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Topic

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Neck of urinary bladder

The neck of the urinary bladder is the funnel-shaped lower portion of the bladder that leads into the urethra. It represents the narrowest and most fixed part of the bladder and plays a vital role in urinary continence and bladder outlet function. Anatomically, it is positioned posterior to the pubic symphysis and superior to the prostate in males, and anterior to the urethra and vagina in females. It is surrounded by smooth muscle fibers forming the internal urethral sphincter, which is under involuntary control.

Synonyms

  • Bladder neck

  • Internal urethral orifice region

  • Vesical neck

Location and Boundaries

  • Superiorly: Continuous with the base of the urinary bladder

  • Inferiorly: Opens into the proximal urethra at the internal urethral orifice

  • Anteriorly: Related to the pubic symphysis and retropubic space

  • Posteriorly: Related to seminal vesicles and vas deferens in males; vagina and cervix in females

  • Laterally: Puboprostatic ligaments (males) or pubovesical ligaments (females)

Relations

  • Males: Superior to prostate gland, anterior to seminal vesicles, posterior to pubic symphysis

  • Females: Anterior to vagina, posterior to pubic symphysis, superior to pelvic diaphragm

  • Inferiorly: Continuous with proximal urethra

  • Surrounding: Enveloped by smooth muscle forming internal urethral sphincter

Function

  • Acts as the outlet of the urinary bladder

  • Provides continence by internal urethral sphincter contraction

  • Coordinates with detrusor muscle during micturition

  • Prevents retrograde ejaculation in males by sphincter closure during ejaculation

Clinical Significance

  • Site of bladder outlet obstruction (e.g., bladder neck obstruction, benign prostatic hyperplasia in males)

  • Important in urinary incontinence when sphincter dysfunction occurs

  • Can be affected by trauma, surgery, tumors, or neurogenic bladder disorders

  • Landmark in cystoscopy and pelvic surgery

  • Imaging target in evaluation of urinary retention, obstruction, or urethral pathology

MRI Appearance

T1-weighted images:

  • No fluid: Neck appears as a dark (low-signal) muscular structure at bladder outlet

  • Fluid (urine): Hypointense, contrasting with surrounding bladder wall

  • Fat: Hyperintense, outlining bladder and pubic region

T2-weighted images:

  • No fluid: Neck appears dark relative to hyperintense bladder lumen

  • Fluid (urine): Bright, filling bladder above neck

  • Fat: Bright to intermediate, surrounding retropubic space

STIR (Short Tau Inversion Recovery):

  • No fluid: Neck remains dark

  • Fluid: Bright hyperintense

  • Fat: Suppressed (appears dark), enhancing contrast of pathology

T1 Fat-Sat Post-Contrast:

  • Normal: Mild homogeneous enhancement of bladder neck

  • Pathology: Tumors or inflammation show irregular or intense enhancement

  • Fat: Suppressed, dark background for better lesion detection

CT Appearance

Non-Contrast CT:

  • Neck appears as a soft tissue density at bladder outlet

  • No fluid: Collapsed bladder neck indistinct, seen as tissue density

  • Fluid (urine): Low attenuation fluid filling bladder above neck

  • Fat: Seen as low-density tissue around bladder in retropubic space

Post-Contrast CT:

  • Normal bladder neck enhances uniformly and mildly

  • Pathology (tumors, inflammation) appears as focal or irregular enhancing tissue

  • Obstruction may show thickening or irregularity of bladder outlet region

MRI image

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MRI image

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MRI image

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CT image

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