Muscularis propria invasion in the urinary bladder

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Muscle invasive urothelial carcinoma. H&E stain.

The presence or absence of muscularis propria invasion in the urinary bladder is a very important determination, as the clinical management changes between T1 and T2:

  • T1: usually conservative treatment (local excision).
  • T2: radical treatment (cystectomy or cystoprostatectomy).

A thin layer of discontinous muscularis mucuosae (MM) is present and, especially if hypertrophic, may be confused with muscuaris propria (MP).

Staging of bladder cancer is dealt with in the bladder cancer staging article.

Muscle invasive bladder cancer redirects to this article and refers to invasion of the muscularis propria.

Bladder muscularis propria invasion and urinary bladder muscularis propria invasion redirect to this article.

General

Comparing muscularis propria and muscularis mucosae

A comparison between muscularis propria and muscularis mucosae - adapted from Paner et al.:[1]

Feature Muscularis mucosae Muscularis propria
Outline/border typically irregular (frayed edges) usually regular (circumscribed)
Size of bundles ‡ classically "small", often "large" (hypertrophic) usually "large"
Isolated fibres yes no
Location in bladder less common in trigone, dome very common everywhere
Depth † superficial, occ. deep deep

Notes:

  • † The lamina propria thickness varies with location. It is thinnest in the trigone (0.5-1.6 mm) and thickest in the dome (1.0-3.1 mm).
  • ‡ Small is defined as <4 muscle fibres; large >= 4 muscle fibres.
    • The presence of hyperplastic bundles ranges from ~20% in the trigone to ~70% in the dome.

Images

Microscopic

Rational assessment of muscularis propria invasion

To call muscularis propria invasion:

  1. Definite tumour must be between muscle.
  2. Muscle bundles must be thick.
  3. Multiple bundles must be adjacent to one another.
  4. Should not be superficial - surface epithelium if present should be distant.

DDx:

  • Invasion of hypertrophic muscularis mucosae.

Images

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Cannot exclude MP invasion

Urinary Bladder Tumour, Transurethral Resection:
- INVASIVE HIGH-GRADE UROTHELIAL CARCINOMA.
-- Extensive invasion into at least the lamina propria.
- Negative for definite muscularis propria, see comment.

Comment:
The tumour is seen around bundles of smooth muscle that are favoured 
to represent muscularis mucosa; however, obliterated muscularis 
propria cannot be excluded. 

Correlation with the clinical findings is required. Additional transurethral
sampling and/or imaging to assess the muscularis propria is suggested.

See also

References

  1. Paner, GP.; Ro, JY.; Wojcik, EM.; Venkataraman, G.; Datta, MW.; Amin, MB. (Sep 2007). "Further characterization of the muscle layers and lamina propria of the urinary bladder by systematic histologic mapping: implications for pathologic staging of invasive urothelial carcinoma.". Am J Surg Pathol 31 (9): 1420-9. doi:10.1097/PAS.0b013e3180588283. PMID 17721199.