Normal urothelial histology. Normal urothelial lining in distended bladder. There are approximately seven layers of urothelial cells. The surface is lined by larger superficial cells with abundant cytoplasm (“umbrella cells”). Capillary vessels are present immediately beneath the epithelium in the lamina propria (H&E)

Normal urothelial cells in voided urine. (a) Superficial (umbrella) cells: normal voided urine may contain relatively few urothelial cells. These cells are of various types, shapes, and sizes and comprise superficial (umbrella) cells and a few cells from the intermediate and deeper urothelial cell layers. Umbrella cells are the predominant cell type in voided urine and are 20–30 μm in diameter, with one flat plane. They are somewhat similar in size to cervicovaginal intermediate squamous cells, but may be larger. Umbrella cells may be mono-, bi-, or multinucleated. The nuclei are central and round with regular finely granular chromatin and occasional small nucleoli (SP). (b) Intermediate cells originating from the deeper layers of the urothelium: resemble parabasal squamous cells from lower genital tract in size and configuration. These cells are often spherical or round with scanty basophilic cytoplasm and spherical bland nucleus. They desquamate singly or in clusters (TP). (c) Multinucleated umbrella cells are rare in voided urine, except after diagnostic and therapeutic procedures. They are normally seen in specimens from ureter or renal pelves. Giant umbrella cells may be mistaken as neoplastic (TP)

Catheterized urine. (a) The cytological features of catheterized urine (CU) are usually similar to voided samples, except for higher cellularity, more sheets, clusters and urothelial tissue fragments, and background inflammation. Some umbrella cells show reactive features with prominent single and multiple nucleoli. The nuclei however are regular and pale (TP). Catheterized urine is considered instrumented specimen and therefore may have artifacts not seen in voided urine, particularly the presence of increased urothelial tissue fragments which may be at first worrisome for low-grade urothelial neoplasia (LGUN). Kannan and Bose [1] found that evenness of fragment borders and the presence of cytoplasmic collars were distinguishing features of instrument artifact. (b) Since urothelial tissue fragments have some three-dimensionality, inflammatory cells and other background cells may appear on a different plane of focus in SP. This does not occur in TP, as fragments seen in those preparations are flat (SP)

Washing specimens in the absence of disease. (a) Bladder washing specimens are usually highly cellular and often include a larger number of urothelial tissue fragments and single urothelial cells. In fact, a specimen that is sparsely cellular may indicate an inadequate sample. Prather et al. [2] determined that a cutoff of 20 well-visualized, well-preserved urothelial cells per ten high-power fields increased the positive predictive value of bladder wash (TP). (b) Deeper urothelial cells are more frequent and may form tightly packed three-dimensional clusters in a “papillary” configuration with relatively smooth borders. In these instances, the cells are often more elongated with regular, oval nuclei, bland chromatin, and small nucleoli. Umbrella cells usually outline these groups. These large clusters are commonly mistaken as representing a papillary tumor, particularly, if the cytologist is unaware of how the specimen was procured (SP). Washings and brushings from upper urinary tract are richly cellular and generally appear similar to bladder wash. Large sheets of urothelial cells may be forcibly removed from surface of ureters or renal pelves resulting in complete denudation of ureteral surface

Ileal conduit urine. (a) Ileal conduit urine (ICU) used in monitoring patients after cystectomy for bladder cancer normally contains a rich population of poorly preserved intestinal cells. The intestinal cells may have vacuolated or granular degenerative cytoplasm and fragmented and/or pyknotic nuclei. Background mucin and Paneth cells may sometimes be seen. Wolinska and Melamed [3] studied ICU and were able to trace the transition from intestinal epithelial cells in clusters to degenerating rounded cells that resemble histiocytes (TP). In less degenerated samples, well-preserved columnar mucus-producing cells with peripheral and round dark nuclei are noted. (b) In this specimen, numerous degenerative cells distract from rare malignant cells in the field; this patient had a recurrence of HGUC (SP). (c) In histological specimens taken from a benign ileal conduit, progressive shortening and ultimately flattening of villi can be seen, as well as an increased number of goblet cells (H&E)

Squamous cells. Urine samples are often contaminated by squamous cells from anogenital region, trigone, or urethra, though this contamination may be limited by procuring a sample through catheterization or instrumentation. Superficial squamous cells are characterized by a small, pyknotic nucleus and abundant cytoplasm, and intermediate cells have a slightly larger, vesicular nucleus. Smaller parabasal cells may be seen, which have an increased nuclear-to-cytoplasmic ratio and share some cytomorphological overlap with urothelial cells. Note cluster of deeper urothelial cells. Pear-shaped Trichomonas vaginalis organisms indicate contamination from the lower gynecologic tract. Occasionally atypical squamous cells (ASC) may be seen, such as koilocytes; in these instances, they should be noted and clinical correlation should be suggested. It can be difficult to isolate the origin of ASC, as they could represent any lesion from condyloma to HGUC with squamous differentiation in voided urine (see Fig. 3.23a, b) (TP). Owens and Ali [4] followed 32 patients with ASC in the urine; 8 patients had bladder carcinoma with squamous differentiation, 2 had cervical carcinoma, and 22 (69 %) had benign follow-up

Acute and chronic cystitis. Mixed inflammatory cells comprise of polymorphonuclear leukocytes, lymphocytes, and eosinophils. Desquamated benign urothelial cells can be seen. These findings are usually nonspecific and require clinical correlation. If necrotic debris is observed, it should raise awareness for tumor in which only necrotic cells are present. In some instances, repeated infections may cause cystitis follicularis, which may result in the presence of dendritic cells with prominent nuclear chromatin and prominent nucleoli, lymphoid aggregates, reactive urothelial cell atypia, and glandular cells, indicating glandular metaplasia [5]. Melamed-Wolinska bodies (dense, round eosinophilic inclusions) can be observed in degenerating urothelial cells. Multiple inclusions of varying sizes may be present and are thought to represent degenerative lysosomal aggregates (TP)

Crystals. Rarely, true uric acid crystals can have a variety of shapes and sizes and are typically yellow or colorless. Possible shapes include rhomboids, hexagonal plates, needles, and rosettes. They typically form under acidic conditions and are not necessarily a sign of an underlying pathological process (TP). Calcium carbonate crystals, which usually appear as large yellow-brown or colorless spheroids with radial striations, are also commonly seen in urinary specimens. They can also be seen as smaller crystals with round, ovoid, or dumbbell shapes. Triple phosphate crystals (struvite) appear as “coffin lids” and form in alkaline urine. They are classically associated with Proteus mirabilis infection. For the most part, crystals are simply distracting noncellular element seen in urine specimens. Wright and Halford [6] found that TP of urine cytology had the same numbers of casts and debris as cytospin preparations, but the amount of crystals and red blood cells (RBCs) were reduced in TP