Microsteatosis and Bile Lakes

Microsteatosis (the presence of tiny fat globules) and bile retention are common and benign findings in the liver.

Quirks of human microanatomy are frequently identified upon post-mortem histological examination. Among the most important lessons in pathology training is the recognition of benign entities that, while interesting, had little or no clinical significance in life. Correct identification and placement of such findings in their proper context is crucial to the determination of cause and manner of death.

One of the functions of the cells of the liver is to produce bile, which aids in digestion of fats. Formed from bilirubin, conjugated bile salts, cholesterol, and phospholipids, bile flows through a series of ducts that terminate in the small bowel. (Excess bile that is not immediately needed is stored in the gallbladder.) Obstruction of the flow of bile can lead to the formation of bile lakes, or areas of pooling within the liver, caused by metabolic or autoimmune disease, malignancy, or (most commonly) gallstones. Bile ranges in color from light amber to dark greenish-black, and such bile lakes are not infrequently encountered in post-mortem liver histology.

The liver is the primary organ for fat metabolism, and retention of fat globules is a common finding in post-mortem histology. Known as steatosis, accumulation of excess fat in the liver has many causes including obesity, alcoholism, infection with hepatitis C, and diabetes mellitus. Histological processing of liver tissue dissolves fat leaving clear spaces within the tissue. However, dyes that bind fat can be applied to make clear the extent and cellular location of the steatosis. In this example, the Oil Red O special stain has been applied to liver tissue to highlight microsteatosis, or the presence of fat particles within liver cells that do not distort the cell structure.