: An interlabial mass in newborn girls is diagnosed usually after birth or during the first days or weeks of life. According to various studies, its prevalence ranges between 1 : 500 and 1 : 7,000 newborn girls. A mass in the vaginal introitus or between the labia majora can cause a diagnostic dilemma and may be suspected even of ambiguous genitalia. Interlabial masses of different etiologies present clinically similar, and therefore, can be misdiagnosed. The most common causes of an interlabial mass in a newborn are hymenal and paraurethral cysts, both of which present as thin-walled spherical formations filled with golden fluid. When diagnosing a cystic interlabial tumor, it is necessary to particularly exclude a non-perforated hymen with hydrocolpos and prolapse of an ectopic ureterocele. In the differential diagnosis, prolapse of the urethra, rhabdomyosarcoma of the vagina or cervix, urethral or vaginal polyps, and extremely rare conditions such as genital prolapse or duplicate rectum cannot be omitted. A newborn girl with an interlabial formation should be examined by a pediatrician, gynecologist, surgeon, or urologist depending on the nature of the clinical findings. Once the etiology of an interlabial mass is identified, expectant management or surgery should be chosen. Early surgical treatment of hydrocolpos and prolapse of a ureterocele can prevent lower urinary tract obstruction and life-threatening renal damage.

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