Muscularis propria invasion in the urinary bladder

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 here and refers to invasion of the muscularis propria.

General

Comparing muscularis propria and muscularis mucosae

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

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

• 

  MM - intermed. mag. (wc)

• 

  MM - high mag. (WC)

• 

  MM - very high mag. (WC)

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

• 

  MIUC - very low mag.

• 

  MIUC - low mag.

• 

  MIUC - intermed. mag.

• 

  MIUC - high mag.

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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

• Urothelial carcinoma.
• Bladder cancer staging.
• Cancer staging systems.