JPC SYSTEMIC PATHOLOGY
URINARY SYSTEM
December 2023
U-M24
SIGNALMENT (JPC # 2194476): A dog.
HISTORY: This dog had persistent urinary tract infections. Contrast radiography revealed irregularities in the mucosal surface of the urinary bladder.
HISTOPATHOLOGIC DESCRIPTION: Urinary bladder (2 sections): Expanding the lamina propria and elevating the overlying hyperplastic transitional epithelium are multiple polypoid masses composed of a core of loosely arranged fibrovascular tissue that contains numerous small caliber vessels and moderate numbers of neutrophils, lymphocytes, plasma cells, fewer macrophages, moderate edema, congestion, and hemorrhage. There are moderate numbers of neutrophils within the epithelium that occasionally form intraepithelial microabscesses. Scattered epithelial cells are swollen and have clear cytoplasm (hydropic degeneration), and there are areas of epithelial attenuation and ulceration. The superficial lamina propria often contains high numbers of closely packed viable and degenerate inflammatory cells. Multifocally, the ulcerated and eroded epithelium is covered by a thin layer of fibrin, serum, and necrotic cells (serocellular crust).
MORPHOLOGIC DIAGNOSIS: Urinary bladder: Cystitis, polypoid and chronic-active, multifocal, moderate, with multifocal erosion and ulceration, hemorrhage and edema, breed not specified, canine.
CONDITION: Chronic polypoid cystitis
GENERAL DISCUSSION:
- Characterized by prominent non-neoplastic nodular, papillary, or polypoid mucosal/ submucosal proliferations, caused by chronic irritation, that can be difficult to differentiate from neoplasia (adenoma, papilloma, urothelial carcinoma, etc.)
- Common in any species, but most common in dogs and cattle
- Most common in the cranioventral bladder wall (opposite of urothelial cell carcinoma)
PATHOGENESIS:
· Likely develop from inflammatory and hyperplastic responses secondary to chronic irritation; cystitis, urolithiasis, drug reactions or other irritants
- Polyps frequently break down resulting in intermittent hematuria; the shape of these proliferating lesions promotes urinary retention and provides numerous sites for bacterial adhesion and invasion of the mucosa, resulting in a perpetuating cycle of infection > proliferation > inflammation > infection
- In cattle, polyps may undergo mucoid degeneration
TYPICAL CLINICAL FINDINGS:
· Nonspecific lower urinary tract signs
- Hematuria (macroscopic)
- Potential sequela of obstructive uropathy
TYPICAL GROSS FINDINGS:
- Scattered, hemorrhagic polypoid mucosal masses (broad-based or pedunculated)
- Bladder wall thrown into folds, or villous-like sessile projections
- May be no gross changes, just a thickened bladder wall
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Mucosa is thrown into many folds or villous-like polypoid projections that must be differentiated from neoplasms and also penetrate into the bladder wall
- Polypoid lesions consist of a core of proliferating connective tissue with varying amounts of stromal hemorrhage and hemosiderin accumulation, edema and congestion, and are infiltrated by numerous neutrophils, mononuclear leukocytes, and/or eosinophils and are covered by thickened proliferating transitional epithelium that, in some cases, may undergo squamous metaplasia
- Fascicles of well-differentiated, interweaving spindle cells may be present within the stroma of inflammatory polyps and should not be confused with urinary bladder fibromas or botryoid rhabdomyosarcoma
- The hyperplastic epithelial changes are referred to as:
- Cystis glandularis: Metaplasia to a mucus-secreting glandular epithelium
- Brunn’s epithelial nests: Hyperplastic transitional epithelial cells in the lamina propria
ADDITIONAL DIAGNOSTICS:
- On cytology, may exfoliate in large cellular sheets of transitional epithelial cells with uniform nuclei, coarse, ragged chromatin patterns and mild pleomorphism (cannot differentiate cytologically from transitional cell papilloma)
- Urinary ErbB2 protein is not present in polypoid cystitis but is found in 35% of urothelial carcinomas (UC) (Sakai, Vet Pathol, 2020)
- HER2 IHC: increased HER2 positivity is present in UC compared with polypoid cystitis (Tsuboi, Vet Pathol 2019)
DIFFERENTIAL DIAGNOSIS:
Gross and histologic
- Follicular cystitis – similar to polypoid cystitis with multiple submucosal 1 mm nodules of lymphoid proliferation usually surrounded by a zone of hyperemia
- Urinary Neoplasms:
- Papilloma: Papillary mass, not more than 6 cell layers thick
- Adenoma: originate from mucous metaplasia of urothelium, have a papilliform or pedunculated appearance and form glands; rare
- Urothelial cell carcinoma: Layers of pleomorphic cells; high mitotic rate, most commonly in trigone (Note: inflammatory lesions may be associated with reactive atypia)
COMPARATIVE PATHOLOGY:
- Can occur in any species buy most commonly reported in dogs and cattle
REFERENCES:
1. Cianciolo RE, Mohr FC. Urinary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:460-461.
2. Sakai K, Maeda S, Saeki K, Yoshitake R, Goto-Koshino Y, Nakagawa T, Nishimura R, Yonezawa T, Matsuki N. ErbB2 Copy Number Aberration in Canine Urothelial Carcinoma Detected by a Digital Polymerase Chain Reaction Assay. Vet Pathol. 2020;57(1):56-65.
3. Snyder L, Seelig D. Urinary System. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2023:407-409.
4. Sula MM, Lane LV. The Urinary System. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:762.
5. Tsuboi M, Sakai K, Maeda S, Chambers JK, Yonezawa T, Matsuki N, Uchida K, Nakayama H. Assessment of HER2 Expression in Canine Urothelial Carcinoma of the Urinary Bladder. Vet Pathol. 2019;56(3):369-376.
