Teaching Case

A 4-year-old boy presented to the outpatient department with complaints of suprapubic pain. He was referred to our department for an ultrasound.

Ultrasound revealed absence of the left kidney in its usual location or elsewhere in the abdominal cavity, suggesting left renal agenesis. Compensatory hypertrophy of the right kidney was observed. In addition, a small cystic lesion was seen posterior to the urinary bladder on the left side, communicating with the left vesicoureteric junction, suggestive of a ureteric bud remnant or extra-vesical orthotopic ureterocele. The left seminal vesicle was bulky and was replaced by a lobulated cystic lesion, suggestive of cystic dilatation of the seminal vesicle secondary to ejaculatory duct obstruction. Ultrasound of the scrotum showed normal position, size and morphology of both testes.

Zinner syndrome is a developmental anomaly of the mesonephric (Wolffian) duct, presenting with a triad of unilateral renal agenesis, ipsilateral seminal vesicle cyst, and ejaculatory duct obstruction [1]. This association between congenital malformations of the seminal vesicle and the ipsilateral upper urinary tract is observed because both the ureteral buds and the seminal vesicles originate from the mesonephric duct [2]. Maldevelopment of the distal part of the mesonephric duct results in atresia of the ejaculatory duct, with resultant cystic dilatation of the seminal vesicle, whereas an abnormality in the ureteral bud leads to renal agenesis [3].

The patients are usually asymptomatic, and diagnosed in the third or fourth decade of life, often presenting with perineal pain or infertility [4]. Depending on the size of the seminal vesicle cysts, there may be symptoms due to pressure effects on the surrounding structures resulting in pelvic/perineal pain, or no symptoms in case of small cysts [3]. With the advent of more advanced imaging modalities, patients are being diagnosed at an earlier age.

The condition is equivalent to the Mayer-Rokitansky-Kuster-Hauser syndrome known to occur in females [5].

Imaging plays an important role in the diagnosis. Ultrasound, as the primary modality, reveals unilateral renal agenesis and cystic nature of the ipsilateral seminal vesicle lesion. On ultrasound, the seminal vesicle cyst is seen as an anechoic lesion, which may or may not show mural calcifications. Presence of internal echoes may suggest intra-cystic haemorrhage or superimposed infection. Trans-rectal ultrasound may be performed for further evaluation. CT urography confirms the absence of the kidney and ipsilateral ureter, with a well-defined retrovesicular lesion of fluid attenuation often seen just above the prostate gland, and demonstrates any ureterocoele if present. MRI is the modality of choice, as it confirms the diagnosis, and better demonstrates the nature of the seminal vesicle cyst and imaging findings of ejaculatory duct obstruction. It is also helpful for accurate preoperative surgical planning if excision of the seminal vesicle cyst is planned.

Differential diagnoses of seminal vesicle cysts include prostatic utricle cysts, ejaculatory duct cysts, Mullerian duct cysts, bladder diverticula, and ureterocoeles. The differentiation is based on the location of the cyst (median, para-median, or lateral), imaging characteristics depicting the intralesional contents, and associated findings in urogenital system [3].

Treatment depends on the symptoms, ranging from conservative (observation) to surgical excision.

Zinner syndrome constitutes a rare constellation of findings in patients presenting with pelvic or perineal pain and symptoms of urinary tract infection. However, it is to be considered in such cases, especially in the presence of unilateral renal agenesis.