Trigone of urinary bladder

Topography and Wall Structure

The urinary bladder (vesica urinaria) is a hollow muscular organ located in the lesser pelvis cavity. Its anatomy includes the apex (apex vesicae), body (corpus vesicae), neck (cervix vesicae), and base (fundus vesicae). The trigone of the bladder is specifically localized at the base of the bladder.

The bladder wall consists of several layers: the mucous membrane (tunica mucosa), submucosal layer (tela submucosa), muscular coat (tunica muscularis, forming the muscle that expels urine — the detrusor, m. detrusor vesicae), and the outer serous or adventitial coat.

The mechanism of fold formation in an empty urinary bladder, where folds run in various directions, and in the ureters, where they are longitudinal, is associated with the presence of a loose submucosal layer. The trigone of the bladder is an exception: the submucosal layer is absent here. The mucous membrane is tightly fused with the muscular layer, so the surface of the trigone remains smooth.

What are the boundaries of the trigone of the bladder?

The area has a triangular shape, the angles of which are formed by important anatomical orifices:

• Apex — directed forward. It corresponds to the internal urethral orifice (ostium urethrae internum).
• Base — directed backward. It connects the orifices of the right and left ureters.
• Interureteric fold (plica interureterica) — a structure that connects the ureteric orifices at the base of the trigone.

Sphincter apparatus, blood supply, and innervation

The internal urethral sphincter (m. sphincter urethrae internus or m. sphincter vesicae) is an involuntary sphincter and encompasses the initial segment of the urethra. The voluntary urethral sphincter (m. sphincter urethrae) is located at the level of the membranous part of the urethra (pars membranacea).

Blood supply to the urinary bladder is provided by branches of the internal iliac artery (a. iliaca interna). Innervation is supplied by the vesical plexus (plexus vesicalis).

Clinical significance (Lieutaud's triangle)

In medical practice, the trigone of the bladder is referred to as Lieutaud's triangle.

• Urothelial carcinoma (transitional cell carcinoma): This type accounts for up to 90% of all bladder carcinomas. Most commonly, the tumor is localized in Lieutaud's triangle and the posterolateral walls of the organ. Macroscopically, the cancer can be papillary — an exophytic tumor on a stalk that does not always invade beyond the basement membrane — or plaque-like: with mucosal thickening without papillary structures. Plaque-like cancer is more frequently invasive; histologically, it may represent carcinoma in situ and typically tends to undergo gradual anaplasia.
• Random Biopsy: In cases of T1G3 diagnoses or carcinoma in situ (CIS), mapping is performed to assess the extent of the process. Tissue collection involves Lieutaud's triangle, the apex, the right, left, anterior, and posterior walls of the urinary bladder, and the prostatic urethra.
• Botulinum toxin type A injection: To improve urodynamics, the drug is injected into the detrusor muscle. The effective dose is 100 units, the maximum is 300 units; urodynamics may improve for several months.

Class and exam questions

What else to study on this topic

• Urinary bladder (vesica urinaria)
• Internal urethral sphincter
• Ureters and their orifices
• Urothelial carcinoma of the bladder

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.