Microcystic Urothelial (Transitional Cell) Carcinoma

Definition

• Invasive urothelial carcinoma with numerous lumens of variable size without glandular differentiation

Note

• Usual papillary urothelial carcinoma is covered separately

Diagnostic Criteria

• Infiltrative pattern
• Numerous, prominent spaces ranging from intracytoplasmic to macroscopic (2 cm)
  • May appear as irregular anastomosing cords and nests of cells forming cysts
  • May appear as large irregular cribriform areas
• Carcinoma cells forming and lining spaces lack glandular/secretory cytoplasmic differentiation
  • Lumens frequently empty, but may contain necrotic debris or PASd stainable material
  • Lining cells are transitional or squamous, PASd negative
    • No goblet cells
• Cytologically bland
• Probably forms a spectrum with nested variant urothelial carcinoma (fewer cysts and spaces) and with lesions described as urothelial carcinoma with acinar/tubular differentiation (extensive formation of small tubules)
  • All three are aggresive, invasive carcinomas in spite of their bland cytology

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates:

Supplemental studies

Immunohistology

• Mucin may be detected in some lumens but lining cell cytoplasm is negative

Differential Diagnosis

• Nested variant of urothelial carcinoma and urothelial carcinoma with small tubules
• Adenocarcinoma
• Urothelial carcinoma with glandular differentiation
• Florid cystitis cystica/glandularis
• Inverted papilloma
  
• Papilloma vs Nephrogenic Adenoma

  Nephrogenic Adenoma	Urothelial Papilloma
  Papillae lined by single layer of cells, frequently hobnailed	Papillae lined by normal multilayered transitional epithelium
  No umbrella cells	Normal umbrella cells present
  Usually associated with tubular submucosal component	No associated tubular component

Grading / Staging

Grading

• Microcystic carcinoma is considered by some to be definitionally low grade

Staging

• Usual rules apply
• Although non-invasive papillary urothelial neoplasms are technically in situ, they are staged as Ta and are not referred to as carcinoma in situ
• If possible, the extent of lamina propria / submucosa invasion should be reported
• Muscularis mucosae is variable and its involvement does not affect staging
  • Generally loose strands of muscle
• Muscularis propria involvement is significant and should be evaluated carefully
  • Dense, well defiined bundles of muscle
  • Depth of muscularis propria involvement cannot be assessed in transurethral specimens
  • Presence or absence of propria should be reported even if not involved
• Lymphatic invasion should be confirmed by immunohistochemistry

Clinical

• Same prognosis as usual invasive urothelial carcinoma
• Should be distinguished from adenocarcinoma
  • Adenocarcinoma has worse behavior
  • Extra-urothelial primary must be ruled out for adenocarcinomas

Classification / Lists

Flat Lesions of the Urinary Bladder

• Flat urothelial hyperplasia
• Reactive urothelial atypia
• Atypa of unknown significance
• Dysplasia
• Urothelial carcinoma in situ

Papillary Lesions of the Urinary Bladder

• Nephrogenic adenoma
• Fibroepithelial polyp
• Polypoid/papillary cystitis
• Papillary urothelial hyperplasia
• Urothelial papilloma
• Papillary urothelial neoplasm of uncertain malignant potential (PUNLUMP)
• Low grade urothelial carcinoma
• High grade urothelial carcinoma

Subtypes of High Grade Urothelial Carcinoma

• Micropapillary urothelial carcinoma
  
• Plasmacytoid urothelial carcinoma
• Small cell carcinoma
• Urothelial carcinoma with chordoid features
• Urothelial carcinoma with sarcomatoid differentiation
• Urothelial carcinoma with squamous differentiation
  

Inverted Lesions of the Urinary Bladder

• Florid hyperplasia of von Brunn nests
• Cystitis cystica/glandularis
• Inverted urothelial papilloma
• Inverted urothelial carcinoma
• Nested variant urothelial carcinoma
• Verrucous squamous carcinoma

Glandular Lesions of the Urinary Bladder

• Nephrogenic adenoma
• Cystitis cystica/glandularis
• Intestinal Metaplasia
• Villous adenoma
• Urothelial carcinoma with glandular differentiation
• Nested urothelial carcinoma with cystic structures
• Non-urachal adenocarcinoma
• Mulllerian lesions
  • Endometriosis
  • Endocervicosis
  • Endosalpingosis
• Urachal lesions
  • Urachal remnant
  • Urachal adenocarcinoma
• Metastatic/direct spread of non-bladder adenocarcinomas

Bibliography

• Murphy WM, Grignon DJ, Perlman EJ. Tumors of the Kidney, Bladder and Related Urinary Structures, Atlas of Tumor Pathology, AFIP Fourth Series, Fascicle 1, 2004
• Eble JN, Sauter G, Epstein JI, Sesterhenn IA eds. World Health Organization Classification of Tumors. Pathology and genetics of tumors of the Urinary System and Male Genital Organs. IARC Press: Lyon 2004.