The development of the male genitourinary tract is a highly coordinated and complex process.

The male reproductive system develops primarily from the differentiation of mesonephric ducts under the influence of testicular hormones and the involution of müllerian derivatives.

Fig 1: Development of the male internal genitalia. Human male and female embryos develop similarly for the first 6 weeks.

Ultrasonography and magnetic resonance imaging (MRI) are the modality of choice for accurate identification and characterization of male pelvic cysts.

MRI is a noninvasive and excellent method to evaluate pelvic cysts that can provide detailed anatomical visualization, allowing differentiating from solid masses and determining the anatomic origin of these lesions. The etiology of these cysts varies, including congenital anomalies, acquired obstructive phenomena, and inflammatory processes.

On the other hand, transrectal ultrasound sometimes makes it possible to carry out therapeutic procedures such as drainage and aspiration of these lesions, which can sometimes be very symptomatic. These lesions may be associated with recurrent infections of the genitourinary tract, hematospermia, pain and postvoiding incontinence.

Cysts of the lower male genitourinary tract can be divided into two main groups: intraprostatic and extraprostatic. Intraprostatic cysts are further divided into median (utricle cysts, müllerian duct cysts), paramedian (ejaculatory duct cysts and urethral diverticula) and lateral cysts (prostatic retention cysts, cystic degeneration of benign prostatic hypertrophy, cysts associated with tumors and abscess).

Extraprostatic cysts include entities such as cysts of the seminal vesicle, vas deferens and Cowper duct.

Utricle cysts and Müllerian Duct Cysts

Traditionally, prostatic utricle cysts are interpreted as an embryologic remnant of the müllerian duct system. However, there is no absolute consensus in the literature regarding its origin, with some authors arguing for a different origin.

Utricle cysts are relatively rare, with an estimated incidence of 1–5% in the general male population. The condition is more commonly found in childhood or early adulthood. These lesions can be associated with multiple genitourinary anomalies, including hypospadias, cryptorchidism, and ipsilateral renal agenesis, among others.

MRI provides detailed visualization of cyst size and location.

Prostatic utricle cysts typically are midline pear-shaped structures that do not extend above the base of the prostate. They communicate with the posterior urethra and generally are smaller than müllerian cysts.

Müllerian duct cysts arise from the remnants of the Müllerian (paramesonephric) ducts and are more commonly seen in adult males (20-40 years).

Unlike prostatic cysts of the utricle, they are generally not associated with congenital anomalies of the external genitalia and do not communicate with the urethra. At imaging studies, müllerian duct cysts typically are midline teardrop-shaped structures with extension above the prostate.

Fig 2: Axial (A and D), coronal (B and E) and sagittal (C and D) T2WI images showing midline high-signal-intensity intraprostatic cysts. The upper panel shows a prostatic utricle cyst in an 80-year-old man. The lower panel shows a prostatic müllerian duct cyst in a 61-year-old man.

Ejaculatory duct cysts and urethral diverticula

Ejaculatory duct cysts presumably arise when obstruction occurs and can be congenital or acquired. They may lead to complications such as ejaculatory dysfunction and can be a major cause of infertility.

Ejaculatory duct cysts typically are paramedian structures, located laterally and close to midline and posterior to the prostatic urethra.

Urethral diverticulum are rare and consist of a saccular dilatation of the urethral wall that can be congenital (10%) or acquired (90%) with a peak incidence around 25-45 years.

While some patients remain asymptomatic, some of them can present with recurrent urinary tract infections, incontinence, dysuria, or fistula formation, among other symptoms.

MRI can show the size and location of the diverticulum, usually a round or ovoid lesion wrapping around the mid or distal urethra and located posterolateral to it.

Fig 3: Axial and sagittal (A and B) T2WI images and axial T1WI images (C) showing an ovoid "saddle-bag" cystic lesion (arrow) adjacent to the left side of the membranous urethra. The lesion is T1WI hypointense and T2WI hyperintense. Axial contrast-enhanced MR images (D) show no enhancement in subtraction DCE.

Prostatic Retention Cysts and Cystic Degeneration of Benign prostatic hypertrophy (BPH)

Prostatic retention cysts are relatively common, particularly in older men. They emerge from dilatation of glandular acini due to an obstruction of the prostatic ducts.

They develop in any zone and position within the prostate gland and appear similar to cysts associated with BPH.

Benign prostatic hyperplasia affects almost 90% of men by the age of 81–90 years and it is the most common cause of lower urinary tract symptoms. It is derived from the increasing number of epithelial and stromal cells located at the periurethral transition zone (TZ). Although MRI is not currently indicated in the routine preprocedural evaluation of BPH, it is a very common finding in patients undergoing MRI for other indications due to its high prevalence.

Cystic degeneration of BPH accounts for most prostatic cystic lesions and is located in the transitional zone of the prostate.

Fig 4: Sagittal (A), coronal (B) and axial (C and D) T2W image MRI of a 57-year-old man showing an enlarged transition zone with heterogeneous signal and several well-circumscribed nodules of different signal intensity compatible with BPH.

Cysts associated with tumors and abscesses

While the majority of prostatic cysts are benign, rarely cystic masses may represent neoplastic conditions or infectious processes leading to significant clinical implications. Radiologists must then be aware of the imaging features that are more frequently suggest malignancy or complications.

Different prostatic neoplasms can sometimes present with cystic components, like multilocular cystadenoma, papillary cyst adenocarcinoma and combined transitional cell adenocarci­noma. Other rare neoplasms that can present with cystic elements are leiomyoma or sarcoma.

MRI can have a pivotal role in identifying these lesions. The presence of blood, signal heterogeneity and soft tissue should raise suspicion.

Fig 5: Axial and coronal T2-weighted MR images (A and B) of a 54-year-old man show a large lobulated heterogeneous mass (*) that has cystic areas (blue arrows) and occupies almost the entire gland. Axial diffusion-weighted MR images (C) and ADC map (E) show multiple areas of restricted diffusion (arrows) within the lesion. Axial contrast-enhanced MR image (E) shows heterogeneous enhancement (triangle) with multiple areas of central necrosis. The patient underwent a biopsy and the histopathologic findings revealed a very rare prostate synovial sarcoma.

Prostatic abscesses are a rare but serious urological condition and represent the most common complication of bacterial prostatitis. The abscesses are usually filled with purulent material, which can have variable signal characteristics on MRI depending on the stage of the abscess. At MR imaging, prostatic abscesses are typically seen as hyperintense lesions on T2WI and high b-value DWI with a corresponding low ADC value due to thick purulent material. Gadolinium-enhanced sequences most typically demonstrate rim enhancement.

Fig 6: Sagittal ultrasound image (A) shoes hypoechoic area (*) within an enlarged prostate gland. Axial CT images of the pelvis (venous phase) (B) showing multiple prostatic collections (arrows) involving the prostatic gland.

Fig 7: Axial T2WI (A) and Axial CT images of the pelvis (venous phase) (B) of a 77-year-old man showing multiple prostatic collections involving the prostatic apex. Axial high– b value diffusion-weighted MR image (C) and ADC map (D) show moderately restricted diffusion. Note: intravenous contrast was not administered when performing the MRI due to reduced renal function.

Seminal Vesicle and Vas Deferens Cysts

Seminal Vesicle cysts are uncommon lesions usually found in patients between 10 and 40 years of age. Seminal vesicle cysts may be congenital or acquired and can be associated with genitourinary anomalies such as autosomal dominant polycystic kidney disease and Zinner syndrome.

While many cases remain asymptomatic, larger cysts can lead to reproductive and urinary complications leading to infections or obstructive processes.

They present as well-defined fluid-filled structures that arise within the seminal vesicles, posterior to the urinary bladder.

Fig 8: Sagittal T2-weighted (A), Axial T2-weighted FS (B) and Axial T1-weighted MR images (C) of a 5-month-old baby showing a large cyst with low T1 and high T2 weighted signal intensity located in the retrovesicular region. Some foci of material with hyperintensity on T1-weighted MR images are observed (arrow), which may reflect high protein content. The lesion was surgically removed and pathological anatomy revealed a congenital seminal vesicle cyst.

Cysts of the Vas Deferens are located superior to the prostate and along the course of the vas deferens, a crucial component of the male reproductive system responsible for transporting sperm from the epididymis to the ejaculatory ducts. These lesions may lead to complications such as infertility or obstruction. 

Cowper Duct Cysts

The Cowper (bulbourethral) glands are responsible for releasing the pre-ejaculatory fluid that promotes lubrification and sperm motility. These glands will drain to the bulbous urethra via a single duct at the base of the penis. Cowper Duct Cysts (syringocele) refers to a cystic dilatation of the main duct of the bulbourethral glands that will be located posterior or posterolateral to posterior urethra.

Fig 9: Axial and sagittal T2-weighted (A and B) and coronal and axial T1-weighted Dixon method (C and D) MR images show a midline unilocular cystic oval structure at the penile base adjacent to the ventral aspect of the bulbous urethra.