Male urethra
The male urethra has a complex structure and is subdivided into several segments, each with its own radioanatomical features:
- Urethral crest / seminal colliculus (verumontanum). Serves as an anatomical landmark where the ejaculatory ducts open.
- Membranous part (membranous portion). Represents the shortest and narrowest segment. It is surrounded by a powerful circular muscle layer — the external sphincter. During retrograde urethrography, this segment is visualized as a zone of physiological narrowing.
- Bulbous part (bulbous urethra). Acts as the widest portion. It is located within the corpus cavernosum's counterpart, the corpus spongiosum (corpus spongiosum). It originates from the urogenital diaphragm, which demarcates the anterior and posterior urethra. The ducts of the bulbourethral (Cowper's) glands empty into the proximal end of the bulbous segment.
- Penile (spongy) part. Represents the distal segment of the anterior urethra, originating from the penoscrotal angle.
Female urethra
The female urethra is significantly shorter than the male urethra, with an average length of about 4 cm.
The canal has a variable diameter along its course: it is widest at the internal orifice (origin) and most narrowed at the external orifice (meatus), which opens into the vestibule of the vagina.
Fibers of the external sphincter intertwine into the middle third of the female urethra. Along the course of the canal, the ducts of Skene's parourethral glands (Skene glands) open into its lumen.
Normal radiological presentation
On a normal male retrograde urethrogram, a characteristic relief can be traced. The key radiologic signs are a clearly defined luminal narrowing at the level of the membranous part and a noticeable dilation in the bulbous urethra zone. Evaluation of these physiological curves and caliber changes is essential for identifying strictures and traumatic injuries.
Briefly: answers to topical questions
What anatomical segments is the male urethra subdivided into?
The male urethra is subdivided into three main anatomical segments, with an additional part distinguished within one of them.
- Prostatic part (pars prostatica) — passes through the prostate gland.
- Membranous part (pars membranacea) — the narrowest part of the urethra.
- Spongy part (pars spongiosa) — includes the bulbous part (pars bulbosa), corresponding to the position of the penile bulb, and the penile part.
What anatomical structures and ducts open onto the seminal colliculus?
Several anatomical structures and ducts open onto and in the immediate vicinity of the seminal colliculus.
- Ejaculatory ducts (ejaculatory ducts) — their orifices are located on the sides of the seminal colliculus.
- Prostatic ducts — open laterally to the seminal colliculus.
- Prostatic utricle (prostatic utricle) — a vestigial remnant of the Müllerian duct, located on the colliculus seminalis just below the verumontanum.
Where are all the physiological narrowings of the male urethra located?
Three physiological narrowings are distinguished in the male urethra.
- First narrowing — located in the membranous part (pars membranacea), which is the narrowest and shortest part of the urethra.
- Second narrowing — located at the internal (vesical) orifice of the urethra.
- Third narrowing — localized at the external urethral meatus.
Which segments comprise the posterior male urethra?
The posterior male urethra comprises two anatomical segments located proximal to the bulbous part.
- Prostatic part (pars prostatica / prostatic urethra) — the proximal segment passing through the prostate gland.
- Membranous part (pars membranacea / membranous urethra) — the short segment following the prostatic part.
Class and exam questions
Which segment of the male urethra is the narrowest?
Membranous part. It is surrounded by the external sphincter and appears as a physiological narrowing on the urethrogram.
Where do Cowper's glands open?
The ducts of the paired bulbourethral (Cowper's) glands open into the proximal part of the male bulbous urethra.
Where is the widest point of the female urethra located?
The widest part of the female urethra is its origin — the internal orifice.
What is the seminal colliculus?
This is an anatomical structure in the male urethra (verumontanum) in the region of which the ejaculatory ducts open.
What else to study on this topic
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- Supernumerary kidney and rotation anomalies
- Radiological signs of left renal agenesis on plain abdominal radiography
- Intravenous pyelography in renal duplication
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