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Liver Segment IVb – Left medial inferior segment

The left medial inferior segment (Segment IVb) is the inferior part of the medial section of the left hepatic lobe in Couinaud’s classification. It lies below the portal plane, bounded medially by the falciform ligament and laterally by the middle hepatic vein. Inferiorly, it is adjacent to the gallbladder fossa, while anteriorly it forms part of the inferior liver surface near the abdominal wall.

Segment IV is divided into IVa (superior) above the portal plane and IVb (inferior) below. Segment IVb corresponds roughly to the classical quadrate lobe described in traditional anatomy, situated between the gallbladder fossa on the right and the ligamentum teres on the left.

This segment is of great surgical importance in cholecystectomy, hepatic resections, transplantation, and oncology, particularly due to its close relationship with the gallbladder and porta hepatis.

Synonyms

  • Segment IVb of liver

  • Left medial inferior segment

  • Quadrate lobe (classical term)

Function

  • Contributes to all hepatic functions (detoxification, metabolism, storage, synthesis)

  • Plays a key role in biliary and gallbladder surgery due to its proximity to gallbladder fossa

  • Involved in oncological resections (liver tumors, cholangiocarcinoma)

Nerve Supply

  • Derived from the hepatic plexus (parasympathetic vagus fibers and sympathetic fibers from celiac plexus)

Arterial Supply

  • Primarily from the left hepatic artery

  • May receive accessory supply from branches of the middle hepatic artery

Venous Drainage

  • Portal inflow from the left portal vein (medial inferior branch)

  • Venous outflow primarily into the middle hepatic vein

  • Minor collateral drainage into left hepatic vein possible

MRI Appearance and Signal

T1-weighted images:

  • Parenchyma appears intermediate signal intensity, isointense to other liver segments

  • Borders defined by falciform ligament (medial) and gallbladder fossa (inferior surface landmark)

T2-weighted images:

  • Normal parenchyma shows intermediate to mildly hyperintense signal

  • Lesions such as cysts and hemangiomas appear bright hyperintense

STIR:

  • Fat suppression improves lesion detection

  • Edema, inflammation, or tumor infiltration show hyperintense signal

T1 Fat-Saturated (Pre-contrast):

  • Shows intermediate signal parenchyma distinct from suppressed fat of falciform ligament and porta hepatis

T1 Fat-Saturated Post-Contrast (Dynamic Gadolinium):

  • Arterial phase: rapid homogeneous enhancement of normal parenchyma

  • Portal venous phase: parenchymal enhancement equalizes with rest of liver

  • Delayed phase: uniform washout unless pathology alters enhancement (HCC, cholangiocarcinoma, metastases)

MRI Non-Contrast 3D Imaging:

  • Provides segmentation mapping of IVb boundaries relative to falciform ligament, gallbladder fossa, and middle hepatic vein

  • Used in pre-surgical planning and transplant donor evaluation

Triple-Phase MRI (Dynamic Liver Protocol):

  • Arterial phase: highlights hypervascular lesions (HCC, neuroendocrine metastases)

  • Portal venous phase: hypovascular lesions (mets, cholangiocarcinoma) become conspicuous

  • Delayed phase: persistent enhancement seen in fibrosis, scar tissue, or cholangiocarcinoma

CT Appearance

CT Pre-Contrast:

  • Isoattenuating to rest of liver parenchyma

  • Bordered by falciform ligament and gallbladder fossa

CT Post-Contrast (Single Phase):

  • Uniform enhancement with rest of liver

  • Pathology stands out based on enhancement pattern

Triple-Phase CT (Liver Protocol):

  • Arterial phase: normal parenchyma enhances homogeneously; hypervascular tumors (HCC, NET metastases) appear hyperdense

  • Portal venous phase: isoattenuating parenchyma; hypovascular lesions (mets, cholangiocarcinoma) appear clearer

  • Delayed phase: uniform washout in normal tissue; fibrosis, cholangiocarcinoma, or scar tissue may persistently enhance

CT image

Liver Segment IVb – Left medial inferior segment CT axial anatomy image-img-00000-00000

CT image

Liver Segment IVb – Left medial inferior segment CT axial anatomy image-img-00000-00000

MRI image

Liver Segment IVb – Left medial inferior segment MRI axial anatomy image-img-00000-00000