1 What cell types are seen in aspirates from normal liver?

Sheets of mesothelial cells (lining cells) may be present in aspirates from normal liver as an incidental finding. It is important not to mistake these cells for neoplastic cells.

2 What is the cytologic appearance of normal hepatocytes?

Normal hepatocytes will be present in small to large clusters or groups as well as individually in the smear. Hepatocytes are large epithelial cells with abundant, light-blue cytoplasm that is generally oval to polyhedral in shape. The cytoplasm often appears grainy because of the contrast between high numbers of blue-staining ribosomes and clear to lightly pink–staining organelles. Hepatocytes generally have round, uniform nuclei with moderately coarse chromatin and one or multiple small nucleoli (Figure 44-1).

Figure 44-1 Normal hepatocytes. Liver aspirate from a dog showing a group of normal-appearing hepatocytes and red blood cells (RBCs). (Wright’s stain; 250×.)

3 What is the cytologic appearance of normal biliary tract epithelial cells?

Biliary tract epithelial cells are generally present in low numbers, with only a few small groups or sheets of 15 to 20 cells observed. These cells are usually cuboidal to low columnar cells. They tend to have a round nucleus that is often centrally placed in a small amount of light-blue cytoplasm. Nucleoli are not visible.

4 List the main pigments seen in liver aspirates.

5 How is bile pigment recognized cytologically?

Bile pigment appears as bright- to dark-green granules within the cytoplasm of hepatocytes or as dark-green to black bile casts between hepatocytes (in bile canaliculi) (Figure 44-2). Increased amounts of bile pigment indicates cholestasis, however, the cholestatic process may not be severe enough to cause hyperbilirubinemia or jaundice. Some bile pigment may be present in the cytoplasm of normal hepatocytes. The presence of bile casts indicates cholestasis. Pigment can be confirmed as bile pigment by staining some smears with Hall’s stain, which causes bile pigments to stain green. Staining to confirm bile pigment is seldom done.

Figure 44-2 Cholestasis. Liver aspirate from a dog showing blood and a cluster of vacuolated hepatocytes with bile casts. (Wright’s stain; 125×.)

6 How is hemosiderin recognized cytologically, and what are some causes of hemosiderosis?

Hemosiderin appears as golden to golden-brown granules within the cytoplasm of hepatocytes or macrophages. Smears stained with Prussian blue can confirm the presence of hemosiderin, which stains blue.

Hemosiderosis occurs with chronic hemolysis and excessive iron supplementation (especially iron injections).

7 How is lipofuscin recognized cytologically, and what is its significance?

Lipofuscin appears as blue-green granules within the cytoplasm of hepatocytes. The presence of lipofuscin can be confirmed by the Luxol fast blue procedure, which stains lipofuscin blue (this procedure is seldom performed).

Lipofuscin is a common finding in hepatocytes of older animals. The accumulation of lipofuscin does not represent a pathologic process but rather an aging process, since lipofuscin is derived from degenerate lipids as the cell ages.

8 How is hepatic copper accumulation recognized cytologically, and in what dog breeds is it most often found?

Copper accumulation must be marked before it can be recognized on cytology smears. It appears as refractile, pale-green to blue-green intracytoplasmic granules. The granules can be confirmed as copper with a rubeanic acid stain.

Excessive hepatic copper accumulation is most often seen in Bedlington terriers, West Highland white terriers, and Doberman pinschers.