Quadrate Lobe of the Liver

The quadrate lobe of the liver is a small, rectangular portion of the visceral surface of the liver. Despite its name suggesting a right-sided association, the quadrate lobe is functionally part of the left liver lobe due to its portal and arterial supply. It lies anterior to the porta hepatis and is bounded by the gallbladder fossa and ligamentum teres. Although not an independent segment in Couinaud’s classification, the quadrate lobe corresponds largely to segment IVb and plays a crucial role in anatomical orientation during surgery and imaging. Its compact size and surface location make it a prominent landmark during hepatobiliary procedures.

Structure

The quadrate lobe is visible on the inferior (visceral) surface of the liver. It is not separated from surrounding lobes by clear fissures but is defined by key anatomical landmarks that make it distinguishable in dissection and radiologic imaging.

Surface Boundaries

• Right: Fossa for the gallbladder
• Left: Fissure for the ligamentum teres (round ligament)
• Posterior: Porta hepatis (transverse fissure)
• Anterior: Inferior margin of the liver, lying close to the anterior abdominal wall

These landmarks are often used in laparoscopic and open surgeries to orient surgeons during gallbladder removal, hepatic resections, or transplant planning.

Segmental Correlation

Although referred to as a "lobe" in traditional surface anatomy, the quadrate lobe is not a separate lobe in functional anatomy. According to Couinaud classification, it belongs to:

Terminology	Classification
Traditional (Surface Anatomy)	Quadrate lobe — anterior part of the visceral surface
Functional (Couinaud)	Segment IVb — medial inferior segment of the left lobe

Ligamentous Associations

• Ligamentum teres: Lies in the left boundary of the quadrate lobe and terminates at the umbilical portion of the left portal vein
• Falciform ligament: Anteriorly attached near the inferior margin and separates it from the anterior abdominal wall

Location

The quadrate lobe lies on the **visceral (inferior)** surface of the liver, specifically in the anterior-central area. It occupies a key position between major portal structures and anterior abdominal viscera.

Topographic Relationships

• Posterior: Porta hepatis (containing portal vein, hepatic artery, bile ducts)
• Inferior: Near the pylorus and first part of the duodenum
• Right: Closely associated with the neck of the gallbladder
• Left: Contacts the anterior portion of the lesser omentum

Due to its proximity to the duodenum and gallbladder, the quadrate lobe is often involved or exposed in upper GI and biliary surgeries. It may be partially retracted or visualized during laparoscopic cholecystectomy.

Function

The quadrate lobe functions as part of the left liver lobe (segment IVb), performing all hepatic functions in terms of metabolism, bile production, and filtration. Though small, it plays a proportional role in hepatic physiology.

Vascular Supply

• Arterial: Supplied by branches of the left hepatic artery
• Portal vein: Receives blood from the left portal vein (umbilical portion)
• Venous drainage: Empties into the left and middle hepatic veins

Bile Drainage

Bile produced in the quadrate lobe is drained via intrahepatic ducts that flow into the left hepatic duct, though minor anatomical variation may lead to partial drainage into the common hepatic duct.

Functional Roles

• Metabolism: Processes absorbed nutrients from portal circulation
• Detoxification: Converts ammonia to urea and metabolizes drugs
• Bile production: Contributes to bile synthesis and flow
• Synthetic functions: Produces plasma proteins and coagulation factors

Clinical Relevance

Though small, the quadrate lobe has clear relevance in hepatobiliary pathology, imaging, and surgery. Its anatomical position near key portal structures and the gallbladder makes it an important reference point in several procedures.

1. Imaging Identification

• On axial CT and MRI, the quadrate lobe is seen anterior to the portal vein bifurcation and medial to the gallbladder fossa.
• Segment IVb lesions (e.g., metastases or adenomas) may be mistaken for gallbladder pathology if not clearly delineated.

2. Gallbladder and Porta Hepatis Surgery

• During cholecystectomy, the quadrate lobe often serves as a reference structure as it lies immediately medial to the gallbladder bed.
• Enlargement or inflammation of the lobe can obscure the critical view of safety during surgery, especially in acute cholecystitis.

3. Tumors and Resection

• Lesions limited to the quadrate lobe are rare but can be surgically resected without compromising the rest of the liver.
• Segment IVb is often included in left hepatectomy or medial segmentectomy.

4. Portal Hypertension and Varices

Because of its proximity to the ligamentum teres and left portal vein, the quadrate lobe may be involved in forming intrahepatic venous collaterals in portal hypertension. These may affect bile duct compression or increase risk during liver biopsies.