma division, utilizing techniques like Pringle maneuver for inflow occlusion.
Parenchymal Dissection:
Dissection is carried out along the avascular Glissonean pedicles or hepatic vein tributaries that define the segmental boundaries
Techniques such as ultrasonic dissectors, harmonic scalpels, or monopolar cautery with suction are used to divide the liver parenchyma with minimal bleeding
Ex vivo assessment of hilar pedicles can aid identification.
Management Of Hepatic Veins:
Careful isolation and ligation of the specific hepatic vein draining the target segment are crucial
Failure to adequately manage these can lead to significant bleeding or postoperative congestion of the remnant liver
Ultrasound can help identify the correct hepatic vein.
Postoperative Care And Complications
Monitoring:
Close monitoring of vital signs, urine output, fluid balance, and laboratory parameters (LFTs, electrolytes, coagulation profile) is essential
Patients are typically managed in an ICU or high-dependency unit initially.
Pain Management:
Adequate pain control is achieved with intravenous or epidural analgesia
Early mobilization is encouraged to prevent complications like deep vein thrombosis and atelectasis.
Common Complications:
Biliary leak (biloma formation) is the most common complication, managed conservatively or with ERCP and stenting
Post-hepatectomy liver failure (PHLF) is a severe complication that can be life-threatening, with risk factors including poor FLR, underlying liver disease, and extensive resection.
Other Complications:
Bleeding from the resection margin, intra-abdominal abscess, wound infection, atelectasis, pneumonia, and venous thromboembolism are also potential complications that require prompt recognition and management.
Key Points
Exam Focus:
Understanding the numbering and orientation of Couinaud's segments (clockwise, I-VIII)
Knowing the major vessels supplying and draining each segment
Differentiating between anatomical and functional lobes
Recognizing the indications for segmental vs
lobar resection.
Clinical Pearls:
Always confirm hilar pedicles before transection
use intraoperative ultrasound to identify vessels and bile ducts
Intraoperative cholangiography or fluorescent cholangiography can aid in identifying biliary anatomy
A functional liver assessment (ICG retention) is critical for selecting candidates for major resections.
Common Mistakes:
Inaccurate identification of segmental vessels leading to uncontrolled bleeding
Inadequate assessment of FLR leading to postoperative liver failure
Incomplete oncologic resection due to poor understanding of tumor spread within segments
Failure to manage biliary effluents effectively, resulting in leaks.