Müllerian choristoma Mimicking imperforate hymen in a female neonate: A case report

Introduction A Müllerian choristoma is histologically normal Müllerian tissue incorporated during organogenesis into an ectopic site. Reported locations include the spinal cord, bladder, pelvis, mediastinum, and vagina. Presentation as a neonatal interlabial cystic mass has not previously been described. Case Presentation A term female was found to have a large midline fluid-filled interlabial mass at birth. Ultrasound showed a 3.4 × 2.6 × 1.3 cm anechoic cystic structure at the introitus, interpreted as hydrocolpos, with otherwise normal renal, bladder, uterine, and ovarian anatomy. On day of life one she underwent examination under anesthesia, cystoscopy, vaginoscopy, and cyst excision. Cystoscopy demonstrated a normal urethra, orthotopic ureteral orifices, and normal bladder. Needle puncture yielded clear fluid (with negative cytological analysis, and on biochemical analysis had a concentration of creatinine lower than serum). After cruciate incision, endoscopy of the cyst cavity revealed a blind-ending pouch. Following decompression, the vaginal lumen was identified posterior to the cyst and vaginoscopy confirmed a patent vagina with a normal cervix. Partial cyst wall excision with marsupialization was performed. Histopathology showed benign PAX8-positive epithelium, establishing Müllerian derivation. She resumed oral intake and began voiding and stooling normally. She was discharged on postoperative day one and had a normal examination at three-week follow-up. Conclusion Müllerian choristoma is a rare cause of a neonatal interlabial mass that can mimic imperforate hymen with hydrocolpos and is clinically indistinguishable from a paraurethral cyst. Stepwise endoscopic evaluation with cyst decompression, cystectomy, and PAX8 immunostaining allows for a definitive diagnosis and treatment.