Teaching Case

An 8-year-old boy was referred to our hospital for an MRI of the abdomen. He was known with a congenital solitary right kidney. On routine follow-up ultrasound of the urinary tract, a cystic lesion behind the bladder was noted for which further evaluation was warranted. The patient was asymptomatic. 

MRI showed agenesis of the left kidney with compensatory hypertrophy of the right kidney (figure 1). The seminal vesicle was normal on the right side while the left was clearly dilated with a homogenous hyperintense signal on the T2-weighted sequence (figure 2).  Additionally, there was a lobulated, cystic tubular structure in the left scrotum.  Alongside this cystic lesion was a tubular structure with intermediate signal on the T2-sequence with a length of 2 cm and a diameter of 3 mm. This was thought to be an atrophic testis. The epididymis was not clearly recognisable (figure 3). 

Ultrasound of the scrotum showed a normal testis and epididymis on the right side. On the left side, there was a marked cystic dilation of the rete testis with multiple cysts of varying size. In the periphery, there was a thin C-shaped rim of normal testicular parenchyma. The epididymis on the left side was also normal (figure 4).

The triade of ipsilateral renal agenesis, ejaculatory duct obstruction and seminal vesicle cyst was first described by Zinner in 1914 [1]. It’s a rare congenital malformation and results from a maldevelopment of the mesonephric duct and its derivates during embryogenesis.  The absence of the development of the ureteric bud results in renal agenesis and atresia of the ejaculatory duct which will cause dilation of the seminal vesicle. The mesonephric duct also gives rise to the hemitrigone, vas deferens, epididymis and rete testis.  Any insult can thus result in a different spectrum of Wolffian duct anomalies. In our case, there was also cystic dysplasia of the testis (CDT) which might result from a failure to form a connection between the epithelium of the testis and the caudal end of the mesonephric duct [2].

Patients with Zinner syndrome are usually asymptomatic until their 20s when most are sexually active. Accumulation of seminal fluid causes enlargement of the seminal cysts and results in perineal discomfort, urinary frequency, dysuria, recurrent urinary tract infections and sometimes azoospermia leading to infertility [3]. On the other hand, CDT usually presents as a painless scrotal mass [4].

Several imaging modalities can be used to make an adequate diagnosis. Ultrasound is a useful first-line examination. However, CT and MRI have superior resolution and are better able to differentiate between other causes of cystic masses in the pelvis. Nowadays MRI is preferred because the lack of radiation and the ability to adequately evaluate the relationship of the cyst with the surrounding anatomy which is useful in surgical planning. Classical appearance of seminal vesicle cysts on MRI is a paramedian, periprostatic lesion with low T1 and high T2 weighted signal intensity. Some seminal vesicle cysts may have high T1 and T2 signals due to proteinaceous, purulent, or haemorrhagic contents [3]. Ultrasound is an excellent exam to differentiate CDT from other scrotal masses. The classical image is a cystic dilation of the rete testis with a thin C-shaped rim of normal testicular parenchyma [2].

Patients with Zinner syndrome are usually treated conservatively with regular follow-up ultrasound [2]. Surgical resection of the seminal vesicle cyst and obstructed ejaculatory duct is reserved for symptomatic patients with large cysts or in the case of infertility [5]. CDT Is managed conservatively with some authors suggesting regular follow-up hence the natural history of CDT and its effect on normal testicular parenchyma is not yet fully elucidated [6].

Informed consent was obtained from the legal guardians of the patient.