From the Research
The urinary tract consists of distinct histological layers that enable its function in urine transport and storage, with the most recent and relevant study on urinary cytology in the setting of upper tract urothelial carcinoma published in 2021 1. The renal tubules in the kidneys are lined with simple cuboidal or columnar epithelium specialized for filtration and reabsorption.
- The ureters and renal pelvis feature transitional epithelium (urothelium) that can stretch, supported by a lamina propria, smooth muscle layers (inner longitudinal, middle circular, outer longitudinal), and an adventitia.
- The bladder shares this transitional epithelium but has thicker smooth muscle arranged in detrusor bundles that facilitate contraction during urination.
- The urethra varies histologically by region, with transitional epithelium proximally, stratified or pseudostratified columnar epithelium in the membranous portion, and stratified squamous epithelium distally. This specialized histology allows the urinary tract to maintain urine sterility, accommodate volume changes, and prevent reflux while enabling controlled elimination. The urothelium's unique umbrella cells with their specialized apical membrane create a watertight barrier that protects underlying tissues from urine's toxic components, as noted in the context of urinary cytology and its diagnostic value 1.
In terms of imaging modalities for the urinary tract, computed tomography urography (CTU) is now well established as the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract, having largely replaced excretory urography 2.
- CTU techniques have continued to evolve with the goal of improving urothelial surface visualization.
- Numerous benign and malignant conditions of the kidneys, ureters, and urinary bladder can be accurately depicted by CTU. However, the role of CT and MRI in imaging the urinary tract should be considered complementary, with each technique offering specific advantages and disadvantages 3.
The diagnostic value of abdominal ultrasound, urine cytology, and prostate-specific antigen testing in the lower urinary tract symptoms clinic has also been investigated, with results showing that these tests can help diagnose significant, potentially life-threatening conditions in up to 6.6% of patients 4.
- Abdominal ultrasound scanning, urine cytology, and PSA testing can help to diagnose incidental urological malignancies, urinary tract calculi, or abdominal aortic aneurysms.
- The addition of these tests as part of an LUTS assessment protocol may justify these additional investigations, despite the individual pick-up rate of each condition not being higher in the LUTS patient than in the general population.
Overall, the urinary tract's histological structure and function are critical to its role in maintaining urine sterility and enabling controlled elimination, and imaging modalities such as CTU and diagnostic tests like urine cytology play important roles in evaluating and managing urinary tract conditions 1, 2, 3, 4.