These are denominated cysts of the Müllerian ducts by some authors. At US, they appear as rounded or oval formations that can also be palpable and as large as several centimeters in diameter. They are localized on the midline, proximally to the seminal colliculus, and extend inside the prostatic base toward the insertion of the seminal vesicles (Fig. 22.1). Histologically, there is no communication with the urethra, and the utricle has a normal morphology with a cuboid or columnar epithelium [8, 9]. Infectious complications of these cysts are less frequent because of the lack of communication with the urethra. Yasumoto et al. reported the characteristics of the fluid aspirate obtained by transperineal puncture of midline cysts, referring that the fluid did not contain spermatozoa and the prostate-specific antigen (PSA) concentration in the fluid was 90,000 ng/ml [11].

Unlike utricular cysts, in a cystic utricle, there is an outlet from the cyst to the urethra, which is why it can also be called a cystic dilation of the utricle. It is drop shaped (owing to the communication with the urethra) or ovoid and localized on the midline. It is sometimes indistinguishable from a utricular cyst as regards the site and US features, although in other cases, it is possible to identify a virtual (obliterated) or a real (pervious) outlet. The former picture is visible as a hyperechogenic line at the level of the seminal colliculus surrounded by a narrow hypoechogenic rim (Fig. 22.2). On the basis of embryological studies, it seems that these cysts develop during the last stages of maturation of the utricle as a consequence of an obstruction of the physiological communication with the urethra. Histologically, the communication between the urethra and the cystic utricle is recognizable [8]. Infectious complications of these cysts are frequent because of the urethral outlet, and so they may have a homogeneous content (see infected cyst).

This shows a characteristic, wide outlet from the utricle to the urethra. It is a congenital malformation that is also known as a remnant of the Müllerian duct or a male vagina and is generally diagnosed in youths or boys with other malformations like hypospadias or virilization defects. It is not a true cystic formation, because a wide defect is present that causes an ample passage between the utricular cavity and the urethra. The seminal colliculus is sometimes absent, while a dilated tubular structure with a squamous epithelium is evident at histology [9]. Both at US and at retrograde cystourethrography, a cyst with an anechoic content is evident on the posterior midline, showing an ample outlet to the prostatic urethra (Fig. 22.3). The enlarged utricle corresponds to a Ritchey Type 2 cyst [10]. Symptoms include urinary infections, recurrent epididymitis, pain, and post-micturition dribbling. The cyst cavity may be palpable during rectal exploration. Rarely, complications such as calculi in the cystic cavity or neoplastic degeneration can be observed (reported by Sondergaard et al. in 6.3 % of autopsies) [12]). The tumors that can originate from these structures have a distinct histology, prognosis, and clinical behavior: those that originate from the multistratified epithelium of the cyst wall give rise to squamous carcinoma, whereas those that originate from the ductal epithelium of the seminal colliculus develop into ductal (or endometrioid) adenocarcinoma [13].