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Penile urethra

The penile urethra, also known as the spongy urethra, is the longest segment of the male urethra. It runs through the corpus spongiosum of the penis and extends from the distal end of the membranous urethra to the external urethral meatus at the glans penis. It is surrounded by erectile tissue and associated glands, and serves both urinary and reproductive functions. Because of its superficial location, it is vulnerable to trauma, infection, and stricture disease, making it highly significant in clinical and radiologic practice.

Synonyms

  • Spongy urethra

  • Anterior urethra (distal portion)

  • Penile segment of male urethra

Location and Course

  • Begins at the distal end of the membranous urethra (at the perineal membrane)

  • Passes forward through the corpus spongiosum of the penis

  • Traverses the penile shaft up to the glans penis

  • Ends at the external urethral meatus at the tip of the glans

Relations

  • Anteriorly: Opens at the external urethral meatus

  • Posteriorly: Continuous with the membranous urethra

  • Superiorly: Surrounded by corpus spongiosum and covered by penile skin and fascia

  • Inferiorly: Lies below the corpora cavernosa of the penis

  • Associated glands: Receives ducts of the bulbourethral (Cowper’s) glands and numerous urethral glands (of Littre)

Function

  • Serves as the final passageway for urine excretion from the bladder

  • Transmits semen during ejaculation

  • Maintains patency and protection through the corpus spongiosum

  • Contributes to continence with help of urethral sphincters proximally

Clinical Significance

  • Common site of urethral strictures, particularly after trauma, catheterization, or infection

  • May be injured in straddle injuries or penile fractures

  • Infections (urethritis) often present in this segment

  • Evaluated in retrograde urethrography, MRI, and CT urethrography for strictures, diverticula, or tumors

  • Important in reconstructive urology and penile surgeries

MRI Appearance

T1-weighted images:

  • Penile urethra lumen appears dark (low signal) if empty

  • Surrounded by intermediate signal of corpus spongiosum

  • Hemorrhage or proteinaceous material in lumen may appear bright

T2-weighted images:

  • Urethral lumen appears bright if fluid/urine present

  • Corpus spongiosum surrounding urethra appears intermediate signal

  • Strictures or fibrosis may appear dark linear narrowing

STIR (Short Tau Inversion Recovery):

  • Fluid-filled lumen appears bright

  • Inflamed or edematous wall of urethra appears hyperintense

  • Fibrotic changes remain dark

T1 Fat-Sat Post-Contrast:

  • Urethral wall enhances mildly and symmetrically

  • Inflammatory lesions, abscesses, or tumors show more pronounced, sometimes irregular enhancement

  • Periurethral abscesses may show rim enhancement

CT Appearance

Non-Contrast CT:

  • Urethra difficult to visualize unless distended with urine or contrast

  • Appears as a thin soft tissue channel within corpus spongiosum

  • Calcifications (e.g., urethral stones) appear hyperdense

Post-Contrast CT (CT urethrography):

  • Urethral lumen outlined when contrast instilled retrogradely or during micturition study

  • Strictures appear as narrowed segments

  • Diverticula appear as contrast-filled outpouchings

  • Wall thickening or irregularity may indicate inflammation or tumor

MRI image

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MRI image

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