Epididymis, Epithelium - Vacuolation

The epididymal epithelium develops many different forms of vacuolation. They are often segmental and region specific. The vacuolation may be the result of a number of degenerative processes, including the accumulation of lipids, phospholipids (phospholipidosis), glycoproteins, or fluids. The vacuoles may be or large (macrovacuolation, Figure 1) or small (microvacuolation, Figure 2) and may appear empty or filled with basophilic or eosinophilic material. Basophilic vacuolation is a common age-related, background finding in a specific segment of the distal caput region of the rat (Figure 1). Large clear vacuoles are frequently seen as an incidental finding at the corpus cauda junction in the rat epididymis. Vacuolation of the epididymis can also be test article related and may be diffuse or segmental. Clear cells are a normal cell type of the epididymal epithelium involved in endocytosis of luminal particulate matter. They are often increased in number and prominence, particularly in the cauda, when there is increased cell debris in the epididymal lumen (Figure 3). Care should be taken to distinguish these normal clear cells from degenerative vacuolar changes. The distinction can be made since clear cells are filled with lysosomes that stain strongly positive with Periodic acid-Schiff.