Here is an example of a "nutmeg" liver seen with chronic passive congestion of the liver. Note the dark red congested regions that represent accumulation of RBC's in centrilobular regions. source: http://library.med.utah.edu

Chronic Passive Congestion. Any condition interfering with the normal flow of blood to the heart may cause an enlargement of the vessel in the liver. This is part of the serious condition known as chronic passive congestion. It is most commonly seen when the heart itself is failing.

The patient suffers from shortness of breath, and his liver may enlarge and very tender. Fluid often gathers in the abdomen as well as in the lower extremities. The treatment is the same as for congestive heart failure.

Chronic passive congestion

Cut surface of the liver showing the typical “nutmeg” picture of a chronic passive congestion.

• This lesion represents alternate areas of dark red color (due to the congestion of the central veins), surrounded by paler, yellowish colored, periportal hepatocytes, which often show evidence of fatty change.
• The fatty metamorphosis is responsible for the yellowish coloration.

Etiology

• Any disease that results in right heart failure can cause chronic passive congestion of the liver.
  Pathogenesis
• Right heart failure results in delayed emptying of the great veins and retention of blood primarily in the central veins of the liver.
• This results in dilatation of central veins and pooling of blood in the sinusoids towards the center of the liver lobule.,

Epidemiology

• Common.

General Gross Description

• Grossly, the liver is enlarged, deep red and somewhat soft.
• The lesion can be palpated clinically by an enlarged liver with characteristically rounded edges.
• On cut surface, the liver oozes a considerable amount of blood.
• The contrast between the central congested sinusoidal space the peripheral paler areas, often with some evidence of fatty change, results in a striking appearance referred to as a “nutmeg” liver, since it resembles a bisected nutmeg.

General Microscopic Description

• The lesion is characterized by distended central veins full of blood, and congestion of sinusoids in the centrilobular area.

Clinical Correlation

• Aside from the enlargement of the liver, chronic passive congestion has no clinical significance.
• If the lesion develops acutely with centri-lobular necrosis, some evidence of liver cell death in the form of elevated transaminases may be seen.

[source: http://radiology.uchc.edu/eAtlas/GI/878.htm]