Hydrocolpos is cystic distention of the vagina caused by accumulation of fluid due to a congenital obstruction such as imperforate hymen, transverse vaginal septum, or distal vaginal atresia. Urinary obstruction associated with this anomaly typically presents at birth. This case describes acute urinary retention with presumed hydrocolpos, though the cystic mass was ultimately found to be a sacrococcygeal teratoma.

A 3-month-old previously healthy female presented with 1 day of anuria. Blood work was notable for elevated creatinine and hyperkalemia. A renal ultrasound (US) was performed showing a fluid-filled structure posterior and inferior to the bladder, which was thought to be causing bladder obstruction with hydronephrosis. Due to possible hydrocolpos, a pelvic US was performed which redemonstrated an anechoic fluid-filled structure behind the dilated bladder. Straight catheterization of the bladder was easily performed. External genital exam was unremarkable with patent hymen and normal distal vagina noted. A foley catheter was placed, and electrolyte abnormalities improved. Pediatric gynecology and urology performed an exam under anesthesia, cystoscopy, and vaginoscopy notable for a normal pre-pubertal vagina that was displaced anteriorly secondary to a posterior, smooth bulge palpated on rectal exam. The vagina was not enlarged, and there was a single normal appearing cervix. There was no evidence of fistulous or extravaginal connection or drainage into the vagina. The urethra, bladder neck, and bladder were also displaced anteriorly. Given lack of hydrocolpos with no clear explanation for the dilated structure seen on initial imaging, a pelvic MRI was done showing a 3.0 × 2.5 × 2.6 cm complex, multicystic mass lying anterior to the coccyx compatible with a Type IV sacrococcygeal teratoma. Anterior and superior to the presumed teratoma was an additional 3.9 × 5.0 × 3.5 cm cystic structure described as likely hydrocolpos. The patient underwent an uncomplicated resection of a single multicystic mass with pediatric surgery with no intraoperative concern for Mullerian anomaly. The pathology was consistent with mature sacrococcygeal teratoma.

This case highlights history and physical exam as paramount, with other tools serving as diagnostic adjuncts. In this case, a multi-disciplinary exam under anesthesia was more revealing than imaging. Hydrocolpos is unlikely to present at 3 months of age, lowering its likelihood of causing the urinary obstruction in this patient. A wide differential should be considered for cystic pelvic masses, especially when imaging findings are inconsistent with the clinical impression.