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Urinary bladder

The urinary bladder is a hollow, muscular, distensible organ situated in the anterior part of the pelvis. It functions as a temporary reservoir for urine before micturition. The bladder wall is composed of smooth muscle (detrusor muscle) and lined by transitional epithelium, enabling expansion and contraction. Its location, relations, and imaging features are vital for clinicians, radiologists, and urologists in the diagnosis and management of urinary and pelvic diseases.

Synonyms

  • Vesica urinaria

  • Bladder (urinary)

  • Vesical organ

Location and Parts

  • Lies in the true pelvis, posterior to the pubic symphysis and anterior to the rectum (in males) or uterus and vagina (in females)

  • Consists of:

    • Apex: Directed forward, connected to the umbilicus by the median umbilical ligament (urachus)

    • Body: Main central part

    • Fundus (base): Posterior aspect, triangular in shape

    • Neck: Lowest and most fixed part, continuous with the urethra

Relations

  • Anteriorly: Pubic symphysis, retropubic space (of Retzius)

  • Posteriorly:

    • In males: Seminal vesicles, vas deferens, rectum

    • In females: Cervix and anterior vaginal wall

  • Superiorly: Peritoneum and small intestine (when bladder is full)

  • Inferiorly: Pelvic floor muscles, prostate (males), urogenital diaphragm (females)

  • Laterally: Obturator internus muscles and pelvic fascia

Function

  • Temporary storage of urine (average capacity: 300–500 mL in adults)

  • Maintains urinary continence through sphincteric control

  • Contracts during micturition to expel urine via the urethra

Clinical Significance

  • Bladder outlet obstruction (e.g., prostate enlargement in males)

  • Bladder stones and diverticula

  • Bladder tumors (transitional cell carcinoma is most common)

  • Infections (cystitis)

  • Trauma and rupture following pelvic fractures

  • Important landmark in pelvic surgery and imaging (CT urography, MRI pelvis)

MRI Appearance

T1-weighted images:

  • Urine within bladder shows low signal intensity

  • Bladder wall shows low-to-intermediate signal intensity

  • Blood or proteinaceous content may appear bright

T2-weighted images:

  • Urine appears with high signal intensity

  • Bladder wall appears as a thin, low-signal rim

  • Tumors or thickening show intermediate to high signal intensity

STIR (Short Tau Inversion Recovery):

  • Urine appears bright

  • Pathological thickening or inflammation of bladder wall appears bright, helping detect cystitis or tumors

T1 Fat-Sat Post-Contrast:

  • Normal bladder wall enhances thinly and uniformly

  • Tumors show focal, irregular, or nodular enhancement

  • Inflammatory lesions may enhance diffusely

CT Appearance

Non-Contrast CT:

  • Urine-filled bladder appears as a fluid-density structure in the pelvis

  • Wall is thin and smooth

  • Stones appear as high-density foci within the bladder lumen

  • Hematoma or clot may appear as hyperdense material

Post-Contrast CT:

  • Normal bladder wall shows thin, uniform enhancement

  • Tumors or inflammatory thickening appear as focal or diffuse enhancing lesions

  • Extravasation of contrast indicates bladder rupture (intraperitoneal or extraperitoneal)

MRI image

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Urinary bladder mri male pelvis axial

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Urinary bladder mri male pelvis sagittal

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