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Liver Segment IVa – Left medial superior segment

The left medial superior segment (Segment IVa) is the superior part of the medial section of the left hepatic lobe in Couinaud’s classification. It is located superior to the portal vein and lies between the middle hepatic vein (laterally) and the falciform ligament (medially). Its superior surface is in direct contact with the diaphragm, and it extends to the hepatic dome, adjacent to the pericardium.

Segment IV is divided into IVa (superior) and IVb (inferior) by the level of the portal vein. Segment IVa corresponds to the superior medial portion of the left lobe, whereas IVb represents the inferior part near the gallbladder fossa.

This segment is clinically significant because it lies adjacent to the hepatic dome and diaphragm, making it relevant in oncology, surgical resections, liver transplantation, and interventional procedures.

Synonyms

  • Segment IVa of liver

  • Left medial superior segment

  • Superior quadrate lobe (older terminology)

Function

  • Performs all major hepatic functions: metabolism, detoxification, storage, and synthesis

  • Works in conjunction with other segments of the left lobe for portal and systemic venous return

  • Frequently involved in hepatic tumors, abscesses, and surgical resections

Nerve Supply

  • Hepatic plexus (parasympathetic vagus fibers + sympathetic fibers from the celiac plexus)

Arterial Supply

  • Supplied by the left hepatic artery (branch of the proper hepatic artery)

  • Occasionally receives accessory supply from the middle hepatic artery in variant anatomy

Venous Drainage

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

  • Drains mainly into the middle hepatic vein

  • Small collateral venous channels may drain to the left hepatic vein

MRI Appearance and Signal

T1-weighted images:

  • Segment IVa parenchyma shows intermediate signal intensity similar to adjacent liver segments

  • Borders defined by falciform ligament (medial) and middle hepatic vein (lateral)

T2-weighted images:

  • Normal parenchyma shows intermediate to mildly hyperintense signal

  • Lesions such as cysts and hemangiomas appear bright hyperintense

STIR:

  • Fat suppression enhances contrast between parenchyma and surrounding fat planes

  • Lesions, edema, or inflammation appear as hyperintense foci

T1 Fat-Saturated (Pre-contrast):

  • Parenchyma shows intermediate signal, distinct from suppressed fat in falciform ligament and diaphragm

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

  • Arterial phase: rapid homogeneous enhancement

  • Portal venous phase: parenchymal enhancement matches rest of the liver

  • Delayed phase: uniform washout unless lesions (HCC, cholangiocarcinoma, metastases) alter pattern

MRI Non-Contrast 3D Imaging:

  • Provides detailed mapping of segment IVa boundaries, relation to hepatic veins, and falciform ligament

  • Useful for pre-surgical liver segmentation and transplant planning

Triple-Phase MRI (Dynamic Liver Protocol):

  • Arterial phase: hypervascular lesions (HCC, NET metastases) appear bright

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

  • Delayed phase: fibrosis, scar tissue, and cholangiocarcinoma show persistent enhancement

CT Appearance

CT Pre-Contrast:

  • Appears isoattenuating to the rest of liver

  • Landmarks: middle hepatic vein (lateral border), falciform ligament (medial border)

CT Post-Contrast (Single Phase):

  • Enhances uniformly like other liver segments

  • Lesions show distinct enhancement patterns depending on type

Triple-Phase CT (Liver Protocol):

  • Arterial phase: normal parenchyma enhances briskly; hypervascular tumors stand out

  • Portal venous phase: normal parenchyma isoattenuating; hypovascular lesions become clearer

  • Delayed phase: uniform attenuation unless lesion shows persistent enhancement (fibrosis, cholangiocarcinoma, scar)

CT image

Left medial superior segment — Segment IVa CT axial anatomy image-img-00000-00000

CT image

Liver Segment IVa – Left medial superior segment CT axial anatomy image

MRI image

Liver Segment IVa – Left medial superior segment CT axial anatomy image-img-00000-00000