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Prostatic urethra

The prostatic urethra is the widest and most dilatable part of the male urethra. It passes through the prostate gland and serves as a common channel for the urinary and reproductive systems. This segment contains key anatomical landmarks such as the urethral crest, seminal colliculus, and openings of the ejaculatory ducts. It is clinically significant in urology, radiology, and surgery, particularly in conditions like benign prostatic hyperplasia (BPH), urethral obstruction, and prostate carcinoma.

Synonyms

  • Urethra prostatica

  • Prostatic segment of urethra

  • Proximal urethra (within prostate)

Location and Boundaries

  • Superiorly: Continuous with the bladder neck at the internal urethral orifice

  • Inferiorly: Continuous with the membranous urethra at the apex of the prostate

  • Anteriorly: Related to the anterior fibromuscular stroma of prostate

  • Posteriorly: Related to urethral crest, seminal colliculus, and openings of prostatic ducts and ejaculatory ducts

Relations

  • Lies within the prostate gland, forming its central passage

  • Posterior wall contains the seminal colliculus (verumontanum) with openings of the ejaculatory ducts

  • Surrounded by prostatic tissue, including the transition zone (site of BPH) and peripheral zone (common site for carcinoma)

  • Anteriorly related to prostatic stroma, posteriorly to ejaculatory ducts and seminal vesicles (via openings)

Function

  • Conducts urine from bladder through prostate into membranous urethra

  • Serves as a passageway for semen during ejaculation (receiving openings of ejaculatory ducts)

  • Coordinates urinary and reproductive outflow with sphincteric control

Clinical Significance

  • Benign prostatic hyperplasia (BPH): Causes compression and elongation of the prostatic urethra → urinary obstruction

  • Prostate carcinoma: May invade or distort prostatic urethra

  • Urethral strictures: Can occur from inflammation, instrumentation, or surgery

  • Surgical relevance: Landmark during TURP (transurethral resection of prostate)

  • Imaging relevance: Evaluated in MRI for tumor staging, in CT/US for obstruction, and in voiding cystourethrography

MRI Appearance

T1-weighted images:

  • No fluid: Prostatic urethra lumen not visualized; appears as a thin low-signal line within prostate

  • Fluid present: Urine appears as low signal intensity

  • Fat: Bright signal outlining surrounding structures and periprostatic fat

T2-weighted images:

  • No fluid: Urethral lumen appears as a thin dark slit

  • Fluid present: Urine appears as bright signal within the lumen

  • Fat: Appears bright, surrounding prostate margins

STIR (Short Tau Inversion Recovery):

  • No fluid: Urethra poorly seen, normal surrounding prostate tissue intermediate to low signal

  • Fluid present: Hyperintense bright lumen

  • Fat: Suppressed and appears dark

T1 Fat-Sat Post-Contrast:

  • No fluid: Urethral lumen appears as a non-enhancing line

  • Fluid present: Urine does not enhance

  • Fat: Suppressed and appears dark

  • Pathology: Enhancing lesions in periurethral prostate or urethral wall thickening may be seen

CT Appearance

Non-Contrast CT:

  • No fluid: Urethra not clearly visualized, seen as a potential space within prostate

  • Fluid present: Appears as a hypodense lumen within prostate

  • Fat: Appears as low-density tissue surrounding prostate

Post-Contrast CT:

  • Urethral lumen remains unenhanced

  • Periurethral or prostatic lesions may show enhancement (tumor, inflammation)

  • Enlarged prostate compressing urethra is well demonstrated

MRI image

prostatic urethra MRI axial anatomy image-img-00000-00000

MRI image

prostatic urethra MRI sagittal anatomy image-img-00000-00000