Urinary Tract Cytology

Urinary Specimens & Normal Cells - What's In Your Wee?

• Specimen Types:
  • Voided (midstream clean-catch): Most common.
  • Catheterized: Avoids vulvovaginal contamination.
  • Bladder Washings/Lavage: ↑ cellularity, for suspected lesions.
  • Ileal Conduit: Post-cystectomy.
  • Ureteric/Renal Pelvic Brushings: Upper tract evaluation.
• Processing & Preservation:
  • Fresh: Examine within 1-2 hrs.
  • Refrigerate (4°C): Up to 24 hrs.
  • Fixatives: 50% Ethanol, Saccomanno (Carbowax).
• Normal Cellular Elements:
  • Urothelial (Transitional): Superficial (umbrella), intermediate, deep (basal).
  • Squamous: Common (esp. females); usually contaminants.
  • RBCs: <5/HPF.
  • WBCs: <5/HPF (neutrophils).
  • Casts: Occasional hyaline.
  • Crystals, mucus, spermatozoa.

⭐ Deep urothelial cells naturally show a higher N/C ratio than superficial cells; misinterpreting this as atypia is a common pitfall.

Benign & Reactive Atypia - Not Always Bad News

• Non-neoplastic cellular changes that can mimic malignancy; crucial for differential diagnosis.
• Common Causes:
  • Inflammation (UTI): Neutrophils, bacteria, reactive urothelial cells.
  • Urolithiasis (stones): Mechanical irritation, cell clusters, mild atypia.
  • Instrumentation (catheter, cystoscopy): Sheets or clusters of reactive cells.
  • Therapy-induced changes:
    • Radiation: Cytomegaly, nucleomegaly, bizarre cell shapes, smudged chromatin, but often maintained N/C ratio.
    • Chemotherapy (e.g., Cyclophosphamide, Thiotepa): Similar to radiation; multinucleation common.
• Key Cytologic Features:
  • Mild nuclear enlargement, smooth nuclear membranes.
  • Finely granular, evenly distributed chromatin (or smudged/degenerated).
  • Prominent, centrally located nucleoli (if reactive).
  • Inflammatory background, cytoplasmic vacuolization.

⭐ Polyomavirus (BK virus) infection characteristically produces "Decoy cells": urothelial cells with large, homogenous, basophilic or amphophilic ground-glass intranuclear inclusions, which can be mistaken for High-Grade Urothelial Carcinoma (HGUC), especially in immunocompromised patients like renal transplant recipients.

Urothelial Neoplasia & Paris System - Grading the Grim

The Paris System (TPS) for Reporting Urinary Cytology standardizes diagnosis, enhancing High-Grade Urothelial Carcinoma (HGUC) detection and reducing Atypical Urothelial Cells (AUC) rates.

• Core Principle: Identify HGUC; other findings are secondary.

• Key TPS Diagnostic Categories:

  • Non-Diagnostic (ND)
  • Negative for HGUC (NHGUC)
  • Atypical Urothelial Cells (AUC)
  • Suspicious for HGUC (SHGUC)
  • High-Grade Urothelial Carcinoma (HGUC)
  • Low-Grade Urothelial Neoplasm (LGUN)

• HGUC Cytomorphologic Criteria (Mandatory):

  • Nuclear to Cytoplasmic (N/C) ratio ≥ 0.7
  • Severe hyperchromasia
  • Marked nuclear pleomorphism (size/shape variation)
  • Irregular nuclear contours/notched nuclei
  • Coarsely granular, clumped chromatin

⭐ The Paris System (TPS) aims for high sensitivity for HGUC (>85%) while maintaining specificity, significantly improving interobserver reproducibility for HGUC diagnosis.

Other Malignancies & Ancillary Tests - Beyond Urothelial Scope

• Non-Urothelial Primaries:
  • Squamous Cell Ca (SCC): Chronic irritation (Schistosoma). Keratin, bizarre cells. Markers: p63, CK5/6.
  • Adenocarcinoma: Glandular, mucin. Primary (e.g., urachal) vs. metastatic (colorectal, prostate). Markers: CK7, CK20, CDX2, PSA.
  • Small Cell Ca: Neuroendocrine. Nuclear molding, scant cytoplasm. Markers: Synaptophysin, Chromogranin.
• Metastatic Tumors: Most frequent non-urothelial. Common sources: prostate, colorectal, renal (RCC), lung, melanoma, lymphoma.
• Ancillary Tests (General):
  • Immunocytochemistry (ICC): Key for lineage. Examples above.
  • Molecular: FISH (UroVysion for urothelial Ca, detects aneuploidy of chr 3, 7, 17; 9p21 loss).

⭐ In urine cytology, adenocarcinoma cells from prostate typically show PSA & PSAP positivity.

High‑Yield Points - ⚡ Biggest Takeaways

• Voided urine is most common; catheterized for upper tract. Papanicolaou stain is standard.
• Decoy cells (polyomavirus) are key mimics of High-Grade Urothelial Carcinoma (HGUC).
• HGUC criteria: high N/C ratio, marked pleomorphism, coarse chromatin, irregular nuclear membranes.
• Low-Grade Urothelial Neoplasms (LGUN) show minimal atypia, making cytology diagnosis challenging.
• The Paris System (TPS) standardizes reporting, emphasizing HGUC detection.
• Schistosoma haematobium infection is a risk factor for squamous cell carcinoma.