About transitional epithelium

From the pelvis to the beginning of the urethra, the walls of the urinary tract is lined with a stratified transitional epithelia. In the bladder, the epithelia is formed of around seven layers of cells. The deepest cells are cylindrical while the intermediate layer cells are variable. The surface cells are typically transitional. These cells are also named urothelial cells.

Transitional cells

Transitional cells are normal elements of the urinary sediment. The cell's shape changes slightly according to the section of the lower urinary tract. The typical bladder cells are round with a round centered nucleus. In the cytological nomenclature, one speaks of: balloon cells, umbrella cells, kite cells... All these designations correspond to transitional cells originating from different levels: bladder, uretere, pelvis.

The presence of transitional cells is more frequent in the elderly population. Occasionally, because of morphological changes, the identification of transitional cells is difficult. Although these changes are not always associated to a pathology, atypical cells must be watched for in this prevalent population. Holmquist has demonstrated that a simple urinary routine sediment can play an important role in the early detection of TCC ( Transitionnal Cell Cancer).

Transitional epithelial fragments

Contrarily to the isolated cells, the presence of transitional epithelial fragments is almost always associated to an abnormal situation. In the majority of cases, the cells have a normal aspect and form a thin sheet where it is easy to delimit each cell. These sheets are said to have a brick-wall-like aspect. The presence of this type of fragments can be the result of a urinary catheter or of another condition that provokes an erosion of the surface of the bladder's epithelium.

In some sustained irritating conditions, transitional cells can become reactive. In these conditions, the cells and the nucleus increase in size. The size of cells can be variable, but the ratio nucleus/cytoplasm is well preserved. Binuclated cells can be seen. 

This situation is quite different from the atypical fragments as seen in a TCC of high grade. The finding of atypical urothelial fragments is an important element in the detection of an otherwise silent TCC.