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Ureteric Orifice

The ureteric orifice (ureteral orifice) is the terminal opening of each ureter into the urinary bladder, located at the posterolateral angles of the trigone. It marks the ureterovesical junction (UVJ) and acts as a physiological valve preventing retrograde urine flow (vesicoureteral reflux).

The orifice appears as a slit-like or crescent-shaped opening, oriented obliquely, allowing smooth entry of urine while collapsing during bladder contraction. Its structure is formed by the intramural ureter, detrusor muscle fibers, and the submucosal tunnel, creating a passive flap-valve mechanism.

Synonyms

  • Ureteral orifice

  • Ureterovesical junction opening

  • Ostium ureteris

Location and Structure

  • Position: At the posterolateral corners of the bladder trigone, between the interureteric ridge and bladder neck.

  • Shape: Slit-shaped, slightly curved, with oblique orientation.

  • Components:

    • Intramural ureter (within bladder wall)

    • Submucosal tunnel

    • Ureteral papilla or raised mucosal fold

  • Orientation: Directed inferomedially toward the bladder neck, forming the trigonal landmarks.

Relations

  • Medially: Bladder mucosa of trigone

  • Laterally: Detrusor muscle and intramural ureter

  • Superiorly: Interureteric bar (Mercier’s bar)

  • Inferiorly: Internal urethral orifice

  • Posteriorly: Terminal ureter and perivesical fascia

Function

  • Allows low-pressure, unidirectional urine flow from ureter to bladder

  • Prevents reflux during bladder filling and voiding

  • Acts as a passive valve via:

    • Oblique intramural course

    • Submucosal tunnel compression

    • Detrusor support of ureteral passage

  • Maintains urinary continence and protects kidneys from backflow

Clinical Significance

  • Vesicoureteral reflux (VUR): Dysfunctional or malformed orifice allows retrograde flow

  • Ureteric obstruction: Stones, edema, or strictures often occur at the UVJ

  • Ectopic orifice: May be located outside bladder trigone in congenital anomalies

  • Tumors: Ureteric orifice distortion occurs in bladder carcinoma

  • Surgical relevance: Landmark in ureteroscopy, TURBT, and ureteral reimplantation procedures

MRI Appearance

T1-weighted images:

  • Ureteric orifice itself is not well defined but appears as a low-signal slit within the bladder wall

  • Surrounding bladder wall: intermediate signal

  • Urine: low signal

  • Intramural ureter: low-to-intermediate tubular structure

T2-weighted images:

  • Urine: very bright

  • Intramural ureter: slightly darker tubular tract entering bladder

  • Orifice: seen as a tiny low-signal interruption at trigone

  • Detrusor muscle: intermediate-to-low signal

STIR:

  • Urine: bright

  • Bladder wall and ureteric orifice region: intermediate-to-dark

  • Subtle visualization of edema or thickening around orifice if present (not describing pathology here)

T1 Fat-Sat Post-Contrast:

  • Ureteric orifice: minimal enhancement of mucosal surface

  • Bladder mucosa enhances thinly; intramural ureter enhances slightly

  • Urine remains non-enhancing, providing contrast with enhancing walls

CT Appearance

Non-Contrast CT:

  • Urine: low attenuation

  • Bladder wall: soft-tissue density

  • Ureteric orifice: very small slit-like opening, indirectly inferred by intramural ureter course

  • UVJ is a common site where ureteral stones may lodge (not describing pathology features)

  • Trigone region clearly visualized based on anatomy

Post-Contrast CT:

  • Bladder wall and mucosa show subtle homogeneous enhancement

  • Intramural ureter enhances as part of the ureteral tract

  • Ureteric orifice appears as a small soft-tissue interface between enhancing mucosa and contrast-filled ureter or bladder

  • CT urography clearly outlines the intramural ureter until it terminates at the orifice

MRI image

Ureteric Orifice MRI sag image-img-00000-00000

MRI image

Ureteric Orifice